experiments on tyre tread patterns · experiments on tyre tread patterns abstract this report...
TRANSCRIPT
ROAD RESEARCH LABORATORY Ministry of Transport
RRL REPORT LR 122
EXPERIMENTS ON TYRE TREAD PATTERNS
by
G. Maycock
CROWTHORNE ROAD RESEARCH LABORATORY
1967
CONTENTS
A b s t r a c t
1. I n t r o d u c t i o n
2. T e s t m e t h o d s and c o n d i t i o n s
2. I M e t h o d
2 . 2 S u r f a c e s
2 . 3 T y r e s
3. E x p e r i m e n t 1 - E f f e c t of n u m b e r of r i b s
3 . 1 E x p e r i m e n t a l d e t a i l s
3 . 2 R e s u l t s
4 . E x p e r i m e n t 2 - E f f e c t of g r o o v e wid th
4 . 1 E x p e r i m e n t a l d e t a i l s
4 . 2 R e s u l t s of t e s t s a t C r o w t h o r n e
4 . 3 H i g h s p e e d t e s t r e s u l t s
5. D i s c u s s i o n of t he r e s u l t s o f b o t h e x p e r i m e n t s
5 .1 G e n e r a l
5 . 2 S u r f a c e d r a i n a g e e f f e c t s
5 . 3 T y r e d r a i n a g e
5 . 3 . i G e n e r a l
5 . 3 . 2 P e a k a n d l o c k e d w h e e l e f f e c t s
6. C o n c l u s i o n s
7. Acknowledgements
8. References
P a g e
1
1
1
1
2
3
3
3
4
6
6
6
7
7
7
7
8
8
9
10
10
10
Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1 st April 1996.
This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.
EXPERIMENTS ON TYRE TREAD PATTERNS
ABSTRACT
This r e p o r t d e s c r i b e s two e x p e r i m e n t s c a r r i e d out t o i n v e s t i g a t e t he i n f l u e n c e of c e r t a i n f e a t u r e s of t r e a d p a t t e r n d e s i g n , on the s k i d r e s i s t a n c e of t y r e s . M e a s u r e m e n t s w e r e m a d e of p e a k a n d l o c k e d w h e e l b r a k i n g f o r c e c o e f f i c i e n t s , on s e v e r a l we t s u r f a c e s a t s p e e d s b e t w e e n 20 and 105 m i l e / h , u s i n g a f r o n t whee l b r a k i n g t e c h n i q u e .
In the f i r s t e x p e r i m e n t f o u r t y r e s w e r e u s e d h a v i n g r e s p e c t i v e l y 5, 7, 9 and 13 s t r a i g h t cut r i b s a n d h a v i n g the s a m e o v e r a l l t r e a d a r e a . The r e s u l t s s h o w e d tha t the d i f f e r e n c e s b e t w e e n t h e s e t y r e s w e r e s m a l l , e x c e p t on the m o s t p o l i s h e d s u r f a c e , w h e r e t h e 5 - r i b t y r e g a v e a l a r g e r d e c r e a s e of c o e f f i c i e n t wi th i n c r e a s i n g s p e e d .
In t he s e c o n d e x p e r i m e n t , the r i b w i d t h w a s h e l d c o n s t a n t , a n d the g r o o v e wid th v a r i e d . I n i t i a l l y , s i x t y r e s w e r e t e s t e d ; a 2½" w i d e s m o o t h t y r e , and s i x r i b b e d t y r e s h a v i n g f ive ½ in . r i b s a n d a r a n g e of g r o o v e w id th s . The r e s u l t s s h o w e d t h a t no a p p r e c i a b l e i n c r e a s e in c o e f f i c i e n t was o b t a i n e d when the g r o o v e w i d t h e x c e e d e d a c r i t i c a l v a l u e . T h e o p t i m u m v a l u e o f g r o o v e to r i b wid th r a t i o f o r t h e s e t y r e s w a s 0 . 4 .
The r e s u l t s of t h e e x p e r i m e n t s a r e d i s c u s s e d in t e r m s of w a t e r d r a i n a g e and l u b r i c a t i o n e f f e c t s in the t y r e - r o a d c o n t a c t r e g i o n .
I. INTRODUCTION
P r e v i o u s e x p e r i m e n t s have shown the i m p o r t a n c e of t r e a d p a t t e r n s in i n c r e a s i n g the sk id r e s i s t a n c e of t y r e s in wet c o n d i t i o n s , p a r t i c u l a r l y on p o l i s h e d , f ine t e x t u r e d s u r f a c e s , and a t h igh s p e e d s . T h e s e e f f e c t s w e r e e x p l a i n e d in t e r m s of the way i n wh ich the p a t t e r n , a s s i s t e d in e l i m i n a t i n g t h e l u b r i c a t i n g f i l m of w a t e r f r o m the r e g i o n of c o n t a c t b e t w e e n t y r e and r o a d , e n a b l i n g the t y r e t o e s t a b l i s h r e l a t i v e l y d r y c o n t a c t wi th the g r o u n d , l , 2 , 3 . T h e e f f e c t i v e n e s s of a s i m p l e c i r c u m f e r e n t i a l r i b and g r o o v e t r e a d p a t t e r n in a c h i e v i n g t h i s o b j e c t , m a y be c o n s i d e r e d a s d e p e n d i n g upon a n u m b e r of p a r a m e t e r s , s u c h a s , n u m b e r of r i b s , r i b width , l e n g t h of r i b m a k i n g c o n t a c t wi th t h e g r o u n d , g r o o v e w i d t h , g r o o v e dep th e t c . Some of t h e s e t r e a d p a r a m e t e r s w i l l , of c o u r s e , be i n t e r d e p e n d e n t . In o r d e r to d e t e r m i n e t h o s e f e a t u r e s of a t r e a d p a t t e r n t h a t a r e i m p o r t a n t f r o m the po in t of v i e w of s k i d r e s i s t a n c e , i t w a s c o n s i d e r e d d e s i r a b l e t o c a r r y out e x p e r i m e n t s in which a s i n g l e p r o p e r t y of the p a t t e r n w a s v a r i e d , w h i l s t t h e r e m a i n d e r , a s f a r a s p o s s i b l e , w e r e he ld c o n s t a n t .
The p r e s e n t r e p o r t d e s c r i b e s t w o such e x p e r i m e n t s . In t he f i r s t , the n u m b e r of r i b s was v a r i e d w h i l s t the s u m of t he r i b w i d t h s r e m a i n e d c o n s t a n t , and in t he s e c o n d , t h e g r o o v e wid th was v a r i e d w h i l s t t h e r i b w i d t h r e m a i n e d c o n s t a n t . D e t a i l s of the e x p e r i m e n t s a r e g i v e n s e p a r a t e l y l a t e r .
2 .1
2. T E S T METHOD A N D C O N D I T I O N S
Method
The f o r c e s d e v e l o p e d b e t w e e n t y r e a n d r o a d w e r e m e a s u r e d on wet s u r f a c e s at s p e e d s b e t w e e n 20 and 105 m i l e / h u s i n g a f r o n t w h e e l b r a k i n g
2 . 2
t e c h n i q u e . T h e t e c h n i q u e i n v o l v e s i n c r e a s i n g the b r a k i n g on t h e f r o n t w h e e l s o f a v e h i c l e u n t i l t h e y l o c k , a n d m e a s u r i n g t h e r e s u l t i n g d e c e l e r a t i o n o f t h e v e h i c l e b y m e a n s of a d e c e l e r o m e t e r a n d f i l m r e c o r d e r . F r o m t h e d e c e l e r o m e t e r r e c o r d s b o t h t h e m a x i m u m ( p e a k ) v a l u e of t h e b r a k i n g f o r c e c o e f f i c i e n t w h i c h i s r e a c h e d j u s t b e f o r e t h e w h e e l s l o c k , a n d t h e l o c k e d w h e e l v a l u e w e r e d e t e r m i n e d . A s e p a r a t e t r a c e p r o v i d e d t h e s p e e d s a t w h i c h t h e v e h i c l e w a s t r a v e l l i n g a t t h e s e i n s t a n t s , a n d t h e s e a r e t h e a b s c i s s a e in F i g s . 1 - 1 0 . F o r e a c h s e t o f t y r e s t h e t e s t r u n s a t t h e v a r i o u s s p e e d s w e r e m a d e i n r a n d o m o r d e r t o m i n i m i s e t h e e f f e c t of p r o g r e s s i v e c h a n g e s in t y r e o r s u r f a c e . T h e t y r e s w e r e a l s o t e s t e d in r a n d o m o r d e r . F u r t h e r d e t a i l s o f b o t h t h e t e c h n i q u e a n d t h e t e s t p r o c e d u r e a r e g i v e n e l s e w h e r e . 2
S u r f a c e s
T h e m a j o r i t y o f t h e t e s t s w e r e c a r r i e d out on t h e R . R . L . t e s t t r a c k a t C r o w t h o r n e u s i n g t h e s u r f a c e s d e t a i l e d in T a b l e 1.
