Extending rear dropouts

[zigzag]

my single speed aluminium city bike has semi horizontal rear dropouts and i would like to extend them (the slots) rearwards by about 3mm which would give me enough room for tension adjustment as the chain wears (currently there's a gap of about 1mm until the end of the slot, with a new chain). i wonder what is the best technique to do that, bearing in mind that a small error at the dropout can translate into large misalignment at the top of the wheel. an option of removing one chain link doesn't suit as it puts the wheel at the front of the dropout and does not give sufficient mudguard clearance. i'd like to keep the gearing as is. tips and ideas welcome.

[Ian H]

You can still get half-links - https://www.sjscycles.co.uk/chains/jtek-chain-half-link-332-inch-each/

I'd be wary of filing any substantial amount of metal from a drop-out slot, especially aluminium.

[LittleWheelsandBig]

You may be able to find a chainring/cog combination that maintains the same gear ratio as currently but moves the rear axle forward a few millimetres.
https://eehouse.org/fixin/fixmeup

[zigzag]

thanks for the advice. half link would work, but it is a bit of a bodge and adds some extra faff with every chain replacement (which may be once a year, but still). i have played around with the eehouse tool, the only viable option i see is 44x17, which would move the axle ~1cm forward and lower the gearing by one gear inch. currently with 42x16 the rear axle is at 43.5cm, measured from bb. i'll see when i get round to addressing this (non)problem.

[sam]

Lowering the gearing by only one gear inch sounds like a lucky break! With my newest bestest bike requiring a magic gear, and similarly unenthused about half links, I found myself dropping down to just under 65", from a long time regular of closer to 70 (though one of my bikes was also 44x17, or about 68). I was a little worried, but it actually worked out fine thanks to all the hills I have to deal with, and not enough long level straights to be bothered about a bit of extra spinning freewheeling.