Interactions between pneumatic tires and pavement surface

Horne, W. B.

English

NASA Technical Reports Server

INTERACTIONS BETWEEM A PNEUMATIC TIRE AND A PAVEMENT SURFACE 
By Walter B. H o m e  
NASA Langley Research Center 
Langley S t a t i o n ,  Hampton, V a .  
Presented  a t  Che 
Bureau of P u b l i c  Roads Program Review Meeting 
- 1  
Gaithersburg, Maryland 
December 6-8, 1966 
https://ntrs.nasa.gov/search.jsp?R=19680015871 2020-03-23T22:54:06+00:00Z
INTRODUCTION 
The Supersonic Transport  estimated t o  cos t  $30,000,000 and your 
family c a r  have one common f e a t u r e  - t h e  pneumatic t i re .  
widely d i f f e r i n g  veh ic l e s  depend upon t h e  pneumatic t i r e  t o  perform 
th ree  bas i c  func t ions  f o r  s a f e  and r e l i a b l e  ground operat ion.  These 
func t ions  are: 
Both of t h e s e  
(1) To support  t h e  mass of t h e  veh ic l e  and i t s  payload 
under a l l  s t a t i c  and r o l l i n g  condi t ions  
(2) To develop cornering o r  s i d e  fo rces  f o r  veh ic l e  s t e e r i n g  
and t o  oppose ex te rna l  s i d e  fo rces  a c t i n g  on a veh ic l e  
such as from crosswinds,  cen t r i fuga l  e f f e c t s  i n  curves  
o r  t u r n s ,  and g r a v i t a t i o n a l  components due t o  pavement 
crowns 
( 3 )  To develop propuls ive fo rces  from d r i v i n g  wheels t o  maintain 
veh ic l e  motion and t o  develop r e t a rd ing  fo rces  from 
braking wheels t o  arrest veh ic l e  motion 
How w e l l  t h e  pneumatic t i r e  performs these  t h r e e  func t ions  f o r  the 
veh ic l e  depends i n  t u r n  upon t h e  condi t ion  of t h e  pavement t h e  t i r e  is 
r o l l i n g  upon. It i s  a l l  too  t r u e ,  t h a t  t h e  i n t e r a c t i o n s  between t i r e  
and ground, and the re fo re  veh ic l e  s a f e t y ,  vary g r e a t l y  with both t i r e  
and pavement condi t ions .  It i s  t h e  purpose of t h i s  paper t o  b r i e f l y  
desc r ibe  t h e  na tu re  of some of t h e s e  major tire-pavement i n t e r a c t i o n s .  
2 
The p o r t i o n  of t h e  v e h i c l e  mass supported by a flexibl:% pneumatic 
t i r e  causes  t h e  t i r e  t o  d e f l e c t  v e r t i c a l l y  an3 t o  d i s t o r t  so t h a t  t h e  
t i r e  a c t u a l l y  c o n t a c t s  t h e  pavemait over  a w e l l  def ined  area c a l l e d  t h e  
t i re  f o o t p r i n t  as shown i n  f i g u r e  l(a>. 
i s  governed by t i r e  des ign .  For  example, a b i c y c l e  tCre w i l l  have a 
long but  narrow f o o t p r i n t  wh i l e  a rac ing-car  t i r e  w i l l  have a wide but  
s h o r t  f o o t p r i n t .  
The shape of  a t i r e  f o o t p r i n t  
LOAD INTENSITY 
The v e r t i c a l  load supported by t h e  t i r e  d iv ided  by t h e  f o o t p r i n t  
area i s  t h e  load i n t e n s i t y  o r  t h e  average  ground bear ing  pressure .  For  
both a i r c r a f t  and automobile  t i res ,  t h e  s t r e n g t h  ( s t i f f n e s s )  e f f e c t s  of  
t h e  t i r e  c a r c a s s  are  small, and t h e r e f o r e  t h i s  bear ing  p res su re  i s  u s u a l l y  
only  s l i g h t l y  h i g h e r  t han  t h e  t i r e  i n f l a t i o n  pressure .  The ground bear ing-  
o r  t i r e  i n f l a t i o n - p r e s s u r e  i s  very s i g n i f i c a n t  f o r  t ire-pavement i n t e r -  
a c t i o n s .  This  p r e s s u r e  i s  used by pavement d e s i g n e r s  t o  determine r equ i r ed  
pavement s t r e n g t h .  T h i s  p re s su re  a l s o  de te rmines  t h e  maximum a v a i l a b l e  
f r i c t i o n  c o e f f i c i e n t  t h a t  can be developed between t i r e  and ground 
under  d r y  c o n d i t i o n s  as shown i n  f i g u r e  2. The d a t a  show t h a t  t h e  
a v a i l a b l e  f r i c t i o n  c o e f f i c i e n t  dec reases  as t h e  p re s su re  i n c r e a s e s .  
