[AaronR]

I, too, built my 511 with 501X suspension arms.

I broke ONE arm in 2.5 years of racing a 4WD Tamiya (2 501Xs, one 511). Travelling full speed in a straight-away, I got too close to a plywood wall with the front left tire and caught it in a existing hole in the wall.

I really cannot see much else breaking the 501X suspension arms. They are VERY thick!