I am running my Xmods on my slippery concrete basement floor. (I plan to repaint it with higher traction paint soon) With the box stock setup, the cars would oversteer like crazy. I left the front suspension stock, and switch the rear to the softer (red) springs in the upgrade kit. This reduced the problem quite a bit. I then switched to softer rear slicks (fronts still stock) from the tire upgrade and the difference is like night and day. If you run outdoors, use the harder springs from the upgrade kits. I plan to try to get the most out of the cars using just the tire and suspension upgrades for a while . I may buy one of the motor upgrades later. The mini magazine that comes with the car is an excellent source for understanding the purpose of the available upgrades. The best advice is to make only one change at a time to the car(using the info in the mini magazine and upgrade instructions as a guide) and make a note of how that change affects handling for the surface/track you run on. That way if the change has a negative effect to you, it is easier to undo what you changed.
suspension kit - the different steering bars are nice, and i like the different springs - i run blue in front and red in the rear with 4.0 tie rod bar (i like a sharp cut in)
high mah AAA's 750+ - this is a must - 750's are 12.99 at walmart
Linear Mode
