Single Speed Conversions: Single Speed Chainset Chainline Adjustment
In order to ensure the chain on your bike is straight you need the chainline on your chainset and your rear sprocket to be the same (to the nearest 1 or 2 mm).
If you are purchasing a new or used chainset for your bike, or are changing your wheel, you may need to make adjustments in order to get the chainline of your chainset correct.
(Not sure what chainline is and why the above matters? See Is My Chainset in the Right Place?)
Here are three options:
1. Change your bottom bracket
Chainsets connect to the bicycle via a bottom bracket, which is a spindle which passes through the bike.
Bottom brackets come in different sizes in terms of how far they stick out of the bike frame. The longer the axle the further out the chainset will be from the centre of the frame.
This means that by fitting a well chosen bottom bracket to your frame you can get the chainline you need on your bike.
Quick Quiz: If you have a 111mm bottom bracket spindle and you want to reduce the chainline by 4mm, what bottom bracket do you need?
Hint: Not 107mm. Every decrease of 1mm of the axle will move the chainset arm 0.5mm towards the bike, and the left crank arm also 0.5mm towards the bike. The change is split in two.
2. Move the Chainring
On some chainsets – those with a spider and chainring construction – the chainring is a detachable component of the chainset which can be removed and re-positioned on the spider, changing the chainline.
There are two things you can do in this vain:
1. Swap the chainring from one side of the spider to the other – from inside to outside or vice versa. Just remove the chainring by undoing the bolts, move the chainring over and retighten bolts.
2. Alternatively you can add spacers to the stack bolts which hold the chainring onto the spider to space the chainring in one direction.
These two techniques can be experimented with to move the chainline within a range of up to a couple of centimetres
A spider, chainring and stack bolts ready to be put together.
The chainring can be bolted on top of (on the outside of) the spider arms - giving a bigger chainline. Or below the arms (inside) for a smaller chainline; probably by about 8mm. Spacers could also be used to move it away from either position
The complete spider crank - we've put the chainring on top, giving the bigger chainline. We haven't added any spacers
The chainring on this Sturmey Archer track chainset is on the 'outside' of the spider, attached by the silver bolts. But we could detach it and refit underneath reducing the chainline by around 12mm.
3. Replace Your Bottom Bracket and Single Speed Chainset
Of course you could also just replace your bottom bracket and chainset. We sell a range of single speed chainsets and can supply a compatible bottom bracket to ensure you get the correct chainline.