I recently bought new tires, going from the well-worn stock Bridgestones to Yokohama Avids. I’ve noticed an immediate decrease in fuel efficiency - I was averaging low 60 mpg on my mostly highway drive commute with the Bridgestones, and I’ve dropped back to the mid-50s here the last week. I jokingly told my wife all of that tread was increasing the rolling resistance. I wonder if there is some truth to that. I’m running 34lbs pressure in the new tires, same as the old. Any comments or thoughts? I ended my run of 33 straight tanks of 60 plus mpg and was bummed out.
Yeah new tread is deeper, squirms more, accordingly has higher rolling resistance. And the rubber is newer, more pliable, same story. And: a well worn tire has a slightly smaller outside diameter, which means more revolutions per mile, which means when travelling the same distance the car thinks you've gone slightly further, which affects both in the in-dash mpg display and the odometer and trip meters, if you're calculating. And it's two different tires of course.
There is a good article on TireRack.com that discusses why new tires even same type can be less "apparent" MPG. Your tread wear and other things factor into that. Here it is (says Prius could see drop from 50 to 47.5 in theory) Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires
Thanks guys. I sort of thought it might be the case but did not realize the effect would be so noticeable. The stock tires were done; I got about 75k miles out of them and they were on the wear bars. They were getting questionable in the rain and would have been unmanageable in the snow if I had kept them.
On most cars you'd have never noticed. But when you're getting 60 mpgs, a 10% change is still 6 mpgs. On a 25 mpg car, that's only 2.5, so you'd barely notice it, or chalk it up to cooler air.
