Same Gear Inches, Different Wheel Sizes. One Feels Spinnier.
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Same Gear Inches, Different Wheel Sizes. One Feels Spinnier.
I have a 700c singlespeed with 62.5 gear inches.
I also have a 650b singlespeed with 62.3 gear inches.
In Sheldon Brown's Gain Ratios, they are 4.53 and 4.52, respectively.
In meters development, they're 4.66 and 4.36, respectively.
All this tells me that they're so close that they should feel virtually the same, but the 650b bike seems a lot easier to spin up and out.
The only thing I can deduce is that the smaller wheels are lighter, so they accelerate more efficiently, and then I'm just going faster and thus spinning faster.
I'll embark on some trial-and-error, but was wondering if anyone here has a theory. Or maybe it's all in my head?
I also have a 650b singlespeed with 62.3 gear inches.
In Sheldon Brown's Gain Ratios, they are 4.53 and 4.52, respectively.
In meters development, they're 4.66 and 4.36, respectively.
All this tells me that they're so close that they should feel virtually the same, but the 650b bike seems a lot easier to spin up and out.
The only thing I can deduce is that the smaller wheels are lighter, so they accelerate more efficiently, and then I'm just going faster and thus spinning faster.
I'll embark on some trial-and-error, but was wondering if anyone here has a theory. Or maybe it's all in my head?
Last edited by Rolla; 09-17-21 at 04:32 PM.
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Crank length, position of where you sit relative to the BB.
Did you change the wheel size when you did the gear ratio and other calcs?
Weight will go a long way, but total weight will seem more the thing than just slightly lighter wheels. Otherwise we're going to get bogged down in the rotational mass stuff that we love to argue here. <grin>
Did you change the wheel size when you did the gear ratio and other calcs?
Weight will go a long way, but total weight will seem more the thing than just slightly lighter wheels. Otherwise we're going to get bogged down in the rotational mass stuff that we love to argue here. <grin>
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Crank length, position of where you sit relative to the BB.
Did you change the wheel size when you did the gear ratio and other calcs?
Weight will go a long way, but total weight will seem more the thing than just slightly lighter wheels. Otherwise we're going to get bogged down in the rotational mass stuff that we love to argue here. <grin>
Did you change the wheel size when you did the gear ratio and other calcs?
Weight will go a long way, but total weight will seem more the thing than just slightly lighter wheels. Otherwise we're going to get bogged down in the rotational mass stuff that we love to argue here. <grin>
Thanks for the reply. My wheel size numbers are accurate for all the calculations. Crank arm length only figures into the gain ratio numbers, not the others.
Rotational mass may have something/everything to do with it, but I don't want to go there!
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Just because they aren't taken into account in those calculations doesn't mean that crank length won't make it feel different.
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#7
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In meters development, they're 4.66 and 4.36, respectively.
62.5 gear inches is ~4.99 meters of development. 62.3 gear inches is ~4.97 meters of development.
What are the actual gear ratios, and the measured inflated tire diameters?
#8
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Tire pressure ?
tread pattern ?
bike fit ?
frame geometry?
bearings (pedals, bottom bracket wheels) of similar friction ?
tread pattern ?
bike fit ?
frame geometry?
bearings (pedals, bottom bracket wheels) of similar friction ?
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I think the 650 bike feeling spinnier is in line with other people's results. Lots of theories about why that might be
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Yes, I stand corrected on the meters of development calculation.
Bike 1: 700 X 35. 39 X 17. Diameter: 27.2". 170mm crankarms.
Bike 2: 650 X 47. 40 X 18 . Diameter: 26.7". 172.5mm crankarms.
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If everything else is equal .... Never mind.
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#13
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one factor will be the rotational inertia difference in the wheels
Wheels w larger rotational inertia will take more energy to spin up. Rotational inertia is related to the effective rotating mass and the square of the effective radius.
https://en.wikipedia.org/wiki/Moment...tia#Definition
Wheels w larger rotational inertia will take more energy to spin up. Rotational inertia is related to the effective rotating mass and the square of the effective radius.
https://en.wikipedia.org/wiki/Moment...tia#Definition
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Different riding positions, wheel base, rotational weights, crank arm lengths are a couple ideas....