Jeremy85

So they'd look wrong, I get that.
Lower the center of gravity? check
Maintain relative roll centers? check
Increase contact patch traction? check
Reduce unsprung weight? check
Reduce effective flywheel inetria? check
Increase effective axle ratio? check
Increase effective leverage of modest brakes? check
big enough to clear 12" rotors with the right 4-piston calipers? check
So the idea is to find the lightest forged aluminum 15" x 8" wheels, then wrap them in Hankook Ventus R-S4 or BFG Rival S 1.5 or Maxxis Victra VR1 245/40R15s.
This should be capable of better performance in every way, than comparable 245/45R17s, at least, and maybe more.
Any problems I'm not seeing?

paul_huryk

You lose 3" of tire diameter, which reduces tire patch by approximately 12% automatically. That alone should turn you off. If you said 275-35-15, it would probably be a wash with stock 245-50-16 tires.

You would also lower the car enough where clearance may become an issue - same as with large drop springs.

Yes, CoG, weight, and rotating mass would be lower - but there are too many negatives to make an overall positive difference.

Jeremy85

I'm not convinced that the length of the effective contact patch would get any shorter.

Jeremy85

There's a thread on Autocross.US about this, that uses a Miata as an example. If a tire is supporting 1/4 of a 2900 pound car, at 30 psi, then it must make 24.16666667 square inches of contact patch, whether it's 6"x4" or 12"x2".
If we accept that, then a tire with 9" of tread width must deform to a 2.7" contact patch length, whether the tire is 23" or 26" unmounted overall diameter.
There are similar threads on physics forums.com which seem to agree.

Jeremy85

So much for a Paul Huryk's claim of loss of contact patch, he posted nothing since I spelled out the physics of it. I might like him if he could admit he was in error.

Drew

iTrader: (58)

Maybe he's just got better things to do with his time than to argue the absurdly hypothetical.

paul_huryk

Spelling out the physics (when they are incorrect) is not going to get a response from me - let alone to admit I was in error when in fact, I am correct.

Keep in mind that no where have I seen it proven in any statistically significant way what you are saying is correct.

And yes, it is absurd. But half the stuff i think of is also.

Jeremy85

The selection of light, affordable wheels strong enough for street and auto cross is poor, I may end up converting the lug pattern to 5 on 114.3
There are 3 choices for streetable 245/40R15s, and at least as many track-only choices. These are max-effort-Miata tires.
I'm inclined to order a single Hankook Ventus RS4 and a single USMags 15x9, 5x114.3, -13 for a test fit. This wheel is probably a heavy casting, not a light forging, and it may stick out of the front fenders farther than I can be ok with, but ya gotta start somewhere.