Originally Posted by Racing4Evo

You should run your belts as loose as possible on large flowing tracks where you are smoother on and off the throttle. The belts should be tight on small technical tracks where you are using a lot of short bursts of throttle or else you could snap the belt. There's no effect on handling that I have noticed, just on acceleration. Whatever the condition I like to run the belts on the loose side for top speed and fuel milage.