New tires = very poor mpg for Hybrid! What gives?


#1

I purchased 4 new low resistance Michelin Fuel Savers tires at 68k miles for my 2012 Toyota Prius C. For 3 1/2 years and immediately before I had it new tires, I enjoyed excellent MPG and I admit I’m OCD with watching mpg screen enough to know my daily habits.

With this new tires and all tires are set 41PSI…I still get POOR mpg with no changes! I almost never reach 50mpg on any trips!

Before new tires: My AM commute to work…always 53 to 56mpg, my PM commute to home, 52 or so.
New tires: My AM commute to work…barely 43 mpg! maybe 45!, my PM almost never reach 40!

What gives! I e-mailed Toyota service dept, they said did I lose wheel cover? (WTF? It’s the same cover I still have it!) then he said, they need to check into it for $150. No way I’m paying $150! that’s like another tire! Ugh!

What may be the cause? I purchased Mechilen Fuel Savers with LRR tires as recommended. I feel sick to my stomach every time I see piss-poor mpg.

Hope you guys and gals can help me figure out what MAY be the cause. I’ve been driving with this new tires little over 1,000 miles already including 1 day trip to southern California (that trip, 37mpg and 41 back, where the same trips I took before always 54 average depending on the weather and wind directions)


#2

Are they the same size as the previous tires?


#3

Are the new tires a different size, as well as brand or model? Wider = more wind resistance and probably more rolling resistance. Different outside diameter = changes in actual (vs. speedometer/odometer) distance traveled per revolution.

Check Tirerack site to compare your new and original tires on various performance aspects - rolling resistance especially.

The OEMs are likely extra low in rolling resistance. That helps Toyota’s CAFE and gives Prius buyers more of what they want. Your new tires may have some qualities you may come to appreciate, but I feel your pain and would have the same questions you have.


#4

@MikeTheMailman

Hate to tell you, but you probably bought the “wrong” tires

Some hybrids are equipped from the factory with tires which aren’t commonly available, as @shanonia already pointed out

We have lots of hybrid vehicles in our fleet, and our tire shop isn’t having an easy time getting the tires the cars are “supposed” to have

I don’t mean to sound like a total jerk, but your local Toyota dealer is more likely to have the “correct” tires in stock, versus Costco, Pep Boys, or any of the big name tire retailers


#5

Everything’s same size as the old tires I checked it.

I purchased it from Big O tires


#6

Can you tell us exactly what tires were on the car previously and what tires are on there now?


#7

@MikeTheMailman

“I purchased it from Big O tires”

And that might very well be the problem. They probably have “regular” tires for cars and trucks, not tires specifically for hybrid cars

Just because a tire fits your car, does not mean you’ll get the same fuel economy, versus the “correct” tires


#8

The ones that was included when I brought it brand new in 2012 was Goodyear Assurance


#9

When I input from Toyota Dealership it even recommended Mechilen Fuel Savers with exact same size


#10

When did you (OP) last align all 4 tires?


#11

First, new (unworn) tires do not give as good mpg’s as worn tires - all other things being equal. That’s because there is more mass in the tread - as in none has been worn away.

Second, OE tires are almost universally better for mpg’s compared to what you buy for replacements - all other things being equal. That’s because OE tires are designed to the vehicle manufacturers specs, one of which is low fuel consumption - and that is done by sacrificing treadwear and/or traction. Replacement tires are designed to deliver good wear - and that means sacrificing fuel economy.

Third, LRR is a relative term, not an absolute term. It means better fuel economy compared to other tires with similar wear and traction properties - and while an LRR tire would be better than a non-LRR tire (with similar properties) it would not be as good as an OE tire.

And lastly, this time of year is always worse for fuel economy. Not only is it cooler and the car takes longer to warm up (which uses up fuel), but the gasoline has changed so the engine is easier to start and that results in worse fuel economy.

So you’ve taken a number of hits in the fuel economy area just because of the tire change, but there may be other things that occurred at about the same time.


#12

“And lastly, this time of year is always worse for fuel economy”, also because of higher viscosity in the CV joints, the differential, and the transmission.

I’ve seen my economy drop from 34 to 30 MPG in the last month because of colder weather. Same trip, same speed, etc.


#13

@MikeTheMailman - Did you get the “Energy Saver” or the “Energy Saver A/S”? Michelin recommends the “A/S” version for your Prius C, the other is quite a bit different.


#14

Did they do wheel alignment when you replaced the tires?
It’s possible the “Big O” alignment machine was out of calibration and left your wheels in worse alignment than when you came in.


#15

You went from Goodyear Assurance tires to Michelin Fuel Savers? That can account for part of it right there. Changing tire brand/model can change your fuel economy. And as CapriRacer mentioned, it’s cold now. You’re going to get worse mileage.

All that said, the mileage calculator in your car is wrong. How do I know? Because they’re all wrong. They’re a rough estimate at best. The only real way to calculate mileage is to look at how many miles you drove between fillups, and how many gallons of gas you put in.


#16

You have lost quite a few mpgs there…so this is signficant. The other guys pointed out some very real possibilities. If they actually do have “extra low” rolling resistance then the solution might be right there.

You have some homework to do for sure. I’m more than certain that this topic is covered AD NAUSEUM on the Toyota Prius enthusiast sites.

Basically there are several things that could cause what you described. The first being how hard those new tires are and if they actually ARE Low or XLow rolling resistance. The next thing you need to find out is the true outer circumference of the new tires…your new tires may have a larger circumference…and they may be spinning slower which is fooling the computer

Let us know what you find out… You have a lot of areas to check into.

Blackbird


#17

Bottom line is, different tires have different rolling resistance and new tires in particular have higher rotating mass. Ergo, a drop in mileage isn’t unheard of when getting a different tire.

I had this happen to me once too. I got some tires, same size same ratings, that had fantastic traction and handling… but the mileage dropped, and the rotating mass was so much higher I could feel the difference. Fortunately their very soft rubber compound wore out fairly quickly and I replaced them with something more normal. My mileage went back up… but the handling went back to normal.

I think your solution is going to be the same as mine was. Wear 'em out and get something different at that time.


#18

+1 to tsm. Rotating mass is a significant factor in acceleration and therefore in fuel consumption.


#19

Agree with @shadowfax about the mpg calculator; I have no idea all the factors that go into the calculation. If you really put a lot of stock in the mpg calculator, see how accurate it is by doing in the old-fashioned way periodically.
One factor Tom and Ray frequently mentioned with a gas mileage question is a change in driving behavior. This response usually accompanies a question about one of the “As Seen on TV” devices that’s supposed to increase gas mileage. Although a tire change is not likely to prompt a behavior change, it can’t hurt to ask yourself the question.
And if none of these paths (tires, weather, calculator, behavior) get you a satisfactory answer, you can get some comfort in knowing that your mpg is still two times larger than most of us!


#20

Prius tires are selected for one thing only; minimum rolling resistance at the expense of other qualities, such as traction handling and long life.

One reason I don’t really want a Prius. But these models will really help Toyota in the new CAFE fleet MPG standards in the future.