Last weekend while suffering my way up Alpe du Zwift on TdZ’s stage 6 I began to wonder how much double draft was adding to my speed. We all know drafting doesn’t help much at low speeds, but it still has some effect.
When I finished with a new PR the question was stuck in my head: how much of that PR was from the draft?
Fortunately, I didn’t need to put together an automated speed test to figure it out. Soon after finishing my effort I noticed another Zwifter had already done the test for me: and he did it with his own legs!
Meet John Bytheway, a level 25 Zwifter from Bournemouth, England. He rode the Norseman Winter Race event up the Alpe on Saturday, then followed it up the next day with TdZ Stage 6. Two Alpe efforts only 1 watt apart in terms of average power–impressive pacing! Same bike (Tron) for both events, but the Norseman events have drafting disabled, while TdZ used double draft. A nearly perfect experiment.
Here are the details of John’s two rides:
Norseman effort (see it on Strava):
- No drafting
- Average Power: 229 watts (3.5 w/kg)
- Speed: 13.22km (8.2 miles) per hour
- Time up the Alpe: 55:31
Tour de Zwift effort (see it on Strava):
- Double draft
- Average Power: 228 watts (3.5 w/kg)
- Speed: 13.36km (8.3 miles) per hour
- Time up the Alpe: 54:47
Mind you, this experiment isn’t perfect: John could have applied his power differently between the two efforts. And he wasn’t constantly in the draft during his TdZ climb, although with thousands of riders participating he was in the draft for most of it (John estimates he was drafting for 75-80% of the effort).
That said, I’m comfortable enough with the numbers to say double draft trimmed approximately 45 seconds off of John’s no-draft effort. As speed (and w/kg) increase that margin would grow, since the draft effect would be amplified.
Ride on, John!
Watch John’s Norseman ride:
Watch John’s TdZ Stage 6 ride:
How many feathers/other powerups did he use on his two attempts?
None on either…that I can think of.
This is interesting. I did the same pair of workouts last weekend: Norsemen race on Saturday and TDZ Stage 6 on Sunday. On Saturday I went hard from the start and on Sunday I rode a moderate pace on the flats to save energy for the climb. Two other differences: 1) on Saturday I stopped for ~20 seconds at the beginning of ADZ (while on the climb clock) to change equipment, and 2) my avatar rode with the Specialized helmet on Saturday and no helmet on Sunday. On Sunday I didn’t draft much, maybe 5-10% of time, but I did ride through several groups on the lower slopes. Here is my Alpe Du Zwift climb data from the two segments recorded on Strava:
NORSEMEN RACE:
Average Power: 316 watts (3.92 w/kg)
Speed: 9.1 miles per hour
Time up the Alpe: 50:11
TOUR DE ZWIFT STAGE 6:
Average Power: 327 watts (4.05 w/kg)
Speed: 9.5 miles per hour
Time up the Alpe: 47:58
Thanks for the interesting article and thanks to David Merry on Team Free Flite Masters for sending me the link!
Would the margin really grow if you go faster? The drafting effect would increase, but you also finish sooner, so you get the draft benefit for less time.