Mo tires, Mo problems

"roflcopter" (roflroflroflcopter)
03/19/2014 at 13:32 • Filed to: None

So I picked up two new rears for the rx8 and got them mounted yesterday(decided to go cheap this time, usually run Kumhos exclusively), and threw them on last night. They're a bit wider, went from a 225/45 to a 245/40 on the same 8in wheel. Immediately realized that they wouldn't fit nicely when they rubbed through the first turn. Ran home and pulled the spacers off and went for another spin. Now it under steers a bit harder(expected and I can live) but the real issue is the rear being REALLY floaty and it being very twitchy under decel. Guess I'll be rechecking my rear toe and maybe throwing some more caster on the front tonight. -_-

DISCUSSION (23)

Party-vi > roflcopter
03/19/2014 at 13:49

When you decreased your aspect ratio you also increased the turn response of your rear tires (lateral stability) but decreased their longitudinal stability. That, and you added 20mm of rubber to each side in the rear, which increased your contact patch and might increase the effects of tramlining, or your tires' tendency to follow ruts in the road.

roflcopter > Party-vi
03/19/2014 at 13:59

This is the first time I've had any experience with running staggered sizes, what would you suggest to get rid of the funkiness? There's not much I can do for the under steer without sacrificing grip, if I'm understanding correctly, or without spending money on suspension upgrades.

I was thinking slight toe in on the rear to make it follow better and be less floaty, then a bit more caster in the front to fix the tendency to over correct that it's doing now(even when changing lanes on the highway.

bill19696 > roflcopter
03/19/2014 at 13:59

I have always found it's best to stay with the stock tire dimensions on a car. They are made that way, so you don't have too much tire spilling or stretching them. Both adversely affect performance.

roflcopter > bill19696
03/19/2014 at 14:00

The 225s are actually slightly stretched on the stock wheel, I figured I'd try something wider and see what happens.

Takuro Spirit > roflcopter
03/19/2014 at 14:02

Probably the fault of the el-cheapo tire brand. Just sayin'.

d1ck > roflcopter
03/19/2014 at 14:08

If you add rear toe you're going to increase the tendency to understeer. It does make the car more stable though. I'm going to take the easy way out and say it's all caused by the cheap tires. I really don't know enough about suspension tuning though.

bill19696 > roflcopter
03/19/2014 at 14:13

What are the OEM specs for your car's tires? I would go with that.

Reigntastic > roflcopter
03/19/2014 at 14:23

Best way to handle understeer is to properly manage weight transitions when going around turns.

roflcopter > Reigntastic
03/19/2014 at 14:31

I'm not worried about the under steer, just the floatiness and tendency to turn in wayyyy too quick.

roflcopter > d1ck
03/19/2014 at 14:32

The under steer is manageable for street tires, and unless the sidewalls are made of noodles it wouldn't be doing this kinda weirdness.

roflcopter > Takuro Spirit
03/19/2014 at 14:33

I'd agree if it weren't for the fact that it still handled fine with the spacers on, but I can't run them due to rubbing.

Party-vi > roflcopter
03/19/2014 at 14:47

I'm not sure why you went wider anyway - usually a staggered setup is to avoid oversteer on vehicles prone to it. Are you sure your RX-8 did already have a staggered setup? Toe-in would help on the back, but you will accelerate your tire wear - I'm not sure by how much. Is your wheel width enough enough for such wide tires? If the wheel isn't wide enough you'll experience wonky handling as well.

Dogapult > roflcopter
03/19/2014 at 14:48

Dude. Breh. Bro. Roll your fenders, breh, it'll be hellasick!
(sarcasm)

roflcopter > bill19696
03/19/2014 at 16:48

225/45/18 stock, but people run 285s on these things with no problem. It's a pretty well known fact that 225 is too narrow for both the stock wheels and the car as a whole.

roflcopter > roflcopter
03/19/2014 at 16:49

roflcopter > Party-vi
03/19/2014 at 16:56

Fuck kinja... No posting except for mobile apparently. But the car was 225/45/18 the whole way around from the factory, slight tail happy in this setup, I got spacers to make it flush a while ago and that made it under steer just a tad but very balanced for the most part. I picked up these 245/40/18s to go on the rear and they fit fine on the 8in wheel that they are on. But I had to take the spacers off to stop the rubbing. And I will be going to 245s the whole way around here soon, just trying to make it not twitchy in the mean time.

roflcopter > Dogapult
03/19/2014 at 16:58

Actually... That probably will happen sometime soon.

Party-vi > roflcopter
03/19/2014 at 17:18

Hold up, I was incorrect.

You want toe-out to reduce understeer. With toe-out, the inside tire will turn at a greater rate than the outside tire, pulling the front in the direction of a turn. The problem with this is, if there is too much toe-out and you hit water, the car will pull to the side that still has traction. Your car is RWD and should have some toe-in already built in to the rear suspension, which will make it understeer (push around corners). See if you can dial-in zero toe-out/in, which should give you just a bit of toe-out while at highway speeds. This should fix your issue. Alternatively, you can decrease the PSI in your rear tires in 2.5psi increments and increase PSI in the front in 2.5psi increments.

naallday > roflcopter
03/19/2014 at 18:35

That's all great and everything. But is there any up side to owning an rx8? Just wondering. All I hear is bad things about them.

Reigntastic > roflcopter
03/19/2014 at 18:54

Yeah, tbh I'm not sure exactly what would cause that. I definitely lack in my experience with alignment or suspension.

mrazekan > Party-vi
03/21/2014 at 10:49

I think you nailed it. I saw your reply after I posted an explanation of tramlining on rofl's align,went post. I had no idea it was called tramlining!

mrazekan > Party-vi
03/21/2014 at 15:10

Here is the explanation.

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Party-vi > mrazekan
03/21/2014 at 15:16

Thanks for the update!