Umrswimr

Last week I had the car re-aligned to
Front & Rear:
-1 degree camber, 0 toe
Front only: +6 caster

Well, I just got back from another autocross which went pretty well (Aside from the E-mod cars, I got FTD). Tire pressure was 35 psi cold all around and the outside temp was about 75 degrees. Overall, the car had decent turn-in and slight understeer once the tires were warm. I'll be honest, though- the course was VERY small which led to a little power-induced oversteer in the corners... Basically I was unable to get a solid feel for the tires- it was just too tight.
However, I pulled the tires (Victoracers-275/35/17) off tonight to find some peculiar tire wear. This is the front tire (they both look the same). Outside edge is to the left on the pics: (pics are huge)

http://www.digitex.net/ecarter/david/v700/IMG_0139.jpg
http://www.digitex.net/ecarter/david/v700/IMG_0140.jpg

Notice how the outside tread blocks are showing considerably more wear than the inside. In fact, the inside blocks are virtually untouched. However, another thing I can't figure out- the outside MIDDLE tread block looks the worst- notice how it's obviously more worn that the corresponding INSIDE block. There's obviously been a lot of heat in that tread block- why no where else?

Is this normal? If no, then what am I doing wrong? More air pressure, less air pressure, what? I'm afraid of running any more negative camber because this car sees 99% of it's time doing normal driving. More camber would kill my street tires... But the lack of inside tire wear seems lack a BAD thing...

Dick Elliott

I once tryed running as much caster as your running and ended up with strange tire wear like yours. What is happening is with that much caster, you are ending up with 4 or 5 deg of negative camber at full lock in both dirrections. Now I know your not useing full lock, but you are some where in between. 6 deg caster is what we run on the salt flats and at the drag races, not auto-x or even road racing. Think what your wheels would do if you were running 45 deg of caster. Think what your tires would do now if you turned the steering wheel. This is what your doing, only not to such a extreem deg. Back off the caster and I think you'll be ok.

reza

The victo has shallower thread on the outside when new. Thus your wear maybe even, its just that the outside blocks will dissapear first before the inside. That is what happening to mine.
This is my first time using the victos.

I can see you still have hairs on both inside and outside edge, that means your pressure is too high.
I am running 38psi hot front and 34psi hot rear.
From first run to last run, I kept bleeding the pressure to make sure it stays at those pressures.
This is on FD.

turbojeff

iTrader: (30)

Tire wear, where.

Dude my tires get little ***** of superheated rubber stuck to them... I think you don't have enough wear to think about yet.

reza

Here are mine,

left front: http://www.berudu.com/rx%2D7/photos/.../leftfront.JPG

right rear: http://www.berudu.com/rx%2D7/photos/.../rightrear.jpg

looks like front does not have enough camber...
the rear seems to wear evenly...

Umrswimr

Now THAT is a possibility.. I never even considered that the outseide would have less tread when new.

Thanks for your help, guys. I'll try running less tire pressure next time and see the results. Time to start a log.

Umrswimr

Damn double post.

DamonB

As reza said when brand new the Victo has shallower tread on the outside shoulder so that it will wear down to a "slick" in that area faster than the rest of the tire.

As for umrswimr's tire pics the car doesn't have enough camber in it. The tire pressure was holding the sidewall up well enough but the outside of the footprint was still forced to do too much work. Lots of caster does increase negative camber when the wheels are turned but this would still wear the insides of the tires more, not the outside. From the pics it looks like you were on concrete and the tires never got a chance to warm. As turbojeff says when they get to temp the rubber will begin to distort on the leading edges of the blocks and they will pick up all kinds of rubber off the track. The sides of the blocks facing the outside shoulder will also distort into a small circumferential ridge from the cornering forces trying to roll the rubber off the tire. You can see this just beginning to happen in your second pic where the outside edge of the tread blocks on one of the middle rows is just beginning to wear away. Those tires never got a chance to get going. How long was the course? I would have tried dropping the tire pressure. The car would get mushy and still wear the outside more but at least the tires would heat.

reza's pics look like asphalt and not enough camber. You guys are really only using about 2/3 of your tread width and don't realize it. Put some more camber in there

You should see my tires from the Tour: 200 cars on race tires passing every 30 seconds and everytime you drive through the shutdown area and into grid the tires pick up GLOBS of rubber and debris I had to scrape off before every run. I think my Victoracers had a special liking for the 710 rubber my competitors were on as I picked up all that crap while theres stayed warm and soft yet clean.

