Drivebelt damage

[B&H Racing]

Am I doing something wrong, I have taken my BX outside on tarmac twice and twice I have damaged the drivebelt.

Also damaging rear pulley and spur gear.

The damage has occured where stones have got wedged in the rear diff and underneath the belt.

Three of us took our bx`s out onto a car park for testing this morning, the testing lasted 2 mins with 3 belts with chunks out of them and 2 x spur gears with flat spots.

I have got the lexan front and rear diff covers on my car and have also placed a vertical piece of lexan at the very back of the diff.

The pic shows the rear piece of lexan removed so as the pic could be taken.