We have completed an extensive series of test laps to provide hard data quantifying the impact of watt, weight, and equipment changes in Zwift.
View data for all test laps >
Weight/Watt/Height Observations
- A 75kg rider completes a full lap at 4 w/kg 3:40 faster than a lap at 3 w/kg. Therefore, each increase of .1 w/kg makes a difference of approximately a 22s in your full Richmond lap time in this weight and power range.
- If we look at the lap times for a 250w lap for riders of 100kg and 83.3kg weights, we can surmise that in this weight and power range, each kilogram of weight you lose will cut 5.8 seconds off your Richmond lap time.
- If w/kg stays constant, the heavier rider will always be faster, even up hills. At 3w/kg a 100kg rider finishes a full Richmond lap 3:45 seconds ahead of a 50kg rider.
- Increasing your wattage makes you faster–and the heavier you are, the more difference it makes. The same wattage increase (from 200 to 250 watts) tested with different weights resulted in very different Richmond lap time spreads.
- At 50kg a difference of 2:36
- At 75kg a difference of 3:11
- At 100kg a difference of 3:50
- As wattage increases for riders of various weights their speeds get closer together. Anywhere over 400 watts riders of various weights travel at essentially the same speed, while at 150 watts a 50kg rider is 8:28 faster than a 100kg rider over a full Richmond lap.
- The taller you are, the slower you’ll go. The test laps we’ve done show that it works out to ~30 seconds longer on a full Richmond lap for each 15cm (approximately 6″) of height added. Or to put it another way: a 5′ rider will be ~1 minute faster than a 6′ rider (all other things being equal).
Equipment Observations
- Equipment does matter–especially wheels! The Zipp 808’s (the level 10 unlock) are 19 seconds faster over a full Richmond lap than the “stock” 32mm carbon wheels. The fastest bike available to all riders (other than the TT bike) is the Tron bike, which is 68 seconds faster than the stock Zwift Carbon over a full Watopia Figure 8 lap.
- The difference between the stock setup (Zwift Carbon and 32mm carbon wheels) and the fastest race-legal setup (Tron bike) over one hour of riding is approximately 60 seconds.
- The Zipp 808’s are the best wheel on all current courses. In the real world you might choose to avoid such a deep wheel due to wind/handling issues, but on Zwift this isn’t a factor so aero wins the day. They may be a bit heavier in Zwift’s calculations than a wheel like the Zipp 404 or 202, but the aero advantage wins out when all your courses are loops.
- Upgrading your bike and wheels has a synergistic (not just an additive) effect. That is, the overall lap time saved by upgrading your bike and your wheels is more than what you would get if you added the savings of just upgrading the bike to the savings of just upgrading the wheels. Who knows why? It just works.
- Baseline Richmond lap time (Zwift Carbon, 32mm carbon wheels): 29:39
- Cervelo S5 with 32mm wheels: 29:28 (-11s from baseline)
- Zwift Carbon with Zipp 808 wheels: 29:20 (-19s from baseline)
- Logically combining Cervelo S5 with the Zipp 808’s would save a total of 30 seconds. But instead, it saves a total of 33 seconds. Total lap time with Cervelo/808’s is 29:06.
Riding up Libby Hill at 150 watts and 100kg is a slooooow process!
@Andrew
Your normal rides probably aren’t at the same intensity right?
Suggest:
Increase your tire pressure and/or increase tension on the trainer until slipping stops?
It may only need subtle changes, you shouldn’t need to crank it down.
You may also get better results with a dedicated trainer tire if you are not already using one.
In my experience, most slipping tends to occur under sudden hard accelerations, so you can probably test your configuration that way without having to do a full FTP test. 😉
I have the same issue as the OP. I tried doing the FTP and whenever it asked me to hit 200W or higher, I would get the “Tire Slippage” error and told to wind down my Watts.
I use a Vittoria Zaffiro Pro trainer tire (red coloured) filled to 130 PSI (max is 142 I think?) on a CycleOps Fluid 2. This is paired with a Garmin 500 + Speed/Cadence sensor and USB cabled Ant+ dongle rubber-banded to the chain-stay next to the cadence sensor.
Shouldn’t be getting slippage or dropped speed/watts but here we are.
Think it’s clear that Zwift is meant or is designed ideally for power meters of once kind or another – wether it’s a Smart trainer or pedals or other, imho.
Eric, I know this is old post, but there is an element I don’t understand. Which is the convergence of times at 400w for different weights. I have also done recent testing to establish approx CdA values for riders of different weight and height. And what I do see is that the CdA value Zwift attributes is bigger for heavier riders than lighter riders (even at the same height). So I cannot understand how at 400w+ riders of different weights could travel at the same speed, because their different CdA’s cause different speeds. The heavier rider slower due to higher CdA. What am I missing? Did Zwift do an update to vary CdA relative to weight after your early 2016 tests? Happy to send you my own test data if you’d find it interesting! :- ) Kenny
Thanks for all the great data. I have a suggestion for another data point to test. I would like to see some data on acceleration. Perhaps standing start to 500 watts for 30 seconds and then measure the distance covered.