T A B L E 1
D e t a i l s of t e s t s u r f a c e
C o d e
A
B
C
D
E
N a m e
P o l i s h e d c o n c r e t e
Fine Cold Asphalt
Asphalt with chippings (White)
R o u n d e d G r a v e l C a r p e t
Asphalt with chippings (Black)
Des cription
C o n c r e t e f l o o r i n g , s p e c i a l l y p o l i s h e d a n d h a v i n g v e r y s m a l l a s p e r i t i e s .
C o l d a s p h a l t t o B . S. 1690 u s i n g b l a s t f u r n a c e s l a g a g g r e g a t e - a " s a n d p a p e r " t e x t u r e .
Ho t r o l l e d a s p h a l t t o B . S. 594 w i t h ½" M e l d o n w h i t e c h i p p i n g s r o l l e d i n t o t h e s u r f a c e .
B i t u m e n g r a v e l c a r p e t w i t h 34" B r i d p o r t g r a v e l . T o p s of s t o n e s r o u n d e d a n d h i g h l y p o l i s h e d .
H o t r o l l e d a s p h a l t to B. S. 594 w i t h 3,, p r e - c o a t e d c h i p p i n g s r o l l e d i n t o t h e s u r f a c e .
F B r u s h e d C o n c r e t e
• Not a l l t h e s u r f a c e s g i v e n i n t h i s t a b l e w e r e u s e d in b o t h e x p e r i m e n t s . S u r f a c e E i s a r e c e n t l y l a i d s u r f a c e , a n d c o r r e s p o n d s t o t h e a s p h a l t i c s u r f a c e t h a t i s b e i n g l a i d o n m a n y r o a d s a n d m o t o r w a y s a t t h e p r e s e n t t i m e .
C l e a r l y , in e x p e r i m e n t s o f t h i s k i n d , i t i s i m p o r t a n t to m a i n t a i n a s c l o s e l y a s p o s s i b l e a c o n s t a n t d e p t h of w a t e r on t h e t e s t s u r f a c e . T h i s i s f a c i l i t a t e d a t t h e l a b o r a t o r y ' s t r a c k b y t h e u s e of b u i l t in s p r a y b a r s , w h i c h e n a b l e s w a t e r t o b e s p r a y e d o n t o t h e t e s t s e c t i o n s a t a r o u g h l y c o n s t a n t r a t e t h r o u g h o u t t h e t e s t s . T h e w a t e r d e p t h m e a s u r e d a b o v e t h e t o p s o f t h e a s p e r i t i e s in t h e s u r f a c e w a s e s t i m a t e d t o b e , on a v e r a g e , b e t w e e n 0. 020 a n d 0. 040 i n c h e s o n t h e f i n e - t e x t u r e d s u r f a c e s .
A n u m b e r of m e a s u r e m e n t s in t h e s e c o n d e x p e r i m e n t ( the e f f e c t of g r o o v e w i d t h ) w e r e m a d e a t s p e e d s u p t o 105 m i l e / h on a b r u s h e d c o n c r e t e s u r f a c e ( s u r f a c e F , T a b l e 1, ) w h i c h f o r m e d p a r t o f t h e p e r i m e t e r t r a c k of
2
2 . 3
a n a i r f i e l d a t G r e e n h a m , B e r k s h i r e . In o r d e r t o m a i n t a i n t h e r e q u i r e d u n i f o r m i t y of s u r f a c e w e t t i n g on t h i s a i r f i e l d , a p o r t a b l e s p r a y b a r s y s t e m w a s u s e d . T h i s s y s t e m c o n s i s t e d of 18 s p r a y b a r s e c t i o n s , e a c h 16½ f t . l o n g , and c e n t r e fed w i t h w a t e r u n d e r p u m p p r e s s u r e f r o m a 1500 g a l l o n w a t e r t a n k e r . T h e s p r a y b a r d e l i v e r e d a b o u t 300 g a l l o n s p e r m i n u t e , a n d w e t t e d a s e c t i o n a p p r o x i m a t e l y I 0 0 y d s . l o n g a n d 10 f t . w i d e t o a d e p t h of r o u g h l y 0. 035 in . T h e i n s t a l l a t i o n i s i l l u s t r a t e d i n P l a t e 1. A l l s i x s u r f a c e s u s e d i n t h e s e e x p e r i m e n t s a r e i l l u s t r a t e d in P l a t e 2.
Tyres
The tyres used were all 185 x 15 radial ply construction, moulded smooth with the experimental straight rib patterns hand cut afterwards to a
depth of 8 am.
The tread material which was oil extended S. B.R. , was the same for all the tyres, and the tyres were inflated to 24 Ibs/in" 2 when cold.
3 .1
3. E X P E R I M E N T 1 - E F F E C T O F N U M B E R O F R I B S
E x p e r i m e n t a l d e t a i l s
T h e o b j e c t of t h i s e x p e r i m e n t w a s to d e t e r m i n e t h e e f f e c t on b r a k i n g f o r c e c o e f f i c i e n t s of v a r y i n g t h e n u m b e r of r i b s on the t y r e w h i l s t k e e p i n g the t o t a l t r e a d a r e a c o n s t a n t , t h a t i s , t h e t o t a l r i b a r e a w a s k e p t c o n s t a n t a n d t he r i b s w e r e d i s t r i b u t e d o v e r t he s a m e a r e a of t y r e s u r f a c e . F o u r s e t s ~ of t y r e s w e r e m a d e hav,ing r e s p e c t i v e l y 5, 7, 9 a n d 13 s t r a i g h t r i b s . I n o r d e r to k e e p t he s a m e o v e r a l l t r e a d a r e a on t h e t y r e , t h e r i b w i d t h w a s r e d u c e d a s the n u m b e r of r i b s w e r e i n c r e a s e d . In c u t t i n g t h e s e p a t t e r n s , t h e i n t e n t i o n was to k e e p the r a t i o of g r o o v e w i d t h t o r i b w i d t h a s n e a r l y c o n s t a n t as p o s s i b l e . P l a t e 3 i l l u s t r a t e s the t r e a d p a t t e r n .
It was t h o u g h t at f i r s t t h a t t he a p p r o p r i a t e m e a s u r e of r i b a n d g r o o v e w id th of t h e s e t y r e s w o u l d be t h a t o b t a i n e d f r o m c o n t a c t p r i n t s . C o m p a r i s o n of t h e p r i n t s w i t h the a c t u a l t y r e s , s h o w e d h o w e v e r , t h a t t h e s t a t i c c o n t a c t p r i n t u n d e r e s t i m a t e d the r i b w i d t h s , a n d o v e r e s t i m a t e d t h e g r o o v e w i d t h s , p o s s i b l y b e c a u s e of the r o u n d e d c o r n e r s of t he i n d i v i d u a l r i b s . It w a s d e c i d e d t h e r e f o r e to u s e a v e r a g e v a l u e s of r i b a n d g r o o v e w i d t h c a l c u l a t e d f r o m a n u m b e r of m e a s u r e m e n t s a t v a r i o u s p o i n t s a r o u n d t h e t y r e s . U n f o r t u n a t e l y , w h e n t h i s d e c i s i o n w a s m a d e o n l y t h e a c t u a l r i b w i d t h s ~vere a v a i l a b l e , and t h e s e a r e g i v e n in T a b l e 2, t o g e t h e r w i t h g r o o v e w i d t h s e s t i m a t e d f r o m the c o n t a c t p r i n t s a l l o w i n g f o r t h e e r r o r m e n t i o n e d a b o v e .
T A B L E 2
D i m e n s i o n s of t r e a d p a t t e r n s u s e d i n E x p e r i m e n t 1
N u m b e r of R i b s
5 7 9
13
G r o o v e wid th* i n
0 . 2 8 0 . 2 0 0 . 1 6 0 . 1 2
R i b w i d t h t i n
0 . 9 0 . 6 5 0 . 5 2 0 . 3 6
G r o o v e w i d t h R i b w i d t h
0 . 3 1 0 . 3 1 0 . 3 1 0 . 3 3
* E s t i m a t e d f r o m c o n t a c t p r i n t s ( s e e s e c t i o n 3 . 1 ) t A v e r a g e v a l u e o b t a i n e d f r o m m e a s u r e m e n t s a t
s e v e r a l p o i n t s a r o u n d t h e t y r e p e r i p h r e y ( s u p p l i e d by t h e D u n l o p R u b b e r C o . )
3 . 2
T h e g r o o v e t o r i b w i d t h r a t i o i s s e e n to be of t he o r d e r of 0 . 3 1 to 0 . 3 3 f o r a l l t h e t y r e s .
