Fuel Economy Loss With Michelin Primacy MXV4

[The Critic]

I installed a set of Michelin Primacy MXV4 onto my Prius about 650 miles ago. The previous tires were a half-worn set of the original LRR Yokohama Avid S33d tires. Both sets of tires have been ran at 37F/35R, which is a 2psi over the 35F/33R recommended by Toyota.

So far, I have noticed a 3-5% decline in fuel economy during long-distance highway driving, and an 8-10% decline during city driving. Part of this must be due to the 23 lb weight of the Primacy MXV4 tires vs. the 18 lbs of the Avid S33d. I was expecting about a 5% drop over the OE tire, so these results are sort of what I expected, but it is still amazing how much of a difference in fuel economy tires can make.

So, I am now at 41-42 mpg overall vs. the 45-46 I was previously at. But grip, noise and handling are noticeably better.

 

[Colt45ws]

Should also last longer which will save you money there as well. Those Michelin's are, what, 80k mile tires? And the factory tires were on their way to being trash before 30k miles?

 

[JOD]

Originally Posted By: The Critic
Part of this must be due to the 23 lb weight of the Primacy MXV4 tires vs. the 18 lbs of the Avid S33d.


It's not the weight. You're talking about 20 lbs on a 3000lb car. To be honest, the tire's aerodynamics are most likely a much bigger factor, in particularly the rim/tire interface is a pretty high-drag area; but the biggie the is the Crr. The OEM tires probably roll better. I'm assuming they're a special low Crr tire that's spec'd on the Prius?

 

[The Critic]

Originally Posted By: Colt45ws
Should also last longer which will save you money there as well. Those Michelin's are, what, 80k mile tires? And the factory tires were on their way to being trash before 30k miles?

60K. Though threadlife is not a major concern since I like to replace tires "recreationally."

Originally Posted By: JOD
Originally Posted By: The Critic
Part of this must be due to the 23 lb weight of the Primacy MXV4 tires vs. the 18 lbs of the Avid S33d.


It's not the weight. You're talking about 20 lbs on a 3000lb car. To be honest, the tire's aerodynamics are most likely a much bigger factor, in particularly the rim/tire interface is a pretty high-drag area; but the biggie the is the Crr. The OEM tires probably roll better. I'm assuming they're a special low Crr tire that's spec'd on the Prius?


Yeah, the rolling resistance is likely much lower with the platform-specific Yokohamas that were original. But an extra 5 lbs/tire of unsprung mass could not possibly be beneficial either.

 

[tom slick]

We're also transitioning to winter gas right now. That's make a hit like you've seen.

 

[OldCowboy]

I don't think unsprung weight has anything to do with gas mileage. Handling - yes; mileage - no.

 

[ueberooo]

Originally Posted By: The Critic
I installed a set of Michelin Primacy MXV4 onto my Prius about 650 miles ago. The previous tires were a half-worn set of the original LRR Yokohama Avid S33d tires. Both sets of tires have been ran at 37F/35R, which is a 2psi over the 35F/33R recommended by Toyota.

So far, I have noticed a 3-5% decline in fuel economy during long-distance highway driving, and an 8-10% decline during city driving. Part of this must be due to the 23 lb weight of the Primacy MXV4 tires vs. the 18 lbs of the Avid S33d. I was expecting about a 5% drop over the OE tire, so these results are sort of what I expected, but it is still amazing how much of a difference in fuel economy tires can make.

So, I am now at 41-42 mpg overall vs. the 45-46 I was previously at. But grip, noise and handling are noticeably better.

I find that significantly colder temps possibly along with a switch to winter fuel, can lead to that sort of decrease. The fact that city mpg's decreased that much more vs highway may point to the temperatures. On very short trips, bringing the car up to temp takes that much longer in colder temps, plus the engine under a certain temp runs in a choke-like mode burning rich and inefficiently till slightly warm.

My guess is that most of the observed decrease is seasonal.

 

[sciphi]

And they're new tires compared to worn-out tires.

3-5% can be temperature/fuel related. It's much more noticeable in a high-MPG vehicle like a Prius since 10% is 4-5 mpg.

