Single speed conversion damaging chain?

[screenman]

In my humble opinion, chain line should be within ~2mm for single-speed, and within ~1mm for fixed.

You only have one gear, so the chain takes a beating every time the road goes upwards. To withstand that level of use, the chainline should be perfectly straight, as that's when the chain is strongest. If it fits, I'd run a proper single-speed/fixed chain, with a three piece link, rather than a regular derailleur chain.

Please explain to this thicky how chain tension varies as you go up hill, when compared with multi geared machine. I would see it as the chain taking the same load whatever gear you are in.

 

[fossyant]

Please explain to this thicky how chain tension varies as you go up hill, when compared with multi geared machine. I would see it as the chain taking the same load whatever gear you are in.

Think he means more load as you end up grinding up hills more, than with gears.

 

[screenman]

Think he means more load as you end up grinding up hills more, than with gears.

Surely the load on the chain does not change, only the load on your legs.

 

[fossyant]

Load on legs = load on chain ! You have to pedal much harder than you would if you could drop 3 or 4 gears. Harder pedalling = more drive chain load.

TBH with singlespeed, you can run 3/32 chains. It's when you get to fixed you really need the beefy 1/8 chains. These aren'f flexible like the 3/32 so chain line is important.

 

[screenman]

Load on legs = load on chain ! You have to pedal much harder than you would if you could drop 3 or 4 gears. Harder pedalling = more drive chain load.

TBH with singlespeed, you can run 3/32 chains. It's when you get to fixed you really need the beefy 1/8 chains. These aren'f flexible like the 3/32 so chain line is important.

Nope still not clear enough, the gears are the gearbox, the chain the propshaft surely strain is the same to propel the bike forwards and upwards? Say BW is going up hill and 375 watts now that power is going through the chain I believe, if he changes down or up the sprocket but remains at the same power the strain on that chain is surely the same.

Power meters I think used to take the measurement from the chain, some may still do so, these work regardless of the gear you are in for the reason I stated.

 

[GrasB]

Load on legs = load on chain ! You have to pedal much harder than you would if you could drop 3 or 4 gears. Harder pedalling = more drive chain load.

TBH with singlespeed, you can run 3/32 chains. It's when you get to fixed you really need the beefy 1/8 chains. These aren'f flexible like the 3/32 so chain line is important.

Doesn't work like that. Chain tension is dictated by the chain speed, given the same power & wheel speed then you need to look at the size of the rear sprocket to work out the chain tension, which is inversely proportional to the sprocket size.

Start with the same power output (thus all 200w). As I know the tyre size (622x28), sprocket teeth & chairing teeth I can work out the gearing in mph/100rpm (not shown here) which gives me the cadence. From there I back work the torque in Nm, it's easy enough to work out the chaining diameter & thus radius from the tooth count & now you have all the information you need convert from Nm to Nforce (eg tension) transmitted via the chain.

 

[fossyant]

Geek alert !!

 

[raleighnut]

Surely the highest torque is from a standstill when all of a riders weight is put onto the pedal through the chain. I've seen chains snap (on tv) when riders begin from the starting stands at Velodrome races. (Tech term not known for these stands)

 

[JoeyB]

From the two pics of chain line you have posted, I wouldn't be happy with either of them.

 

[GrasB]

[QUOTE 3140809, member: 45"]And if the power output is the only variable?[/QUOTE]
All other variables held constant chain tension is directly proportional to power.

Surely the highest torque is from a standstill when all of a riders weight is put onto the pedal through the chain. I've seen chains snap (on tv) when riders begin from the starting stands at Velodrome races. (Tech term not known for these stands)

Pulling off is an edge case as anything much bellow 40rpm becomes muscle force limited so the chain tension will stay the same no matter the power. If you assume I'm only pushing as hard as my body weight on 165mm cranks my 1-45rpm chain tension on a 42t chainring is 1598.6N, or about 4.5x the chain tension in the lowest example there.

Geek alert !!

And?..

 

[JoeyB]

This is mine, just took a quick pic...

 

[GrasB]

The curve could also be static chain droop. To me he's not taking a photo directly down the chain line.

 

[raleighnut]

All other variables held constant chain tension is directly proportional to power.


Pulling off is an edge case as anything much bellow 40rpm becomes muscle force limited so the chain tension will stay the same no matter the power. If you assume I'm only pushing as hard as my body weight on 165mm cranks my 1-45rpm chain tension on a 42t chainring is 1598.6N, or about 4.5x the chain tension in the lowest example there.


And?..

Now increase the crank to 175 and stick 13.5 stone on it ( about average for a 6 footer)

 

[GrasB]

About 1750N, anyway track cranks are usually 165, hence why I used that length

 

[screenman]

[QUOTE 3140837, member: 45"]Chain tension is affected by (leg) power output and by gearing. On a single speed bike, to apply more power to the back wheel your only option is to pedal harder, and this increases the pulling force on the chain.[/QUOTE]

Which of course would be the same no matter what gear you were in.