Initial Fuel Economy Loss With Michelin Primacy MXV4 Tires

I doubt the extra tire weight would effect gas mileage in a measurable amount.

There are other possible reasons for the "gas mileage" change.
1) With new tires, "gas mileage" will often be lower because the tire is taller (greater diameter) compared to the used tire. A smaller tire will rotate more times over a fixed measured mile. Your displayed gas mileage goes by the number of tire rotations per mile.

2) Rolling resistance has a measurable effect on gas mileage. In real life, there are compromises. One is that less rolling resistance often means less grip. There's also a trade off in tire wear verses rolling resistance/grip/etc.

3) Tire sizes are like dress and pants sizes. In other words, in reality, there is no standard. There are just "recommendations" that are often ignored for cost/marketing reasons. And, it gets better. Tire manufactures even often change specs for the same exact tire model and size between years.


Also, you mentioned that you correctly checked air pressure. You're in Southern Cal. However, for most of the country, the max/min temperature swings easily go past 50F. People often say ~1psi drop for every 10F drop. But, it varies a lot. And, sometimes, the tire pressure recovers when the temperature rises, sometimes it does not. Hence, the reason for the Federal mandate for "tire pressure" monitoring on the new cars.



So, it's really a total cr*p shoot when trying to get accurate distance measurements from tire rotation.


FWIW, self driving cars use a lot of different sensors to help them know where they are. GPS and acceleration sensors help a lot. But, "visual" imaging with prior knowledge of the exact locations and landmarks is still the most accurate.


For some more neato techie info check out::
DARPA Grand Challenge
Google's self driving car


IMHO, *I* care more about grip than gas mileage. I see grip as being very key in helping to avoid accidents - especially in areas with heavy traffic and classic stop/go traffic. Even for the eco-people, IMHO, there's no way to justify the "carbon foot print/etc" effect for an accident repair verses saving some gas.


I'm glad that you like the MXV4 tires.

 

This pretty much mirrors my experience. I have a daily 52 mile RT commute with 40 miles highway driving. I am beginning to gain a little in highway mpg at 6k miles on the tires, but I take a big hit in town with the stop and go traffic.

In my opinion, the positives of these tires; grip, comfort, handling and quietness, outweighs the negative of loss of mpg. I am still holding out hope that the mpg will continue to increase as the tires continue to wear in and the tread depth decreases.

Good to point this out to those considering new tires so they can weigh the pros and cons for themselves.

 

A tyre's increased friction will always be more apparent in city driving, because tyre friction is a greater fraction of total resistance in the city compared to the highway.

'grippiness' has a price. A couple years ago I bought a set of Falken Zi-Ex thinking I was getting a LRR tyre, but it was actually a soft grippy tyre. Fuel economy dropped over 20% (yes, twenty) for over 10k miles. I paid for three alignments during those months because I thought there had to be a problem with my car, although it turned out to just be my tyre choice.

 

it usually gets better after initial 500mi, then gradually better after 1-2K, depending on tire. The improvements after 1year/10,000mi so gradual they are hardly noticeable.

yes as Sage said with non-LRR tire you take more MPG hit in town. A while back I ran Prius through calculator, and at ~45MPH the rolling resistance and air drag even out. Unless it is extra-urban or freeway you rarely go above 45 in the city.

 

I wouldn't sweat it bru. If you drive 15,000 miles/yr you only lose about $126 assuming:

Avids: 15,000 / 44mpg * $3.70/ga = $1261

MXV4s: 15,000 / 40mpg * $3.70/ga = $1387

$1387
- $1261
.............
$126/yr

How much is your safety and comfort worth???

Form a fiscal standpoint though, you could probably buy a new set of tires with the money saved on the LRR tire. Again, what is most important to you? In my case I would rather lose 6mph during the winter by running my 17" tires (they are outstanding in wet traction) rather than my ultra-efficient 15" tires (summer tires with less wet traction).

Despite the mpg loss I think you made a good choice. Especially in the Monterey area where fog and mist make the roads wet more often than a lot of other regions.

 

Ohh, you can practice some basic hypermiling techniques to help recoup the money if you really wanted to. I am averaging 49mpg with my 17s if I try hard. Otherwise mpg drops back to 47ish or even 45mpg if I drive like an idiot.

 

Check out this table from Wayne Brown. If you simplify frictions to air and tyres, breakeven is at 65 mph.

 

Very possible!

This summer we can swap my summer tires on your car and see what the difference is. lol

 

Don't forget that you will see much less MPG's when it is "cold" outside. Cold being relative. But the local temps have dropped off a lot in the morning and we have had some wet weather recently too, which will also lower MPG's.

I've tried blocking my grill this year so I can somewhat compare it to last year's results (although my tires are a bit more worn, the results should be noticable).

 

I put the Primacys on my 2010 Prius IV in September and the mileage dropped an average of over 4 mpg over 7 tanks. I went back to the tire dealer and he exchanged them for the Bridgestone EP422 at no additional charge. I fully recovered the 4 mpg lost and gained another 2. They are just as quiet as the Primacys but the wear rating is not as high. I am a happy camper now!

 

It's a much better tire, why not explore higher tire pressure and see if you can't find a happy medium where you regain some of the lost MPG but keep the better handling of the better tire?

Maybe try working your way up this ladder?

45/42 high
42/40 med
40/38 low

 

I tried 42/40 but it only got to -4mpg and it felt like a hay wagon. Grip on the Bridgestones is better than the original Yokos.

 

From what I have read the MXV4 is a better tire all around except for the LRR and price factor. So if you want the best MPG then go with the Ecopia. If you want a better performing and safe tire then go with the MXV4. *shrug* There is no right or wrong here. It's all up to personal choice.

FWIW I'll be putting the Ecopia Dueler EP422 on my girlfriend's Rav4 next month or the following.

 

Mike,

Regarding our PM'd conversation on traction versus pressure I completely forgot that in some cases the lower pressure does indeed help with traction but there is a fine line between max traction and poor tire performance including hydroplaning resistance.

During my drag/street racing days I played with tire pressure a lot. Conventional wisdom showed that lowering tire pressure improved off the line traction in drag slicks so we tried it on our street tires to gain every advantage we could as it is very difficult to launch a supercharger or nitrous equipped V8 rear-wheel drive car on street tires. I found that dropping the tire pressure just 5psi or so (from 35psi) helped with off the line traction but go much lower and traction got worse. In each case the car handled worse (sloppy) so after racing everyone would be at the gas station filling their tires back up. I'm not sure where I am going with this but I think anywhere between 35psiand 42psi would be fine for your circumstances. Just remember that an overinflated tire while not optimum is still better than an underinflated tire when it comes to hydroplaning resistance.