T h e t y r e s w e r e t e s t e d , t o g e t h e r w i t h a s m o o t h t y r e on s u r f a c e s A , B, C a n d D ( T a b l e 1). I n o r d e r t o c h e c k t h e r e s u l t s of t h i s e x p e r i m e n t , t he t y r e s w e r e t e s t e d a g a i n on s u r f a c e A ( P o l i s h e d C o n c r e t e ) a t a l a t e r d a t e .
R e s u l t s
T h e r e s u l t s a r e s h o w n g r a p h i c a l l y in F i g s . 1 - 5 .
It will be seen that apart from the smooth tyres and the five-rib tyres on Surface A, there are no very large differences between the absolute values of coefficient obtained with these ribbed tyres. In order to assist in visual comparison of the results and to avoid the complication of drawing individual lines for each tyre, a single line, calculated by the method of least squares, has been drawn through all the results obtained with the ribbed tyres. This gives a 'mean' line relative to which individual sets of points can be assessed. The smooth tyre results are treated separately on all surfaces.
In addition to this visual comparison, a numerical treatment of the results obtained in the original series (Figs. 1-4) has been attempted. It is considered that the single feature of the results that is the most appropriate measure of the drainage properties of the tyres, is the slope of the coefficient - speed graph (speed effect). The speed effects for the ribbed tyres on the four surfaces, together with the 98% confidence limits are shown in table 3.
T A B L E 3
Ra te of D e c r e a s e in c o e f f i c i e n t s wi th i n c r e a s i n g s p e e d ( s p e e d e f f e c t ) , shown as a func t ion of t y r e and s u r f a c e ,
f o r p e a k and l o c k e d w h e e l r e s u l t s
T Y R E
P O L I S H E D C O N C R E T E
FINE C O L D AS PHA LT
(B)
A S P H A L T WIT H
C H I P P I N G S (WHITE)
( c )
R O U N D E D GRAVE L C A R P E T
(D)
PEA K
L O C K E D W H E E L
P E A K
L O C K E D W H E E L
PEA K
L O C K E D W H E E L
P E A K
L O C K E D W H E E L
5 - R i b
5 .2 + 1 .2
7 .0 -+0.6
2.1 -+1.3
4 . 4 -+0 .8
S P E E D E F F E C T in ( m i l e / h ) -1 x 103
7 - R i b
3.1 -+0.9
6.0-+0.6
2.1-+1.1
3 . 8 - + 0 . 8
9 - R i b
3 . 3 - + 0 . 8
5.5-+0.7
3 . 4 + 1 . 3
4 . 7 - + 1 . 3
13 - R i b
2 . 8 + 0 . 5
6.0-+0.7
1 . 2 - + 0 . 7
3.6-+1.3
2 . 0 - + 1 : 2 . 1 . 1 - + 1 . 2 2 . 7 - + 1 . 3 1 . 2 - + 1 . 4
5 . 7 - + 1 . 5 6 . 0 + 0 . 6 6 . 5 - + 1 . 2 6 . 5 + 1 . 3
1 . 7 - + 0 . 9 1 . 6 - + 0 . 5 1 . 1 + 1 . 0 0 . 2 + 1 . 2
1.4 -+ 0.6 1.2-+0.4 1 . 3 + 0 . 7 1.6-+0.6
The r a n g e of e r r o r s shown in t h i s t a b l e a r e t h e 95% c o n f i d e n c e l i m i t s .
T h i s t ab l e s h o w s tha t a p a r t f r o m a c u r i o u s l y h igh s l o p e f o r the 9 - r i b t y r e p e a k c o e f f i c i e n t on s u r f a c e B, the on ly s i g n i f i c a n t d i f f e r e n c e s w e r e on s u r f a c e A ( P o l i s h e d c o n c r e t e ) , w h e r e bo th p e a k and l o c k e d w h e e l r e s u l t s f o r t h e 5 - r i b t y r e w e r e l a r g e r t h a n t h e o t h e r s , and on s u r f a c e D, w h e r e the 1 3 - r i b t y r e gave a v e r y f l a t c o e f f i c i e n t s p e e d r e l a t i o n s h i p f o r P e a k r e s u l t s c o m p a r e d wi th the o t h e r t y r e s .
T h e s e r e s u l t s a r e d i s c u s s e d in s e c t i o n 5 t o g e t h e r wi th the r e s u l t s of e x p e r i m e n t 2.
The r e p e a t t e s t s on s u r f a c e A , shown in F i g . 5, a l t h o u g h g iv ing s l i g h t l y d i f f e r e n t a b s o l u t e v a l u e s of c o e f f i c i e n t f r o m the f i r s t s e r i e s , c o n f i r m e d the e a r l i e r r e s u l t s in r e s p e c t of the r e l a t i v e c o e f f i c i e n t s o b t a i n e d u s i n g the v a r i o u s p a t t e r n s .
4 . 1
4 . E X P E R I M E N T 2 E F F E C T O F G R O O V E W I D T H
E x p e r i m e n t a l d e t a i l s
In t h i s e x p e r i m e n t t h e n u m b e r o f r i b s a n d t h e r i b w i d t h w a s h e l d c o n s t a n t , w h i l s t t h e s p a c i n g o f t h e r i b s w a s v a r i e d . I n i t i a l l y , f i v e s e t s o f t y r e s w e r e m a d e , e a c h h a v i n g f i v e ½ i n . w i d e r i b s w i t h n o m i n a l g r o o v e w i d t h s o f 0 . 0 2 , 0 . 1 , 0 . 2 , 0 . 3 a n d 0 . 4 i n . r e s p e c t i v e l y . A s m o o t h t y r e w a s a l s o m a d e w i t h a t o t a l w i d t h o f 2½ in . P h o t o g r a p h s o f t h e s e t y r e s a r e s h o w n in P l a t e 4 , a n d d i m e n s i o n s o f t h e a c t u a l r i b a n d g r o o v e w i d t h s g i v e n in T a b l e 4 .
T A B L E 4
D i m e n s i o n s o f t r e a d p a t t e r n s u s e d in E x p e r i m e n t 2
N o m i n a l g r o o v e N u m b e r o f G r o o v e w i d t h R i b w i d t h G r o o v e w i d t h w i d t h in R i b s in in R i b w i d t h
0 . 0 2 0 . 1 0 . 2 0 . 3 0 . 4
0 . 0 2 0 . 1 0 0. 215 * 0 . 2 9 * 0 . 3 6 *
0.5 (Nominal) 0.51 0.49 t 0 . 5 2 + 0 . 5 4 %
0.04 0.20 0.44 0.55 0.67
A d d i t i o n a l t y r e : -
0 . 1 9 5 0 . 2 0 * 0 . 5 2 t
• M e a s u r e d u s i n g v e r n i e r c a l i p e r s a t h a l f g r o o v e d e p t h . M e a n o f 32 r e a d i n g s t a k e n in a l l f o u r g r o o v e s o f b o t h t y r e s , a t f o u r p o i n t s a r o u n d t h e p e r i p h e r y .
t M e a s u r e d a s a b o v e . M e a n o f 24 r e a d i n g s t a k e n on t h e c e n t r e t h r e e r i b s o f b o t h t y r e s , a t f o u r p o i n t s a r o u n d t h e p e r i p h e r y .
0 . 3 8
T h e s e s i x t y r e s w e r e t e s t e d u p t o s p e e d s of 80 m i l e / h on s u r f a c e s A , B a n d E ( T a b l e 1) .
4 . 2 R e s u l t s o f t e s t s a t C r o w t h o r n e
T h e r e s u l t s a r e s h o w n g r a p h i c a l l y in F i g s . 6 - 8 . T h e r e a r e r a t h e r wide v a r i a t i o n s in t h e c o e f f i c i e n t s o b t a i n e d w i t h t h e t h r e e l a r g e s t g r o o v e w i d t h s in t h e c a s e o f p e a k r e s u l t s . T h e r e a s o n s f o r t h e s e v a r i a t i o n s a r e n o t a p p a r e n t , a n d a s in t h e p r e v i o u s e x p e r i m e n t a s i n g l e ' m e a n ' l i n e h a s b e e n d r a w n t h r o u g h t h e p o i n t s .
