Bike Forums - the difference between 20 mph compared to 25 mph

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- - the difference between 20 mph compared to 25 mph (https://www.bikeforums.net/road-cycling/683416-difference-between-20-mph-compared-25-mph.html)

Quote:

Originally Posted by Brian Ratliff (Post 11530304)

It's about double.

Power is roughly proportional to velocity cubed:

P2/P1 = (V2^3)/(V1^3)

= (25^3)/(20^3) = 1.95 ~ 2

(P1, V1 are the power and velocity respectively at 20mph. P2, V2 are the power and velocity at 25mph)

Oh that's much easier to understand...:crash:

Quote:

Originally Posted by WHOOOSSHHH... (Post 11530628)

Really?

Really what?

I suppose you are asking about the question of whether v * v is the sole drag component. There could be changes in air's turbulence behavior as speed changes. There could be small resistance components from bearings or chain or tires which are not simply proportional to v squared; for example, as the rider shifts gears the chain resistance changes because its speed changes, though admittedly its contribution may be very small. The rider may hold his/her body differently as the speed or pedalling load changes.

The point is, the algebra is precise but the physical world isn't required to obey it precisely. Or to put it causalistically correctly, the algebra is not necessarily an accurate reflection of the physical world.

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The difference between theory and practice is a lot bigger in practice than it is in theory.

For me this is easy....

20 MPH is attainable and sustainable.

25 MPH is attainable but NOT sustainable.

edit: unless I get aero wheels, right?!?

Quote:

Originally Posted by wacomme (Post 11530978)

5 mph.

Nearly 30 replies and finally an answer that makes sense.

There is no difference. Neither sounds impressive to the chick at the bar.