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one of my r-comp tyres has a flat spot from panic braking wheel lock....how safe is this to use on the track? been driving around on them for a bit and there is a slight vibration & rhythmic hum from the rear (swapped from front to rear).

Not safe at all. The first time you hit the brakes hard you WILL find the spot again and make it worse. But, if there is any tread left in the flat spot area, have the tyre buffed to that level and get it balanced. Good luck.

thanks mate. yea there is thread left on the flatspot, but not enough to make buffing the tyre worth while. I've tried to do a burnout to get the same level of thread, but don't have enough torque in the car to continue the burnout and tyres hook up ...lol

Depends how they were flat spotted. If you flat spotted a front tyre then it would have happened when the front suspension was fully loaded and therefore at max neg camber. That might mean that only the inside shoulder is affected. If that's the case then get a tyrefitter to flip them on the rims and put the bad one on the back.

If it's only a slight vibration, my experience is that they'll be fine for track use. Not as quick as a tyre in good condition, but certainly not "unsafe". Best to put the flat spotted tyre on the rear ... unless you like understeer.

cant recall when I flatspotted the tyres...unfortunately rcomps dont tend to squeal when loosing traction ...but must have been in a straight line where i've misjudged threshold braking coz the flatspot is in the centre patch.

have moved it to the rear but can definately hear a faint rhythmic thud and slight vibration.

looks like i'll have to fork out for a new pair

One option is to take it to a motorsport tyre guy and see if he has enought meat to shave the tyre.
Might give you a little more life