For oil and filter changes on engine and Allison tranny I can squeeze under without using jacks, most times just drive front tires up on jack pads for added space. I don't change tires on our rig and certainly would not consider relying solely on our coach's power gear jacks for doing service work where rig tires were not firmly on the ground. Sure, it adds extra time to the job but the proper set up for safety reasons allows me to do the task effectively, I don't like being in a hurry due to safety concerns.