Winter tires: they are not necessarily your main FE hit

But am I correct in assuming you are comparing a narrow lighter tire with a wider heavier summer tire?

 

You are blowing smoke.
The difference in rolling resistance between summer tires and winter tires can easily lower the gas mileage by 10%.

 

Winter tires may drop mpg but weather and temperature is likely to have the largest effect on mpg. I've never run winter tires yet my winter mpg drops significantly despite living in a fairly mild climate. Going from a summer tire to an all-season tire is not likely to significantly reduce mpg if size is kept the same but a true winter tire is more likely to reduce mpg.

 

Wow, that is a huge amount of rolling resistance, more than I thought serviceable tires should produce.

Are you sure that you are accounting for temperature / weather / precipitation / fuel blend (energy content) differences? These winter factors knock more than 10% off my gas mileage without any tire change whatsoever, both on this Prius and on its two immediate non-hybrid predecessors.

 

'Can' does not mean that it 'must'; nor does it mean that it 'will'.

Simply that it 'might'.

 

Exactly. I was going to post the same comment. It all depends on the tire. Some winter tires have much lower rolling resistance than others, just as with summer tires. There are too many exceptions to make any meaningful generalizations in this area.

Tom

 

We've just swapped over again from our stock Michelin Pilot HX MXM4 215/45R17 (OEM, LRR all-seasons) to our snow tires on steel rims: Michelin X-ice 195/65R15 (Winter tires, with the mountain/snowflake symbol, also described as LRR).

They're doing pretty good, maybe a slight drop in mpg, but: it seems like the higher/narrower profile cancels out most of the differences in rolling resistance. Also beneficial for snow traction, if we ever get any.

 

I don't think my winter tires give me as much of a hit to FE than the colder temps coupled with my short drive. Right now, with full lower grill block, I'm barely at 47 mpg with temps around 35(L)/55(H). When we get to the real winter, I'm usually in the low 40s, so I think my hit isn't as bad from the tires as it is from the temps. I can usually pull upper 40s on the highway in winter, and that includes heater usage usually then.

I hope to hear from Mendel more about how his X-ice perform all winter. I'll be swapping my Blizzaks back on probably around Thanksgiving (I will have a few days left of vacation, though it's earlier than I'd like to do it) and it will probably be the final year for those tires. I'll need to look for something else to replace them and the X-ice look like they got pretty good ratings.

 

My apologies if I misunderstood you.:redface:
In general, I agree with your observation.

 

I live alongside a river. Sometimes we got fog mist from the river, when the ground is below freezing temps the fog will settle on the pavement and form 'black-ice'. A thin layer of ice that is difficult to see. It is so slippery that you can not stand on the pavement without falling down.

Regardless of the effect on Fuel Economy we use studded winter tires.

I do not like flying into the ditch. Landing in the ditch may cause damage to the vehicle.

 

The technical name for black ice is "clear ice". It is commonly called "black ice" by drivers since it looks shiny and black when formed on asphalt. The color comes from the underlying surface.

The other form of ice build up is hard rime, sometimes called rime ice. Rime ice looks more like Styrofoam, with a white, fluffy, opaque look. It is not as hard as clear ice, and less slippery due to its texture. Rime ice looks a lot like packed snow.

The fog mist from the river is called "advection fog". It occurs when warm, moist air from the river drifts over the cold ground, causing the air to cool and water droplets to condense. We see a lot of that here around the Great Lakes.

Tom

 

We are, in the State of Michigan, but only if the tires meet a standard not met by any tire. So technically studded tires are legal in Michigan, but practically they aren't.

Tom

 

I have the same set up except I have alloys for the winter tires. I see no difference in mpg between my 15 inch winter and 17 inch summer set up.

 

Try reversing this by running your 17s in the winter and your 15s in the summer then report back. There will be an increase in mpg during the summer and a big hit in the winter. The point is, you're masking the difference of the winter tire and winter weather by using a smaller and lighter tire. I just performed such a swap because my 15s are summer tires and my 17s are all-season and are rated for incredible wet weather performance. Thankfully we have received much rain so I'm still getting 49mpg tanks on average. Unless I start speeding.

 

I used the numeric-entry calculator at bikecalculator dot com (a site I maintain) to put some boundaries on what you should expect. A 25% increase in rolling resistance can decrease mileage somewhere between 2.0 and 3.3 mpg.

Details: I used these input parameters: 60mph, 1361 kg, 0.25 Cd, 2.5 m^2, 77F. The change in mileage assumed a baseline of 50mpg. The lower figure above comes from Crr's of 0.004 and 0.005; the higher figure from 0.008 and 0.010. The lower Crr's are probably unrealistic for car tires, while the higher Crr's are not as high as they might go for aggressive snow tires on a rough surface. Actual Crr's are hard to come by, even from purported measurements - too many factors are involved.

In another recent thread, I calculated that the effect of temperature alone is around 3 mpg (difference between 77F and 0F, aerodynamic forces only). A rough conclusion is that if you change tires for winter (I do not despite my location), the tire effect is about the same as the temperature effect (aero). There are additional effects, of course.