21 inch tires and t < 40F

[EVCar]

Have you driven your car with 21-inch tires when the temp falls below 40F?
As I understand, these summer tires may crack at this temp.
Have you noticed any issues?

 

[Shuasha]

No. But if you hit snow or ice it will be extremely unsafe.

 

[hmp10]

Have you driven your car with 21-inch tires when the temp falls below 40F?
As I understand, these summer tires may crack at this temp.
Have you noticed any issues?

All rubber tire compounds experience "glass transition" at some point as ambient temperatures drop. Different parts of a tire are made of different compounds and thus have different glass transition points which will vary by tire and by brand. However, virtually all summer-rated tires start to see significant loss of traction and increased sidewall stiffening as temperatures dip into the 40's. At temperatures near freezing, cracks can also develop in the compound. Summer tires should not even be stored in cold temperatures, much less driven on.

There may be minor differences between summer-rated tires in terms of their glass transition points, so it is best to consult the manufacturer's recommendation . . . and follow it. The warranty coverage for compound cracking on the Pirelli P Zeros on the Air terminates with use below 45º.

What I don't know is whether the heat generated by tire flexion while driving will give you a few more degrees of margin on the road, assuming the car was not parked in cold temperatures. For instance, if you left home in 50º weather and hit some temperature dips along the way, will the tread temperature stay enough above the ambient air temperature to keep you safe?

 

[borski]

All rubber tire compounds experience "glass transition" at some point as ambient temperatures drop. Different parts of a tire are made of different compounds and thus have different glass transition points which will vary by tire and by brand. However, virtually all summer-rated tires start to see significant loss of traction and increased sidewall stiffening as temperatures dip into the 40's. At temperatures near freezing, cracks can also develop in the compound. Summer tires should not even be stored in cold temperatures, much less driven on.

There may be minor differences between summer-rated tires in terms of their glass transition points, so it is best to consult the manufacturer's recommendation . . . and follow it. The warranty coverage for compound cracking on the Pirelli P Zeros on the Air terminates with use below 45º.

What I don't know is whether the heat generated by tire flexion while driving will give you a few more degrees of margin on the road, assuming the car was not parked in cold temperatures. For instance, if you left home in 50º weather and hit some temperature dips along the way, will the tread temperature stay enough above the ambient air temperature to keep you safe?

Well, we had a few very cold (read: mid-high 30s, above freezing) nights in the bay area the past few weeks, and no issues with my 21s, fwiw.

 

[hmp10]

Well, we had a few very cold (read: mid-high 30s, above freezing) nights in the bay area the past few weeks, and no issues with my 21s, fwiw.

In my olden days in Chicago and the northeast, there were years when we'd get a sudden temperature dip before I got around to switching my cars to winter tires (something I hated doing and always put off as long as I dared). I never experienced any problems but, then again, I knew the issue, kept the trips local, and took extra care in how I drove. And I never would have ventured onto even a dusting of snow or light icing on summer tires.

It's worth bearing in mind that the Air is a very heavy sedan on relatively narrow tires (even with the 21's wider rear tread) so, even in the best of circumstances, you're already driving nearer the edge of the tires' performance envelope even with the Pirellis specially engineered for the car.