Rolling Resistance vs. Temperature
 

Has anyone ever seen any data for tire rolling resistance vs temperature? I've searched around and so far haven't been able to find anything.

From my own experience, I know that it goes up significantly as the temperature drops. For example, I typically back into my driveway (which slopes off towards teh street. The street is basically flat for about 100 ft or so and then slopes down slightly out to the first stop sign. Typically, I just start out in neutral in the driveway and just coast to the stop sign. I never get going very fast (3-4 mph tops). When it's really cold, however, (<20 deg F), I usually can't make it past the flat spot on the road and I have to start using the starter.

Another example is a section between stop signs I drive frequently. I do one pulse & glide for the whole section (~0.5 mi). When it's warm outside I only need to pulse up to ~30 mph to be able to coast the whole way. When it's really cold, it can take a pulse of ~40 mph to make it the same distance.

I watch my tire pressure and keep them pretty constant regardless of temperature, so I think I've cancelled out that effect. Also, I'm talking about low vehicle speeds so aero should be affecting things much.

Anyone ever seen hard data on this subject?

I don't have the source handy, but I saw a study of bicycle tires that said RRC doubles from 30C down to 0C.

I've noticed a similar effect on my coasting in the cold. I figured it was because things like bearings, fluids and the drivetrain in general (maybe the rear differential in your case) are all much tighter when its cold and are creating extra drag. Maybe the differntial fluid is slightly denser as well. Heat tends to make metals expand right. So mabye thats why the car doesn't roll as well. For example I've heard of people using dry ice to help press things into a motorcycle case. Never done it myself so I'm not sure if it works. Just a thought on why your truck might not roll as well.

I'm sure things like differentials, wheel bearings, etc, all play a role. I'm thinking tires probably are still the predominant source of rolling resistance, but I could be wrong.

Ya I'm not sure either. You could try heating your differntial/transmision along with all the other components that you already preheat and see if you notice a difference. Its not really that cold here at the moment so I cant really properly test it myself. Edit: [At least it would eliminate those factors as variables in the equation]

Using ecomodder's calculator with my car's specs, doubling the RRC drops the 35 mph mileage by 31%. That's without any oil viscosity changes, or air density changes, or the cold engine is more powerful effect. Sounds about right to me.

Hi Diesel_Dave,
See here.
The EPA temperature adjustment for tire rolling resistance:
So tire RR decreases about 22% at 0 compared to 68 degrees F. Which is going the wrong direction. The largest contributor to RR in modern tires is the stiffness in the steel belts, and that is almost unchanged for the range of temps that a tire sees. The change in the flexibility of the rubber at low temps is likely unimportant. In fact, as the rubber gets stiffer it flexes less so it should roll easier. I'd look at the viscosity of bearing and gear greases as the main culprit.
-mort

So that means they assume it's linear and the RR increases 1% for every 3 deg F you drop from 68 deg F.

That seems ballpark reasonable. Several flolks around here have a rule of thumb for FE vs. temp which is ~1% FE change per 2 deg F change. I think if you calculate air density changes you can ascribe ~1/2 that to aero.

This paper from '77 does talk about the changes to the rubber hysteresis, however, they don't give much data (see page 8):
http://www.edccorp.com/library/TechRefPdfs/EDC-1038.pdf


I also found a reference to an SAE paper from '80, but haven't found the full text yet:
http://papers.sae.org/800090/

I disagree.

As a winter bicyclist I'm keenly aware of a massive increase in r.r.. Bearing losses for motored vehicles are considered by SAE to be small enough to ignore in performance calcs (and their bearings have draggy lip seals); indeed when I spin a bike wheel in the cold it seems to spin nearly as well as ever (WARNING! Completely subjective!). I blame the tires themselves.

You say steel belts are the biggest contributor to r.r. when actually they are the biggest thing that reduces r.r.; steel springs back efficiently thus returning nearly all the energy it took to deform it vs rubber which due to hysteresis doesn't return as much when "undeforming"; thus the rubber is the culprit in absorbing energy when rolling.

I think the amount of flexion isn't changed much by temps (???) because the load on the tire is constant.

Oh, to have low r.r. steel belted bicycle and motorcycle tires!!! I think the super low r.r. tires used on solar racers are steel belted...

We know that tubeless tires have lower r.r. than tubed; more rubber = more r.r.

I once put some elastic bands in a fridge, and they became very stiff and hard to bend. One piece broke when it fell on the floor, which seemed very strange once the parts warmed up again.
Not all rubber will act the same, but tire rubber will not completely escape from this effect imho.

Also I think the stiffness increases exponentially with lower temps rather than linear. Otherwise the rubber band would not have broken like that.

I'd expect less than stunning performance from solar racers when temperatures are way below freezing anyway. Can't just blame the tires for that ;)