tyre traction: ambient temp or tyre temp?

[major one]

so i was jonesing for the m4 today and even though the temps were below freezing here in chicago this morning, i took her out on the motorway. i still have the summer tyres installed as i have another sled to use for the winter ,,, but it ain't no m!

this led me to think of you guys and that is i need some of you smart ones to tell this dumb bookkeeper whether it is the ambient air temps or the temps of the tyres themselves that matter when we discuss proper traction in the cold. i noted that my tyres were running 50-55 (f) even though the air temp was 28 (f).

i didn't notince any degradation in traction but the roads were dry. so - what say you and why? im serious here - as i don't understand the physics or engineering of traction behind the hard rubber compound of the summer tyre vis-a-vis temps (air vs. tyre). cheers.

[ASAP]

Both... one directly relates to the other... remember road temp has to do w ambient temp as well.

[pertierr]

Originally Posted by major one

this led me to think of you guys and that is i need some of you smart ones to tell this dumb bookkeeper whether it is the ambient air temps or the temps of the tyres themselves that matter when we discuss proper traction in the cold.

If my understanding is correct, assuming the road is 'just cold' i.e there is no ice, water or snow, and ignoring changes in tire pressure, it is the temperature of the tire compound itself at any moment that affects how well it grips.

That said, the road/ambient temperature obviously determines in great part the tire compound temperature, so if it is cold it is reasonable to assume the compound will be cold. The front tires will have the benefit of engine heat but it is a wise guideline to judge the effectiveness of a particular tire by the ambient temperature, because in the compound temperature will tend to reach equilibrium with the ambient temp. And obviously if there is water/ice/snow then that changes the characteristic of the surface in addition to temp, so you'll need a tire designed for that surface.