Originally Posted by gsa103

You didn't mention solo vs pack, at those speeds it makes a huge difference.

Stage 3 of this year's TdF was 160 km with 1500m of elevation gain in England. The pack finished at 3:38, which is an average of 44 km/h.

Stage 8 was 161km (2500m) with the pack finishing at basically 4hrs, for an average of 40 km/h.

The best comparison is actually Stage 21 (Paris) was 137km (2175m) and the finish was 3:20 for an average of 41 km/h.

Keep in mind these are racers in huge packs, so drafting dramatically reduces the effort required. On a solo effort, over these course, the times would certainly drop below 40 km/h. Its certainly possible to hit that speed/time, but its a very tall order.

To pull off a solo run, you will need to have combination of: lucky genetics, perfect physique, and/or PEDs. In a fast group, a strong amateur rider could probably do it, but you'd need to be a very strong rider.