Rolling Resistance Increases as the temperature drops!

[CapriRacer]

From Tire Business May 8, 2023

How does temperature affect rolling resistance?

By Erin Pustay Beaven

GREENVILLE, S.C.

Range can be a very tricky thing. Electric vehicle range is, simply, inconsistent.

It changes over time, across driving conditions and with temperature fluctuations. And while there are a number of factors contributing to the fluctuation in range, it’s understood tires play a role. Especially when it comes to colder temperatures.

And that leaves a lot of questions to be answered. Questions such as: Exactly how much of an EV’s drop in range can be attributed to the tires? And how does temperature fluctuation impact rolling resistance?

That’s exactly what Smithers is working to solve, according to Matt Kent, technical director of the Smithers Tire & Wheel Center in Ravenna, Ohio. Because answering those questions — among others — gives the industry the leverage it needs to design tires better targeted for new mobility.

“Electric vehicles show a significant decrease in range in cold temperatures,” Kent said during his presentation at the recent Clemson University Global Tire Industry Conference in Greenville. “But current test standards only evaluate rolling resistance at room temperature — it’s actually 24 degrees C. And understanding rolling resistance performance at cold temperatures could provide an opportunity for tire design improvements to support an increase in range.”

When it comes to testing and ultimately understanding the ways in which cold temperatures impact rolling resistance, Smithers is turning to its Suzhou, China, facility, which houses a cold chamber rolling resistance machine.

This machine, Kent said, is capable of testing tires at temperatures ranging from 40 degrees C to -40 degrees C.

“It has been really interesting seeing the data and seeing them bring this thing online,” Kent said.

Using a torque method for the study, Smithers tested four different tire brands, each of them at four temperatures—35, 25, -10 and -20 degrees C.

What the team found, Kent said, was “the trends were all the same. But the big difference was they all performed very differently down here at the lower temperature.”

Each of the tires showed significant increases in rolling resistance as the ambient temperatures dropped. With each drop in temperature, the rolling resistance increased.

Tire rolling resistance performance is strongly influenced by temperature,” Kent said. “RRC increased as temperature decreased and is more sensitive at low temperatures as opposed to high temperatures. So clearly, we have a lot of data at 24 degrees C, and around that range there’s some difference, but they are not hugely substantial.”

In the Smithers study, the best performing tire showed a 56% increase in rolling resistance between the highest and lowest temperatures, while the worst performing tire, Kent said, saw rolling resistance increase by 116% between the highest and lowest temperatures.

And this, of course, is just the start. Smithers plans to take its testing further and expects to have further data compiled by the summer of 2023. Additional tests, Kent said, include examination of EV-specific tires that are a mixture of original equipment and replacement tire fitments

 

[JavierH19]

Was the psi matched in the high or cold temps? The colder it gets the lower the psi and thus more tire makes contact.

 

[CapriRacer]

Was the psi matched in the high or cold temps? The colder it gets the lower the psi and thus more tire makes contact.

I assume they followed standard testing procedures and matched the pressure. The only difference would have been the temperature of the room. It would make no sense if they didn't match the pressure.

 

[billt460]

In the Smithers study, the best performing tire showed a 56% increase in rolling resistance between the highest and lowest temperatures, while the worst performing tire, Kent said, saw rolling resistance increase by 116% between the highest and lowest temperatures.

That makes sense. Rubber gets very stiff and much less pliable in cold weather.

 

[PandaBear]

I know for sure air density decrease as temperature increase, so it is much easier to push through the air.

 

[CapriRacer]

I know for sure air density decrease as temperature increase, so it is much easier to push through the air.

Except that RR testing takes place in a closed room. They are not reporting on the effect temperature has on pushing the car through the air - just the affect on tires.

 

[JohnnyG]

Another huge surprise!

 

[barryh]

I presume that it's the running tyre temperature that's impacting on rolling resistance. Ambient temperature will affect the running temperature that the tyre achieves and that it will be lower in colder conditions and if the tyre temperature is lower then the running pressure will also be lower.

