Have you ever gotten a recommendation for cold weather riding gear and found yourself frozen stiff or steaming hot, despite that recommendation being from a usually reliable source or friend? Me too. It's been over 10yrs now since I posted this, but my metric has held up very with experience, so I'm going to repeat it in plenty of time for Christmas shopping.
Here's my RX:
Multiply your average ride wattage by your BMI (body mass index) and use that number to compare with others when they recommend winter clothing.
It turns out this is an excellent way to estimate how much core you have to retain the heat you generate in making whatever power you do.
For example, after working out in the gym for 20+ years I have a LOT of core, and am also somewhat barrel chested. I also have short legs, so I have a high BMI of 28. I also make pretty good power (for my age), 225 RWGPS or 115 Strava watts, so not surprisingly I don't need much clothing to keep warm when riding. As long as you both use the same reference watts the fact that RWGPS and Strava differ doesn't matter. For me the challenge is to keep from over-dressing and sweating profusely, which can actually become quite dangerous when riding near dark, or if you have a mechanical and need to wait for a ride. Hypothermia kills.
On the other hand I used to ride with a woman who was 5'2" and 105lbs (BMI=19), making 55-60 Strava watts and 100-110 RWGPS watts, she would freeze to death trying to get by with the clothing appropriate for me (drafting off someone can be a big help if you're getting cold as they break the wind and pass heat back to you - it works). However, one of our older ride leaders was 6'4" and weighed about 150lbs, with a BMI of 18, making about 150 RWGPS and 65 Strava watts, so his recommendations were pretty helpful for her. The closer the product of BMI x Watts is, the better the recommendations will be.
Worth mentioning here that your head is the one extremity you can't completely cover, so what you can cover, cover with the best stuff money can buy. I have 4 Balaclavas, and find them priceless in keeping warm. It's also worth considering buying a winter helmet that isn't so aggressively vented, which is just the opposite of what you want in summer.
Of course, there are always subtleties to be aware of. For example, while it is slightly uncomfortable, especially at the start of rides, I've found having my arms cold doesn't really affect my performance, while having my hands cold seriously impairs my ability to shift and brake. Also, my size 11 feet tend to get cold easily, and that leads to a lot of discomfort and eventually, calf cramping. Finally, my quads just above my knees tend to cramp easily in the cold.
If you want to dress for comfort in winter, start keeping a log of temps before, during and after rides and the clothing you selected. In a month or two you will almost NEVER get surprised and be inappropriately dressed.
One bit of hard-earned wisdom. If riding with a group, especially at night, carry an extra layer of clothing in way it stays DRY, because when riding in winter with a group you're almost always going to have to wait for someone to fix a flat or mechanical, because some idiots just don't get that winter is the worst time of all to compromise on tires, lights & other gear, so you'll be somewhat wet with sweat, and then have to wait for 10-20 minutes in the cold while making zero heat.
Adding more layers, which will also get soaked with sweat, only makes things worse. You'll be more sweat-soaked and much quicker. You need a layer you've kept dry that you can quickly don without losing much body heat. For me this is a jacket over my vest or a convertible jacket I can zip the arms onto. Whatever you do, time is of the essence. Save all that beautiful heat ASAP. You'll be thanking yourself in < 10 minutes.
Hope you have a long, fun winter of riding, and don't ride alone after dark. Fun at times, and beautiful beyond belief at others, but very unforgiving.
