My guess is rubbing under full suspension compression. Running an 18x9 +29 with 255 Z1s that run wide rub on stock rear fenders under full suspension compression if you don't have much camber. This was happening to me and were rubbing my NT05's with +28 offset and same size wheels with the suspension compressed. Thats what I would put my money on. Funny thing was only one size rubbed and it was the passenger side which is the side yours blew on.

You are one lucky guy though...so many things could have went wrong. Spinning at 120 and having your rim catch pavement your car could have rolled like a donut for a few hundred feet....

 

my camber in the rear is either -1.2 or -1.7 i cant remember

 

ok maybe like 50 bricks but you get the idea

 

lol yeah man it was fun

 

Are your rears rolled? Sorry if I missed that... Also, what kind of pressure's were you running?

Personally I feel englishtown isn't safe enough for any thing more than an autox event. Glad you walked away unharmed.

 

My fenders arent rolled... I usually autocross on this track and inflate to 40psi all around... This event i inflated to 38 psi all around.

 

38 psi cold? Ohhhh, that's most likely waaay to high. I target 38 hot right off the track on my z1's. This weekend at CMP, that actually equated to 29 psi cold for the fronts and 32 cold in the rears. If you started at 38 cold, you may have been in the upper 40's after a few hard laps. I run the 255/40/17's on 17x9 rims.

Glad you and the car made it through in one piece and not banged up!

 

It was 38 psi after the 2 hour drive there... so i figured when they were hot it would be about 42 43psi... it was cold out we were the first ones on the track... the track wasnt warmed up yet so i thought that would be good.... i could have been terribly wrong though

 

The track heats up tires wayyyyyy more than a 45sec autoX. 20 minutes of hard driving should be pretty obviously harder on tires. You should start closer to street temps. However, I'm not an expert, but I don't believe psi or heat was the factor here. He only got 4 laps in on the first session of the day. That's the slowest, coolest session of the day in a low level HPDE. No way that did it. No way.

I'm with dbsears on wide wheels, low offset, soft stock suspension and no rear fender rolling being the culprit. I bet you were rubbing on compression this whole time. Although I'd expect you would have noticed it, no offense, but if you don't have a jack, I can't think you're very mechanically inclined or aware of what's going on with your car. Check the other tire like Smike said because that one might be ready to blow next...

Oh, and as to why you blew one side rather than the other from rubbing dbsears, it was probably due to the track configuration (assuming you were on the track). For example, Lime Rock is almost all right handers which would load/compress the driver side. Just a guess.

 

I would probably guess more around -1.2. Getting -1.7 in the rear on stock suspension is pretty hard. I know for myself with same size wheel widths and offset that it took minimum of-1.5 degrees to clear. I still rolled my fenders to be safe because under full compression with my old Bilstein and Swifts in the rear it would rub badly.

It took 1 corner at about 100mph on that suspension for my tire to rub and it rubbed a groove probably 2mm deep into the top portion of the tire. Have that happen 2-3 times and with no doubt in my mind your tire would blow. I personally would ALWAYS roll the rear fenders if running more aggressive tire and wheels on the track.

 

It's just part of learning track stuff. As I have progressed I realized a 10psi increase in the fronts on a 20 minute track session is around what I expect.

This weekend at CMP, it was 40 degrees for the first session, very cold track, and I still picked up 8psi in that session in the fronts.

Just something to keep an eye on.

 

Despite your belief I am quite mechanically inclined. I actually work for NASA (govt NASA) and im an engines specialist. I work on the SSME and the new J2X. When you pack out your car with tents, chairs, friends and 20 gallons of e-85 its kind of hard to fit a full size jack in the car. Plus without having a set of designated track rims with r comps i really see no reason to have a full size jack. The stock jack works fine in situations like this. Given if i was switching rims every track day to r-comps i would agree more.

And when i was talking about which side blew i wasnt talking about side of car i was talking about side of tire. My question was if under full compression the outter wall would rub the fender, would a puncture in the outer wall cause a blow out on the inner wall?

I have to check the spec sheet again but it might be -1.2. The car is actually going in friday for a fender roll... and next season i have a real nice coilover system coming.



Thanks man, yeah this was my first experience on an actual track. Like i said i have autocrossed on that track many of times. Thats good to know though about tire temps going up around 10-12 psi. Im used to 2-3 in an autox lap but theres alot more demand on the tires. Thanks for the advise and next time ill run around 30psi and monitor it.

 

sounds like you got a freak tire.

forgetabout all our comments we all think we know something.

 

Well, some of us do know about this...

I highly doubt it was a "freak tire" -- most-likely cause was rubbing or psi.

 

Smike would rubbing on the outside wall with the fender cause a blow out on the inside like this?

Here are some shots of it when the rim was still on the car