Rolling Resistance w/ New Tires

That makes some sense to me, because the MXV4 in 185x65x15 weighs 20 lbs which is heavier by a few pounds than the OE tire or other replacements which weigh 17-18 lbs.. So, getting them up to speed requires extra effort to overcome their weight, but once you get there you have inertia of motion on your side.

 

Marvin,

Another explanation is that tire rolling resistance tends to be higher at low temperatures and higher speed heats up your tires. True Low Rolling Resistance (LRR, using silicates in the rubber compound) tires tend to remain flexible and have lower rolling resistance at low temperatures which is when they make the most difference. This also tends to give LRR tires better traction in cold weather.

JeffD

 

It could also be that at low speeds friction and rolling resistance play a significant part in the overall vehicle losses whereas at high speed wind resistance tends to dominate. So tires are going to play a much smaller part in the overall losses at high speed.

 

All valid points being made. I just wish I had the same results as the OP - my highway MPG took a pretty steep dive too with the MXV4s. With such a large number of reduced MPG threads popping up lately tho, I'm not ready to fully blame the tires. I think the cold is the main issue. Or perhaps 2+2=5 in this case: cold weather impact = 2, tire impact = 2, combined impact = 5. Just a theory.

- D

 

I'm in the same boat. I put the Primacy MXV4 tires on my Prius at the end of November. My final tank of fuel on the Integrities yielded 54.6mpg. The next tank was split between the old and new tires and I ended up with 52.4mpg. The temperature dropped well below freezing during that tank of gas and we received some snow. I was glad to have the Primacies on, because I was slipping even in the rain with the Integrities (replaced at 34k miles). I am around 42mpg on this current tank, run entirely with the new tires. Because of several mornings below 10F, it is hard for me to tell what kind of effect the new tires are having on fuel economy. I tend to be in the low- to mid-40mpg range during winter, so I may not be seeing much negative impact on fuel economy from the Primacy MXV4.

When I called Discount Tire, the guy seemed surprised I was putting this tire on a Prius. As soon as I mentioned the low rolling resistance, it made sense to the tire guy.

 

Just out of curiosity, why were they surprised you were putting that tire on and did they recommend something different for you?

-Thanks

 

Low rolling resistance tires wear out faster too because of the use of silica in the tread and that is also why winter tires wear out faster as well. The other reason they wear out faster is some manufactures start with less initial tread depth, many are only 8 or 9/32" when new, where as standard tires are usually 11 or 12/32" deep new. As your tires wear out they automatically improve in lowering rolling resistance due to the tread being worm down.

If a LRR tire starts with 8/32" vs 11/32" std tire, you loose 4/32" of usable tire. In this case the LRR tire has 6/32" usable tread and the standard tire has 3/32" or 50% more usable tread. Are LRR tires really worth it at about $400 a set.

 

Don't know why they were surprised. They just said this was the first time someone with a Prius had ordered that tire. They didn't try to steer me toward something else, but it makes me wonder what they recommended to other Prius owners.

One thing I looked at when comparing tires was tread depth. The Primacy MXV4 was 11/32", the OEM Integrity was 10/32", Goodyear Assurance FuelMax was 11/32", and Michelin Energy Saver A/S was 9/32". As soon as I saw that, I didn't bother giving the Energy Saver a second look. Since I drive in snow in the winter, I wanted more tread depth since the Integrities performed worse with each season as they wore out.

 

I just had Michelin X-Ice snow tires mounted today, so I'll be waiting a few tanks to figure out their MPG impact. I expect to lose MPG, but don't know how much to expect.

In any case, my little test-runs in an empty parking lot first on OEM tires, and then hours later on the snows, demonstrated that the snow tires do provide much better control and traction. I think I'll appreciate them most when I make my next trip from Michigan to south-central New York State.

 

I installed Michelin X-Ice XI-2 a month ago, and have noticed no loss in MPG compared to my General Altimax HP all-season tires, and maybe even a bit better mileage. The X-Ice tires have Michelin's "Green X" technology for gas savings.

From Tire Rack:
"Many of Michelin's most fuel-efficient Original Equipment (O.E.) and replacement tires are branded with their Green X symbol to provide visual confirmation of the tire's positive contribution to vehicle fuel efficiency and the global environment. The application of the Green X symbol is determined by laboratory testing on a model-by-model, size-by-size basis. It is Michelin's guarantee that the tire provides a level of energy efficiency among the highest in the market for its category without compromising other key characteristics, such as traction and tread wear."

 

Hmmm.

Am at the Toyota dealership now, and am replacing my stock Integrities with MXV4s. I've been getting 70MPG for the last few months (55MPG in the winter) and I keep a detailed tank-to tank record, including noting the tanks where I drive a lot of highway, and the miles at the first pip drop.

I'll be using the same high pressure (48 front, 45 rear) as I was before.

It will be interesting to see how everything changes.

The Integrities, BTW, lasted 60k before becoming nearly bald (front) and 5 mm tread (rear). The guy here says that's pretty much par - folks who get lower MPG can expect the tires to go by 35k (i.e. short of the 40k warranty)

They were good for getting my current MPG rates, though.

I drive the car for good mileage - not sure if it is "hypermiling", though as I have no Scangauge and drive at pretty normal speeds. . However, since I do pump up the tires and block the grille in winter,I suppose I am a "mild" hypermiler.

 

I noticed that on a previous car with Nokian WRG2, which served as "snow" tires. At low speed around town they imposed a 0.5~1.0 liter per 100 km penalty. On the highway they seemed to do as well as the LRR OEM all-seasons.

 

If you drive for max fuel economy I would have chosen a different tire unless you require better snow traction.

Your Integritys were bald so expect to take a hit in mpg due to increased rolling resistance, larger diameter tires, and the necessary break in period. After a couple thousand miles your mpg may return.