Two cyclists are stopped at a top of a large hill. Who coasts down faster?

Question

This has been a discussion for a long time. I think the one with the bike which is tuned better wins. (bearings lubed, tires inflated properly, etc) Another argues that weight plays a factor. ie the heavier cyclist wins. Are we forgetting something?

Answer 1

the one with the best aerodynamics will go down faster. its like in the time trial they cant turn very well but the aerodynamic position will cut lots more time off. weight will make u less aerodynamic because its mroe surface area for air to hit. and as long as one of the bikes isnt an old rust bucket, but in the general area of the other, it shouldnt be that big of a deal....i dont think.

Answer 2

Interesting question.

Analytical Cycling (See link) have a calculator that shows -- all other things being held constant the heavier rider will have a higher terminal velocity on a long downhill (I used "0" for power to simulate coasting, and even if you allow for higher frontal area for the larger rider you still reach the same conclusion).

Newtonian physics re velocity being independent of weight is ONLY applicable in the absence of air resistance ... and air resistance is a BIG factor in cycling. Since frontal area is non-linear with weight heavier riders will descend faster (Assuming similar aerodynamic positioning).

I believe this agrees with observation.

Answer 3

We play this game regularly but I don't know the science behind it.  Usually the lighter bike and rider and most aerodynamic body position wins.

Answer 4

Being a bigger rider and riding in events all the time I can say I am faster down hill and the little guys are faster up hill.

Answer 5

I ride with a club and, in the winter we tend to do more roads and tracks, a lot of our rides involve some nice downhill roads.  You would think that the lighter bike, leaner rider, etc would win, but I have regularly breezed past people with bikes 5 - 6lb lighter than mine and with better hubs (Hope 2s are popular at the moment.)

The biggest factor, other than getting low over the bars is tyre selection.  I use skinny 1.8s at 45 psi in the winter.  This offers less roling resistance than somebody on a 2.1 with 30 psi.

Servicing helps, but all of the club riders take care of their bikes because of the abuse we tend to put our bikes through.  

So although choice of hubs, weight etc is important, I would have to say that tyres will have the greatest influence, especially if you have chosen a lighter weight tyre (1 lb saved on the tyre, due to rotational forces, can be the same as 4 or 5 lbs on the frame).

Luck

Answer 6

I agree with AGB...,  if all other things are held equal, the heavier rider will make it to the bottom faster.  Just like, if all other things are held equal, a lighter rider will make it to the top of a hill quicker.

Of course, in the real world, lots of other factors, including aerodynamics and power, enter into the picture.  Only in a theoretical world can all other factors be held equal.

As speed increases, wind resistance becomes more and more of a factor.  Thus, a ligher rider in a slightly more aerodynamic stance may overtake the heavier rider.  

A slightly more powerful rider can overcome lighter weight.

Even rolling resistance comes into play.

I also suggest going to the analytic cycling site.  I ran the model examing the effect of lower weight.  

http://www.analyticcycling.com/ForcesLes...

Coasting down a 1000m slope of 5%, a rider weighing 5KG less would be 2.36 seconds behind the heavier rider.

Hope this helps.

Answer 7

Galileo proved that weight doesn't matter.

Rolling resistance and aerodynamics are the two factors in this equation.   This is a race I usually win.   Continental 650x19 tubulars at 150psi, carbon aero wheels, agressive aero position.    

Of course, you were to allow a faired recumbent, it would be no contest.

Answer 8

i am a big guy 6'2" 200lbs, and in my experience there are two times weight helps.  one is going downhill.  my smaller buddies always have to pedal to stay with me, even with superior bearings and such.  i know my friend's ceramic bearings in his wheels are much faster than mine, but downhill i can still outcoast him.  the second time weight helps is on very rough roads.  weight has a certain amount of momentum that seems to help when things are bumpy and rough.