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I'm looking for some idea of the fastest speed possible under normal conditions. Just a person, out on their bike, in shorts and a t-shirt. No pacing behind a vehicle or a peloton. No TT bike or TT bars, just a road bike with drop handlebars on flat ground on a calm day.

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    You're not going to find it. "Regular clothes" doesn't have a precise definition. Flat ground and a calm day isn't normal conditions. The speeds are going to vary whether its over 100meters or 100 miles. What are you really after? Commented Feb 25, 2021 at 5:32
  • Does this answer your question? Fastest sprinter and their top speed? Commented Feb 25, 2021 at 5:33
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    Even specifying shorts and T-shirt, are they baggy cargo shorts or short shorts? Close-fitting T-shirt or flappy? And then is that peak speed or maintained for some length of time (what length?) Pro stats are unlikely to be helpful. While clothing has improved, even in the 1930s TdF riders weren't wearing what you'd call normal clothes
    – Chris H
    Commented Feb 25, 2021 at 8:03
  • Far to many variables to set up standard conditions for competitors.
    – Carel
    Commented Feb 25, 2021 at 8:23
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    For years when I was at the university I have seen a cyclist riding a fancily decorated TT bike wearing nothing more than a thong and sunglasses.
    – L.Dutch
    Commented Feb 25, 2021 at 11:49

1 Answer 1

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Until there is an "International Union of Regular Guy Cyclists," there will be no measured record for this because cyclists who are contending for records use the best equipment they can, under the best conditions they can find.

Aerodynamics are very important in cycling, and the faster you go, the more important they get. Elite sprinters reach ~45 mph in 200-m sprints, which takes ~1700 W (depending on weight). 40 mph would require ~1200 W. But this is assuming form-fitting clothing in a tuck.

There are two factors determining aerodynamic drag: frontal area (the size of the hole you are punching in the wind) and drag coefficient (how slippery you are relative to a flat surface). These are usually multiplied together to produce a number represented as CdA.

Your bike position affects both terms: the Cd part and the A part. You might have a frontal area of .533 m^2 on the tops, .426 m^2 on the drops (1); your drag coefficient on the tops is 1.15 (literally worse than a flat board), on the drops 0.70 (2).

You can plug these numbers into this calculator to get some ideas of the wattage you would need under different scenarios. If you want to ride at 40 mph on the tops (and you have a normal weight for a fit man of average height), you need to produce 2250 W, which is superhuman. Note that this doesn't take into account clothing aerodynamics.

Specialized has their own wind tunnel, and has produced a bunch of videos showing how much you can benefit from various changes to your setup. Here's one for clothing, and one for position. They don't express their results in terms relevant to sprinting, but they're still informative.

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  • "Aerodynamics are very important in cycling, and the faster you go, the more important they get" - Yep. To sum it up for the OP, power goes up with the cube of your speed. To go from 20mph to 40mph, a rider needs to put about 8 times as much power in. Commented Feb 25, 2021 at 23:24
  • Note that the drag coefficient is not measured "relative to a flat surface", it is a dimensionless constant. In fact, C_d of a flat surface in a flow typical for cyclists (~10 m/s, air at STP) will not be 1, and it also will also depend on the shape of the flat surface. Commented May 8, 2022 at 11:54

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