Correct angles for rear gear changer

[Old timer]

I`ve been experimenting with different chainrings on two bikes. Increasing the the size. (single front chain ring) I`ve added the same amount of new chainlinks as the increase in ring size( 48T-55T added 7 links)
Is this correct?

Also I can`t seem to find any decent images or diagrams as to how the rear changer should look when you have the chain length correct. ( say the angle of the two main sections) Any links?

Thanks

 

[gbb]

'The best technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer. Mesh the two ends on to the large chainwheel so that they could be connected (outer link meets inner link), then make the chain one complete link (one inch) longer than that. In almost all cases, this will give the optimum length.'

Taken from ...
http://sheldonbrown.com/derailer-adjustment.html#chain

 

[ASC1951]

Ah - beat me to it.

 

[hubgearfreak]

I`ve added the same amount of new chainlinks as the increase in ring size( 48T-55T added 7 links)
Is this correct?

no, if you go from a 30tooth front ring to a 50 tooth one, you'll need 10 more links, not 20. the chain is only on one half of the chainring at once.
unless you've fitted the chain really wrong.

 

[Old timer]

no, if you go from a 30tooth front ring to a 50 tooth one, you'll need 10 more links, not 20. the chain is only on one half of the chainring at once.
unless you've fitted the chain really wrong.

Yeh! but doesn`t the new diameter of the larger chainring pull the chain forward by more than half it`s circum?

So! changing from a 48-57 means a increase of between 4 or 5 links then rather than the 9 I`ve added? and adding too many links will give chain sag?

Are you counting a link as 1 where one tooth can go in or 1 where you get both types of link( apair)

 

[Old timer]

'The best technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer. Mesh the two ends on to the large chainwheel so that they could be connected (outer link meets inner link), then make the chain one complete link (one inch) longer than that. In almost all cases, this will give the optimum length.'

Taken from ...
http://sheldonbrown.com/derailer-adjustment.html#chain

I`ve looked at Sheldon page and drawings, I still find it hard to take in that a chain run around the largest rear cog and then onto the chain ring + 1" will be enough chain to also thread through the gears. I understand that the smaller cogs take up less chain but you still have to have adequate length of chain to go onto the largest cog and through the gears

I`m obviously missing something

 

[Hacienda71]

I`ve looked at Sheldon page and drawings, I still find it hard to take in that a chain run around the largest rear cog and then onto the chain ring + 1" will be enough chain to also thread through the gears. I understand that the smaller cogs take up less chain but you still have to have adequate length of chain to go onto the largest cog and through the gears

I`m obviously missing something

No it is right. Tried and tested, I know it seems odd but it is the easiest way of doing it correctly.

 

[gbb]

I`ve looked at Sheldon page and drawings, I still find it hard to take in that a chain run around the largest rear cog and then onto the chain ring + 1" will be enough chain to also thread through the gears. I understand that the smaller cogs take up less chain but you still have to have adequate length of chain to go onto the largest cog and through the gears

I`m obviously missing something

It does work...honest
I followed those instructions to the letter when i built my winter commuter from scratch. Its been running correctly ever since. I know what you mean about it then running through the derailleurs, it doesnt look right at first, but it'll be ok.

 

[Smokin Joe]

Save all that faffing about -

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

 

[Old timer]

It does work...honest
I followed those instructions to the letter when i built my winter commuter from scratch. Its been running correctly ever since. I know what you mean about it then running through the derailleurs, it doesnt look right at first, but it'll be ok.

Right, I know better than any long term tried and tested method

So! I did as the diagram said, waitng for everything to sieze up, just did 5 miles changing gears at will and you are right! it`s works
Now to repair the second puncture in two days( rear this time:-(