well we didnt have a problem before aswell when we had our old tires on the car, potenzas, but now we got a set of Nitto's on there and they grip pretty good. When we got our suspension and tires all worked out properly on the first run we broke the diff. Then we found another diff, same r34 gtr one, had 4-5 runs with it and then snapped again...Atm i think we got around 300kw at the wheels and for sure the stock diffs cant handle it..