Do Bigger Winter Shoes = Different Muscles
I have ridden about 5000 miles year. It is my first winter. I'm trying to learn to dress right. Just when the combo is right, it drops another 10 degrees. So for the last two weeks, I have been wearing a new pair of spd shoes in a size 40. I normally wear size 38. They don't slip off my heal, and I wear two pair of wool socks. The extra room appears to be in the toe area. Also wear Pearl Izumi boot covers. It made a lot of difference with my toes staying warm. I have a Lemond bike and it seems I use the muscles on the outer thighs and my butt to ride usually. Now my quads in front about 1/2 between the knee and top of leg are sore to the touch. Does anyone else have this problem when they switch to their larger winter shoes, or am I doing something wrong? I haven't added any additional sports, and I have noticed my average speed has dropped from 17-18 to around 14-15.
Slow Moving Vehicle
First of all, some speed drop in colder weather is inevitable, so if that was your only problem I wouldn't be too concerned. Pain is another matter. I would suspect the problem may be in the positioning of your cleats or saddle. A bigger shoe may have your foot position changed if you positioned the cleat in the same spot it was on a smaller shoe. You need to fit the position of the cleat for each individual shoe. Also check the thicknes of the sole of your shoe, winter shoes often have thicker soles and may need an adjustment in saddle height. Likewise, the added layers for cold weather riding may mean you need to adjust your saddle position, usually down & back a tiny amount. The added layers may change your riding dynamics and you just may be using a slightly different set of muscles, as you suggested but you may also be bumping your thighs against the handlebar more than you realize.