T h e s e r e s u l t s i n d i c a t e t h a t f o r t h e p a r t i c u l a r r i b w i d t h a n d w a t e r d e p t h u s e d in t h e s e t e s t s , t h e r e i s a n o p t i m u m v a l u e o f g r o o v e w i d t h a b o v e w h i c h n o f u r t h e r i m p r o v e m e n t in e i t h e r p e a k o r l o c k e d w h e e l b r a k i n g f o r c e c o e f f i c i e n t i s o b t a i n e d . I n v i e w o f t h e i m p o r t a n c e of d r a i n a g e i t s e e m s r e a s o n a b l e t o u s e t h e r a t i o o f g r o o v e w i d t h t o r i b w i d t h a s t h e m e a s u r e of t h e e f f i c i e n c y o f a s i n g l e s t r a i g h t r i b p a t t e r n . V a l u e s of t h i s r a t i o a r e s h o w n in T a b l e 4, a n d t h e s e in c o n j u n c t i o n w i t h F i g . 6 s h o w t h a t t h e c r i t i c a l r a t i o l i e s s o m e w h e r e b e t w e e n 0 . 2 0 a n d 0 . 4 4 . In o r d e r t h e r e f o r e t o d e t e r m i n e t h i s c r i t i c a l v a l u e m o r e e x a c t l y , a n a d d i t i o n a l p a i r o f f i v e r i b t y r e s w a s c u t h a v i n g a g r o o v e t o r i b w i d t h r a t i o o f 0 . 3 8 ( s e e T a b l e 4) . T h i s t y r e , d e s i g n a t e d a s 0 . 1 9 in . n o m i n a l g r o o v e w i d t h , w a s t e s t e d w i t h t h e o r i g i n a l f i v e t y r e s on t h e p o l i s h e d c o n c r e t e ( s u r f a c e A ) a t C r o w t h o r n e a n d on t h e b r u s h e d c o n c r e t e ( s u r f a c e F ) a t G r e e n h a m . S i n c e in b o t h t h e s e s e t s o f r e s u l t s t h e a d d i t i o n a l
4 . 3
t y r e s h o w e d the s a m e b e h a v i o u r , on ly t h o s e r e s u l t s o b t a i n e d on t h e b r u s h e d c o n c r e t e a r e i n c l u d e d , and fo r c o n v e n i e n c e , t h e s e a r e c o n s i d e r e d in t h e
n e x t s e c t i o n .
R e s u l t s of the t e s t s a t G r e e n h a m
It was thought p o s s i b l e t h a t t he t h r e e w i d e s t g r o o v e t y r e s , w h i c h g a v e s i m i l a r r e s u l t s on the C r o w t h o r n e s u r f a c e s up to 80 m i l e / h , m i g h t h a v e d i v e r g e d at h i g h e r s p e e d s . T o c h e c k t h i s p o i n t , a n d a t the s a m e t i m e t o t e s t the e x t r a g r o o v e width t y r e on the b r u s h e d c o n c r e t e s u r f a c e , b r a k i n g t e s t s w e r e c a r r i e d out up t o s p e e d s of 105 m i l e / h on s u r f a c e F . T h e r e s u l t s f o r p e a k and l o c k e d w h e e l c o e f f i c i e n t s r e s p e c t i v e l y a r e s h o w n in F i g s . 9 a n d 10. The r e s u l t s show tha t e v e n a t the h i g h e s t s p e e d s , the d i f f e r e n c e s b e t w e e n the t h r e e l a r g e s t g r o o v e wid th t y r e s a r e s m a l l . T h e a d d i t i o n a l t y r e h o w e v e r , s h o w s a s m a l l but s i g n i f i c a n t r e d u c t i o n in c o e f f i c i e n t v a l u e s a t t he h i g h e r s p e e d s as c o m p a r e d wi th the l a r g e r g r o o v e d t y r e s , in bo th p e a k a n d l o c k e d w h e e l c a s e s . T h e s e f i n d i n g s s u g g e s t t h e r e f o r e , t h a t the o p t i m u m v a l u e o f g r o o v e to r i b wid th f o r t h i s wid th of r i b i s a b o u t 0 . 4 .
5.1 •
5.2
5. DISCUSSION O F R E S U L T S
G e n e r a l
It ha s b e e n r e c o g n i s e d fo r s o m e t i m e t h a t when a t y r e i s m o v i n g a c r o s s a w a t e r c o v e r e d s u r f a c e , t h e r e a r e two p h a s e s in t h e p r o c e s s of t h e d i s p l a c e m e n t o f w a t e r f r o m the c o n t a c t r e g i o n 1 ' 4 . T h e p h a s e s • c o r r e s p o n d t o the g e n e r a t i o n of f l u i d p r e s s u r e s by t w o d i s t i n c t m e c h a n i s m s . C o n s i d e r a b l e i n e r t i a l p r e s s u r e s c a n be g e n e r a t e d a t the f r o n t of t h e c o n t a c t r e g i o n , a s a r e s u l t of the t y r e d e f l e c t i n g t h e bu lk of• the w a t e r ou t of i t s p a t h . T h i s p r e s s u r e i n c r e a s e s a s t h e s q u a r e of t he s p e e d 5, a n d t e n d s t o s p r e a d u n d e r the t y r e , p a r t i c u l a r l y in t h i c k w a t e r f i l m s , a s t he w a t e r p r e s s u r e a p p r o a c h e s the t y r e i n f l a t i o n p r e s s u r e .
A f t e r the bu lk of the w a t e r has b e e n r e m o v e d a t h i n f i l m r e m a i n s , w h i c h , owing to i t s v i s c o s i t y , m a y s u s t a i n a p r e s s u r e b e c a u s e i t r e s i s t s b e i n g s q u e e z e d out , and b e c a u s e r e l a t i v e m o v e m e n t of t y r e and r o a d m a y g e n e r a t e p r e s s u r e s a s in v i s c o u s l u b r i c a t i o n . T h e s e v i s c o u s p r e s s u r e s w o u l d no t a p p e a r to be n e a r l y a s s p e e d d e ~ e n d a n t o v e r t he l a r g e r p a r t of t he s p e e d r a n g e as the i n e r t i a l p r e s s u r e s and m a y in s o m e c a s e s be c o n f i n e d t o a s m a l l a r e a of an i n d i v i d u a l r o a d s t o n e . F o r e x a m p l e , t h i s t y p e of l u b r i c a t i o n m a y p o s s i b l y e x p l a i n t he l ow c o e f f i c i e n t s on c o a r s e p o l i s h e d s u r f a c e s (e. g. s u r f a c e D) w h e r e the a s p e r i t i e s of the s u r f a c e m a y be u n a b l e t o b r e a k t h r o u g h t h e w a t e r f i l m .
One of the m a i n r o l e s of r o a d s u r f a c e t e x t u r e a n d t r e a d p a t t e r n i s t o r e d u c e w a t e r l u b r i c a t i o n e f f e c t s by d e c r e a s i n g f low p a t h l e n g t h s a n d i n c r e a s i n g the n u m b e r and a r e a of d r a i n a g e c h a n n e l s . The e x p e r i m e n t a l r e s u l t s w i l l now be d i s c u s s e d in t e r m s of t h e s e c o n c e p t s .
S u r f a c e d r a i n a g e e f f e c t s
The d i f f e r e n c e in the r a t e of f a l l of c o e f f i c i e n t w i t h s p e e d ( s p e e d e f f e c t ) b e t w e e n s m o o t h and w e l l d r a i n e d t y r e s i s d e p e n d e n t u p o n the d r a i n a g e p r o p e r t i e s of the s u r f a c e . P r e v i o u s w o r k h a s s h o w n 2 t h a t on a s u r f a c e With p o o r d r a i n a g e p r o p e r t i e s the d i f f e r e n c e in s p e e d e f f e c t b e t w e e n s m o o t h a n d r i b b e d ~tyres wi l l be l a r g e , w h e r e a s l i t t l e d i f f e r e n c e w i l l be o b s e r v e d on a
5 . 3
w e l l d r a i n e d s u r f a c e . In a g r e e m e n t wi th t h e s e e a r l i e r f i n d i n g s , the s m o o t h t y r e r e s u l t s o b t a i n e d in e x p e r i m e n t 1 on t h e two fine t e x t u r e d s u r f a c e s A a n d B ( F i g s . 1 and 2), s h o w e d a v e r y p r o n o u n c e d f a l l off in c o e f f i c i e n t a s t h e s p e e d was r a i s e d c o m p a r e d wi th the o t h e r s . S u r f a c e D on the o t h e r h a n d g a v e s m o o t h t y r e s p e e d e f f e c t s w h i c h w e r e on ly s l i g h t l y g r e a t e r t h a n t h o s e o b t a i n e d w i th the r i b b e d t y r e s ( F i g . 4) and s u r f a c e C, a s u r f a c e wi th l a r g e s t o n e s e m b e d d e d in a f ine t e x t u r e d a s p h a l t , gave i n t e r m e d i a t e r e s u l t s ( F i g . 3). S i m i l a r o b s e r v a t i o n s m a y be m a d e c o n c e r n i n g the r e s u l t s of e x p e r i m e n t 2, when the s p e e d e f f e c t of the 2½ in. w ide s m o o t h t y r e i s c o m p a r e d wi th the wide g r o o v e t y r e s , b e a r i n g in m i n d t h a t s u r f a c e E h a s s i m i l a r t e x t u r e t o s u r f a c e C.
