Autocrossed Sunday and Wednesday, after a few runs Wednesday I noticed one of my front tires was coming apart on the outside edge. I have already replaced 2 of the Dunlops because of the same problem but not this severe. I was running the fronts at 38 psi and I attributed the undue wear to too much roll over and too much heat build up. I've increased the pressure to 42 psi in the front but the tire was from the original set and even at 42 psi the shredding (actually it's more like chunks of rubber) still occurred. I need help. What am I missing or doing wrong?
I ran Falken 615's for the last 2 years, autocrosses and PDE's, and never had this problem. I have a 2007 MCS with the sport suspension, LSD and a stock alignment.

 

Someone in our region just posted pix of his chunked Star Specs in the last week. The problem he has was running them too hot (they run cold really well, but don't like getting too hot). Are you using a water sprayer?

 

what were the conditions on Wednesday? Tempurature and surface?

how does the car feel on course? is it balanced, or understeering?

what pressures were you running out back?

is your driving style aggressive? do you use significant slip angles on the front end?

what size wheels, and what size tires are you running?

thanks,

charlie

 

Answers to all the questions:
No, I was not using a water sprayer between runs.
Conditions of Wednesday were 77 and cloudy.
MINI felt good of the course, balanced but understeered in the tight turns.
42 lbs. front, 48 lbs. rear
I would consider my driving style aggressive. I usually place well in class.
Rota Slipstreams 16 x 6.5, 205/50 tires.

Wednesday was a "low-key autocross" on the racetrack's skidpad. A course is setup, there is someone with a stop watch and you can run as often as you like. I'm thinking that possibly I ran too many runs too close together and therefore caused excessive heat buildup.
When my first 2 Dunlops went I had run a "low key" and ran 38 front and 42 rear. It was shorly after that they came apart. The tire that chunked last week was from the same set. I may have 1 more ready to go.

Thanks for the responses. All suggestions are more than appreciated.

 

MiniC,

Koitus is correct regarding heat. And they do not like too many heat cycles as well. I have chunked two sets already. I think I am going to use something else next.

 

i'm running 225s on a 15x7 rim this year [Toyo R1R], and have noticed from photographs and wear patterns that under good conditions the rim moves to the outside of the tread (rim is narrower than tire by .5" or more)

i've tried front tire pressures at 43, a good 5 psi higher than I ran on the 195/55-15 Z1 last year, but still have a bit of a roll over as evidenced by the shoulder of the tread

next time out I'll try a few more pounds, but I'm starting to think that if I want that much tread I need a wider rim

is it possible that your 6.5" rim is deflecting toward the outside of the tire under max load? if so the contact patch would also shift to the outer edge would it not? with stock camber I'd bet that the outer half of the tire could be doing two thirds of the work, and therefore receiving two thirds of the heat too.

i'm running -2.5 up front, and historically have had no issue with roll over or tire wear, but these tires are wider than anything the car has ever worn (on a par with the Hoosier AS304, which I believe has a much stiffer sidewall)

so heat might be a symptom rather than the whole story perhaps?

can anyone else shed a bit of light with their experiences pushing the ratio of rim width to tread width?

cheers,

charlie

 

I haven't had any issues with mine. They're on my summer rims, so they get regular use, as opposed to exclusive autoX use.

 

Since I have increased the tire pressure to 42 psi I've had a lot less rollover and tire deflection. You are right the outside and center of the tire tends to heat up the most. I'm locked into the 16 x 6.5 wheel if I want to run G stock and 16" wheels. I guess I'll just finish this year with the Dunlops, if they last that long.
Last year I ran a Falken 615 in 215/45 x 16 and the wider section and lower profile actually worked well but the Falkens tended to get greasy as they heated up.
Next year I'll start fresh with a good alignment, maybe go to 17" wheels and find a better tire. For what I've spent on 7 Dunlops this year I certainly could have gone to a more expensive tire and maybe not had these problems.
Thanks again for everyone's information.

 

I've been running the Dunlops for two seasons now and have yet to ruin a tire. On smooth asphalt I run normal street pressures on all four corners 32psi. On courses that have rough torn up asphalt I bump the fronts to 38 psi. It sounds like you may be over driving the corners if you are tearing the tires up. In slow, out fast.

 

If you want to run the Dunlop Star Specs on the track, shave them. They last about 8 days.

If you run them full thread, they will likely chunk.

I think they are more for AutoX than track as they do well without too much heat but when they are fully heated up, they can get greasy.

 

Thanks for the additional information and advice. Every year is a learning experience and I hope each year I get a little better. Happy New Year!