Sorry for the cumbersome title. Before I buy cogs, just looking to see what the max difference I can expect to be able to run with two different cogs in track ends. With the small cog, the wheel would be toward the back, and with the large, toward the front, but there's obviously a limit on the differential. I'm hoping to get away with maybe 4 teeth.

I dont see any Measurements , Do some.

I cannot measure Your Frame for you , the radius Of the cog can be calculated based on a chain's 1/2" Pitch.

Yeah, I'm traveling right now, doing some idle speculation in a hotel room. So no measuring right now. Instead, I pass my time on BF before I catch the shuttle to the airport.

Here's the thought:
Pugsley frame.
32t crank.
Two rear wheels. One 18t, one 22t.

Unless you bike has very short track ends - 4T difference should be fine. What frame do you have?

Yes, it will work on Pug. I don't have Pug but I have Moonie, KM, Krampus and 1x1, they all can handle 4T difference with 32 in front

I get a roughly 8mm difference in the radius.

I suppose the other concern is that on the large cog, the wheel would need to be so far forward that wheel installation might be a real bear. Not a lot of wiggle room to get the chain around the cog if it's at the forward limit.

This is easy math you can do yourself.

Every tooth = 1/2" of sprocket circumference.
the chain only wraps 1/2 way around so it calls for 1/4" of chain
that 1/4" is divide equally between the upper and lower loops so it's only 1/8"

So, for every tooth added or subtracted, your axle will move 1/8".

Measure the usable length of your dropout, figure 1/8" per tooth, and you'll know your usable range without changing the chain.

Each tooth added or subtracted will move the axle 1/8 inch. So four teeth would move the axle 1/2 inch (~12.7mm). That's not very much at all. If I recall correctly most track ends are around 30-35mm deep.

This is no help to the OP but I had a fx gear frame made with an long "L" shaped rear dropout, not a track end. The slot is closed in back and runs forward and slightly down, then opens at the front down. This enables the wheel to be located anywhere along the slot so I can (and do) run cogs from 12 teeth to 23 teeth without messing with the chain. (A 24 would work but I Have yet to find one.)

I am a road fix gear rider and I have zero use for track ends. Road chains get dirty. Road dropouts make it far easier to pull and flip the wheel and doing it keeping one's hands clean is child's play. (Not an issue at a velodrome. They are near hospital sanitation clean. So are the chains on the bikes.)

The bike that inspired this bike was a Reynolds 501 sport Peugeot. A blast to ride fixed but the horizontal drop was so short I could just barely get a 2 tooth cog difference and 1/2 links were required to get the chain length just right to do that.

"L" shaped dropouts angled 11 degrees (a compromise between rim brake track angle and horizontal to not affect BB height that allows the brake shoe to stay on a semi deep Velocity Aero rim) are cool. I highly recommend them!

Ben

Back when there were cog boards for Freewheels ,
Shimano made a plastic gage to count the teeth by the scale of diameter change with every tooth , rather than counting them.

Me too. Also nicer for fenders. Getting real hard to find new bikes with horizontal dropouts though.

it is not that hard - loosen the bolts or nuts (whatever you have), chain should be lose just enough to get it off the chainring. Now that it is off the chainring - easy to take the wheel out or slip the chain on another cog.
Forgot to mention - frame size and corresponding chainstay length may affect how far your wheel needs to be. I had no problems with 4t difference on Moonlander and Krampus size Small, KM and 1x1 size Medium and on 1x1 size small.
I don't recall if different size Pugs have different chainstay length and what is the difference with my frames. But it almost certainly will work

Wheel removal on the Pugs would be a LOT nicer with horizontal drops than it is with track ends. I get a lot of chain grime on my fingers.

There are a few tricks that make it possible to remove and replace track wheels without getting your hands dirty.

The easiest is to pack a small rag or piece of paper with which to pick up the chain. Of you can even pack a latex or nitrile glove. Or you can scrounge a leaf or twig to use.

I don't bother. I use bolt on track wheels, so I have a wrench which is easy enough to use to pick and place the chain. Otherwise, it's easy enough to slacken the chain, hold up the rear triangle, and tilt the bike while turning the cranks to either drop or pick up the chain.

That last is a nice trick indeed! Any good tricks for getting the chain back on if there's limited room?

Limited room how. When setting up a track bike, you need to make sure the rear wheel can slide forward about 1/4" minimum so the chain can be derailed. I prefer more room to work, so my bikes usually have 1/2" or more to move forward, so I've never had any issues changing wheels easily.

Also, whether by design or accident, the rear wheel can spin freely when fully forward in the slot, so if I hold the bike vertical, resting on a "tripod" of the turned front wheel and handlebar, it's very easy to spin the chain onto or off the chainring.

BTW - I might add that I'm impressed by the various issues and workarounds that many fixie riders seem to deal with. BITD when we weren't so bright, we simply pulled our wheels back, tightened them, them rode without worry until a flat or need to change a sprocket made us remove them. Wheel slippage wasn't anything we dealt with because it simply didn't happen.

Just a follow up to this thread. It totally works. Almost the outside limit of tooth difference, but it does work.

I only clicked on this thread because it said 'dinglespeed,' which is hilarious. As you were, everyone.

-Jeremy