<VV> Stock wheels or not???

[Bill Elliott]

On Tue, 2 Aug 2005 10:20:37 -0400, N. Joseph Potts wrote:

>The changes you describe aren't just in the RATINGS or even just
>width/aspect ratio of the tire - the changes are in the WHEEL (rim) size,
>which I suspect is most important.
>     And my own experience backs you up as far as my own driving style can
>allow: I changed from 13 to 14 primarily for size availability, and as I've
>reported many times on this forum, I experienced GREAT improvements above
>50mph in switching from Firestone 205/70R13s to Dunlop 195/70R14s.
>     So I have no argument, or even suggestion of it, where it comes to
>uprating (increasing) the WHEEL size. Best thing I even did for my Corvair's
>performance, and no perceptible loss of comfort, either.
>     Now, here's the story on the RATINGS of the tires in this tale. The
>13-inch tires would appear to have NO suffix. (No rating? Does that mean the
>tires are old, which they aren't, or is no rating a "rating"?) The 14-inch
>tires have a 90S suffix, which I think is bottom of the heap, but still
>better (?) than no rating. 195/70R14 90S


I agree that increasing wheel diamter has a positive effect on handling... because of less sidewall flex. 

That is the same sort of improvement that you get with a higher speed rated tire as well. If you'd gone to 
say a V-rated 195/70VR14 (not that such an animal exists) you would have seen an even bigger change 
to your already GREAT imporvement. Generally the higher the speed rating, the stiffer the sidewall.  Of 
course the other improved aspect of the speed rated tire is a softer rubber compound so your grip is up 
substanitally as well.

On the other hand, the handling on my Corsa GREATLY improved when I dropped down from a 
215/60TR14 to a 205/60VR13... so SOMETHING was at work here besides rim size and aspect ratio. 
That's the sidewall stiffness and the rubber compound (along with the reduciton in unsprung weight.)

"S" is a real speed rating (112mph) that has to be attained through lab tests. Since speed ratings are 
not mandatory in this country (many places in Europe you cannot replace a tire with one of a lower 
speed rating than the car came with) companies that don't export tires have no reason to get a 
certification. Tires without a certification are assumed to be rated for 99mph. (The new "Q" rating that 
you often see on snow tires is also 99mph and I understand can be obtained without the same 
certification test necessary for the "S" rating.

Two other ratings you should look at are the traction and temp ratings. Almost all modern radial tires 
have at least an A traction rating...usually only V-rated tires (and up) have an AA rating (new rating that 
came out since everyone was meeting the A). 

Temp ratings show how well the tire withstands heat buildup (due to speed, load, and inflation). Cheap 
tires  may only have a C rating... I demand at least a B for this rating... and usually only H-rated tires and 
above have an A rating.

Bill