G
Guest
·Hi folks,
The tire contact calculation post reproduced below is so elegant. Mathematics by keeping track of units is an amazingly simple way to get things right.
But this physics exercise has curious implications that I am having trouble putting my finger on (despite a month of occasional reflection)! For those on digest I'll repeat the salient part.
Doug wrote,
“also here's calculation to help explain this...car weight 2700 lbs
+ 2 passengers...say 350 lbs + cargo say 50 lbs..= 3100 lbs.
if tires ARE at 50 psi (assume equal weight distribution for now)
then the average required area in contact to road is = 3100/50 = 62
sq.in. / 4 = 15.5 sq.in per tire..approx. equal to a 3 x 5 spot on
the ground..conclusion ..lower pressure requires more surface area in
contact..and 175 tires don't deform uniformally to accomodate a
larger surface contact area..thus cupped wear pattern. and why at 35
psi michelins need to be 185's.”
<me again>
Could this mean that
1. On the moon or on Jupiter the tire contact area is the same (independent of gravity).
2. Two narrow tires instead of one wide tire, would give half the contact area.
But why oh why?
Puzzled in Pennsylvania
nathan
The tire contact calculation post reproduced below is so elegant. Mathematics by keeping track of units is an amazingly simple way to get things right.
But this physics exercise has curious implications that I am having trouble putting my finger on (despite a month of occasional reflection)! For those on digest I'll repeat the salient part.
Doug wrote,
“also here's calculation to help explain this...car weight 2700 lbs
+ 2 passengers...say 350 lbs + cargo say 50 lbs..= 3100 lbs.
if tires ARE at 50 psi (assume equal weight distribution for now)
then the average required area in contact to road is = 3100/50 = 62
sq.in. / 4 = 15.5 sq.in per tire..approx. equal to a 3 x 5 spot on
the ground..conclusion ..lower pressure requires more surface area in
contact..and 175 tires don't deform uniformally to accomodate a
larger surface contact area..thus cupped wear pattern. and why at 35
psi michelins need to be 185's.”
<me again>
Could this mean that
1. On the moon or on Jupiter the tire contact area is the same (independent of gravity).
2. Two narrow tires instead of one wide tire, would give half the contact area.
But why oh why?
Puzzled in Pennsylvania
nathan