fc2se

iTrader: (2)

My car has 245/40-18 Bridgestone RE-01R tires on stock wheels (from previous owner). I could be misinterpreting things, but it appears the front and rear tires reach the traction limit at different speeds. (I noticed it during autocross last year and some recent spirited driving.) Has anyone else had a similar experience? (My car has the Mazdaspeed suspension setup which may react a little differently than the stock suspension.)

My only comparison point on this car is to my snow tires. The snow tires have noticeably less grip, but they break away in a much more even fashion. When approaching the maximum speed in a constant radius turn, the snow tires all start to squeal a bit and seem to all get loose together. For me, this type of handling is relatively easy to push to the traction limit without going over it.

I'll have to do some more testing this year to get a feel for how my summer tires break away at the traction limit. I am curious to hear if anyone has experience to say that going back to the stock width will make the traction limit more manageable with this type of tire or not. Would moving back to the stock tire size of 225/45-18 help the situation?

Highway8

iTrader: (11)

This should be in the wheels, tires, suspension section, not racing.

The car does tend to understeer, it is much safer for the average street driver. Many factors could change the under/ over steer balance. Driving style, tire pressure, springs, struts and sway bars to name a few. Most influential is the alignment. If your car is understeering (I'm guessing it is) the first thing would do is an alignment. Start with stock sport and then add a little more negative camber to the front and maybe less toe in, just leave the rear stock for now. Also check tire pressures, you could have excessively high front pressures which will hurt grip. If your going to do a lot of across driving, a more aggressive alignment could and should be used, but sounds like your a ways a way from there.

40w8

My GT 8 was the best handling car I've ever driven, and it took me about 4 or 5 track days to realize how bad the understeer was.

I had excessive neg rear camber, -2.1 from the factory, and when I dialed that down to the minimum the tech could get, -1.65, and the fronts about the same, the 8 started acting neutral. The front toe is the least toe out he could dial, and the rear toe is the least toe in he could dial.

The tire wear became even, and after rotation at 7k miles the front left was 6/32 wear with the others at 5/32.

On a drizzling track day, I was about the only guy that didn't spin off, and no fast cars could catch me.

I decided to always track with the tcs on, and it doesn't interfer unless I've made a mistake.

I've heard a few guys here hand wring about whether a track alignment is safe on the streets for noobs, but I feel most confident with this track alignment on the street.

You still have to drive too fast to get the 8 to spin unlike say a Porsche 911 that's complete oversteer at any speed.

40w8

I know lots of guys like to run 245/40r18's on the stock 8 inch, and like it; I think 245 needs 8.5 inch wheel to give better feel and control.

I go against conventional wisdom, run 225/40 r18 on my Enkei 18 x 7.5 38 offset, and after seeing pics of the car sticking good with the front tire really stressed, I could run 215/40r18.

The wheels weigh 42 #, and I can put DW on and get it down to 38#.

The feel on the track is incredible and even though many cars are faster, I sure wouldn't know it if I was by myself.

I pull all the G's I want.

Highway8

iTrader: (11)

Your new negative camber is a step in the right direction and I agree that it is a good street/track balance.

On the toe, Either you misunderstood the alignment guy or he doesnt know what he is doing. You can get a lot of toe in or toe out. I guarentee your not at the minimum. Maybe the minimum he felt comfortable with. 1/16 toe in for both the front and rear is a safe place for street and track. 0 in the front and it will want to rotate a little more but it wont be quite as stable and on the street it will wonder a little more, so for a street car it is better to increase front negative camber or decrease rear negative camber before playing with toe beyond 1/16 toe in.

And yes 245's on the stock wheels works fine. Some have gone as wide as 275 or 285, but thats on race tires with much stiffer side walls.

40w8

Pure word misunderstanding.

Since the tech could barely run the alignment equipment, I was there to make decisions.

What I meant to say was that: "I told him to zero the toes, but to put the tolerance on toe out in front, and toe in in the back".

I could tell that the rear toe was especially touchy for him, but he got it about .03 toe in for each wheel.

fc2se

iTrader: (2)

Thanks for the information. I will check out that other sub-forum. I see there is an active post on oversteer and understeer. I posted here since the main reason I want to tweak my car is for autocross. I also want to do a track day in it this year. I am by no means a regular racer. I have just done some autocrossing and a few HPDEs for fun. Sorry for posting in the wrong area.