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motch

Transmission Losses On A Bicycle Chainring & Cogs

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In the near future i'm thinking of building up a super lightweight racing Bicycle, possibly with just a single front Chainring, but with the normal multiple cogs on the rear wheel.

My question is regarding the efficiency of putting a compact/smaller front chainring on compared to the normal 52/53 tooth front chainring.

I've read before a slight power loss would be the case if say a 45 tooth front was used compared to a 53 for example.

Having a 11 tooth cog up to around 25 tooth max on the back. Would a 11 cog lose much in efficiency compared to say a 13 tooth cog ?

Any views/figures on here on what the losses may be if any ?

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In the near future i'm thinking of building up a super lightweight racing Bicycle, possibly with just a single front Chainring, but with the normal multiple cogs on the rear wheel.

My question is regarding the efficiency of putting a compact/smaller front chainring on compared to the normal 52/53 tooth front chainring.

I've read before a slight power loss would be the case if say a 45 tooth front was used compared to a 53 for example.

Having a 11 tooth cog up to around 25 tooth max on the back. Would a 11 cog lose much in efficiency compared to say a 13 tooth cog ?

Any views/figures on here on what the losses may be if any ?

I would say pretty much immeasurable and, unless you're close to being a world class time trialler, certainly irelevant. What's your 25 mile time right now?

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In the near future i'm thinking of building up a super lightweight racing Bicycle, possibly with just a single front Chainring, but with the normal multiple cogs on the rear wheel.

My question is regarding the efficiency of putting a compact/smaller front chainring on compared to the normal 52/53 tooth front chainring.

I've read before a slight power loss would be the case if say a 45 tooth front was used compared to a 53 for example.

Having a 11 tooth cog up to around 25 tooth max on the back. Would a 11 cog lose much in efficiency compared to say a 13 tooth cog ?

Any views/figures on here on what the losses may be if any ?

Smaller cogs mean lower rotational inertia from the chain, but the chain needs to be deformed more to fit on the tighter turning radius, which means more friction.

I imagine you could get a 50 page thread going on a cycling forum, with people expressing very firm views on why it makes a colossal difference.

I'd suggest you take a sh*t before you leave the house and you'll likely cover any gains/losses from the decreased body mass and stick with regular components.

If you're not going to the track, why give up a double chainring? The extra mass is miniscule and the flexibility gains are plain.

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Fabulous level of detail here. I own a £30 bicycle purchased from a charity shop which takes me backwards if the wind blows hard enough. :P

turn it round?

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Main thing iirc is to make sure that the shape of the front cog is squashed oval enough at the right angle to properly match your power cycle....

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Smaller cogs mean lower rotational inertia from the chain, but the chain needs to be deformed more to fit on the tighter turning radius, which means more friction.

I imagine you could get a 50 page thread going on a cycling forum, with people expressing very firm views on why it makes a colossal difference.

I'd suggest you take a sh*t before you leave the house and you'll likely cover any gains/losses from the decreased body mass and stick with regular components.

If you're not going to the track, why give up a double chainring? The extra mass is miniscule and the flexibility gains are plain.

Yeah, thats why I didn't post it on a bike forum, just wondered what some guys on here with some physics/engineering type backgrounds or others might think or know on the subject.

It's more of a see how light I can get my bike thing (without making it too unrideable or too easy to break) I live in suffolk so no big hills around.

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Yeah, thats why I didn't post it on a bike forum, just wondered what some guys on here with some physics/engineering type backgrounds or others might think or know on the subject.

It's more of a see how light I can get my bike thing (without making it too unrideable or too easy to break) I live in suffolk so no big hills around.

A big chainring is heavier than a small one. Maybe those BMX dudes are on to something.

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A big chainring is heavier than a small one. Maybe those BMX dudes are on to something.

9 cog on the back sounds good as well.

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Back in the early 90s, Suntour came out with a Microdrive groupset for mountain bikes. Basically, it shrank both the chainrings and the cogs to save weight (and also lower gears). You'll also need a shorter chain - and therefore save weight that way too. But things will also wear quicker too.

Although it didn't sell in huge numbers, it was fairly influential. It's rare to find very big chainrings on mountain bikes nowadays.

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Yeah, thats why I didn't post it on a bike forum, just wondered what some guys on here with some physics/engineering type backgrounds or others might think or know on the subject.

It's more of a see how light I can get my bike thing (without making it too unrideable or too easy to break) I live in suffolk so no big hills around.

A fixie might be suitable, with the correct setup. Track types often have a selection of front rings to swap in, using the play the rear dropouts have to add/remove any slack from changing the size of the ring. It seems not to take much time, although it's been years since I saw that so I might be incorrect. Maybe if you fancy going out for a long ride you can put one ring on, or pootle about town with a different one. More faff, but might be worth considering.

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I would say pretty much immeasurable and, unless you're close to being a world class time trialler, certainly irelevant. What's your 25 mile time right now?

I'm no Bradley Wiggins, but i'm not after a super fast TT Bike, just trying to get a road bike super light.

25 mile around the hour on a local course. Haven't done any drag strip type courses but approx 55 mins on a superfast course on a good day i'd guess. Thats with TT bike with all the trimmings.

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I'm no Bradley Wiggins, but i'm not after a super fast TT Bike, just trying to get a road bike super light.

25 mile around the hour on a local course. Haven't done any drag strip type courses but approx 55 mins on a superfast course on a good day i'd guess. Thats with TT bike with all the trimmings.

Alright, not world class but that's still a pretty decent time! I'll stick with my comment about the size of the gears probably not making a measurable difference compared to, say, getting your riding position exactly right and using TT bars properly though.

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How fast was he pedalling ?