Th i s  f i g u r e  a l s o  shows t h a t  some i n c r e a s e  i n  f r i c t i o n  may be obta ined  
by a p p r o p r i a t e  t r e a d  rubber  compounding, as i n d i c a t e d  by t h e  h ighe r  
f r i c t i o n  c o e f f i c i e n t  developed wi th  s y n t h e t i c  rubber  t r e a d s  on au to  
t i res  as a g a i n s t  t h a t  f o r  t h e  n a t u r a l  t r e a d  rubbers  used on a i r c r a f t  
t i res .  Research r e s u l t s  a l s o  show t h a t  pavement t e x t u r e  has  but  l i t t l e  
3 
e f f e c t  on f r i c t i o n  c o e f f i c i e n t s  developed on d r y  s u r f a c e s  as shown i n  
f i g u r e  3 .  The d a t a  shown i n  t h i s  f i g u r e  a l s o  i n d i c a t e  a speed e f f e c t  
i n  t h a t  t h e  f r i c t i o n  c o e f f i c i e n t  tends  t o  dec rease  somewhat as v e h i c l e  
speed i n c r e a s e s .  The e f f e c t  of i n f l a t i o n  p res su re  i s  a l s o  i n d i c a t e d ,  t h e  
ugper  curve  i s  f o r  140 pounds per  square  inch  and t h e  lower curve  f o r  
290 pounds pe r  square  inch.  
TIRE SLIP 
The a b i l i t y  of a t i r e  t o  develop f r i c t i o n  on d ry  pavements depends 
t o  a g r e a t  ex ten t  on whether t h e  t i r e  i s  r o l l i n g  o r  s l i d i n g  upon t h e  
pavement as shown i n  f i g u r e  4 ,  where braking anLd sideways f r i c t i o n  
c o e f f i c i e n t s  are p l o t t e d  a g a i n s t  s l i p  r a t i o .  
as t h e  r a t i o  of t h e  v e h i c l e  speed minus t h e  braked wheel speed to t h e  
v e h i c l e  speed.)  I n  t h i s  f i g u r e  a f r e e l y  r o l l i n g  unbraked wheel h a s  a 
s l i p  r a t i o  of 0 wh i l e  a f u l l y  sk idding  ( locked)  wheel has  a s l i p  r a t i o  
of 1 .0 .  These p a r t i c u l a r  d a t a  w e r e  obtained by r o l l i n g  t h e  t i r e  a t  a 
yaw a n g l e  of e i g h t  degrees  t o  develop a co rne r ing  o r  s i d e  f o r c e  and 
then apply ing  wheel brakes t o  t h e  po in t  t h a t  t h e  t i r e  locked up. The 
sFeed of t h e  t es t  w a s  30 miles per  hour and t h e  pavement w a s  d r y .  Con- 
s i d e r  f i r s t  t h e  dashed curve  f o r  t h e  sideways f r i c t i o n  and n o t e  t h a t  
t h e  t i r e  develops  a s teady  s t a t e  s i d e  f o r c e  a t  s l i p  r a t i o  of 0 .  A s  
Che brake i s  a p p l i e d ,  t h e  braking f r i c t i o n  ( s o l i d  curve)  i n c r e a s e s  t o  
a maximum va lue  a t  about  a s l i p  r a t i o  of 0.18 and then dec reases  t o  a 
lower va lue  a t  wheel lockup ( s l i p  r a t i o  of 1 .0) .  The sideways f r i c t i o n ,  
( S l i p  r a t i o  may be d e f i n e s  
4 
however, r a p i d l y  dec reases  wi th  i n c r e a s i n g  s l i p  r a t i o  and approaches 
- zero  a t  s l i p  r a t i o  of 1.0.  The lesson  t o  be learned  h e r e  i s  t h a t  a 
completely locked o r  f u l l y  sk idding  wheel has  no s t e e r i n g  c a p a b i l i t y  
whatever;  a t i r e  cannot develop any s i d e  o r  co rne r ing  f o r c e  i f  t h e  wheel 
i s  locked,and d r a s t i c  l o s s e s  i n  s i d e  f o r c e  can be expected i f  t h e  t i r e  
s l i p  r a t i o  exceeds t h e  i n c i p i e n t  skidding va lue ,  which f o r  t h i s  c a s e  
i s  about  0.18. These f a c t s  p o i n t  wi th  f avor  toward t h e  u s e  of a n t i -  
skid o r  ant i -wheel  locking  dev ices  i n  v e h i c l e  braking systems t o  prevent  
wheel lockups and i n s u r e  adequate  t i r e  co rne r ing  o r  s i d e  f o r c e  c a p a b i l i t y  
du r ing  heavy wheel braking.  
