I tried it on my long ride this morning. After about 2.5 hours of it, I was getting pretty tired. By then I was heading back home, and had the wind against me. My overall average speed was only 12.81. That's actually fast enough for Tour de Cure -- but here's the catch. TdC will have hills!
It might be better to do this kind of tempo ride on weekday mornings, when I'm not going to be riding much over an hour. During such rides it makes more sense to push the pace hard.
Gosh, I remind myself of a joke I read many years ago: "Did you hear about the conductor who kept having tempo tantrums?"
Tempo Ride – A tempo ride is meant to be a fast but fun ride. Start out your ride fairly easy, but build yourself up to a brisk ride. You want to spend 20 minutes or so at a pace that you could probably hold for about 45 minutes. Then drop yourself back down to an easier pace for 10-15 minutes, and either cool down of follow it up with a second tempo pace of 15-20 minutes. These rides get your cardiovascular system up there, but lack the amount of muscle burn associated with intervals or long rides.