An over the highway truck or tractor suspension with traction enhancement. Air springs are provided for the rear axles of a 2.times.6 vehicle. Normally the load is evenly divided between driven and tag axles. When enhanced traction is desired, the tag axle springs are communicated with an auxiliary tank to reduce pressure in them while air under pressure is supplied to the driven axle springs to increase the pressure in them and thereby increase the portion of the load on the driven axle to provide enhanced traction.