Wargasm

Hello, I have 255/40 17 Toyo RA-01 mounted on 17x10 CCW rims. They have only been mounted on there for maybe 100-200 miles of driving at the most. Today when I was doing some other work on the car, I just happened to notice that on the front wheels, the edges on both front tires are slightly worn (not new), and the centers of both tires look very new still. In other words, the inside AND outside edges of both front tires are a little not-new looking, but the centers look new by comparison...

What's up with that? Before you blame it on my 10 inch wide rims, Toyo does say that you can put their 255/40 17 RA-01 on a 10 inch rim... so I don't think it would be that. My inflation pressure is around 29 PSI cold and the alignment is set for 0 toe and about 1.1 degree negative camber.

I just want to make sure that my tires are doing their job, and if they're not wearing out in the middle, they're not doing their job are they?

aussiesmg

iTrader: (1)

That is a classic sign of under inflation, over inflation wears the center.

RX7Crazy_84

iTrader: (1)

just curious aussiesmg how do u know that under inflation is causing that?!?! dont know too much! i thought it would be cuz too much toe is out!!

Swolbynos

not enough air to bulge the center out to wear even

also, the rim size.....even though they say it will work, might want to up the pressure a bit to make up for it

RETed

Not enough air...underinflated, agreed.


-Ted

DamonB

The tire is too narrow for the wheel.

Being able to fit the tire on the wheel and having it be optimal are two different things.

Right.

The sidewalls are stretched in order to fit the tire on the too wide wheel and this makes them very stiff. Therefore the edges of the tire are already loaded and are trying to do most of the work rather than allowing the entire tire footprint to "squash" against the road properly. A higher inflation pressure will help get the center to do more work by forcing the circumference to bulge but I still believe you're going to need so much more pressure to accomplish this that grip will be compromised anyway.

Regardless of what Toyo says 255/40 is not wide enough for a 10" wheel IMO. To get the contact patch to really work you're going to be forced to run much higher than optimal pressures. I bet that same tire on a 9" wide wheel would be much happier and give you more grip than it does on the 10" wide wheel.

Wargasm

Yeah I guess it's being caused by the wide rims... I got a set of them for a good deal, so I figured I'd go for 255/40 up front this time (to make sure that I had extra clearance) and then maybe go wider later if the 255s worked out OK.

I'll check the back rims to see what's going on there and maybe try a little bit more air to see if that makes any difference.

Assuming the width is the problem, couldn't I just drive them down flat? They're R compound, so they would wear down fast

Brian

RETed

As much as DamonB likes to blame hipari for the weird wear pattern, if Toyo says the 255 is okay on a 10.0" wide rim, it should be alright.

I just read the part about 29psi...damn that's low.
What's the max pressure printed on the side of the tire?
It has to be at least 40+psi? 43psi?
If so, I wouldn't run anything lower than 35psi...
I usually run my street tires 5psi to 10psi within max rating.

Unless we're talking about wear on the track?


-Ted

impactwrench

Tire pressure need to be set according to wheel loading. From what I remember from a 1980's hotrod mag, strike a fat chalk line across the face of each tire. Drive around the block the way you usually drive and look at the chalk marks. I f chalk is missing in the center of the tire you are overinflated, and visa versa

Wargasm

OK a little more info... I checked the back tires and they look exactly like the front. The inner and outer 1/3 are lightly-scuffed, and the middle 1/3 is almost new (feels smooth and slightly slick like a fresh tire).

This is with street driving only... I pretty much just cruised around for about an hour on the interstate and some side roads to test them out some and then that was it.

I checked my inflation pressures and it was 25 PSI at all four corners... the temps went from 80s to about 30s over the last month or so, so I'm guessing I'm a bit lower than I should be hahah. I set them to 29 when I first got them, but that was +50 degrees ago, so I guess they need some more air.

I'm going to reset the pressures to around 35 cold as an experiment... I'm going to see if it improves the situation or not. If it does not, I'm considering these three options:

1 - Taking these tires off and buying 275/40 and selling my practically not even driven on 255/40s. The downside here is that 275/40 is "meatier" and will lessen my already-tight fender lip and fender liner clearances. I also have to figure out how to sell 4 255/40 race tires.

2 - Buying new rim halves from CCW to re-make my rims as either 17x9.5 or 17x9 rims.... A lot of bolt-turning and probably expensive.

3 - Sell my 17x10 CCW to someone with a track car who wants to run 275/40 and buy new 17x9 CCW and put my 255/40 on those. Again, expensive... and can be hard to sell stuff (flaky buyers, shipping hassles, etc).

I hope I can get these to work by increasing the pressure some to a more normal value.

*edit* here's a link to some pictures of my wheels/tires on the day I got them. If you look at the second picture, it seems like there is dirt across the whole tire on the part you can see... the weather was a LOT warmer then.....

About 2 megs of pictures... modems beware!

http://www.zeroglabs.com/rx7/ccwrims.htm

FutureRx7

If you decide to sell your wheels PM me a price.

DamonB

Higher pressures will definitely improve your problem and should be able to get you to a point where the tread wears more evenly. I think the tire will still be slightly handicapped on that wide of a wheel though.
The max pressure on the side of the tire is merely the maximum pressure the tire can safely sustain at its speed rating. You'll never actually run pressures that high unless things are out of whack.

aussiesmg

iTrader: (1)

Under-inflation causes the center of the tire to have less pressure upon it, the sides are held in place by the sidewalls resisting the deflated effects, overinflation causes the center to bulge due to excessive pressure against the center of the tread, but the sidewalls retain the sides in contact with the rim. Pure logic, you have been running under-inflated tires.

Toe in causes the outside of the front tires to wear, they will show feathering along the tread blocks trailing edges, toe out the opposite wear to the inner edge.

Camber causes similar wear but without the feathering caused by the tires pushing across the tread blocks.

DamonB

These are only true if camber is zero.

If the car runs any negative camber at all the wear will always be on the inner edge of the tire regardles of toe in or toe out.

Wargasm

I bumped up my cold inflation pressures from 25 to 34 on the front and from 25 to 32 on the rear. The middle of the tires seems to be wearing now. It's awfully hard to test R compound tires on the street in 30 degree weather because they are very very hard to heat up. They feel a little slippy since it's right around freezing here and the pavement is not only cold, but damp too.

What I wanna do now is get a Pyrometer and see what areas are getting what temps to be sure they are working well.

I have a laser-type surface temp reader, but I know that a probe type is more accurate for tires. Think I can at least get an idea from the laser one?

RETed

Recommended or we-as-tire-manufacturers-are-not-liable-if-you-run-higher-psi ratings...yes.

I knew a guy who used to autocross Supras who used to run 60+ psi tire pressures just to get the tire pyrometer to read even across the tread.


-Ted

DamonB

Great. That's the only way you'll know for sure.

Laser temps are useless for tires IMO. You can get an "idea", but that's no good if you're actually trying to tune the tire and/or setup. Use a probe. You want to know the temperature of the tire carcass, not the very outside of the tire.

In 30 degrees you will not get any race tire to warm and you'll never get one to warm on the street regardless of outside temp. Running 30 minutes at a time in the cold (40ish degrees) on a roadcourse recently I was only able to get the tires up to around 110+F. The same tires on a 40 second autox run in warm weather get to 140+F easily.

Sometimes you can find pyrometers cheap on ebay but you can buy a "one temp at a time" type probe for around $100 from just about anywhere.