So is this study revealing that rubber stiffness is increasing rolling resistance or is it simply reflecting that cold ambients don't allow a tyre to reach the same running temperature that it would in warmer conditions. The inference here that even if inflation pressure is set the same at each ambient temperature before the test commences, the actual tyre running temperatures and therefore pressures will still be different during the test and that will will impact on rolling resistance.

 

[Traction]

Seems like a harder tire should roll easier. Moving something around on wheels, I've found stuff easier with a hard tire vs a soft one.

 

[JWC86]

Seems like a harder tire should roll easier. Moving something around on wheels, I've found stuff easier with a hard tire vs a soft one.

I find this interested as I also expected the same. Colder tire should be harder and less “sticky” so I would have thought it would roll easier.

 

[billt460]

I find this interested as I also expected the same. Colder tire should be harder and less “sticky” so I would have thought it would roll easier.

The sidewalls still have to flex. The colder the temperature is the stiffer the rubber becomes, and the rolling resistance increases.

 

[JWC86]

The sidewalls still have to flex. The colder the temperature is the stiffer the rubber becomes, and the rolling resistance increases.

Oh interesting. It’s the resistance to flexing that makes it harder to turn. That makes sense.

Thanks!

 

[CapriRacer]

Oh interesting. It’s the resistance to flexing that makes it harder to turn. That makes sense.

Thanks!

And it's even more complicated than that!

It's actually the difference in the amount of energy you put in vs what you get out. Think of the tire as a spring and the rolling resistance as the internal friction of the spring. There is always some energy loss.

 

[Nick1994]

And it's even more complicated than that!

It's actually the difference in the amount of energy you put in vs what you get out. Think of the tire as a spring and the rolling resistance as the internal friction of the spring. There is always some energy loss.

If they filled the tires at room temperature and then succumbed them to super cold temperatures, the PSI would drop, and potentially cause more rolling resistance right? So even if they didn't adjust the tire pressure for the cold weather, this test provided less rolling resistance and if the tire pressure was then adjusted for the temperature, their results should improve even more.

 

[KB3MMX]

Guys and Gals here's what's happening to cause this.

Hyper miling a tire usually involves a 10-20% increase in the max inflation as standard practice to REDUCE sidewall flexing to INCREASE fuel mileage.

Physics wise it's the actual LACK of pressure increase delta from operation in cold seasonal air (vs hot) and the colder outside gets.... the less the increase in pressure..... IE you need to INCREASE static tire pressures more the colder the temperature gets ..

Think of this like your cooling system for the engine. As outside temperatures increase it gets closer to the temperature of the coolant which is a delta reduction that dramatically lowers the rate of heat transfer.

Increasing that delta accelerates the rate of transfer. Think of cooling a motor on a 110F day versus a 10F day the difference in heat transfer is enormous from the Delta.

Regarding tires;

For example: a 455/55-22.5 SS tire during 80F summer starts at 120psi and at 65mph with grid weight load usual achieves 150-160F and 145-155Psi

The same tire in 10-20F conditions only achieves a temp max of 110-120F and 130-135 psi.

This is leading me to believe that winter inflation needs to be INCREASED by 10-20% minimum as a standard practice instead of a Niche Hyper Miler practice.

Just to spitball it... I would say a 10% increase in cold inflation PSI for every 35-40F below the 70F Ambient "Cold" inflation standard.

For a real curveball, remember that adding PSI to a tire also reduces the total delta of maximum pressure achieved due to heat losding as the rolling resistance is decreased so does the heat load go down and the max expansion of the air.

For fuel efficiency purposes we are wanting to ADD cold inflation PSI on cold outside temps to achieve the SAME normal summertime max operating pressures achieved and comparable rolling resistance.

Tires carry load with pressure and changing that operational pressure higher within structural engineering limits , desreases the amount of sidewalk flex resistance losses in the side wall.

80psi summer tire should be around 90psi cold inflation during winter (32F or colder) to achieve similar max pressures, rolling resistance and Fuel economy when operating.

 

[Kestas]

I agree with others that the results are counterintuitive. The cold should reduce sidewall flexing and decrease rolling resistance. Perhaps they forgot to bring the pressure up to where it was at room temperature.