A f u r t h e r f e a t u r e of the r e s u l t s of e x p e r i m e n t 2 i s w o r t h c o m m e n t . The c o e f f i c i e n t s o b t a i n e d wi th the s m o o t h and 0 .02 in. g r o o v e d t y r e s a r e a f f e c t e d t o t he l a r g e s t e x t e n t r e l a t i v e t o t he wide g r o o v e t y r e s by the i n c r e a s e in s u r f a c e d r a i n a g e c o n s e q u e n t on go ing f r o m s u r f a c e A to s u r f a c e s B o r E . T h u s , w h e r e a s c o e f f i c i e n t s o b t a i n e d with the 0 .1 in. g r o o v e d t y r e r e m a i n s i g n i f i c a n t l y l o w e r on a l l s u r f a c e s than t h o s e o b t a i n e d wi th t h e w i d e r g r o o v e d t y r e s , the s m o o t h and 0 .02 in. g r o o v e d t y r e r e s u l t s b e c o m e m u c h c l o s e r to t h e 0. 1 in. t y r e on s u r f a c e s B and E . T h i s would f o l l o w , i f t h e t r e a d d r a i n a g e of t he 0 .1 in. g r o o v e d t y r e , w h i l s t b e i n g i n f e r i o r t o t h a t o f t h e w i d e r g r o o v e d t y r e s , was n e v e r t h e l e s s s t i l l s u f f i c i e n t f o r i t s e f f e c t no t t o be a f f e c t e d g r e a t l y by s m a l l i n c r e a s e s in s u r f a c e d r a i n a g e . No te t h a t the l i m i t e d s u r f a c e d r a i n a g e of s u r f a c e B was i n s u f f i c i e n t to a l t e r t h e s m o o t h and 0 .02 in. g r o o v e d t y r e r e s u l t s at the h i g h e r t e s t s p e e d s . ( C o m p a r e wi th r e s u l t s on s u r f a c e E) .
T y r e d r a i n a g e
5 . 3 . i G e n e r a l . In e x p e r i m e n t 2, t he s m a l l s p e e d e f f e c t o b s e r v e d with the w i d e g r o o v e t y r e s when c o m p a r e d wi th the s m o o t h t y r e s , p a r t i c u l a r l y on f ine t e x t u r e d s u r f a c e s A , B and F , r e p r e s e n t in bo th p e a k and l o c k e d w h e e l c a s e s , t h e b e t t e r a b i l i t y of the g r o o v e d t y r e s to r e m o v e t h e l u b r i c a t i n g w a t e r f i l m f r o m the r e g i o n of t y r e - r o a d c o n t a c t . The r e s u l t s i n d i c a t e t ha t a t a g r o o v e to r i b w id th r a t i o of 0 . 4 , an o p t i m u m c o n d i t i o n of t r e a d d r a i n a g e e x i s t s , when the v o l u m e of the g r o o v e s is s u f f i c i e n t to a l l o w t h e w a t e r d i s p l a c e d by the r i b s to e s c a p e e a s i l y . A b o v e t h i s o p t i m u m r a t i o , and t h e r e f o r e f o r the t h r e e l a r g e s t g r o o v e w i d t h t y r e s , e a c h r i b m a y be c o n s i d e r e d a s a c t i n g i n d e p e n d e n t l y of i t s n e i g h b o u r . It s h o u l d b e n o t e d t h a t in a l l p r o b a b i l i t y the w a t e r dep th w i l l h a v e a s i g n i f i c a n t e f f e c t upon the c r i t i c a l va lue of t h i s r a t i o . In d e e p e r w a t e r f i l m s i t w o u l d be e x p e c t e d t h a t m o r e d r a i n a g e v o l u m e in r e l a t i o n to r i b wid th wou ld be r e q u i r e d , i m p l y i n g a l a r g e r o p t i m u m r a t i o . W h e t h e r in f a c t t h i s s i m p l e r a t i o is ~he c o r r e c t func t ion to u s e , a n d e q u a l l y a p p l i c a b l e t o o t h e r v a l u e s Of r i b wid th c o u l d on ly be d e t e r m i n e d b y f u r t h e r e x p e r i m e n t s u s i n g t y r e s with o t h e r v a l u e s of r i b w i d t h .
It i s p o s s i b l e a t t h i s s t a g e to r e v i e w t h e r e s u l t s of E x p e r i m e n t 1 in t h e l i g h t of t h e s e f i n d i n g s . T a b l e 2 s h o w s t ha t the g r o o v e to r i b w i d t h r a t i o of the t y r e s u s e d in E x p e r i m e n t 1 w e r e a l l abou t 0 . 3 1 , w h i c h i s s l i g h t l y l e s s t h a n the o p t i m u m r a t i o a s d e t e r m i n e d f o r the ½ in . r i b b e d t y r e s of E x p e r i m e n t 2. A s m e n t i o n e d e a r l i e r , i t has not b e e n p o s s i b l e f r o m t h e p r e s e n t r e s u l t s t o s t a t e tha t t h i s o p t i m u m r a t i o i s i n d e p e n d e n t of r i b w i d t h . I t i s not p o s s i b l e t h e r e f o r e , to d e t e r m i n e w h e t h e r t h e l a r g e r s p e e d e f f e c t of the 0 . 9 in. r i b wid th t y r e ( 5 - R i b t y r e ) on s u r f a c e A ( E x p e r i m e n t 1}, was due to the d i f f e r e n d e in
8
5 . 3 . 2
d r a i n a g e b e n e a t h the ind iv idua l r i b s of d i f f e r e n t wid ths e v e n if ful ly d r a i n e d and ac t i ng i ndependen t l y , o r w h e t h e r it was due to the i n a d e q u a c y of the d r a i n a g e p r o v i d e d by the t r e a d g r o o v e s .
P e a k and l o c k e d wheel e f f ec t s
If the peak and locked w h e e l s p e e d e f f e c t s of the t h r e e we l l d r a ined t y r e s a r e c o m p a r e d (F ig . 6), it wi l l be n o t e d tha t the p e a k c o e f f i c i e n t s a r e l e s s speed dependan t t han the l o c k e d whee l v a l u e s . T h e s e r e s u l t s a r e s i m i l a r to t h o s e o b t a i n e d in the e a r l i e r e x p e r i - ments.2:, in which the 'wel l d r a i n e d ' t y r e s u s e d had t r e a d p a t t e r n s i n c o r p o r a t i n g m a n y s m a l l s l o t s or s i p e s . The s m a l l e r s p e e d e f f e c t o b s e r v e d in the p e a k cond i t ion was t h e n e x p l a i n e d as be'ing a c o n s e q u e n c e of m o r e e f f i c i en t r e m o v a l of the th in w a t e r f i lm r e m a i n i n g b e n e a t h the r i b s . In the p e a k c o n d i t i o n , the r o t a t i o n of the t y r e a l lows s i p e s to act m o r e e f f e c t i v e l y a s r e s e r v o i r s , due to the con t inua l f l ex ing of the t r e a d , and a l s o c a u s e s f r e s h s i p e s to be p r e s e n t e d to the r o a d s u r f a c e . H o w e v e r , in the p r e s e n t t e s t s , the t y r e s had no t r a n s v e r s e s l o t s , and a l t h o u g h f l ex ing of the t r e a d m a y s t i l l p l ay a s ign i f i6an t p a r t in i m p r o v i n g the w a t e r r e m o v i n g a c t i o n of the wel l d r a i n e d t y r e in the peak c o n d i t i o n , v i s c o u s l u b r i c a t i o n and t e m p e r a t u r e e f f ec t s a l m o s t c e r t a i n l y m a k e d i f f e r e n t c o n t r i b u t i o n s to the peak and l o c k e d wheel r e s u l t s .
Dur ing s l i d ing when t h e r e is l a r g e r e l a t i v e m o v e m e n t b e t w e e n the t y r e and r o a d , the v i s c o u s d r a g be tween the t y r e and the w a t e r , m a y tend to i n c r e a s e the extent of , and the p r e s s u r e s in, the l u b r i c a t e d a r e a of the c o n t a c t r e g i o n (Ti l t ing P a d T h r u s t (Miche l l ) B e a r i n g ) . In the peak c a s e the r e l a t i v e m o v e m e n t b e t w e e n the s u r f a c e s is m u c h l e s s and the th in f i lm l u b r i c a t i o n e f f e c t s m a y be l e s s p r o n o u n c e d . In addi t ion a l a r g e r l ocked wheel s p e e d e f f e c t m a y be e x p e c t e d due to g r e a t e r t e m p e r a t u r e r i s e s in the c o n t a c t r e g i o n in t h i s c a s e t h a n fo r a s l ipp ing wheel . Th i s a s p e c t of the p r o b l e m is c o n s i d e r e d f u r t h e r e l s e w h e r e 6 , 7 .
