A new drive-axle system consists of the Dana Spicer S21-170DE high-entry, single-drive axle and Dana Spicer R21BS reconfigurable tag axle. The combination of drive and tag axles means weight savings, says Dana, over a traditional tandem. The air bags of the tag axle are exhausted when the differential lock is engaged; this temporarily shifts all the weight to the driven axle at a low speed, which provides the same traction as a traditional tandem axle. Single-axle design requires fewer points of lubrication.