weight versus speed
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weight versus speed
Is there a general equation for the relationship between the weight of the rider and the speed of a bike as it coasts down a hill, all else being equal?
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Originally Posted by jessica3333
Is there a general equation for the relationship between the weight of the rider and the speed of a bike as it coasts down a hill, all else being equal?
know what you need to know for and why.
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Originally Posted by Xtrmyorick
Yes. Speed will be the same no matter the weight.
RGC
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In perfect conditions (IE-Vacuum) then weight means nothing. Gravity acts the same on all bodies.
But in the real world, other things must be considered. Primarily, aerodynamics. It's possible for the heavier rider to have better sectional density than the lighter one. It has been observed that clydesdale-sized riders do tend to gain on their lighter brethren on steep descents.
But there's a point of vanishing returns, however. If you are so large as to present a surface area that overcomes the sectional density advantage...
Also, if the descent has a lot of turns, the lighter rider will be at advantage again, as he'll be able to drive harder through the turns without loosing traction.
But in the real world, other things must be considered. Primarily, aerodynamics. It's possible for the heavier rider to have better sectional density than the lighter one. It has been observed that clydesdale-sized riders do tend to gain on their lighter brethren on steep descents.
But there's a point of vanishing returns, however. If you are so large as to present a surface area that overcomes the sectional density advantage...
Also, if the descent has a lot of turns, the lighter rider will be at advantage again, as he'll be able to drive harder through the turns without loosing traction.
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Originally Posted by Xtrmyorick
Yes. Speed will be the same no matter the weight.
Pay attention to all the words when thinking of things from High School Physics.
IN A VACUUM all abjects fall at the same speed.
But on a cycle we are not in a vacuum, in fact on a road bike over 80% of the work you do at speeds of 20MPH is overcoming aerodynamic drag. Now look at an object, rider sphere whatever. The cross section goes up as the square of the height (diameter) the mass goes up as the cube. Result bigger riders decent faster. In the more real world there is more than just scale . Take a nice big beer belly. It has no impact at all on the cross section (provided it is a perfect beer belly and only sticks out forward) thus it contributes even more to the downhill speed.
You will not find formulas as position counts as does the bike. But a nationally ranked woman rider in excellent aero position will decent Mullholland Drive at the same speed as a very average 220lb rider sitting up. (Experimental results because the club regroup point is at the top of the climb).
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Originally Posted by jessica3333
Is there a general equation for the relationship between the weight of the rider and the speed of a bike as it coasts down a hill, all else being equal?
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https://www.kreuzotter.de/english/espeed.htm
Thankyou. For once I didn't have to post this site first.
This site has been very helpful in the past for doing certain preparations for different events on different terrains. For instance, I was torn between taking my tailfairing with me on a 7 day tour in Tennessee. I was worried that the extra 6 lbs worth of weight would hurt me on the long climbs. After plugging in some wattages with the stock bike setup and the tailfaired bike setup on different grades, it appears that the extra weight of the tailfairing will on the average only slow me down by .2 mph at the most.
The benefit will be on the flats where I can gain 5-6 mph over the stock setup. I'd rather cruise at 28 to 30mph on the flats and pay a .2mph penalty on the uphills.
oh, if you want to get faster on a downhill, try one of these.
https://groups.msn.com/BicyclingForum...o&PhotoID=7408
on a -5 percent grade, a 200 lb rider in the drops will reach a terminal speed of 35.7mph
on my tailfaired lowracer on the same downhill 5% grade I will hit 56.1 mph
( been there done that) many times
Thankyou. For once I didn't have to post this site first.
This site has been very helpful in the past for doing certain preparations for different events on different terrains. For instance, I was torn between taking my tailfairing with me on a 7 day tour in Tennessee. I was worried that the extra 6 lbs worth of weight would hurt me on the long climbs. After plugging in some wattages with the stock bike setup and the tailfaired bike setup on different grades, it appears that the extra weight of the tailfairing will on the average only slow me down by .2 mph at the most.
The benefit will be on the flats where I can gain 5-6 mph over the stock setup. I'd rather cruise at 28 to 30mph on the flats and pay a .2mph penalty on the uphills.
oh, if you want to get faster on a downhill, try one of these.
https://groups.msn.com/BicyclingForum...o&PhotoID=7408
on a -5 percent grade, a 200 lb rider in the drops will reach a terminal speed of 35.7mph
on my tailfaired lowracer on the same downhill 5% grade I will hit 56.1 mph
( been there done that) many times
Last edited by lowracer1; 09-12-05 at 07:15 PM.
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Downward force on a hill is m*g*sin(phi)
m is the mass of the object (rider+bike)
g is the gravitational acceleration on Earth (9.81 m/s^2, or 32.2 ft/s^2)
phi is the angle that the hill is inclined
MASS does matter!!!
If a bike slid down a hill (rather than rolling), then mass would cancel out of the equations, but rolling resistance is difference than kinetic friction.
m is the mass of the object (rider+bike)
g is the gravitational acceleration on Earth (9.81 m/s^2, or 32.2 ft/s^2)
phi is the angle that the hill is inclined
MASS does matter!!!
If a bike slid down a hill (rather than rolling), then mass would cancel out of the equations, but rolling resistance is difference than kinetic friction.
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Originally Posted by lowracer1
For instance, I was torn between taking my tailfairing with me on a 7 day tour in Tennessee.
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Originally Posted by lowracer1
The benefit will be on the flats where I can gain 5-6 mph over the stock setup. I'd rather cruise at 28 to 30mph on the flats and pay a .2mph penalty on the uphills.
I am an old guy at 63, however.