XRAY - Model racing cars

You shoudl slowly break them in (see supplementary sheet). The has a bit more under running in the M18T section (applicable for both).

Basically in a nut shell you want to set both until they just dont slip. You should never ever have to tighten the diff until the screw bottoms out. You will make the action rough, and put flat spots into the balls. On surfaces with more traction like carpet, will be tighter versus a surface like untreated asphalt which you will want a tad looser. Ususally you want the front diff tighter than the rear in order to help pull the car forward, and to keep from oversteer.