Re: Contact patches

[QSHIPQ@aol.com]

> > Sure it does, Dave.  FE, put a 255/50 15 @ 32psi on a 15X6 stock
>  > audi turbo
>  > quattro coupe wheel.  What happens to the tread near the sidewall?  What
>  > about overall diameter?  Put the 255/50 15 @ 32psi on a 15x9 Urq
>  > racing rim.
>  > Any difference in contact patch?  Elementary to the proper sizing of rim
>  > width to tyre width.  We could speak of the contact patch of a
>  > 245/40 17 on a
>  > 17X7 in RS2 wheel too I suppose. ;)
 
Then PWilson writes: 
>  With a radial tire, theoretically speaking and give a reasonable rim width,
>  the tire contact patch should not change. 

Statically you're correct, "theoretically speaking and give a reasonable rim 
width" (Geez that sounds like a bunch of rules omitted in Mr. E's post:).  
Not the claim.  Dynamically (like in a turn),  the contact patch changes 
significantly, even between a 6 and 7in wheel, many folks have measures of 
that.  The more overhang you have on a rim, the more the contact patch will 
distort (reduce) in turning.  It's also the nature of a radial tyre.  

> That's part of the point of
>  radial tires.  If you take a 255/50 tire and put it on a 6" wide rim, yes
>  the contact patch will probably be effected.  A 255/50 on a 6" rim is
>  unreasonable.  If you compare a 225/50 on a 7" vs. an 8" rim, there won't 
be
>  much of a difference.  What can change slightly is the outside diameter of
>  the wheel/tire combination.

Statically correct, not dynamically, you can measure with a gtech or ganalyst 
a huge difference between the two, btdt, it results in a better cornering 
g-force.  The only way to account for that is contact patch, same tyre and 
pressure, different rim.   "Unreasonable?"  Never saw that in any posts but 
yours.

Scott Justusson

>  
>  > Try www.thetirerack.com.  They do a fine job of explaining the elementary
>  > wheel and tyre questions.  Plus sizing is in there for you too.
>  >
>  > Scott Justusson
>