 

[supton]

I assume they followed standard testing procedures and matched the pressure. The only difference would have been the temperature of the room. It would make no sense if they didn't match the pressure.

I’d be interested if they did both. Some people are very careful and keep their tires at the stated placard pressure year round—others tend not to be so diligent in the colder temps *cough*.

 

[oil pan 4]

Well yeah.
Equipment that I can move no problem in the summer I can't move at all during the winter.

 

[KB3MMX]

I agree with others that the results are counterintuitive. The cold should reduce sidewall flexing and decrease rolling resistance. Perhaps they forgot to bring the pressure up to where it was at room temperature.

But it's more than that. During cold weather your tires don't achieve the same operational pressure rise as summer time.

You actually need to raise the Cold Inflation pressure higher for the winter, NOT match the summer cold PSI


The test only involved a standardized PSI used warm wx and cold wx and didn't consider that cold WX operation doesn't have the same pressure rise after warming up tires during operation.....

Operating PSI on a warmed up operated tire is where the difference is being generated.

Winter WX it's much lower peak PSI operating if you start with the same PSI.


Easy method is check your Summer PSI after tires are warmed up then achieve that same pressure during winter.... You'll need to add a fair amount of air.

 

[BMWTurboDzl]

From Tire Business May 8, 2023

How does temperature affect rolling resistance?

By Erin Pustay Beaven

GREENVILLE, S.C.

Range can be a very tricky thing. Electric vehicle range is, simply, inconsistent.

It changes over time, across driving conditions and with temperature fluctuations. And while there are a number of factors contributing to the fluctuation in range, it’s understood tires play a role. Especially when it comes to colder temperatures.

And that leaves a lot of questions to be answered. Questions such as: Exactly how much of an EV’s drop in range can be attributed to the tires? And how does temperature fluctuation impact rolling resistance?

That’s exactly what Smithers is working to solve, according to Matt Kent, technical director of the Smithers Tire & Wheel Center in Ravenna, Ohio. Because answering those questions — among others — gives the industry the leverage it needs to design tires better targeted for new mobility.

“Electric vehicles show a significant decrease in range in cold temperatures,” Kent said during his presentation at the recent Clemson University Global Tire Industry Conference in Greenville. “But current test standards only evaluate rolling resistance at room temperature — it’s actually 24 degrees C. And understanding rolling resistance performance at cold temperatures could provide an opportunity for tire design improvements to support an increase in range.”

When it comes to testing and ultimately understanding the ways in which cold temperatures impact rolling resistance, Smithers is turning to its Suzhou, China, facility, which houses a cold chamber rolling resistance machine.

This machine, Kent said, is capable of testing tires at temperatures ranging from 40 degrees C to -40 degrees C.

“It has been really interesting seeing the data and seeing them bring this thing online,” Kent said.

Using a torque method for the study, Smithers tested four different tire brands, each of them at four temperatures—35, 25, -10 and -20 degrees C.

What the team found, Kent said, was “the trends were all the same. But the big difference was they all performed very differently down here at the lower temperature.”

Each of the tires showed significant increases in rolling resistance as the ambient temperatures dropped. With each drop in temperature, the rolling resistance increased.

Tire rolling resistance performance is strongly influenced by temperature,” Kent said. “RRC increased as temperature decreased and is more sensitive at low temperatures as opposed to high temperatures. So clearly, we have a lot of data at 24 degrees C, and around that range there’s some difference, but they are not hugely substantial.”

In the Smithers study, the best performing tire showed a 56% increase in rolling resistance between the highest and lowest temperatures, while the worst performing tire, Kent said, saw rolling resistance increase by 116% between the highest and lowest temperatures.

And this, of course, is just the start. Smithers plans to take its testing further and expects to have further data compiled by the summer of 2023. Additional tests, Kent said, include examination of EV-specific tires that are a mixture of original equipment and replacement tire fitments

Wow. I would've thought the exact opposite. Low temps = hardening of the rubber = less flex of rubber. Bizzare