JSR_AP2

I'm running 245s on a 7" wide wheel and as expected, the outter edges are pinched in a bit, so the edge of the tread doesn't contact the ground. I'd assume those running 265s on the OEM 7.5" wide wheel would see the same problem. Do you run the normal pressures?...or do you run lower pressures to get the edge treads to better contact the ground? It would seem to me that running a low enough pressure for the edge tread to contact the ground would be too low a pressure and have far too much sidewall flex, but I was wondering what ppl do when a wide tire is pinched to a narrower wheel and the side tread is unused. Thanks.

glagola1

I think it's probably best to just do some testin and tunnin. Get out to the track or a skid pad and take some lap times, feel and response and tire temp data. Often times, I just do what feels best. You'll find that you'll get trade offs for variations in tire pressure. For example, a higher pressure may give better turn in but may sacrifce ultimate grip or lower pressures might give better grip at the cost of sloppy feel.

I don't think anyone will be able to give you a definative answer.

Race Miata

I haven't had much experience with my S yet, but I've had various wheel/tire combo experience on my miata (from 215/50/13 on 6" wheel to 235/45/13 on 9" wheel) and my BMW. From my experience, narrower-than-optimal wheels need to run higher pressure on the tires for cornering performance (I assume this is what you're after).

Yes, a narrower-than-optimal wheel will have the sidewall slanted outwards which lifts the outermost tread above the pavement at rest position. However, when you corner, the outside sidewall of the outside tire flexes towards the centreline of the car. This sidewall at some point stands straight up pushing the outermost tread on the pavement. This is where non-linear handling comes in. The remedy is to run extra tire pressure and/or extra -ve static camber.

On the other hand, when you run an optimal-width wheel for a given tire, the sidewall stands straight up or even be slanted inward (like in my case of 235/45/13 on 9" wheel) at rest position. When you corner, again the outside sidewall of the outside tire flexes towards the centrelilne of the car. As the outside sidewall flexes inward it pulls the outermost tread away from the pavement which is like generating -ve camber! That's why optimal wheel-width gives linear and predictable handling without extra tire pressure or extra -ve static camber setup or tires with unreasonably stiff sidewall.

And this is why I would sacrifice tire width for optimal wheel fitment if at all possible (if I have to stick with a certain wheel). Now if you're talking about limited wheel/tire choice or you want ultimate cornering grip over handling characteristics, that's a different story.

glagola1

Wow, that's cool about the non-linear cornering characteristics.

JSR_AP2

Thanks Race Miata! Great info. Yes, I'm trying to maximize cornering performance w/ the current setup (16x7 w/ 245/45/16). So, it seems the outside tread will eventually contact the pavement (while inside will not), but will result in non-linear, less predictable grip mid-corner. Thanks!

jguerdat

Hmph. Empirically, the 265/45-16 seems to be working fine at 30 psi. This is for both the Victoracers and 710s...

Race Miata

[QUOTE=jguerdat,May 12 2005, 04:43 PM]Hmph.

jyeung528

so what is the solution.