Poor wear on Hoosier Radial slicks - need advice

[heavy85]

I've now run them in two high speed autox (full race track) and one parking lot style autocross. On the big track the insides were running about 20 deg hotter than the outside. Just looked at my tires and the outside edge - only about 1" worth if that - is wearing off FAST to the point one is barely starting to show chord. The rest of the tire has gobs of tread with little wear from new. Any obvious things here I'm missing that could be causing this extreme edge wear? I notice the radials have a very squared off edge compared to the the bias ply which are rounded from the get go. I never had this issue with the bias ply slicks. Running 24 lb of air in them.

 

Thanks

Cameron

[EMWHYR0HEN]

Sound like a camber problem. What alighnment specs are you running?

[JMortensen]

Sounds like you need more neg camber. You can swap them on the rims to get a little more life out of them if they're not already too far gone.

 

This might be one of those things that would get better with a big jump in spring rate, less roll being the difference.

[heavy85]

... but I'm already seeing the insides 20 deg hotter than the outsides. I always thought the rule of thumb was 10 deg. More camber would work the inside just that much more and make them that much hotter than the outsides???

[JMortensen]

I think simply stated the problem is that when the car rolls you lose camber. You can either add camber or reduce the roll. What I used to do when I started autoxing was to mark the edge of the treads with shoe polish and inflating the tires enough to make sure that the tire wasn't rolling onto the sidewall. This was done before moving on and trying to adjust pressure for even temps. When I was running far too little camber on the Yoko slicks I had about 5 or 6 more psi than I did after adding more caster and neg camber, so you might give that a try, but I think you really need to take the next step to stiffer springs. You're generating too much grip for soft springs in my opinion.

[74_5.0L_Z]

Is the accelerated wear occurring on all four corners, or is it happening more on the front or more on the back? How often do you swap the tires from front to back?

 

What are your alignment settings?

What do the temperatures look like in the middle of the tire?

Regardless of tire temperatures, if the inside and middle aren't wearing but the outside, I would add more negative camber.

 

I have't used the radial slicks, so I dont how much air pressure is typical. I run 32 psi in rear and 36 psi in the front with my Hoosier A6 tires. I swap the tires front to rear every other event (approximately every 10 runs).

 

I put the Hoosier A6 tires on in May and now have about 50-60 runs on them. This set of tires is wearing very well compared to the two previous sets that I had on the car (Hoosier A3S04, and Kumho V700). The outside edge has gotten just slightly rounded, but not bad. I plan to flip them on their rims and swap sides before my next event in two weeks. I should be able to get better than 100 runs on this set of tires if the wear stays consistent.

 

I think the main reason why this set of tires is wearing so much better than my previous tires is that I went with a much stiffer set-up. The car previously had 200 lb/in front and 250 lb/in rear springs with a 1" front sway bar, and now has 450 lb/in front and 425 lb/in rear springs with a 20mm front sway bar.

 

Good luck and sorry for the ramble, but its 2 AM and I can't sleep....

[Clifton]

Are you running FA tires?

[tube80z]

Are you running FA tires?

 

Good question. And it would be good to have the rest of the temps and alignment. We had similar problems earlier this year and have ideas on how to fix it assuming you have the FA tires.

 

Cary

[johnc]

... but I'm already seeing the insides 20 deg hotter than the outsides. I always thought the rule of thumb was 10 deg.

 

Nope. Course configuration, lap times, driver technique, and tire wear (as you're learning) are also factors. Some cars and drivers work better with much higher inside temps. Also, incorrect tire pressures (giving somewhat even tire temp readings) may mask camber problems.

 

EDIT: I'll qualify my Nope. The rule of thumb is just a starting point to help folks get in the ballpark. You have to look at the additional factors I list above and continue to adjust, always keeping an eye on the temps to make sure you haven't gone way out of whack. I did a minor bit of development help with the T3 Mazda RX8s and they worked best at WSIR with a 50 degree difference across the tires at that particular track.

[heavy85]

Yes FA. Yes all four tires appear similar but it's hard to tell exactly if there is a subtle difference. Yes I rotate tires front to rear each race. Specs:

 

51.7% front, 48.3% rear

2,574 lb incl driver

24 PSI

-3 deg F, -2 deg R

1/8 out F, 3/16 in R

23x9.5x15 R25 compound Hoosiers

225F/250R

big n little bars

Outside ~ 110 deg, middle ~120 deg, inside ~130 deg, fronts ~ 5 deg hotter than rears.

