Is it just cold when this happens or is it after a long stop (like a red light) where perspiration has soaked through and now you have a heavy conductive path in the area that can't evaporate quickly enough back to normal? I have that soak-through situation some days, and its effect when below about 15F are enough that I bought a cheap pair of ski bibs and had an alterations shop cut them off mid-thigh. So, I still soak-through with those, but the loose and thick bibs keep the heat in. Commute time is about an hour, sometimes 70 minutes on days below 15F as the temps often bring wind as well.
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Longbikes Slipstream