what happens is that on dirt, were the ground is loose and bumpy the car is so fast and light that it is constantly 'hovering' when tires balloon on the ground so its just almost gliding when it hits full speed thats not good if you even hit the smallest of bumps because changing its path while gliding means it has no grip on the ground so it starts to crash - and the parts aren't excctly durable (broken a-arms most common, buckled chassis etc...) so its really too fast for its own good