I already did that for 7 years, and my back and hips all fawked up. All those truck, tractor, & loader tires have put my back in bad shape. There are days I have problems walking!! I used to be able to do a set of drives in 45 minutes. And now I'm paying the price of it, I'm only 33 and have lost most of my disks in my lower back cause of it!! 
maybe you should try to lift with your legs and not your back? That sucks, it really does. I've been ther for 8 months and now I'm in the alignment side so I'm looking good.