 

[Smoky14]

My Primacy Did the same thing, after about 2K milesw it started to improve and @ aboutn 6K I was back up to about 1% better.
YMMV

 

[carwreck]

Look at lots of tire threads, loss of mpg is common with new tires.

There are a lot of variables that could explain this. Slight difference in tread width, diameter, revs per mile, rolling resistance...

But the number 1 variable is your brain. You just bought a new set of tires.

I suggest that you might be driving more aggressively (such as accelerating harder out of corner ) to test out the new tires!

This would also explain why the mpg improves after about 2,000 miles. You eventually go back to driving the same as you did with the old tires.
______________________________________________

1999 Olds GLS 3.4L

 

[Quattro Pete]

Originally Posted By: carwreck
Look at lots of tire threads, loss of mpg is common with new tires.

Yup. New tires with full tread = more tread squirm = lower MPG.

 

[CharBaby]

Critic my friend,
As stated in another thread you posted, I replied with a stetement that the tires may need to wear in. Not that the MXV4's will ever be as LRR as the OE tires were but, they will get a bit better as they wear, than when they were new. Every set of new tires I put on a vehicle, the MPG went down for awhile before returning to, what I would call "normal" for that vehicle.

Now, when we buy vehicles, we buy them for a variety of reasons that we like. OK? So, as we replace items(in this case, tires), we tweek the things that we don't like about the vehicle as how it came from the factory(tires, brakes, wipers etc.) You did't like many of the short comings of the OE tires and changed those short comings with the better MXV4's.

Now, there is an MPG drop but, you certainly got a better overall tire that will perform in many areas that you didn't like in the OE tires. And too, the MPG is still better(doesn't suck) than just about any other vehicle you ever had prior! And better MPG than just about anything on the market too. And you got MXV4's!

I beleive as I stated before, let the tires wear in some. I think that the MPG will increase although maybe not to where the OE tires were. But, the OE tires weren't to your liking and look at the tires you just bought...MXV4's

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2428950&page=all

 

[Papa Bear]

Originally Posted By: The Critic


So far, I have noticed a 3-5% decline in fuel economy during long-distance highway driving, and an 8-10% decline during city driving. Part of this must be due to the 23 lb weight of the Primacy MXV4 tires vs. the 18 lbs of the Avid S33d. I was expecting about a 5% drop over the OE tire, so these results are sort of what I expected, but it is still amazing how much of a difference in fuel economy tires can make.


Probably due to the added weight and wind drag from that clear bra you installed ....

 

[Whimsey]

Two years ago I purchased Michelin Exalto A/S tires to replace my nine year old but not totally worn Michelin Pilot's. Then I took a trip to Key West from NJ, around 3,400 miles RT. My mpg was down from 36 mpg on the highway to 31mpg. The steering was squirmy. After around 6,000 miles I got my highway mpg back and the steering is now spot on. Some tires need a "breakin period".

Whimsey

 

[JHZR2]

wait, why would you swap a set of tires that had 50% tread? Do you get lots of snow where you are in CA?

Sems a bit silly. Did you sell the used tires at least?

 

[The Critic]

Originally Posted By: JHZR2
wait, why would you swap a set of tires that had 50% tread? Do you get lots of snow where you are in CA?

Sems a bit silly. Did you sell the used tires at least?


No snow. My tire shop gave me $50/tire credit ($200 total) towards a new set. So my cost for upgrading early was about $20/tire.

 

[JHZR2]

Originally Posted By: The Critic
Originally Posted By: JHZR2
wait, why would you swap a set of tires that had 50% tread? Do you get lots of snow where you are in CA?

Sems a bit silly. Did you sell the used tires at least?


No snow. My tire shop gave me $50/tire credit ($200 total) towards a new set. So my cost for upgrading early was about $20/tire.


You must have stolen them then, considering that they sell for $115/tire at tirerack, plus shipping and plus installation and balancing.

If I went and bought a set they look like a $130 tire easy to get out the door.

 

[mechtech2]

Your mileage may not be as bad of a drop as initially observed.
This is because the new tires have a larger diameter with new high treads. Each registered mile may be shorter than you are actually travelling.