[335BOY]

Originally Posted by stevehecht

(Warning: The following is a long discussion of my choice to purchase A/S tires for use in the winter in Santa Fe. You might find the analysis helpful if you're on the fence about the choice between A/S and winter rubber because of your geographical location. You might also find it interesting if you love talking about tires, as I do. The website I reference below is a goldmine of information concerning the climate of any given city, town, or area.)

How does the loss of stopping distance with A/S <7C* compare with the loss of braking distance with winter rubber >7C* (especially when the pavement is warmed by the sun)? The graph above indicates that the drop-off in performance happens more rapidly for winter rubber in warmer temperatures than it does for A/S rubber in cooler temperatures. Presumably one measure of performance used for this graph is braking ability.

We know that A/S rubber is not as good as winter rubber in cold temperatures and not as good as performance/summer rubber in hot temperatures. We all know that A/S rubber is a compromise in both directions. But what about a dry winter climate that regularly swings ~7C* both above and below 7C* on a daily basis?--and where even on colder days the sun is usually out to warm the asphalt during the day? I'm thinking about areas like northern New Mexico and Arizona here.

Here is some data on snow precipitation in Santa Fe:


http://weatherspark.com/averages/315...-United-States

Putting this into practical terms: There are approximately 90 days in the cold season from November 21 through February 19. During this period 24% or 21.6 days will have precipitation. Of these days, 21% or 4.5 days per winter (5%) will have moderate snow. (Heavy snow occurs in .2 days per winter, or once every five years.) I made the call that those 4-5 days of the year when winter tires would make a meaningful difference in moderate snow are not enough reason to compromise performance on the other 75-95% of the winter days that are dry and the temperature is close to or above 7*C (40*F).

What about temperature fluctuations during the Santa Fe winter? At no time does the average high temperature drop below 40*F. Even in the coldest part of the year (Dec.-Jan.) the chances of the average high temperature falling below 35*F is less than 25%. That means that for 75% of the days in the coldest part of the year the average high temperature will be close to or above 40*F (7*C). It's true that A/S rubber will be compromised <7*C, but by how much? According to the graph above, at 0*C (32*F) the loss in A/S rubber performance is negligible. At -15*C (5*F) the loss in performance is mild (assuming dry roads).

Nobody in Europe uses A/S tires? I find that hard to believe. Europe is a big place and the weather in Stockholm is the polar opposite () to that of Cannes. Does your generalization include areas of southern Europe such as the south of Spain, Portugal, France, Italy, and Greece? Middle and northern European climate is much like the northeast USA, and I would agree with your colleagues at Pirelli on that count. But it would be foolish to buy winter tires for the freak snowfall if you lived in a Mediterranean climate.

I thought about my decision to go with A/S in northern New Mexico a lot, and I remain unconvinced that I made the wrong decision. (Note: We own a Subaru that I can use for those rare days--4-5 per winter--where there actually might be more than a bit of snow on the roads. But I would have made the same decision even without owning the Subaru. I'm retired and I can always just stay home.)

The bottom line is to evaluate what your priorities and personal needs are. If you want to be as safe as possible in any possible winter situation then you should get winter tires even if you live in northern Florida because it snows there once in a blue moon (http://www.srh.noaa.gov/tae/?n=snow). But if you want to enjoy your bimmer's handling as much as possible without taking undue risks, then you have some serious analysis to do if you live in a transition zone that gets occasional snow and sub-freezing temperatures.

Steve by saying on snowy days you can use the Subaru you are implying that forward motion is your main motivation? I'm sorry I didnt realize where you live when I replied above but you may be confusing those that live north of you. having said that I think you make a lot of great points.You know exactly what the guy above meant when he mentioned Europeans don't use A/S.

[stevehecht]

Originally Posted by 335BOY

Wow. Youre really fighting it. Fact is winter tires will stop car way shorter than A/S in cold winter (snow or no snow).

IMO, that's way too general to mean very much. And that's my whole point. What do you mean by "cold winter"? What do you mean by "cold"? Do you mean 41*F, 31*F, 21*F, 11*F? Fact is, winter tires WILL stop a car a lot sooner at 5*F (-15*C), but at 32*F (0*C) the difference is much less pronounced. (Refer to the graph above.) At 32*F the graph shows that the performance of A/S rubber is just barely below "good". If the roads are dry and warmed by the sun (likely in Santa Fe) that A/S rubber performance can only improve. Are you trading off a margin of safety for improved handling the rest of the time by going with A/S? Of course, and the decision about whether the trade-off for safety is rational depends on the climate you're living in. In my judgement, the winter in Santa Fe allows a rational trade-off of that kind.

Originally Posted by 335BOY

[B][COLOR="rgb(255, 140, 0)"]Steve by saying on snowy days you can use the Subaru you are implying that forward motion is your main motivation?[ I'm sorry I didnt realize where you live when I replied above but you may be confusing those that live north of you. having said that I think you make a lot of great points.You know exactly what the guy above meant when he mentioned Europeans don't use A/S.

This comment in green is a good point. I realize that AWD doesn't mean crap when you're taking a corner too fast or trying to stop short in snow. On the other hand, AWD with A/S is a better way to go in snow than FWD or RWD with A/S. I'm confident that my wife's Subaru with A/S can handle the snow situation in Santa Fe and environs quite adequately. It does pretty damn well here in Massachusetts in the winter.

But thanks for pointing out that folks who live in the northern tier should not easily dismiss the need for winter tires even on AWD cars. My wife and I are retired and we don't HAVE to go anywhere if the roads are in bad shape. If you HAVE to get to work or whatever regardless of road conditions and you live in colder climates, you're going to be better off with two sets of tires for winter and non-winter. It's not any more expensive in the long run.

I don't understand what you're saying with the comment in orange.