~3/4" rake

 

This was high speed autox so one hot lap and one hot lap back to the pits not an extended session.

[JMortensen]

This was high speed autox so one hot lap and one hot lap back to the pits not an extended session.

This is something else that might be a problem. Depending on how you're taking your cool down lap, the insides of the tire might be heating up because the outsides aren't getting worked like they do when you going at it full bore.

[Clifton]

Cary could give you more insight on the Hoosiers, I've only run Goodyear and Yoko FA tires but on my car running 2.5* front camber I have to run 35 psi or it will roll the outside edge too much and kill the outer 3/4" or so. I have run up to 40 psi cold. I'm running alot higher spring rates and 350 lb less weight too. I'm going to try 3* this weekend on a short autoX coarse. I can't remember what I was running the FA fronts at on the rear without digging through my book. I'm running FA rears now and very low pressure.

[heavy85]

... or it will roll the outside edge too much and kill the outer 3/4" or so ...

 

Sounds EXACTLY like what I'm seeing - wear on only the outer 1" or so. Maybe I need to jack up the air pressure like 10 lbs or more.

 

One of these days I may have to take the plunge and go up in springrates. Since I drive between 1 and 3.5 hours each way to races on crappy roads I've been very leary going higher. Wonder how much difference it'll really make though in ride? Maybe I'll just go back to the bias plies if I can still get them (doubt it).

 

'Cool down' lap is actually hot other wise you get run over by the next car on their hot lap.

 

 

Cameron

[Clifton]

I have zipped up the street a few times with my track car and it isn't something I would want to do often with high spring rates. If it was to get to the track only, that's different. If yours is a street car too, you might not enjoy driving it as much going stiffer. I would try bumping the pressure up and try that first. How is that thing on the street with 1/8" toe out? Gotta be horrible, or do you change it at the track?

 

Sounds EXACTLY like what I'm seeing - wear on only the outer 1" or so. Maybe I need to jack up the air pressure like 10 lbs or more.

 

One of these days I may have to take the plunge and go up in springrates. Since I drive between 1 and 3.5 hours each way to races on crappy roads I've been very leary going higher. Wonder how much difference it'll really make though in ride? Maybe I'll just go back to the bias plies if I can still get them (doubt it).

 

'Cool down' lap is actually hot other wise you get run over by the next car on their hot lap.

 

 

Cameron

[tube80z]

Yes FA. Yes all four tires appear similar but it's hard to tell exactly if there is a subtle difference. Yes I rotate tires front to rear each race. Specs:

 

51.7% front, 48.3% rear

2,574 lb incl driver

24 PSI

-3 deg F, -2 deg R

1/8 out F, 3/16 in R

23x9.5x15 R25 compound Hoosiers

225F/250R

big n little bars

Outside ~ 110 deg, middle ~120 deg, inside ~130 deg, fronts ~ 5 deg hotter than rears.

~3/4" rake

 

This sounds very similar to the setup on Dave's LS2 car. We use the FA rears but had issues with the fronts earlier this year. We had been using pictures and a pyrometer to set camber and running similar temps to yours. After watching closely what it appeared was we were killing the tires by dragging the inside in the corners. We had a couple of pictures where we could see a line around the tire that showed what was touching the ground, which also seemed to be where they wore out. On the inside 1.5 inches or so (familiar?)

 

I just noticed you have outer edge wear. Do you have any pics of the car loaded up in a corner? Are you running camber plates or stock isolators? It still sounds like you have too much roll or perhaps a compliance steer problem that's leading to excessive toe-in (you might check the steering joints). The rest of the advice is probably not worth a lot but I'll leave it in case you find it interesting.

 

To fix this we reduced the camber to about 1.5 degrees negative in the front. Added more caster 8 to 10 degrees (may do more but ran out of adjustment and into tire clearance issues). This helped the brakes work better and tire temps were down a bit (5 to 10 hot on the inside).

 

Also keep in mind I'd run at least double your spring rate. I think that's a problem. You also need to be very aggressive at controlling roll. We did this using droop limiters. This will help you run a lot less camber too.

 

You may want to check the toe too. Here's a trick. Try running the car over a piece of sheet aluminum on top of some salt or glass beads (something low friction) with about half lock on on the inside tire. Does the car push the sheet away or pull it under? You can use this to help figure out if you need more toe out (although I wouldn't go beyond 3/8 of an inch). We run 1/4 to 5/16.

 

My suggestions

 

1. Double spring rates

2. Less camber

3. More caster

4. Limit droop for better roll control

 

Hope this helps,

 

Cary