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I have been riding indoor on spin bike and I average 40 km/h, would someone help me translate these speed to outdoor cycling?

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  • This is a very confusing question.. wouldn't 40km/h inside be the same as 40km/h outside...? (Or 24.85 miles per hour for us American folk)
    – Nate W
    Commented Apr 7, 2016 at 18:43
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    That's fairly difficult to do with the limited information you have provided. That's a fairly high average speed, close to what pro tour riders maintain, so I am guessing it may not be that accurate. Every trainer/spin bike will have it's own eccentricities with regard to displayed speed. I would guess your average speed on a road bike with wind resistance and rolling resistance coming into play to be significantly lower. And much much lower on dirt (or snow).
    – Deleted User
    Commented Apr 7, 2016 at 18:45
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    I know, since it's a spin bike not trainer it only has resistance and doesn't emulate a real bike ride. I wanted to know whether someone has experience with both so he/she might know how much air resistance has impact on speed.
    – haar
    Commented Apr 7, 2016 at 18:52
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    sheldonbrown.com/rinard/aero/formulas.htm
    – stijn
    Commented Apr 7, 2016 at 19:21
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    It would be more useful to know that number of Watts the trainer says you're putting out, your weight, and the type of bike. For example, in a velomobile 250W should get you to 40km/h-60km/h quite easily, but on a beach cruiser type bike bike you'd be lucky to get 20km/h at that power level. And you're right that drag isn't purely quadratic, the power/speed curve is more complex than that.
    – Móż
    Commented Apr 7, 2016 at 22:36

2 Answers 2

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I'm going to let you answer your own question - Think how tired you are after an hour on the spin bike, and compare that with how tired you are after an hour on the road bike.

Work in some fudge factors based on

  • the amount of headwind/tailwind you had (ride out and back on the same route)

  • Number of stops for traffic lights or road signs... getting going again from stopped adds to the workload and decreases your average.

  • Grade - try and road bike a flat path with minimal climbs or descents.

Afterwards subjectively compare, and I'd estimate a 25 km/h road ride ~= your 40 km/h trainer ride.

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    That's okay for me, that's my speed at 90-95 revolution par minute with average hearth beat 110, one hour and half duration and I am absolutely fresh after it. I reckon it's 28/30 km/h with no head wind other than the wind I create myself. I still have 100 heart bit to go.
    – haar
    Commented Apr 10, 2016 at 16:20
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Based (very roughly) on this calculator here, I'll guess 28 km/h or less.

Using a 0 weight rider and bike with no wind and 200 watt output you get roughly the speed you are getting on the trainer (the weights are used for rolling resistance). Leaving the power the same and changing to 80kgs, a 9kg bike and 15 km/h wind it gives 28 km/h which is a significant drop. I am not sure about all the formulas the calculator is using, but introducing rolling resistance and wind resistance will surely take big chunks out of that speed.

I am not sure what kind of spin cycle you are using, but depending, it may be introducing some sort of resistance that it equates to rolling/wind/mechanical resistances. However, it's likely much less than what you would encounter out on the road.

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  • Thanks I did a fairly rough approximation and I thought I would be around then 25-30 km/h, most likely lower middle end of the spectrum, thanks.
    – haar
    Commented Apr 7, 2016 at 19:09
  • This is a better answer than the current Accepted Answer.
    – Criggie ♦
    Commented Jan 5, 2019 at 19:53

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