axle spacing

[young Ed]

so if i take a standard cr*p cheap bike with gears and convert it to single speed with free wheel by replacing chain set and removing rear free wheel and just screwing on a cheap single speed jobbie what happens with axle spacing does it still fit correctly with out the free wheel cog? do i need to make up a custom spacer?
Cheers Ed

 

[Tim Hall]

By axle spacing, do you mean the "over locknut dimension"? This is independent of the the number of cog and is a function of the width of the hub and the spacers fitted to the axle. So if the wheel fits the bike before you swap the freewheel cluster for a single speed, it'll fit after.

What is more important is the chain line, even more so on a fixed wheel than a single speed. Some adjustment can be achieved by judicious use of spacers beneath the sprocket (bottom bracket cups are ideal for this). Often the fixed wheel sprocket is stepped so screwing it on one way round produces a different chainline to screwing it on the other way. Not sure about SS freewheels though.

 

[young Ed]

okay lets talk about chain line then!
I'm guessing if i just fit one of these

and one of these

the chain won't automatically be in line and it will jump off?
Cheers Ed

 

[jazzkat]

okay lets talk about chain line then!
I'm guessing if i just fit one of these

and one of these

the chain won't automatically be in line and it will jump off?
Cheers Ed

The chances are it won't all line up properly
http://sheldonbrown.com/fixed-conversion.html
Probably better with some spacers on your cassette
http://www.velosolo.co.uk/shopsingle.html

 

[young Ed]

spacers aren't an option as i have a screw on free wheel leaving it looking like this when you have removed free wheel with cog cluster

Cheers Ed

 

[Tim Hall]

What length axle does the current Bottom Bracket have? If that's a Stronglight ST55, this article from road.cc has some useful info:

Curiously, Stronglight recommend a bottom bracket length of 119mm- ample for an mtb frameset with snake-stays but 107mm axles are more realistic for an accurate chainline on most fixer/singlespeeds irrespective of whether they are purpose built or road conversion.

 

[Smurfy]

It's easy to measure the chainline from the centre of the seat tube to the centre of the chainring teeth. The chainline at the back isn't too hard to measure either, but you'll probably need to make a few measurements and jot them down on a bit of paper, together with a sketch of how it all fits together. Once you've done that you'll know how much longer or shorter your BB needs to be than it is at the moment to get the alignment right. I'd aim for a misalignment of 2mm or less for single-speed, and 1mm or less for fixed-wheel.