Chain Tensioner

[MacB]

Thanks for the help on the frame discussion folks, I'll still be getting a frame but decided to run the new hub gear wheel on my vertical drops bike for now. So this means a chain tensioner, I don't want to take the EBB step yet.

Looking at what's available and the choice is bewildering, though the Surly seems to get good reviews. I have seen mention made of whether the tensioner pushes up, ie wraps more chain round cog, or pushes down limiting chain and cog meshing. The bike I want it for is the Giant CRS Alliance 2008

http://www.giant-bicycles.com/en-GB/bikes/lifestyle/2138/31773/?collections_id=3

Is there any way, other than trial and error, of working out in advance which tensioner would do the best job on this bike?

 

[MartinC]

You need to check how much deflection in the chain you'll need to get the tension right. It needn't be much - the chain only needs to be just too long (1 full link longer than too tight). In this case up or down makes little difference - there should be plenty of chain wrap and tension.

You also need to check that the tensioner you select can match the chain line you've got - if it's low (around 40mm) the jockey wheel may not adjust inwards enough. Assuming you chainline is good (straight) you can measure this at the chainring - distance from the middle of the chain to the seat tube + 1/2 the seat tube diameter. Or you may have the manufacturers figure for the hub (depends which way round you fit the sprocket on a hub gear).

To confuse you even further you can get half links for chains - with one of these you can adjust the chain length to within 1/2" and dispense with the tensioner.

And even further - Shimano make an Alfine chain tensioner that has 2 jockey wheels like a rear mech. Downsides are more inefficiency from 2 wheels and the chain line is fixed (43mm or so IIRC).

 

[mickle]

you cant go wrong with a surly singleator. Writing this on my phone. Its like painting the hall through the letter box!

 

[MacB]

thanks guys, and well done on the phone, I couldn't do it, no patience

 

[e-rider]

+1 for the surly - i've been using one for over a year now with no probs - it is quite noisy though! Not sure if that's normal or whether I have a dodgy one!

 

[andrew_s]

I'd go for the half-link myself.
Chain tension is only really important for fixed. On road, not pedalling at silly RPM, the chain is pretty unlikely to come off in normal riding, and with a freewheel it's only a minor inconvenience if it does. Using a single speed chainring rather than a derailleur one will help.