Originally Posted by ZDan,Aug 8 2010, 08:35 AM

But in S2kland, I see a lot of people giving up tire width potential in order to run lower offsets, which IMO is a net disadvantage.

Originally Posted by ZDan,Aug 8 2010, 08:35 AM

If you'd tried the 10" front wheels/295 tires on the new track width setup, you could have a basis to say which really made the big difference. If I had to guess, I would suspect that 10% wider tires on 20% wider rims made a bigger difference in balance than 6.4% greater front track width.

And shouldn't increasing front track width, by itself, no other changes in wheel/tire width or spring/swaybar rates, give relatively more front roll stiffness, loading the outside front relatively more and the outside rear relatively less, giving more understeer?



Running up front means taking an advantage wherever you can, of course.

But in S2kland, I see a lot of people giving up tire width potential in order to run lower offsets, which IMO is a net disadvantage.

Originally Posted by c32b,Aug 9 2010, 12:57 AM

Hi, just wondering why you say you'd feel it was a disadvantage to give up tyre width vs track with?

I am not the most technical person but I am curious to know the net comparison of say a 245/40/17 rear with +45 offset vs a 255/40/17 +55 offset.

Originally Posted by ZDan,Aug 9 2010, 06:48 AM

255/245 = 1.04, 4% more tire width (which doesn't equate to 4% greater lateral grip, of course, but still...)

track width increase = 2x(55-45) = 20mm
20mm/1500mm = 1.33% (which also doesn't equate to 1.33% greater lateral grip)


But that's not a valid comparison, really. If you can run a given offset with 245s at the verge of rubbing, you can run 255s with offsets only 5mm greater, you wouldn't need to go 10mm greater offset. So the track width "advantage" of running 245 tires instead of 255s isn't really 1.33%, it's only ~10mm/1500mm = 0.67%, less than a percent increase in track width, for a 4% reduction in tread width.

Basically, you're sacrificing a lot more in tread width than you're gaining in track width.

Originally Posted by ZDan,Aug 9 2010, 06:48 AM

255/245 = 1.04, 4% more tire width (which doesn't equate to 4% greater lateral grip, of course, but still...)

track width increase = 2x(55-45) = 20mm
20mm/1500mm = 1.33% (which also doesn't equate to 1.33% greater lateral grip)


But that's not a valid comparison, really. If you can run a given offset with 245s at the verge of rubbing, you can run 255s with offsets only 5mm greater, you wouldn't need to go 10mm greater offset. So the track width "advantage" of running 245 tires instead of 255s isn't really 1.33%, it's only ~10mm/1500mm = 0.67%, less than a percent increase in track width, for a 4% reduction in tread width.

Basically, you're sacrificing a lot more in tread width than you're gaining in track width.

Originally Posted by FF2Skip,Aug 9 2010, 02:38 PM

My head hurts, but I read through all the posts- some twice.

I'm limited on tire width(245 Hoosiers by choice because of pts for NASA TT's). Currently I'm running +63 17x9 CE28N's x 4. Weight of these wheels is about 14.5 lbs, iirc. I have not moved to the 949 6ULR 17x9 +48 wheels because of weight(18 lbs).

Valid stance or would a potential lateral g increase offset decreased acceleration/braking?

Originally Posted by markhs2,Aug 9 2010, 10:04 PM

Why not run CE28 17 X 9.5 +47?

Still very light, and a workable offset.

The Hoosiers are usually very wide so I am sure the 9.5 width would be more optimal as well.

Originally Posted by FF2Skip,Aug 9 2010, 01:38 PM

My head hurts, but I read through all the posts- some twice.

I'm limited on tire width(245 Hoosiers by choice because of pts for NASA TT's). Currently I'm running +63 17x9 CE28N's x 4. Weight of these wheels is about 14.5 lbs, iirc. I have not moved to the 949 6ULR 17x9 +48 wheels because of weight(18 lbs).

Valid stance or would a potential lateral g increase offset decreased acceleration/braking?