I have a single speed bike with track dropouts. I am thinking about getting an additional freewheel that is 2 teeth bigger than what I currently have. I sometimes switch freewheels and would prefer not to switch chains if at all possible. If I get a freewheel that is 2 teeth larger than what I have now then how much closer would it move the axles to the beginning of the dropouts? Thanks

1/2"

It is common to have a flip flop hub with sprockets 2 teeth different.

As the chain goes along the top and also along the bottom, a change of sprocket by 2 teeth equates to moving the axle by the length of one chain link. If the chain is the right length, then you can swap between sprockets easily if the difference is 2 teeth.

2 teeth doesn't sound much, but as a percentage, the difference between say 16 and 18 is about 1/8 or 1/9 (12.5% or 11.1%) which you will notice.

I believe it will move 1/4”. The chain path around the freewheel will only get one tooth longer (1/2”) and the difference is made up by shifting both the parts above and below by 1/4”.

Another way I look at it is that changing a total of four teeth is equivalent to adding a complete 1” inner plus outer link of chain, which causes an axle shift of 1/2”. So changing two teeth causes an axle shift of 1/4”.

Otto

I ride with 16t on the drive side and 19t on the non drive side (both Freewheels) and I don’t need a different chain when I flip to 19t. With the 16t my axle sets in the middle of dropout. With the 19t the axle sets towards inside of the dropouts with enough room to push forward so I can remove the chain. You should be fine.

Be aware that even if the chain can accommodate the new cog, with rim brakes you'll have to adjust your pads if the axle changes position a lot. I used to run two FW sizes so I could flip the wheel, but I never once bothered to actually do it.

This is definitely something to watch for. The pads of rim brakes mounted on a seat stay bridge are usually pretty close to parallel to a semi-horizontal dropout, so the change may be slight, but it’s worth checking.

I can run 42/16 in two places on my Schwinn’s dropouts and I use the rearward option because it reduces the needed brake reach just slightly and helps provide more pad clearance from the rear tire.

OTOH, the pads of a chainstay mounted U-brake will be perpendicular to the dropout , so they will shift on the rim about the same amount as your change in axle position. That could cause the pads to rub the tire if you shift the axle back too far.

Otto

I have run 17T/19T or 16T/18T combinations on flip-flop hubs for many years with no problems, including the brake pads still lining up and being functional - and that's with the stylish but stupid-for-the-road rear-opening track ends. If I had been wiser and had spec'ed standard forward-facing, slightly-slanted "horizontal" dropouts instead, I'd probably be able to go more than just two or three teeth difference, but hindsight, you know?

OTOH, you might have found that slanted, front-facing dropouts create more problems for brake pad alignment, since the axle (and rim height) rises or falls in correspondence with the slant, in addition to shifting fore or aft.

I believe the semi-horizontal dropouts are more nearly perpendicular to the seat stays than true horizontal dropouts and will thus create less change in rim brake pad alignment at the braking location as the axle location is changed.

Otto

Otto said it better than I can - but this is my experience. This is, if memory serves, the whole reason such dropouts are at this angle, to permit manual gear changes like this a la the TdF before derailleurs were permitted, and probably a whole host of British riders in the 30s-50s.

Hey, you're right -- nice!

Thanks for the responses. Does anybody who rides a singlespeed bike swap out chainrings to get different gear ratios? Is this less than a hassle of swapping freewheels? Would this allow me to get even more gear ratios while riding with the same chain?

You can probably find a chain length to work. My fixed gear has a 15 on one side and a 17 on the other. I haven't had to deal with rim brakes for awhile, but I seem to remember setting the pads for the smaller cog and they were good enough with the bigger cog.

Also, I'll be replacing my worn KMC Z610 chain with a new Z610 chain. When I replace my singlespeed chainring due to wear can I get a multi-speed chainring or will I need a chainring that is only compatible with 3/32 inch chains? Thanks

I think swapping freewheels is less of a hassle than swapping chainrings, but you can do either or both. Or neither. While the idea of changing gear ratios sounds good, I never bother to actually do it. To me, part of the appeal of singlespeed is "set it and forget it."