F ig . 6 shows tha t a l though the p e a k c o e f f i c i e n t s o b t a i n e d wi th we l l d r a ined t y r e s fa l l l ess r a p i d l y with s p e e d t h a n do the l o c k e d w h e e l c o e f f i c i e n t s , in the c a s e of the p o o r l y d r a i n e d t y r e s the r e v e r s e is t r u e . The 0.1 in. g r o o v e width t y r e i s i n t e r m e d i a t e b e t w e e n t h e s e t w o , with the peak and l ocked wheel speed e f f ec t s a p p r o x i m a t e l y equa l .
If the f r a c t i o n a l r e d u c t i o n in c o e f f i c i e n t wi th i n c r e a s i n g s p e e d is ca l cu l a t ed it wil l b% found that the peak c o e f f i c i e n t f a l l s m o r e s l o w l y t h a n the locked wheel c o e f f i c i e n t fo r s m o o t h t y r e s j u s t a s f o r the wel l d r a ined ones . Tha t t he se p r o p o r t i 0 n a l r a t e s of fa l l off a r e m o r e c o n s i s t e n t , s u g g e s t s , as one would e x p e c t , t ha t t he f a c t o r s d e t e r m i n i n g the c o e f f i c i e n t s a r e m u l t i p l i c a t i v e in t h e i r e f f e c t s r a t h e r t h a n addi t ive . Indeed it is e a s i l y s e e n that the b e h a v i o u r of the s m o o t h as c o m p a r e d with the wel l d r a i n e d t y r e s when a b s o l u t e v a l u e s a r e c o n s i d e r e d is to be expec ted . T h e c u r v e s in F i g . 6 f o r the s m o o t h t y r e fa l l off v e r y r a p i d l y b e c a u s e t h e y a r e bo th a f f e c t e d by the i n c r e a s i n g l y p o o r d r a i n a g e as the speed i n c r e a s e s . The a v e r a g e r a t e of fal l off be tween the va lues at low s p e e d and the s m a l l v a l u e s a t h igh speed m u s t t h e r e f o r e be r o u g h l y p r o p o r t i o n a l to the low s p e e d v a l u e s .
6. C O N C L U S I O N S
S p e c i f i c c o n c l u s i o n s of t he two e x p e r i m e n t s r e p o r t e d in t h i s p a p e r , a r e a s f o l l o w s :
1. In an e x p e r L m e n t in wh ich t h e r a t i o of g r o o v e t o r i b wid th was a b o u t 0: 3, i n c r e a s i n g the n u m b e r of r i b s f r o m f ive t o t h i r t e e n , w h i l s t k e e p i n g the t o t a l t r e a d a r e a r o u g h l y c o n s t a n t , d id not a l t e r the c o e f f i c i e n t s o b t a i n e d e x c e p t on the s m o o t h e s t s u r f a c e . On t h i s s u r f a c e ( P o l i s h e d c o n c r e t e ) the f ive r i b t y r e (0 .9 in. r i b w i d t h ) , gave a s i g n i f i c a n t l y l a r g e r r e d u c t i o n of c o e f f i c i e n t wi th i n c r e a s i n g . speed ( s p e e d e f f e c t ) t h a n d id t h e r e m a i n d e r , fo r b o t h p e a k a n d l o c k e d w h e e l c o e f f i c i e n t s . F r o m the r e s u l t s of t h e s e e x p e r i m e n t s it i s not p o s s i b l e to d e d u c e w h e t h e r t h i s e f f e c t i s due t o a d i f f e r e n c e in the d r a i n a g e of r i b s of d i f f e r e n t wid ths e v e n w h e n f u l l y d r a i n e d , o r t o i n c o m p l e t e d r a i n a g e due t o a n i n a d e q u a c y of the g r o o v e s f o r r i b s o f t h i s w id th .
2. F o r a g i v e n r i b w i d t h , g r o o v e d e p t h a n d w a t e r d e p t h , t h e r e w a s a g r o o v e width a b o v e Which no f u r t h e r i n c r e a s e in e i t h e r p e a k o r l o c k e d whee l c o e f f i c i e n t o c c u r r e d . I t i s c o n s i d e r e d t h a t w h e n t h i s c o n d i t i o n was r e a c h e d , e a c h r i b was a c t i n g i n d e p e n d e n t l y of i t s n e i g h b o u r s . In t he p r e s e n t e x p e r i m e n t t h i s c o n d i t i o n w a s r e a c h e d when the r a t i o of g r o o v e w i d t h t o r i b w id th was 0 . 4 . F u r t h e r w o r k i s n e e d e d t o d e t e r m i n e how t h i s o p t i m u m r a t i o v a r i e s wi th o t h e r p a r a m e t e r s , p a r t i c u l a r l y r i b w i d t h , g r o o v e d e p t h a n d w a t e r d e p t h .
T h e f o l l o w i n g g e n e r a l c o n c l u s i o n s w e r e d r a w n f r o m the w o r k .
3. P r e v i o u s f i n d i n g s w e r e c o n f i r m e d in s h o w i n g t h e i m p o r t a n c e of t r e a d p a t t e r n s in i n c r e a s i n g the s k i d r e s i s t a n c e o f t y r e s u n d e r we t c o n d i t i o n s . The r e s u l t s a l s o i l l u s t r a t e d the r o l e of r o a d s u r f a c e t e x t u r e in t h i s r e s p e c t .
4. T h e r e s u l t s of t he e x p e r i m e n t s a r e d i s c u s s e d in t e r m s of the l u b r i c a t i n g e f f e c t s of w a t e r in t h e t y r e - r o a d c o n t a c t r e g i o n . I t is s u g g e s t e d t h a t the wide g r o o v e t y r e s r e d u c e t h e s e e f f e c t s by m a x i m i s i n g t h e e a s e wi th w h i c h the l u b r i c a t i n g w a t e r f i l m c a n be d i s p l a c e d . The d i f f e r e n c e s in the r e s i d u a l s p e e d e f f e c t s of t h e s e w e l l d r a i n e d t y r e s in p e a k and l o c k e d whee l c o n d i t i o n s , i s a t t r i b u t e d to d i f f e r e n c e s in t h i n - f i l m l u b r i c a t i o n e f f e c t s , and p o s s i b l y t e m p e r a t u r e d i f f e r e n c e s .
7. A C K N O W L E D G E M E N T S
T h e a d v i c e Of M r . A . J . H a r r i s in t h e f o r m u l a t i o n of the e x p e r i m e n t and in the d i s c u s s i o n of r e s u l t s i s a c k n o w l e d g e d . T h e m e m b e r s of the r e s e a r c h t e a m who t o o k p a r t in t h e s e i n v e s t i g a t i o n s w e r e G. M a y c o c k , E . S. L a w r e n c e and J . K. M e a d e s .
8. R E F E R E N C E S
1. G I L E S , C. G. w e t c o n d i t i o n s . L o n d o n 1963.
2. M A Y C O C K , G. w e t s u r f a c e s .
3. S A B E Y , B. E . B r i d . G r a n i t e a n d W h i n s t o n e F e d .
F a c t o r s i n f l u e n c i n g t h e f r i ' c t i o n b e t w e e n t y r e and r o a d u n d e r I n s t n . M e c h . E n g r s . S y m p o s i u m on C o n t r o l of V e h i c l e s ,
S t u d i e s in t h e s k i d d i n g r e s i s t a n c e of p a s s e n g e r c a r t y r e s on P r o c . I n s t n . M e c h . E n g r s . 1965-66 , 180(2A).
R o a d s u r f a c e c h a r a c t e r i s t i c s and s k i d d i n g r e s i s t a n c e . J o u r n a l 1965, 5 No. 2.
10
4. A L L B E R T , B. J . , and WALKF.R, J. C. T y r e to wet r o a d f r i c t i o n at High Speeds . P r o c . Ins tn . Mech. E n g r s . 1965-66 , 180(2A).
5. HORNE, W . B. , and J O Y N E R , U. T. , P n e u m a t i c T i r e H y d r o p l a n i n g and Some E f f e c t s on Veh ic le P e r f o r m a n c e . S . A . E . I n t e r n a t i o n a l A u t o m o t i v e E n g i n e e r i n g C o n g r e s s , D e t r o i t , J a n u a r y 1965.
6. GROSCH, K. A. The r e l a t i o n b e t w e e n the f r i c t i o n and v i s c o e l a s t i c p r o p e r t i e s of r u b b e r . P r o c . Roy. Soc. A 1963, 274, 21-39 .
