IAA-C63

Thanks for the suggestion. I searched again on Tire Rack, and Conti Extreme DWS is highest rated among all-seasons in this size, so that's what I'm going with.

Jons95c36amg

I have the DWS on both my cars. Good in the snow,slush. But not ice. My clk55 is my daily driver had some bad snowstorms here and its driveable with these tires.

Jons95c36amg

Good choice!

venchka

I have run Pirelli Scorpion STR tires on our 2004 XC70 AWD since new. Since 2005 the XC70 has lived about 100 miles east of Dallas and goes down to Houston and back several times a year. No worries in rain and our light snows. Stay home after our ice storms. More to avoid clueless idiots who will ruin your whole day than any fault of the tires. Our new GLK arrived with Pirelli Scorpions also. Heading to the mountains of North Carolina for Christmas. Stay tuned for an update.

Wayne
Driving Pirelli M+S shod AWD vehicles in East Texas.

Case1906

Is this your DD? I'm here in Maryland with you. We don't get enough snow for me to put winters or all-seasons on the car. If it snows, I park it. We have to be careful on cold tires, but you will get some heat in them even in temps below 40 degrees. I've never had a problem. If the 63 was my DD/beater car maybe I'd throw some all-seasons on it.

IAA-C63

I don't have a specific DD at this point. The wife and I are sharing the C63, 911 cab (RWD), Cayman R (RWD), and crappy old BMW AWD wagon. The wagon can take care of snow, but the other three cars currently have summer tires. My thought is that, by putting all-seasons on the C63, maybe we can leave summers on the Porsches, driving them carefully when it gets under 40 and not at all when it snows.

I've been trying to find the precise relationship between ambient temp and tire grip for summer tires (ie, a curve), but no luck so far.

grane

Why do think it is a curve and not a step function?

Winter grip depends on more than just the compound; testing provides some of the answer. Having a winter compound is a necessary but not sufficient condition. I use 7 centigrade about 45 F on a regular basis as my indication to change from summers to winters.

Look at that 1010 tire site for the sort of diagram you want that makes sense. You are over thinking an issue, I suspect.

IAA-C63

It could be step function, but my experience and the comments I've heard regarding the experiences of others suggest otherwise. For example, I've recently been driving with PS2s in temps down to the low thirties and haven't noticed an obvious loss of grip (in heavy braking and normal cornering), even though the recommended minimum temp for the tires is 40. If it's a step function, the step certainly isn't at 40, so there's at least some conservatism there. I don't want to be stressing out driving on these tires at 35, if that's not warranted.

Do you have a specific link within the 1010 site?

venchka

From 1010 tires:



http://www.1010tires.com/store/t-Winter-Tires-USA.aspx

This may be of interest.........

Severe Snow Conditions Grading

On February 1, 1999 the Rubber Manufacturer's Association (RMA) and the Rubber Association of Canada (RAC) introduced a winter tire grading.
These tires are specifically designed for severe snow conditions and meet snow traction performance requirements. Tires meeting this standard are marked with a pictograph of a snow flake within a mountain peak . This standard helps drivers choose a tire that will help make their winter driving safer.
Wayne

IAA-C63

^ Thanks much for the graph. It looks somewhat generalized, so I'm not sure how much to trust it, but it's the most specific graph I've seen so far. If the graph is accurate, some implications:

- All three categories of tires have the same "performance" (however that's defined) at 7 C (45 F, not 40 F).

- Winter tires have poor performance at warmer temps.

- The drop in performance at lower temps for summer tires is somewhat gradual, rather than sudden. So not a dramatic difference between 40 F vs 35 F.

- Summer tires need warm temps (above say 70 F) to get close to their full performance. It's not that everything above 40 F is equally good.

Thoughts?

Case1906

Good questions. I'm calling on this chart.

gthal

I think you guys are taking the chart too literally. The purpose is to show that as temperature changes, the available traction of various tires changes. At around 7 deg celcius, summer tires begin to provide poor traction as their compound gets too cold. The chart isn't trying to say that winter tire traction is as good as summer tire or all season traction at 7 deg. Rather, it is trying to show the impact of temperature on the tread compound and its ability to provide grip. The "rule of thumb" is that at 7 deg, summer tire compounds provide poor grip even on dry pavement. Think of the diagram as more of a "suitability" chart for various tire compounds at various temps.

Anyone who has used winter tires in summer would attest to how poor the traction is. Likewise, if you use summer tires in very cold winter temps (even on dry pavement), you can attest to how poor traction is. All seasons are always in the middle... never "bad" but never "great" either.

IAA-C63

That's what I meant when I said the curve is generalized. But if someone is going to bother with showing two axes with numerical labels, and then plot curves, why not do it accurately, and also define what "performance" means? We still need to know how grip varies with temp, regardless of the type of tire we're using, so that we can drive appropriately. For example, can I go flat out on my summer tires at 45 or 50 F? Can I drive on them at all at 35 or 30 F? Sure seems like it's not simply at step function at 40 F.

grane

What I think you want is a controlled set of tests of a given range of tires on a specific car going from summer conditions to ice and snow. Say the Continentals, Pirelli, or Bridgestone range from summer to all season to winter. Tire Rackhas a series of tests like this that have become quite sophisticated.

As far as a step function goes, consider the transition from dry pavement to hitting black ice shod with a set of UHP summer tires even at a slow speed or while braking.

That's why I change from my Hankook V12 to Icebears when the average daytime temp hits 45 as well as changing my transmission and ABC settings according to conditions as recommended by the CL OM.

As an aside, I go to Blizzaks on the G500 one season of the year so I can drive up and down! snowy hills and leave CL in the garage. You have a Cayenne, yes?

Your driving environment may vary. Safety first.

IAA-C63

Any chance you have a link handy for graphs at Tire Rack? I've looked at their site, but don't recall seeing any graphs.

grane

I'd go to the 1010 tire and tire rack and look for their comparisons tests and chart of the three types of tires in winter conditions. They have charts of braking, starting, going through curves, all sorts of stuff, videos, etc.

Consider doing your own research and reporting back.

I am going to the gym. Punkt.

Case1906

Agree, and as a result thereof the chart received the coveted designation.

adrenaline rush

We're running Michelin X-Ice 2's in the 225/45/18 size on our C63. They've been good in the rain and cold weather but we have yet to get any big accumulations yet - hopefully we'll be able to see what they can do in the snow soon.

IAA-C63

I researched those sites and didn't find a relationship between tire temperature vs grip, other than the generalized graph already noted above in this thread. I did however find that, as a rule of thumb, tire pressure changes by about 1 psi for a 10 F change in temp: http://www.tirerack.com/tires/tirete....jsp?techid=73

I've also found that driving the car can increase the tire pressure by 1 to 5 psi, presumably warming up the tires by around 10 to 50 F. So closely tracking tire pressures (using your TPM) and starting temp may be an effective way to determine if summer tires are sufficiently warmed up to be driven in colder weather.