PAVEMENT CONTAMINATION 
The most adverse  t i r e - s u r f a c e  i n t e r a c t i o n s  occur  when pavements 
become contaminated wi th  water, snow, s l u s h ,  i c e ,  and combinations of  
road d u s t  and water, o r  o i l  and w a t e r ,  and can  under  c e r t a i n  c o n d i t i o n s  
r e s u l t  i n  a lmost  complete l o s s  of  t i r e  t r a c t i o n .  Three phys ica l  phe- 
nomena c h i e f l y  r e s p o n s i b l e  f o r  t h e s e  adverse  e f f e c t s  are l i s t e d  i n  
f i g u r e  5. ‘These phenomena are des igna ted  as dynamic hydroplaning,  
t h i n - f i  l r n  l u b r i c a t i o n  ( o r  v i scous  hydroplaning)  , and r eve r t ed  rubber  
sk id .  
Dynamic Hydroplaning 
When a r o t a t i n g  o r  s l i d i n g  t i r e  runs  i n t o  t h e  s t a t i o n a r y  water 
on a f looded pavement, a s t a g n a t i o n  p res su re  deve lops  a t  t h e  tire-water 
i n t e r f a c e  a c r o s s  t h e  width of t h e  t i r e .  Th i s  dynamic water p re s su re  
5 
b u i l d s  up  as t h e  square  of  v e h i c l e  speed, and a t  a c r i t i ca l  speed, 
c a l l e d  t h e  hydroplaning speed, equals  t h e  average  t ire-ground bear ing  
p res su re  o r  approximately,  t h e  t i r e  i n f  l a t t o n  p res su re .  A t  v e h i c l e  
speeds i n  excess  of t h e  hydroplaning speed, t h e  dynamic water p res su re  
ba lances  t h e  t i re-ground bear ing  p res su re  over  t h e  t i - r ?  f o o t p r i n t  and 
t h e  t i r e  i s  he ld  o f f  from t h e  pavement and r i d e s  on a water f i lm.  Th i s  
i s  c a l l e d  hydroplaning and i t s  p rogres s ive  development wi th  speed i s  
shown i n  f i g u r e  1. 
braking f r i c t i o n  produced by a n  a i r c r a f t  t i r e  i s  shown i n  f i g u r e  6 f o r  
var ious  cond i t ions  of t r e a d  w e a r ,  where zero  w e a r  r e f e r s  t o  a groove 
depth  of 0 . 2 2  inch .  Note t h a t  t h e  t r e a d  grooves are e f f e c t i v e  a t  t h e  
lower speeds i n  r a i s i n g  f r i c t i o n  c o e f f i c i e n t  bu t  are i n e f f e c t i v e  a t  
speeds near  o r  above t h e  hydroplaning speed. Research i n d i c a t e s  t h a t  
i f  t h e  w a t e r  depth  i s  g r e a t e r  t han  t h e  groove depth ,  even grooved 
t r ead  t ires l o s e  t h e i r  e f f e c t i v e n e s s  a t  h igh  speeds and behave as 
smooth t r e a d  t i res .  