7. GROSCH, K. A . , and MAYCOCK, G. In f l uence of T e s t Cond i t i ons on the Wet Skid R e s i s t a n c e of T y r e T r e a d C o m p o u n d s . T r a n s . Ins t . R u b b e r Ind. 1966, 42 No. 6, T . 2 8 0 - T . 306.
Printed by Direct Design Products, Christchurch, Hants. Dd. 398196 11/67 11
I ~ " -
> • O~o.
• ~ o t o ~ o o o ®' f o
°,, I ~ o ; ® =
' " ~ ' ~ I - ' : ~:
, N • e-. t -
I I ' o " =~ ~- /q ": ~ , =
I c ' / r o ,- ,=, ~ =
l J -: U ' J l " ~" ~
q N m , . ,-
o~
,~1 '~ - ~ -
9 , . 0 , . .
~ ° ~ ~
Ao o '= .., . . . . ~r "~ , . n ~ ._~
• m ~ ~ 0 • A v
/ I u - - I I - ~ = 1 1 o
o
0
i 0
• 0 ~ .~ ~ o
( I f ) ~,ue.:31~le0.3 e:3J0~ 5 u ! > l ' 0 J B
,/I ("~,1
I
~o I I !
I/1
~ A
";'- ~ 0
- ~ . o
o/.
o ~ !
i i
ml
i t ! -| o
I
• I I
~ 0 J I"1
i
°1 !
I o I 'q ' ;
"° !2__/ o./ ~
o , e l i ~ / / , I
I
0
0 0
A
" 0 , -~
e- ~ f f l
"8 4 •
¢-
" U
.~ e a m
X
m
.~ ~
m OC 112.
N o . t
l,,,-
-a--
e-1 ..J
l.l.a
z
,..,I
I.,I.J
!
I - , -
"5"
w.I
X
c~4
Q
o ~ ~ M ~ . O ~ O 0
( I f ) ~ .US! : ) ! : I . J80 : ) a3JO) l , { ) U ! ) I D J 8
0 0
h1~: '~ ~ I i.. _~ o I I "~ ,, _I
-,e,! .,-, / . F
• I~ = ~o /~, _ /
,I~1 ~- I~.~ F ~ kpoj ~,
"l-J" ~. ~t I >
I " / I ~
I, l . r :.I ~/.~.~
• !° I ~ _ / . o~- .'-o .3£ 0
8E e q
0
0
=_
X
GO
n,- n,"
l .-- 0 4
Z
z
m
X w
o~
0
( i f ) ~u~!0 !~ jeo0 a3Jo j 6 u ! ~ o J B
L > , o o,-~- ~ I
~-" "------~ i
g _ ~ L
' ! I
r .
f l u
o _ J
( d ) ~.ug!:)!:l.:l.aoo goJo:~ 5u!MoJg
0 0
- O
0
0
0
0
E ~
¢'~ "10
" tJ . -~
" ~ e -
'q •
~. - . - ~
,_~ e a U~
X
m n,." I1~
N ~ _ m
w
tm.
.U, .J
Z
-....J
1
~ m
2 E
X
u~ ~P I -
. . . , ~
"I0 O 0 ~ 0 0
*=- • :~.',.4r [ - 0 , - , o I "°°" I ~ I
0
.~ ~ i ~
,~I ~, I ° - : . / o ~ d .
• .~ l~ , I .~d
I I
,'~P ~ I ~ / ~
./.o .¢'./,/ ,
- . 0 1 . J*o ! ~ 4 . " '
I 0
0 C3
0
0 . r -
A ,- -d
" G . I
¢ -
X
.~_ ~ Ln n . n ;
D-- 0 •
. , ~ [ "
W
¢.3 Z
w
c ~
. I J
Q .
r ~
D-- =_4
c ~ L4.J G ~
z
c ~ L~J c ~
, z i.I=l
Q ~
. ~
0 O0 (.0
(rY)),ue!3!j~eo3 e3JOJ 5u!)j13J 8
0
N 0
0
1-0
u
0 U
o
t ~ t -
O
a3
E u
0 u
I = l
o tm t - -
o nn
0"8
0.6
.4 -
.2 -
0 0
1"0
0-8
0-6
0.4
0.2
0 0
0 Smooth } • O.02-in. grooves z~ 0 .1 - i n . grooves • 0 2- in . g r o o v e s 7 o 0 -3 - in . grooves " 0 .4 - in . grooves
=-=' t¢~-.--_~_ ,~...o o._ .__" o. • _ _ • ===.===
n
z~
O
10 , 20 30 40 5 0 60 70 80
Speed (mite/h)
(a) PEAK RESULTS
I I I 0 Smooth } • 0.02 -in. grooves
, z~ 0 .1- in . grooves ~ m , • 0.2 - in . grooves'~ c] O'3- in . grooves • O'Z,- in. grooves
~ . ~.t,,~.~
10 20 30 40 50 60 ?0 80
Speed(mite~h) (b) LOCKED WHEEL RESULTS
Tests using 185 x 15 radia l pry tyres having f ive st ra ight r ibs 0 -5 in wide
Fig.6. EXPERIMENT 2 RESULTS ON POLISHED CONCRETE (A)
1-0
0"8
® 0"6 0 u
0
c-
a
a3
.u_
0 U
u I.= 0
iT) t -
O
m
.2
0 0
1-0
0"8
0-6
0.4
02
0 0
.-.n__• • = _ _ . = _ . . . . . _ _ o.. o o - .
; " " .,"
" • i ~ o
O Smooth " ~ ~% i O • 0-02 =in. grooves "~ ~ ,
0.1-in. grooves J O ~ • 0,2-in. grooves 1 o 0 - 3 - i n grooves • 0 4 - i n . ~ ~ ' ~ - - grooves
10 20 30 40 50 60 ?0 80 Speed (mite/h)
(n) PEAK RESULTS
I I I O Smooth • 0-02-in. grooves
, z~ 0.1- in. grooves - - - - ' • 0"2- in. grooves ~ a 0-3-in. grooves ~" • 0"4- in. grooves J
, .
10 20 30 40 50 60 ?0 Speed (miLe/h)
(b) LOCKED WHEEL RESULTS Tests using 185 x 15 radial, ply tyres having five straight ribs 0-5 in wide
Fig.7. EXPERIMENT 2 RESULTS ON FINE COLD ASPHALT (B)
80
E u
0 U
0
¢ -
a L,.
I I l
E U
0 U
0
¢ -
0 L_
m
0.8
0.6
-4 -
-2 -
0
1.0
0"8
0.6
0",~
0.2
O Smooth • 0-02- in. grooves '~ 0 .1 - in . grooves I • 0 . 2 - i n . grooves } m 0-3 - in . grooves m 0 .4 - in . grooves
r"t _ = l ~ '~ - ~ .~,
: "
• IA
A
10 20 30 40 50
Speed(mite /h)
(a) PEAK RESULTS
60 ?0 80
I I I O Smooth } • 0.02 -in. grooves z~ 0 .1 - in. grooves A 0 -2 - in . grooves l a 0 .3 - in . grooves t " J 0"/,- in. grooves . /
10 20 30 40 50 60 ?0
Speed (miLe/h)
(b ) LOCKED WHEEL RESULTS Tests using 185 x 15 radial, pry tyres having five straight ribs 0-5 in wide
Fig. 8. EXPERIMENT 2 RESULTS ON ASPHALT WITH CHIPPINGS (BLACK)(E)
80
. ; ,41
I ° l ~.//
0
• ~ I'~ 0 - o I . , o °
,41 c_ ~
" . i "~ ~ ~, . o ~ ..=,
~ .I / , y i I ,
, - °
" d
X
I-..-
II I
0 0 0 0 0 ~
~ I I I I I I
~ o o o o o o 0
0 0 0 0
lue!3!~Je03 a3JoJ 6u!>loJ13
>I0ad
0
0
0
0
! I I
> > > > > > 0 0 0 0 0 0 0 0 0 0 0 0
¢ - ¢ - ¢" C ¢" e'- C
~ ' 7 " T ' T ' . ' T ' T
U') C:) 0 0 0 0 0
tl
D i I • I - I
~: r ° I C • 4
[>~] : l 1
I > / a l
• I o :¢.,'..'o ,o," °:/ 7
.i., ,of
0 0
(33
t=lu4
CO
c~ z
L
L,u
1.4=I
"(3 tn
@)
3 " "
- . J
X
I,-,,- i - -
0
0
O C ) 0
~,ua!3!,tjao3 a3JO; 6u!MoJ8
6
0
1
L
PLATE 1
The p o r t a b l e s p r a y bar i n s t a l l a t i o n
.~+- .- ~--~_.+-~+:~,+-...~.~.+_,.o-.,+.-:..,:~:-. o • -.+-~ ~++:*- - - : : : . : +, .~ -., ~ . . , i + ~ " +" " " - -+ ~ + ~ % ' ~ + ~ + + " £ , + 4 ~ I I
+ . ~ . - + " I , , : ~ . ' ~ - : + + ~ + ~ . + . + * .++ z " ~ : + + ' - ~ , " + . . - . e + ~ " . z " . . . . + . + . , : . . ~ + ~ _ ~ : + . . . . . . . . +~ +if". . . . . . . . . . . . • ~ . . . . . . + . + . _ . + : , T , , + . . . . . . ~ ~ • ~ + , . . _ ~ v + < +~.I~ : o + + + + + ,: + + ~ . - - + ~ _ . + P ~ + - ~ + , , + . . + + ~ . - + : - . ~ r + ~ +,,.
