If you plan on racing your t maxx DONT put the spool in it!... I put the spool in my max last year and took it out after about a week. It works awsome for climbing but if you turn a corner under ANY decent power with the rear tires locked by a spool it will just spin out. I have a maxx with a rix gear starter box chassis and a OS.21CV in it (lots of power) and have yet to blow out a diff. Just be light on the trottle when it lands and the stock diff's will take alot of power!