The i n f l u e n c e  of dynamic hydroplaning on t h e  
Thin-Fi l m  Lubr i ca t ion  ( o r  V i  scous Hydroplaning) 
Th i s  phenomenon r e s u l t s  from t h e  i n a b i l i t y  of t h e  t i r e  t o  puncture  
and d i s r u p t  t h e  very t h i n  r e s i d u a l  f l u i d  f i l m  l e f t  on t h e  pavement i n  
t h e  t i r e  f o o t p r i n t  area a f t e r  t h e  m j o r i t y  of t h e  t rapped w a t e r  has  
been d i sp laced  by the t i re .  The f l u i d  p re s su re  bui ldup  i n  t h e  f o o t p r i n t  
i n  t h i s  i n s t a n c e  i s  due t o  v iscous  p r o p e r t i e s  of t h e  f l u i d ,  and tes t  
r e s u l t s  i n d i c a t e  t h a t  t h e  phenomenon i s  accentua ted  when f l u i d s  more 
v iscous  than  water, such as o i l  o r  a mixture of road d u s t  and w a t e r ,  
contaminate  t h e  pavement. This problem i s  p a r t i c u l a r l y  hazardous f o r  
smooth t i res  ope ra t ing  on smooth pavements, and one ou t s t and ing  method 
t o  e l i m i n a t e  o r  a l l e v i a t e  t h i s  problem i s  t o  provide a t e x t u r e  t o  t h e  
pavement as shown i n  f i g u r e  7 .  It should be emphasized t h a t  t h e  d a t a  
shown i n  t h i s  f i g u r e  were obta ined  on tesZ s u r f a c e s  which were damp. 
They were not  flooded and containecl no s tanding  water. 
Another ou t s t and ing  method t o  combat v i scous  hydroplaning i s  t o  
provide s i p e s  i n  t h e  t i r e  t r e a d  between t h e  t r e a d  grooves (see t i r e  i n  
f i g u r e  11. 
break through the f l u i d  f i l m  and a l low t h e  t i r e  t o  r ega in  a p o r t i o n  of 
i t s  d r y  g r i p  on t h e  pavement. 
sideways o r  corner ing  c o e f f i c i e n t s  of f r i c t i o n  obtained on a w e t ,  
very smooth, conc re t e  pavement are shown f o r  automobile t i res  having 
smooth, grooved, and grooved and s iped  t r e a d s .  
The sharp  edges of t h e  s i p e s  i n  con tac t  wi th  t h e  pavement 
This  e f f e c t  i s  shown i n  f i g u r e  8 where 
Reverted Rubber Skid 
Th i s  phenomenon i s  named f o r  t h e  appearance of a t i r e  a f t e r  c h i s  
type  of sk id  occurs .  The t i r e  shows a pa tch  of rubber t h a t  has  t h e  
appearance of having been heated t o  t h e  po in t  t h a t  t h e  s u r f a c e  rubber  
has  melted and has  r eve r t ed  back t o  t h e  uncured s ta te .  Th i s  t ype  of 
sk id  happens a f t e r  a prolonged wheel sk id  and once s t a r t e d ,  r e s u l t s  
i n  very low t i re-ground f r i c t i o n  t h a t  p e r s i s t s  down t o  very low 
speeds . 
Presen t  t h ink ing  sugges t s  t h a t  t h e  braked t i r e ' s  con tac t  wi.th the 
w e t  pavement may produce enough hea t  t o  t u r n  t h e  water t rapped i n  t h e  
7 
f o o t p r i n t  i n t o  steam, which would be ho t  enough t o  change t h e  rabber  
i n  t h e  c o n t a c t  patch t o  r eve r t ed  rubber.  It has  been suggested t h a t  
t h i s  pa tch  of s o f t  and tacky rubber  could produce a seal t h a t  keeps 
steam and water entrapped i n  which case  t h e  t i re  would r i d e  on a 
cushion of steam. Thus t h e  d i s t i n c t i v e  whi te  mark l e f t  on a pavement 
by a rever ted  rubber  sk id  may be  t h e  r e s u l t  of t h e  pavement s u r f a c e  
i n  t h e  t i r e  path being steam cleaned .  Fo r tuna te ly  as f a r  as highway 
s a f e t y  i s  concerned, t h i s  phenomenon has  been noted thus  f a r  only on 
high speed a i r c r a f t .  An example of t h e  whi te  s t reak- rever ted  rubber  
skid i s  shown i n  f i g u r e  9 .  