+ + - - - . i ~ . ' * - ~ + + - ' . + " I i _ ~ • " + - - o , - m + ° • ~,.- +~+s._ . . ~ + ,++ . , + , ~ -+:+ +.+++,, : + : + - , : ~ + - ~ + . . s : , : + :.:v~-++t.:., + ~ . . ~ _ ~ - ~ . + . • +..~ , . . ' , , , , , - +.J; ++~+~ +~. ++-++.,..,+:, ++,-, +. ,* .+ . • . + . - ~ , , + + + = . , , + r : ~ . , , ~ + • ,
"''~...+. - a '~ + . ~ ' ; +: " : ' : . . . 4 : 2 . +. +~ . m + ~ • . :" ~" : ' : ~ + +e" " 4 " ~ " " I * + '~+ ":" ' + " + " ; :" ~ t~+"+: : + + + ~ + + i r e . - - , - - : ~ + + + +~-++: -.,+" '++,+" . _." :+.: ~L:+ ~ ' ~ . . + + *.+• "+.-++~ .s+'+:~:+: ."o " : - +'Y "+ : ~ : "+:" ' : L ~" + ~ '+ "A'~+ " + * ' . . . . + "~,+ " + "++++. ~ + . : + " " + + ~ + + ° * + - ' + + " + ~ _ + L ~ " " " ~ " + , • + . : ~ . + ~ i ' + ~ J l +
",++'.+ +~'='~+::. +,,~++ "::"'~-":s-. +. -+'+ -+ .:+++"++-"- ' ° ' + + +_~ +. *-- ' , '+*-.~; : ~ . + : " - ~ - " - + + v ++m + - - + + + ' + - + • 21++ " + ~ - + ' - , ~ , + + .+,:+~. + . . , r ~ . ~ _ + +,+:~ + ,+ . s . +- ~ . . . ~ . ~ ~r + + . - . + . + . . " ~ . 2~..+: . +. I
++,.::'-+ .++-":-,.'+,,,-_+:."/,+:++~2L:+. ' ' + - m t +" - + ~ +++++.: 5+++:2:~. , '*~ .. + • + i -+ . . . . -_-. - . 41.1.+~.~-~ I ' i i * I ~ " !v+%~ . . . . II* + 3 t ' ~ '+" • ~ + - - + - ' G ~+~.t,- • ++..~ ++j~+l+. . .
.+-.~- ':.-~£'~.g.++~+~+~,:-,-,; +: .~+: ,m~-:+ ,: '+'+.,,., -+ ' . . . - +7- • ~+:. +'+.:%., +, . +,,:.+ +:,.,.++;+.,.+,+ ........ +.+ -+.,- _ , . . .~ •+" . . . . +~-+: , . - + . ...... -+.:+~+ ,~k+: +" ++~.:+;, ~++e: +~ "=~ , ' . : ++.++ '+r+~ ,i,+~+++..'+~+++',. +++ ++.e+.+,,~ 1,-_ . - ' - p'+~.~,,+ +j . + + . ~':++ +. . + ~ + - ' l . - - ~ii + + . . . . + • + . > . . ~ i i . . + "
, . . .~:+.:+% +. ~ . . ++++, ++++'7 - e . - .:. ~.. <~ ~++ ++ ~I... ~ . .~ ,~ ++ ; . . a , + . t " : . ++ " ; O h + . V +++"+" .++ ".+ . . . + ' ' . . . . . :+" + ' ~ . . ' + " •" '~ . . '~+:+'~ '
+ . : + l ~ "++ ' + : . -+ + - + ~ : ~ ."~..+ ~ +" % ~ I " + i l ~' ~'.-+~'+ "+ . + - +'+++,;+: + + , , , ~ . * , , . + . _ . - + , + . - . . : . : + + ~ , +...-+ , . . : . -. ~ ' _ ' + + + . ,
+ , z , , , ~ 3 + + + + r + . .+'~+,.. ~ + ' o . - , . ~ . " + + • . ' + + ~ . + + . . . . . . " *+:: + + " ' ~ ~ + + + ~ * . : + +'~+~+,,,. + "L. " ~ + ' : + - + : ~ . . . . " + ~ :-'++,+-+- . J ' ~ + < - . ~ , - + . • , + : , ~ . . + . . + + . . , + . . . . + + + . +~ . - - = ~ J . . . . "++ " + + ~II++'+~ : + ~ +'+Ib'++ + ' ~ ' : * ' ~ + • +* + +++ . - ~ + + + ~ +~ ~ ~ + .+~2,++:. , .+*. + + _ . + , + , + + , . + . + + + , , + + + , + +++ .... ,+.,+, ++,+++,+.,++,.,+
• .++"++-+ • ~ . , - ~ , ~ ' + + ~ - , , > . + : + +~ ' . . t " . + + " ? . - ~ - ~ ". + ~ ' . - : + ++:'+ ~"~':~ .':+,~':, + • "~, . ' * + : : ~ + ~ " " ' :" " ' +*=1+ ++ : + : , t : ~ +,1+ *+.=.*'+ " ' . ~ + . 1 . ~ + . . . . . + " ~ + + ' ~ Z ~ ~ + + " ' ~
+ .o~.,+ ~ + ~ ,-~:., ~.+.~++++,-.-:. o , + . ++:+- '+:: +, ,.:..:.>+~++ +,~,.,-.:P+~+_++~¥+~,++.~++++.:. +. . .,~+:,;.+:~- :~.+,:~ ...--~,*-~. + .,++~- +,,,+ . . . . . + * + , . . . , ,*+.++..~: , ~ , + ; , . .+~ , ~ ~ . ~ , + .,++ .+ + + - , . . . . + + . . . . . . . . . . +~+.~++~.:+.~,+ ++. .+ ~ . : ; .~.
S U R F A C E A S U R F A C E B
P o l i s h e d C o n c r e t e F i n e C o l d A s p h a l t
. + + . -++++'+ ++ , - j ~ . + _ _ - ~
• . __ + • + +.,~ ~
" +.,ll +
• ~.++ ++ ,,
S U R F A C E C
A s p h a l t w i t h C h i p p i n g s { W h i t e )
+ p.~.X+:. . . + ~ : , -.,~+
• • . y - : . , + ~ . + : +,~ ~, • . - .
+ + + + ~ + : : . . + + . ++ • ~ . . . !
S U R F A C E E
A s p h a l t w i t h C h i p p i n g s ( B l a c k )
S U R F A C E D
R o u n d e d G r a v e l C a r p e t
• : , ..+:++e . ~ . • . ~ + - • ;
-+ . + " .,e':.,,~,,++'.-.+'-,: -:,~ z. ~ +':'+~'-;-~++.+-,~,;fi;~2*'~ .'re- + .,++, - + ~ + + . . ' , r . ._..:q+,+.
~.. ,~ .~+.#' . + ~ - < ~ . + : ' ~ + - - - ~ r ~ + . ~ + . ~ ' ~ , ' . +. ... . : . , ;+ - , -+, .-= • , . ~ " : " + t . ' M k ~ , , , , . . . ' + • - r ~ • .- ~ + ' - ' ~ . j + ~ + l , ' : ' e ' , + + + + . ~ - ' , " : + + ~ + . + ~ - z . < ~ : -.- . * - ,+' +" , . " --'~ .
. . . . + + " ~ ++4g, - ~ " + m
S U R F A C E F
B r u s h e d C o n c r e t e
PLATE 2
T h e t e s t s u r f a c e s
S m o o t h
7 - R i b
5-Rib
9 - R i b
1 3 - R i b
PLATE 3
T y r e s u s e d in E x p e r i m e n t 1
0 . 0 2 in . G r o o v e s S m o o t h
O. 1 in . G r o o v e s 0 . 2 in . G r o o v e s
0 . 3 in . G r o o v e s 0 . 4 in . G r o o v e s
PLATE4
T y r e s u s e d i n E x p e r i m e n t 2