0 miles per hour, he had a rocket strapped behind his ar$£!! :blink::D

to pedal at 163 mph or whatever he'd need a front chainring about the diameter of a Bus wheel. :blink:

Balls the size of coconuts though to keep that in a straight line and upright.

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Back in the early 90s, Suntour came out with a Microdrive groupset for mountain bikes.

Predated by Shimano in the late 70s with their 10mm system.

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In the near future i'm thinking of building up a super lightweight racing Bicycle, possibly with just a single front Chainring, but with the normal multiple cogs on the rear wheel.

My question is regarding the efficiency of putting a compact/smaller front chainring on compared to the normal 52/53 tooth front chainring.

I've read before a slight power loss would be the case if say a 45 tooth front was used compared to a 53 for example.

Having a 11 tooth cog up to around 25 tooth max on the back. Would a 11 cog lose much in efficiency compared to say a 13 tooth cog ?

Any views/figures on here on what the losses may be if any ?

Torque (T), speed (w), teeth (N)

T1/T2 = N1/N2 = w2/Sw

T1 = T2*(N1/N2)

Power = Torque * angular velocity --> P=Tw

Do the sums yourself, its easy maths with simple ratios.

http://en.wikipedia.org/wiki/Gear_ratio

Also this is good:

http://www.gearingcommander.com//

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Torque (T), speed (w), teeth (N)

T1/T2 = N1/N2 = w2/Sw

T1 = T2*(N1/N2)

Power = Torque * angular velocity --> P=Tw

Do the sums yourself, its easy maths with simple ratios.

http://en.wikipedia....wiki/Gear_ratio

Also this is good:

http://www.gearingcommander.com//

cheers for the links. What i'm trying to work out is if there's any power lost for example, between say 53x13 and a similar size gear of 45x11 (very similar size gears) no other variables.

so say eg 300 watts to propel the 53x13 at 25mph, what watts would be required to propel 45x11 at 25mph ?

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cheers for the links. What i'm trying to work out is if there's any power lost for example, between say 53x13 and a similar size gear of 45x11 (very similar size gears) no other variables.

so say eg 300 watts to propel the 53x13 at 25mph, what watts would be required to propel 45x11 at 25mph ?

Very interested in this myself

in the late 70`s and early 80`s I was a pretty decent tester........

Bikes for time trials were pretty much the same as road race machines, some had 28 or even 24spoke wheels, mad men even road silk sidewall tubular tyres

I thought of myself as a renegade - I had a single 56 or even a 60 with a 12 on the back, to save weight I only fitted 4 cogs on the rear cassette.....

But.........

Modern machines are un-fathomable to me.........

WHY?

I managed a low 20min 10 and a 50min 25 on the above, modern times are not that awesome (apart from at the very top)

If you are fit you will do the times! ...Oh and save about £10 grand too

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cheers for the links. What i'm trying to work out is if there's any power lost for example, between say 53x13 and a similar size gear of 45x11 (very similar size gears) no other variables.

so say eg 300 watts to propel the 53x13 at 25mph, what watts would be required to propel 45x11 at 25mph ?

The same (300 watts) since you're doing the same amount of work, assuming that the friction losses remain unchanged. Because the latter ratio (45/11) is slightly greater than the former (53/13), the latter ratio will require a slightly higher pedalling speed and a slightly lower torque to achieve the same riding speed.

Edit: That's not what you're really interested in though, is it. You're looking for the optimum absolute sprocket size rather than the optimum ratio for a particular speed. From this link, it would appear that sprocket size is a trade-off between weight (big sprockets) and friction (little sprockets). Weight will always be the same, while friction will increase with higher speed, so larger sprockets would tend to be better for high speeds, I guess. Also, small sprockets will obviously wear faster, while large sprockets will require more material and be more awkward to accommodate.

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The same (300 watts) since you're doing the same amount of work, assuming that the friction losses remain unchanged. Because the latter ratio (45/11) is slightly greater than the former (53/13), the latter ratio will require a slightly higher pedalling speed and a slightly lower torque to achieve the same riding speed.

the friction loss on a smaller chainring (if any) compared to a larger chainring is what i'm trying to establish. eg would it be say 1% less efficient riding a small chainring compared to riding a larger chainring with the same size gearing.

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the friction loss on a smaller chainring (if any) compared to a larger chainring is what i'm trying to establish. eg would it be say 1% less efficient riding a small chainring compared to riding a larger chainring with the same size gearing.

I don't know. I suppose you'd have to work out the amount of chain link movement, and hence friction, per metre travelled as a function of sprocket size. It's also going to depend on how tight and how well lubricated the chain is. It's not a trivial calculation, but there may be some rules of thumb used out there in the cycling world.

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I don't know. I suppose you'd have to work out the amount of chain link movement, and hence friction, per metre travelled as a function of sprocket size. It's also going to depend on how tight and how well lubricated the chain is. It's not a trivial calculation, but there may be some rules of thumb used out there in the cycling world.

cheers anyway :)

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Very interested in this myself

in the late 70`s and early 80`s I was a pretty decent tester........

Bikes for time trials were pretty much the same as road race machines, some had 28 or even 24spoke wheels, mad men even road silk sidewall tubular tyres

I thought of myself as a renegade - I had a single 56 or even a 60 with a 12 on the back, to save weight I only fitted 4 cogs on the rear cassette.....

But.........

Modern machines are un-fathomable to me.........

WHY?

I managed a low 20min 10 and a 50min 25 on the above, modern times are not that awesome (apart from at the very top)

If you are fit you will do the times! ...Oh and save about £10 grand too

Just have to say respect to those times done in 70's and 80's, pre tri-bars and all the gismos.

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