Summary of Techniques f o r  Improving T r a c t i o n  of T i r e s  
on Wet Pavements 
A summary o f  techniques  c u r r e n t l y  a v a i l a b l e  f o r  improving w e t  
t i r e  and w e t  pavement t r a c t i o n  i s  shown i n  f i g u r c  10. Th i s  summary 
i n d i c a t e s  t h a t  t r i e d  and true techniques  o f  t h e  p a s t ,  such as t i re  
t r e a d  d e s i g n  and t e x t u r i n g  of pavement s u r f a c e s ,  whi le  g r e a t l y  b e n e f i c i a l  , 
are unab le  t o  cope wi th  a l l  pavement contaminat ion and v e h i c l e  speed 
cond i t ions  p re sen t  o n  t o d a y ' s  highways and a i r p o r t  runways. Rela- 
t i v e l y  new concepts  such as porous pavements, pavement grooving 
( f i g u r e s  11 and 121, and a i r  j e t s  placed i n  f r o n t  of t ires ( f i g u r e  13 
(see r e f e r e n c e  1 f o r  f u r t h e r  d e t a i l s ) )  o f f e r  promising r e s u l t s  f o r  
improvement i n  t r a c t i o n ,  and. research i n  t h e s e  areas i s  c u r r e n t l y  
underway a t  NASA and elsewhere. 
8 
CONCLUDING REMARKS 
Tire-pavement i n t e r a c t i o n s  on d r y  pavements are f a i r l y  s imple and 
w e l l  understood, and provide adequate  t r a c t i o n  f o r  v e h i c l e  braking 
and d i r e c t i o n a l  c o n t r o l  on p r e s e n t  highways and runways f o r  normal 
o p e r a t i o n s .  Locked wheel skidding or o t h e r  abnormal v e h i c l e  o p e r a t i n g  
procedures can  produce problems which may no t  be s u b j e c t  to  c o n t r o l  
even under i d e a l  cond i t ions .  
Tire-pavement i n t e r a c t i o n s  on contaminated pavements are much 
more complicated t h a n  t h o s e  occur r ing  on d r y  pavements and are n o t  
n e a r l y  as w e l l  understood. Research r e s u l t s  i n d i c a t e  t h a t  t i res  
having smooth o r  badly worn t r e a d s ,  and pavements worn smooth o r  
pol ished from t r a f f i c  o r  i n i t i a l l y  provided with t o o  l i t t l e  s u r f a c e  
t e x t u r e ,  must be i d e n t i f i e d  and r e j e c t e d  f o r  v e h i c l e  and f o r  highway 
usage  i f  highway s a f e t y  i s  t o  be improved. For example, smooth t i r e  
o p e r a t i o n  on highways can  be c o n t r o l l e d  o r  p r o h i b i t e d  as i s  p r e s e n t l y  
being done i n  New York S t a t e  and s e v e r a l  European c o u n t r i e s .  Criteria 
and e v a l u a t i o n  techniques are v i t a l l y  needed t o  d e t e c t  s u r f a c e s  which 
are p o t e n t i a l l y  s l i p p e r y  when w e t  so t h a t  t h e  s u r f a c e  can  be renovated 
by pavement grooving, s u r f a c e  a d d i t i v e s ,  o r  r e s u r f a c i n g  b e f o r e  
skidding a c c i d e n t s  s tart  t o  occur .  An educa t iona l  program t o  alert  
t h e  automotive p u b l i c  on haza rds  of w e t  road d r i v i n g  i s  a l s o  r equ i r ed .  
9 
REFERENCE 
1. Horne, Walter B.; Yager, Thomas J.; and Tay lo r ,  Glenn R.: Recent 
Research on Ways t o  Improve T i r e  T r a c t i o n  on Water, Slush o r  
Ice. Presented a t  t h e  AIAA Aircraft Design and Technology 
Meeting (Los Angeles, C a l i f o r n i a ) ,  November 15-18, 1965. 
Figure 1.- Photographs of typical  production-type t i r e  taken through glass 
Direction of motion l e f t  t o  right. 
plate .  
Yaw angle = 6'. 
Water depth = 0.4 inch. Vertical load = 835 pounds. 
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Interactions between a pneumatic tire and a pavement surface

Abstract

Similar works

Full text

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NASA Technical Reports Server