Just did a little calc on the steepest segment of climb today (1.26km at average of 8%, 99 metres of ascent and took me 5:44). Alpe D'huez averages 7.9% apparently, for an ascent of 1120 metres and 14km - based on my climbing today, and assuming I could hold this for the full distance, I get up the Alpe in about 65 mins.
My best Zwift time is just below 60 mins and I was pushing really hard for that, but I average just over 60 mins so quite pleased with that. I'm hoping one day I'll get to ride the real climb, but for now I'll have to stick to the virtual version, and local roads
For those of you who have ridden the real climb and Zwift how do your times compare?
Edit: also worth noting on Zwift I ride the Alpe on a Tarmac and Lightweight wheels which must save me a few kg compared to real life