Speed too low in comparison with the outdoors

I noticed that my speed is very much lower on Zwift rather than outside. For example when I push 300w on 0% gradient without substantial wind, I hit easy more than 50km outside. I am 72-73Kg. Today I was barely hitting 41km on Zwift. In general my ride similar to the one I had today on Zwift should have been easily more than 4km more on average outdoors.
I ride an Sworks Shiv TT with deep rim Zipp wheel on Zwift so is not the equipment.

What do I do wrong?

Based on power/speed calculations, you’d only manage 39kph outdoors; possibly 40kph hunched down on the drops. Either your bike computer needs calibration or you were going downhill.


Or riding something like this:




Zwift isn’t a perfect simulation, but it’s pretty close as a general rule. Most people complain that speeds are unrealistically fast.


Thanks for your answer. Please note that I am using a TT bike riding on the aero bars. No drops. Speed/Watts ratio on the TT is much different than on a road bike. Much faster on the TT due much less CdA. I experience the difference because I ride both on the same route with much different results.
Does riding on ERG with small gearing may affect the speed on Zwift? I read that somewhere…

Thanks for the reply.

Small ring in theory shouldn’t make any difference at all. However, some people have experienced different power consistency with high versus low flywheel speed; with high speeds smoothing out power spikes.

Considering Lionel Sanders averaged 306 watts in 2017 on the Kona bike course and only averaged 42km/hr, something seems off that 300 watts gets you 50km/hr. Yeah theres a lot of factors, but somethings funky.

Btw Zwift is known for being faster then outdoor scenarios in most road cycling situations, not sure about triathlon or time trial set ups.

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This is the case for me. I cannot nearly ride my Zwift speeds outdoors.

50kph is 31mph. That’s very fast even on level ground on a TT bike if you ask me. I dont see how 300W gets you there even with the most aero bike in the world.


Did a 40k TT last week on Zwift. Fuego Flats route. On TT bike. Avg power for 65 minutes was 242W. 65 minutes means I was well less than 40kph (36.9kph or 22.9mph). I have never gone that fast for so long outdoors and I do have level dedicated bike trail where I can ride a couple hours one direction uninterrupted, no street crossings, signals, etc. The only difference is that I do not own a TT bike IRL.