In another thread, it was noted that the grip of our stock tires is reduced at temps below about 40 F. Does anyone have a link to a curve which shows the specific relationship between grip and temp?

In my area in the winter, the temp is usually above 40, but sometimes it dips into the thirties or lower. I want to know how much to back off on my spirited driving unless/until I get winter tires.

 

+1

I would like to see this as well. While I am sure there is a correlation, I can't stop but think of the marketing aspect behind this. I have driven my car plenty in 20 and 30 degree weather (I live outside of DC and my car is my DD) and have never noticed a difference. I have also driven in light snow and have had no problems.

 

Ok, here is something I found on Google Scholar that my contain an explanation:

Effect of Ambient Temperature on Radial Tire Rolling Resistance

Here is the abstract:
A test procedure for measuring the rolling resistance of automobile tires under ambient temperature conditions ranging from −20°C to 40°C is described. A data analysis method for predicting tire rolling resistance in this temperature range from a minimum amount of test data is presented. The effect of changes in tire inflation pressure and material viscoelastic properties resulting from ambient temperature changes is demonstrated for radial automobile tires with different tread designs and compounds.

And, to give the folks proper credit:

M. L. Janssen - Central Research Labs., Firestone Tire & Rubber Co.
G. L. Hall - Central Research Labs., Firestone Tire & Rubber Co.

 

Had a set of Goodyear runflats on a Corvette that were horrible in cold weather (of course, they were horrible in about every other category also). They would spin at the least little bit of acceleration and I actually almost lost it completely gunning it a little bit early out of a sharp turn. A replacement set of Firestone runflats were markedly better, but not worry-free. In contrast, the Porsche factory supplied Michelins seem to behave much better in cold weather, which could be attributable to weight distribution on the car as much as anything else.

 

I don't know if there's much relationship between grip and rolling resistance. In any case, my understanding is that the tire compound used in performance tires hardens as the temperature drops, resulting in reduced grip. What I don't know is the difference in grip between say 50, 40, 30, and 20 F.

 

different compounds react differently. PS2 tires I had were like glass from below 34-33 degrees something, Z1 star specs were OK at 28 degrees but they all turn into glass at some point, that is how ultra sticky summer rubber is.

 

A related question is how much warming up the tires by driving the car compensates for low ambient temperature. Seems like continued spirited driving should keep the tires warmed up?

 

Winter/snow tires during this season are federal law in Germany, which says a lot about the safety of driving below 40 degrees on summer tires:

http://www.german-way.com/ice-snow-tires.html

My personal experience is that summer tires do get stickier as they warm up (same as they do in warmer ambient temps), though like most things the difference is much more felt on a track than public road.

 

Driving my 997 in weather below 40, there was a marked reduction in traction. Particularly when heading out for the first 5 miles. I had Bridgestone RE050s and you could go into a corner pretty fast and the car would have bad understeer. Very dangerous. I didn't use snows. I used all seasons for the winter. They worked really well in low temps and had good wet and dry traction. I never drove the car in the snow or when snow was expected. I had the Bridgestone Pole Positions.

 

Related question to those of you who change tires for the winter: do you use a different set of wheels, or just switch the tires on the same wheels?

 

I use a different set of wheels (19" 996 Turbo wheels) with Perrelli snows mounted and balanced. I just do the complete wheel re & re once temperatures drop to about 6 degree Celsius on a consistent basis. Up here in the NW, we get a lot of rain in the winter so rolling on hard plastic is in the wet at hight speeds is a little frightening.

 

I used different wheels as well. Much easier to just swap them on my schedule in my garage. Had the winters on the original Carrera Classics and had the sport tires on TT rims.
On the M3 ,I have snows on 18's. If you are going to by a dedicated set, I'd go one step smaller wheels, much better for winter. Go for 18s. And muc better to buy slightly narrower tires for the rear since a 295 or so greatly increases the chance of hydroplaning.

 

i've been swapping summers/winters on the same wheels last few years but decided this year to make my unused lobster forks my permanent winters. keep in mind you need a second TPMS, around $400, for that (unless you can live with the warning lights). the swapping works fine but it costs $$ each time and there's always the chance that the installer will be too aggressive with the spoon they use to separate the tire from the rim, and damage the tire.

although, to be totally honest, i much prefer my Turbo I wheels to my lobster forks so i may go back to swapping next year -- see what works for you.

if i didn't own a set of unused OEM rims i'd probably keep swapping, unless i planned to own the car for 5+ yrs in which case a dedicated set of winter rims that you like makes sense.

if you go with the second set, pick up a guide mounting bolt from suncoast to make the swaps easier.

 

I have my all seasons mounted on OEM Carrera Classics. Will replace the PS2s/V308s with the all weathers between Christmas and New Years. I bought a 3 ton race jack and torque wrench so I can do it myself.

And below 40 my PS2s are like bricks. I can easily step the back end out.

 

I highly recommend using winter tires if you plan to drive the car in sub 40 degree temperatures. I purchased a set of OEM "lobsters" and Perelli Winter Sottozero's from Tire Rack. While I don't drive in the snow, the car corners in dry or wet conditions almost as well as during the summer months. The Bridgestone summer tires were dangerous below 40 degrees and the company pretty much states that in their literature.