Last October I needed new tires, so I had Michelin Defenders put on my 2011 Three in place of the OEM Firestones. The Michelins perform well and are nice and quiet, but... My gas mileage (both indicated on the dash and calculated) has dropped by about ten percent. In researching the two brands of tire, I found that the OEM Firestones are rated at 836 revolutions per mile, and the Michelins are 839. I'm wondering if this is the reason for the apparent change in mileage. I'm also wondering if there's a way to adjust the on-board computers to compensate for the difference. Any insight?
1) true, even the best Low Rolling Resistance tires take about 5000 miles to break in. Every time you get new tires, no matter how good, that happens. 2) To the best of my knowledge, Michelin Defenders are not good LRR tires, the Michelin Energy Saver A/S are about 5 MPG better. 3) Revolutions per mile is not the issue, and no it is not adjustable.
Just had my Energy Savers rotated at the 5000 mile mark and do notice the milage starting to come back up after changing from the OEM Yokohama Tires. Before the change I was averaging about 50-52 mpg but after the new tires I've been more around 48mpg. Hope to get back to where I was or better and that the tires will last longer so my choice will work out eventually.
hard to believe they are going to improve after 5000 miles. is the alignment good? maybe the yoke's are just better for mpg's.
Can't do much about it now but when you go to get your next set of tires look at a different size to change the RPMs. I'm assuming you looked up the wrong information on the RPMs as well. The only Defender at 839 RPM is a 195/70/14. The default size would be 195/65/15 and is 832 RPM and you could change that up by going to the 205/65/15 at 817 RPM. Picking a different size tire will change actual MPG based on unsprung weight, rolling resistance, and aerodynamics but it will also change the dash MPG by changing the RPM math. Going for the bigger tire will make dash MPG worse, but will make the dash MPG more accurate by being closer to actual MPG (similar issues with speedometer and odometer, the OEM sizes vs the size you mount change the math for all at the same time)
You can see Michelin's estimation of rolling resistance, for the: Energy Saver A/S: 10 (out of 10) Premier A/S: 9 Defender: 8 on this page: 2011 Toyota Prius Base Tires | Michelin Tires Not sure how big those steps are, and as the tires wear they'll improve a bit.
Yes and no. Yes there is a problem with accuracy due to the wrong revs per mile. I fixed that on our 2010 Prius by getting slightly oversized Yokohama tires. But the other problem is the specific tire dynamics. Tires can have different drag coefficients based upon rubber compound and construction. Sad to say, we can't get good metrics. However, the other issue is tire pressure which we have some control. You might consider inflating all tires to the max side wall and over a series of mixed driving, let the air out in 2-5 psi increments until you find a value that 'feels right.' Lower the pressure and the ride is easier but steering not as precise. Once you find the 'sweet spot', note it in your handbook and reset the tire pressure sensor (see handbook.) On our 2010, there is about 10 psi slop so set for 51 psi, the alert comes on at ~41 psi. So you might want to do something tricky: 1) inflate the tires +5 psi over your 'sweet spot' 2) set the tire pressure sensor 3) deflate the tires to your 'sweet spot' Our tires lose about 2 psi per month. So this will let the low pressure sensor alert you to top off the tires when they are getting about 5 psi under the 'sweet spot.' Bob Wilson
New tires are less efficient because there is more tread to deform than the old worn down tires. Even if you bought the same exact tires as your old ones, you would get fewer MPGs due to this increased rolling resistance. 10% seems like quite a hit, so there is likely multiple factors playing into it, some of which might be cooler temperatures or differences in your routes. My tanks can vary by as much as 15 MPG mostly because I have the PiP and have varying degrees of EV use.
