There are lots of posts on here about people buying new tires, and immediately losing fuel economy. This got me wondering if worn out tires get better fuel economy. They weigh some amount less, so they take less power to spin up to speed. If there is little or no tread depth left the resulting smooth surface probably rolls easier than a new tire with deep tread lugs. In my own case my lifetime average fuel economy is 50.6 MPG, but the last three tanks have all been well above 60. They are by far my best three tanks, and my factory tires are now nearly bald. There are other factors as well, the weather is perfect and I stopped using cruise control, but I just wonder if my worn out tires are netting me more MPGs.

Don't misunderstand me, I'm not advocating driving on worn out tires, but it may help alleviate a lot of frustration among people who buy new tires and see a loss in efficiency, if they understand going in that new tires are going to be a little harder for the car to push.

You have to "break in" new tires to get your mileage back. Usually takes a few thousand miles.

If the tires are LRR (low running resistance) you will usually get better mileage with them.

Inflating to higher pressures will also improve mileage, but I wouldn't go over the "max. inflation pressure" on the sidewall. Also, higher pressures can make the tires more susceptible to damage from road hazards. Tires with higher max. inflation pressures are usually better quality and stronger than those with lower max. inflation pressures. For example my Nokian WRs are rated around 54 PSI.

But your assumption is correct. Usually worn tires will give better mileage than "good" tires. Until you kill yourself.

Pearl is a
2007 Driftwood Pearl Prius
Package "B" (everything but leather, nav, and rear camera)

New tires have about 8 to 9 mm of tread depth, and the US legal minimum is 1.6 mm. That's when the 'wear bars' are equal to the remaining tread. Problem is that traction (especially on wet surfaces) decreases rapidly below 3 mm. Here's a chart:

http://www.rospa.com/roadsafety/advi...read_depth.htm

Regardless of the continuing small improvement in fuel economy, I hope that my valued fellow hybrid enthusiasts will consider replacing their tires at about 3 mm. Especially if the 'low-traction season' is approaching. Safety first and all that.

DAS

Yeah, like I said, I'm not saying it's a good idea to drive on bald tires... I'm just trying to offer a possible explanation that I have not heard suggested anywhere else, as to why people are seeing such a large decrease in MPG when replacing with new tires. You may be seeing inflated MPG numbers due to your worn out tires, so you will see a loss in MPG regardless of the quality of the replacement tires.

Some (not all) of the MPG change when putting on new tires is explained by the change in revs/mile. Let's take the Integrity (not my favorite tire) as an example. When new they have 855 revs/mile. At end of life they have lost about 0.5 inches in diameter due to tread wear which increases revs/mile by 0.5/24.5 or 2%. So just replacing your tires with identical new tires will seem to reduce MPG by 2%, but it is not real.

As was mentioned, there are LRR tires that definitely help MPG (Nokian WR or WRg2 is my favorite so far - see attachment) and there are others that will reduce MPG dramatically.

JeffD

Attached Files

PriusGasMileage.zip (32.2 KB, 31 views)

need to know which tire best of 05 Prius replacements jeff

Mr. "Salsa" Bosox

In the middle of the east coast I suggest that you look at the Nokian WRg2. It will produce good MPG, handle better than your original tires, and give very good traction in dry and wet weather (not too bad in snow either, but the older WR is better in snow for those who live further north). Just realize that you will get many opinions on this subject as each of us has had different experiences with tires.

JeffD