Did one of your wheels take a hit when you were out in the mud?
I had new tyres on last week and stood around in the shop chatting while they were being put on.
As each wheel came round onto the balance thing the fella would say, 'ah this ones a bit off,' and show me how far out it was.
Not too bad all round, went from over a kg of lead to 150gms or so, amazing what a good tyre guy can do.
But, having the wheels on the spinny thing showed how they can go out of true and cause that kind of wobble.
Or it could be the same hit and cut some of the plies in the tyres which might do the same thing.
Cheers,
Simon.