Umrswimr

You are absolutely correct, Damon- the course was VERY tight and short (33 seconds). It was asphalt, though...
The first run was obscenely slick- I could tell there was no heat in the tires. Buy the third run (we run three runs per heat- maybe 10 minutes between runs), the car was handling better, but the course was really too small to tell. There were two spots on the track where I didnt think my car would even make it THROUGH the cones....

At this point, more camber is not an option-I'll tear up my street tires. At $250 each, it gets real expensive REAL quick. I'll be changing to cheaper Kumho MX's for my street tires soon, but until then I don't want to run any more camber on the stiff sidewalled runflats.

reza

More camber Damon? I got 2.7 degrees up front there. And 2.2 rear. Looks like the rear has enough camber.
I was running on airport tarmac concrete, this past weekend. Very abrasive.

in2twins

You are running too much pressure, this is why thje center is overly worn, I have ruined a new set in a day running too much pressure, those tires should be ~32lbs hot IME. Problem is with such a tight course getting the pressures right. you have to re-do them every time out, not to mention, the simple fact that one side of the car is probably in the sun can effect your pressures by at least 5#s. At some point you may want to invest in adjustable upper A arms, this will allow you to run whatever you want at the track, and then set it back for the street(the Vette has A Arms right?). For the most part though I think pressure followed by camber are your two issues. You might call Roger Krause and get some starting alignment settings for an AX Vette. Carl

cpa7man

iTrader: (2)

Yea, mine look all melted and ****.

My first thought was that you have too much air in the tires.

Jims5543

iTrader: (2)

Can you get your hands on a Pyrometer?

I am running 6° of caster too. I have found -0.5° of camber to be ideal especially when you start heading to 245 or wider tires.

A pyrometer (surface one) will give you an idea if your running too much camber too little tire pressure or too much.

Its a good investment. It has told me volumes about my setup. I used to run -2° camber thinking it was the way to go.

I still like my 6° of caster. I would play with less camber first.

RX744CSP

iTrader: (4)

Your tires look just like mine as far as wear goes, and I definitely didn't have enough camber. Notice that the tread blocks next to the wear indicator are worn more on the outside, this comes from the tire 'rolling under'. A lot of caster is a good thing, but take it from me the camber is just as important. Check with Ground Control for their recommendations, they know their RX7's.

Umrswimr

Where can I get a pyrometer?

DamonB

Damned near anywhere that carries racecar type stuff. Longacre makes some common ones and most others are just rebadged Longacres. Decent one is just under $100. I see them on ebay often too.

Don't bother with an IR pyro, you need a probe type. Anything else is fooling yourself.

Read one temp at a time and you write them down:


Reads and stores all three readings from each tire (12 readings) and will store 10 sets of those for reference:

I missed a steal on this recently on ebay; didn't have the money. New they are over $300.

Umrswimr

So the probe type are better?

DamonB

For measuring tire temps they are. For tire temps you actually want the temp of the carcass inside, so the probes are sharp and pierce through the outer layer of rubber. IR just measure the surface of the tire which can be misleading for tire temps, but fine for stuff like brakes and such.

reza

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

I used to use this. I am selling it now for low low price.

Umrswimr

Damn, you could skewer a Moose with that thing.

How do you know how far into the tire to put it?

reza

You can just touch the material to sense it, it will take air temperature as well when not touching. If you blow hot air on it, it will register, unlike the IR, you can't shoot blank objects.
That is a good question. I never push it in the tires, I just know from reading above that I need to push it into the carcass...

Jims5543

iTrader: (2)

Probe type are great for Road racing.

Surface temp is your best bet for Autocross. Some events I see temps as low as 110° and that is hardly warming the tire up.

It is important to get temp readings ASAP after a run. We had a guy waiting in the pit lane and we would pul over to the side and take readings right as we got off from a run. He would yell them out. We would take 3 readings per tire. Inside edge / middle / outside edge.

Carl Byck

I agree with Jim on this, an IR is really the only way with AX due to the short runs, I typically see ~130-145 after a ~45sec AX course. Carl