go to joe250.com and that'll tell you whats involved in putting 285's on

 

Eric I would agree if the diameter is too different. The front and rear wheel speeds are always different whenever you are turning, it's not like a little slip is going to hurt it (that is what it's there for). The trick is finding out how much it will tolerate before it adversely effects handling and/or longevity.

It sounds like during you testing that the handling gets squirrelly before you hurt the diff (?). So...there may be room to play.

Time attack JDM guys commonly run narrower rear rims to remove some rear grip and they have been doing it back before the EVO 4/5 days which had a viscous centers like ours. The narrow rim crowns the tire which makes it a little taller (and the contact patch a little smaller).

Can you tell us more particulars about you test? Were there any corner types where you felt it worked and where was it didn't etc. Turn-in, mid-corner, exit and in slow, medium and fast corners. Come on, spill it. It sound like you really tried to make it work

Thanks

 

One thing I found interesting is the JDM time attack evos don't run any tires wider than 255 even they have huge fender flairs or widebody kits. Example, the two fastest car on Tsukuba, HKS Evo with 40mm widebody and HRS CyberEVO with 25mm front fender flairs. They can easily fit 285 or even larger tires on but choose not to. I wonder what's the reason behind it since mods are unlimited.

 

I ran 285/30-18's on the front and 245/40-17's on the rear. I tried Kumho Ecsta V700 (got them for free...) and Hoosier A3S04's. The Kumhos were exactly the same circumference and the Hoosiers were a little smaller in the rear if I remember correctly.

The differential issues were not related to tire diameter it was relative grip level. On the throttle the car would tend to spin the rear tires immediately and the coupling would lockup to try to keep the axle slip to a minimum. It's hard to describe the effect unless you've ridden in the car - very violent inside and definitely only happened with different width tires on one axle. I did run the wider tires on the rear once and the effect was no better. With the active center differential the locking effect may be more progressive and have a better chance of working.

Eric

 

Eric,
Thanks for the input. I am still not sure whether or not the monster tires are needed. I read somewhere that with the big tires you guys were getting up on two wheels. lol. I guess I have some experimenting to do.
Mark

 

Obviosly by the user name I can't offer much...

I can say that I've never noticed Erics car on two wheels. I do remember seeing the stock EVO's on two wheels at the DC Tour last year (in pictures-I didn't go)

I'm not sure what you guys consider cheap for wheels but I'll offer my experiences. For us (4th gen f-body) reproduction Grand Sport Vette wheels are available and there are TONS available so they are dirt cheap. But they also weigh TONS.

Last year I bought two Fikse wheels that were basically brand new and for a song...But the cost of two more new wheels, would be just barely less than what John at CCW was willing to sell....

In the end, I paid $1,895 shipped to my door-FL to MI, for a set of 2 17x11's, and 2 17x12's.

 

One other question. This maybe the best place to ask since very few or no pony cars have experimented with 18" wheels.

Last summer I heard some folks grumbling that the 18x10's they bought were a waste, since the 275's were faster than the 285's. And this was directly related to the sidewall height. Where a shorter overall tire, on a lighter 17" wheel, would accomplish the same thing.

Tunnel, on both the M3 and 330, and I heard the same thing about Butts' IS300. Note this was a Hoosier tire issue so mayb that was the cause....

So are you guys running the really short sidewall because you get the extra width with a shorter overall height? So you also beleive it to be faster than a taller sidewall, yet narrower width.

Given the choice would you, run a shorter sidewall in front, or taller, given the same tread width....

I would like to try a 18x11 front with a 315-18 tire, but wonder why no one else has. And at $900 for wheels, and close to$500 for tires, it'll be quite the expensive test.

 

My car was routinely up on two wheels with the large tires. I have several pictures with daylight between the inside tires in sweepers as well as some corner worker comments from slaloms.

Eric

 

I did a test at Peru with the 275 and 285 Hoosiers and the 285's were consistently faster. The smaller tire definitely helps the gearing which is a consideration with a torqueless 4 cylinder....

Eric

 

Eric what kind of differences in responsiveness did you notice between the 275 and 285's. I'm understanding correct that the 275 is actually a taller sidewall tire right?

So was the 285 faster because of absolute grip, or more a measure of the responsiveness due to the shorter, stiffer sidewall.

 

There really was no comparison between the two tires - the 285 definitely had better overall grip. The car pulled out of the corners harder with the 285's as well. The 275 does have a taller sidewall and just felt like it was constantly sliding around in the corners compared to the 285. I don't remember much about the responsiveness.