I have a pompino and run it SS and fixed occasionally, on the road. In order to try and get a bit more off-roady I want to drop the gear ratio down a little.
If I fix 2 sprockets onto the hub, I’m happy to manually drop the chain off and swap it over when I want to change – wont happen very often, and should only take a couple of mins anyway.
Does anyone know what size change in sprocket teeth number the track end can accommodate whilst keeping the chain the same length?

I was thinking along the lines of 42t front and a 16 / 19t rear which would give me about 70 and 60 gear inches respectively.
What does this equate to in terms of the (effective) chainstay length? Is there a (easy!) way of calculating it?

my pompino easily does 42:16/18 on a flip flop hub.

you might need to play with a half link so that 16 is all the way back and 19 is all the way forward.

the bigger your tyres the less adjustment you will have.

HTH.

good point about the tyres. the 19t would be used with cross tyres, so that may limit it.
i have some 38’s in there and the wheel needs to be most of the way back. hmmmm…..might have to have a bit of a play with it and see what fits

Why not dinglespeed it?

2 rings on the front. Just keep the sum of the front and rear cogs the same eg 48/16 = 64 and 42/22 = 64 or any other combination that suited you.

Why not dinglespeed it?

cos i wanna keep it simple and cheap (ie what i have in the shed) and i think that 3t difference will be enough. The only problem could be the tyre clearance.

2 rings on the front. Just keep the sum of the front and rear cogs the same eg 48/16 = 64 and 42/22 = 64 or any other combination that suited you.

is it that simple ? thought pi was involved in it ?

To go from 42-16 to 42-19 you have to slide your wheel in 8.87mm (roughly)

i have an old spreadsheet.. can email it if you like

jono

trail_rat – Member
…is it that simple ? thought pi was involved in it ?

It’s close enough.

Pi is for when you come in from a good ride + beer. 🙂

or just put two sram links in your chain so you can remove the link or two extra?

I have two chainrings on my alfined bike and do this occasionaly – when I want to drop the gear for use in snow

thanks jono, that sounds like plenty of room, I’ll have a bit of a play with it.
TJ, that was my other thought and probably the next “least hassle / cost” solution if i dont get even room with the same chain length.