climbing the load roller

Hi guys , i have just watched the table resolution module , and have a question ,in an earlier module regarding strapping the car to the dyno it was mentioned the driven wheels climb on to the load roller and i have just seen this in this module , my question is ,do the wheels need to drive both rollers or just the load sensing roller under power , i have always struggled with traction as i have tried to keep the tyres in contact with both rollers thinking that it will affect the inertia readings .

cheers keith

It really depends on the dyno manufacturer but I know with Mainline all the load sensing is done on the front roller and it's prefered that the car climbs onto it under load, the rear roller doesn't require contact under load