Single speed conversion damaging chain?

[screenman]

[QUOTE 3141190, member: 45"]No, it would depend on how much power you're putting though your legs.[/QUOTE]
Yes we know that, but 20 mph is putting the same strain on the chain no matter what gear you are in, it is the legs that feel the difference.

 

[GrasB]

Yes we know that, but 20 mph is putting the same strain on the chain no matter what gear you are in, it is the legs that feel the difference.

No, that's covered by the first table - 29/11 is 345N, 52/20 is 190N both at 200w @ 20mph

Basically a smaller rear sprocket means a slower chain so more force is applies per 1/2" of chain pulled.

 

[screenman]

No, that's covered by the first table - 29/11 is 345N, 52/20 is 190N both at 200w @ 20mph

Basically a smaller rear sprocket means a slower chain so more force is applies per 1/2" of chain pulled.

So please explain how the power meter that uses the chain tension Polar I think works.

 

[GrasB]

So please explain how the power meter that uses the chain tension Polar I think works.

Power is force multiplied by time. You measure the chain tension & you can work out the force being exerted, you measure the chain speed & you work how quickly that force is being exerted. You now can work out how much work is actually being done by that force, aka power.

200w == 345.4N @ 579mm/s == 237.5N @ 842mm/s == 190.1N @ 1052mm/s

A chain tension measurement device by necessity also is a chain speed measurement device as the same techniques apply for the raw signal, it's just the way you process the data that defines what you measure. You simply & run different analysis on the chain data at the same time and you have speed & tension, or power

 

[screenman]

[QUOTE 3141228, member: 45"]I think, though I'm open to persuasion, that your mistake is saying that the chain is the equivalent of the property shaft on a car. That's not correct as the chain is in the middle of the "gearbox" and not the final drive. The propshaft rotation of a car is always at the same ratio to the rotation of the wheels. On a bike the force on a chain is lower in a lower gear and requires more chain distance travelled to keep the same speed.[/QUOTE]

That is the bit I am having trouble getting my head around. So if I stand on the pedals with my back wheel locked the chain between ring and sprocket will be x if it is on say the 13t but y if it is on the 21t.

 

[GrasB]

That is the bit I am having trouble getting my head around. So if I stand on the pedals with my back wheel locked the chain between ring and sprocket will be x if it is on say the 13t but y if it is on the 21t.

No, because in both cases there is no time difference so no work is being done.

Once time is involved things get a little different. Assuming the same chainring at the front, if the rear wheel is turning at 10rpm then you'll fall at different rates. The closer you get to falling at an accelerating rate of 9.81m/s/s the lower the force being applied will be less. A bigger sprocket means more chain travel, that means you'll be falling faster & thus exerting less force on the chain.

 

[raleighnut]

No, because in both cases there is no time difference so no work is being done.

Once time is involved things get a little different. Assuming the same chainring at the front, if the rear wheel is turning at 10rpm then you'll fall at different rates. The closer you get to falling at an accelerating rate of 9.81m/s/s the lower the force being applied will be less. A bigger sprocket means more chain travel, that means you'll be falling faster & thus exerting less force on the chain.

But the static chain is experiencing load and if the load increases it will eventually fail, if load is applied to the lever of the crank arm and the other end is stationary

 

[GrasB]

But the static chain is experiencing load and if the load increases it will eventually fail, if load is applied to the lever of the crank arm and the other end is stationary

But the load isn't increasing. It's staying at the same level as the same constant force is being applied. Slowly, very, very slowly, this will stretch the chain & if there are any flaws in the metal it may cause them to expand & thus the chain will break.

 

[GrasB]

[QUOTE 3141264, member: 45"]If you're in first gear it's really easy to pedal. It's easier for the chain to pull on the big ring at the back, but it has to travel further for the same output at the road. To travel at the same speed in say 6th gear you have to push harder with your foot but for less distance travelled of the chain. The pull on the chain is stronger to get the wheel to turn, so the chain is exposed to more force.[/QUOTE]
But the load on the pedal isn't increasing & the rear wheel isn't turning so the chain tension, for the same chain ring size, will stay the same.

 

[raleighnut]

The OP still managed to knacker a chain though

 

[pclay]

The OP still managed to knacker a chain though

Yes i did, Now going back to gears. Going to sell the Raleigh for about £50 if i can. considering a £200 fixie from ebay.

 

[GrasB]

Yes i did, Now going back to gears. Going to sell the Raleigh for about £50 if i can. considering a £200 fixie from ebay.

On that subject, I think part of the chain damage problem is that you're using a non-toothed tensioner with a multi-gear chain & chainring setup. This will allow the chain to move much more than it would normally. I'm still of the opinion that the chain damage was caused by it trying to change chainrings but not quite being able to so the chainring trying to lever the side plates off.

Personally I'd go buy a 1/8" sprocket, chain, chainring & chainring shims then try again if I was to run that bike but getting an already setup single speed may well be the best option for you.

 

[GrasB]

[QUOTE 3141301, member: 45"]I'm not talking about a static wheel am I? This discussion stemmed from a claim that there will be more force on a fixed chain going up a hill, than on a bike with the option of easier gears. And that's correct. Introducing static wheels is just confusing things.[/QUOTE]
But this doesn't answer the question that screenman asked.

 

[GrumpyGregry]

I saw damage like that when using a pined and ramped chainwheel off an mtb chainset on my first ss mtb which didn't have a chainguide in place. Basically under pressure, far higher and more sustained that it would ever be on a geared biike, thanks to the ramps, the chain was trying to move to another chainwheel that wasn't there. Mashtastic, horrid noises, much swearing. This is exacerbated if the chainline isn't good imo.

On the next bike, now sold, I used a plain, non-ramped, all teeth same size, no pins, Salsa chainwheel. No problem.

 

[GrasB]

[QUOTE 3141955, member: 45"]He asked how chain tension varies when going up a hill on a fixie. It addresses that question. As I said, the business of chain tension when the wheels aren't moving is irrelevant and is confusing the issue.[/QUOTE]
Then quote the CORRECT post then. Also static tension is never irrelevant & writing it off as being confusing/irrelevant means you're making sure he can never understand what's actually going on.