To produce a Torque figure, the RR needs to have a Resistance factor, decent RR's will have this facility. Strapping a car down to aid the Torque Figure is cheating.

Single Roller RR's are pretty good and don't suffer from much in the way of wheelspin.

With Twin Roller Systems, alot of operators think you must pull the car as hard into the rollers as possible. The problem is that if you do this you will bias it towards one roller or the other (depending on whether the strap goes forward to backward). By doing this it will encourage wheelspin as the wheels will be 'light' on one of the rollers. The Tie-down straps should only really be used to apply gentle pressure to stop the car buggering off sideways and 'just incase' it decides to climb the rollers and make a bid for freedom.