I'll ride down to -15F I have a fleece lined bellaclava (sp?) and wear ski goggles. I also have a merino hat as another layer. You don't need those handlebar covers with big expedition mitts, but then I ride a single speed at those temps so there are no shifters to fiddle with.
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1 Super Record bike, 1 Nuovo Record bike, 1 Pista, 1 Road, 1 Cyclocross/Allrounder, 1 MTB, 1 Touring, 1 Fixed gear