I'm trying to decide what gear ratio to use for my conversion.
Here is the question; standard riding by myself i'm thinking 15t but when I put my sons attached bike on I'm thinking 17t (or more).
I'm using my wifes wheels off here bike (she got made that I got another bike so I took her wheels) and taking the sprocket off and picking the gear of choice but I use this bike for 2 totally different riding styles.

Has anyone ever used two gears in the back?

Will it cause a chain issue or something else?

Thank you

If you have enough room in the dropouts it should be fine.

Any dropout should have plenty of room. Size your chain to the larger cog and you should be able to have a 4 tooth difference, even with a compact dropout.

If you don't want to steal your wife's wheel you can run 2 different freewheels on a standard flip/flop hub [as opposed to running a fixed cog and a freewheel or 2 fixed cogs]. This would allow you to keep a straighter chainline.

You can run a single chainring up front with a Surly Dingle in the back and the chainline isn't off by much.

Or run a double up front and the Dingle in the back and have two perfect chainlines and two not so perfect chainlines.

Couple things- Don't ride a fixed gear with a kid in tow, thats putting him at risk. If you are planning on freewheeling on a single speed then I dont recommend a 15 tooth freewheel-there is only 1 brand made and it sucks hard.

Here is what I do for a situation similar to yours:

Run a flip flop hub- freewheel both sides-or at least the side you will ride with your son on
Use a 16 tooth for yourself, use an 18 tooth with him in tow

run a double crank- Pick a chainring that works for your 16 tooth for the outside chainring, and get one that is 2 teeth smaller for the inside.

My frame is a single speed cross frame that I ride road in a higher gear ratio and off road in a lower ration. At long as you have the same number of teeth on both drive setups your chain can be 1 length. If you want to run 1 chainring you will need a chain tensioner unless you have really long dropouts/track ends.

If the difference is only 2 teeth he shouldn't need a tensioner. I run 16/18 free/fixed with one chain and the difference is less that 1/2" of travel in the dropouts.

Seconding this, my singlespeed with the old surly sub-11 dropouts has no problem dealing with a 5-tooth difference in back.

If he has adequate brakes there's nothing more dangerous about pulling a kid with fixed than SS.

I loled so hard

I run a double/double (road crankset/2 cog FW)


Since you stole a wheel that almost certianly means it was a cassette wheel, so you can run any two cogs you want.

My option, keep ONE of your front chainwheels (either the 52 or 42/39) and match it with a rear cog you want to cruise on on your own. Then find the gear your like to pull you kiddo in. Once you find that, figure out the gear inches using Sheldon's calculator. Then try to find the right front chainring and rear cog that will match the tooth differences from your ride-alone gear.

E.g.
Your preferred ride-alone gear is a 48/16
You want to get an easier gear for your pull-the-kiddo setup, so you can run a 47/17, 46/18, 45/19, 44/20

If you match the tooth differences, your chain can be the same length which means you may not need a tensioner, and it makes everything easier.

I run a 48/45 front 16/19 rear setup and it works PERFECTLY. Hope that makes sense. The 3 tooth difference is very noticable. Hopefully you have a 130 or 110 BCD crank so rings will be easier to find.

Here's another interesting option: https://forums.mtbr.com/showthread.php?t=399610 You could actually do it without a front derailer if you just grab the chain and put it on whatever ring you want before the ride.