Excessive front end vibration on the track

Spent the weekend at the track. Was experiencing a lot of vibration under brakes, through the steering wheel yesterday. So bad in the first session I had to pit. First thought were warped rotors. So I jacked the car up and rotated the front wheels by hand. They didn't seem to catch at all. Did notice my wheel bolts were not that tight. Strange as they were tight the day before. So did them up firmly and went back out about an hour later when it was my turn. Vibration wasn't present until about half way through the session and mild vibration returned. Although not as bad as before and not enough to warrant ending the session. Came in and after about 30mins I checked the wheel nuts again and they were fine. Wish I had checked when they were hot though.

Anyone experienced anything like this? I'm thinking something to do with the wheel bolts expanding and contracting at a different rate to the hub causing them to loosen. Or warped rotors. Or poor alignment. I must admit I did not get a wheel balance or alignment prior to the event.

If the vibration only happened during braking, it's most likely not on your wheel balancing or alignment.

Other than wrapped rotors, inconsistent pad deposit can also cause massive vibration during breaking. There's an article (I believe published by Stoptech) that most vibration that people experience is mostly due to inconsistent deposit due to improper bedding, instead of wrapped rotors.

If you're rotors are still good, I would give good sanding and try to re-bed the pads.

On the lug bolts, if you properly torque them before hitting the track, they shouldn't come loose.
Regardless, it's always good to check in between session.


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FWIW you shouldn't torque the bolts when they are hot, when they cool down they might end up being stretched more than they would cold and then you essentially over torqued them.

Pad deposit as mentioned is most likely the cause for most of the vibration under braking issues. Avoid standing on the pedal when the car is stationary after a session. I wouldn't necessarily sand the rotor, but try to rebed the pad will sometimes help getting rid of the uneven pad deposit.

How many miles are on the car? Brake/suspension modifications? Was it really just happening under braking? What about sustained high speed?

I agree with moon that it could have been bedding-related. You may want to look up bedding procedures and give that a shot if your local roads allow it.

Thanks for the responses everyone. It was indeed only under braking, no issues at any other time including 200+ kph on the main straight. Car is completely stock other than the pads and fluid.
I haven't heard of pad deposits before but sounds plausible. I bedded in the pads as I usually do. Multiple 100-20kph brake applications. The pads in question are actually now in a dumpster as the next run they hit the wear markers and had to be swapped out. I should have taken pictures of them. Literally had 20mins to swap them before my turn. (Replacements were my stock pads). I will have a read up of techniques. Especially if any are specific to my next set of pads.

As mentioned before, most likely pad deposit due to insufficient ventilation
and inappropriate pad compound, since you did run stock pads.