Hey all, so I have a kid due any day now, and am starting to think about hauling a trailer with him/her in it... I have 3 bikes, one new BMC road racer, and two single speeds, one with coaster one with a freewheel and brakes. I am not sure about putting the burley on the BMC, and even though I am in Minnesota, I dont think I want to climb hills with a single speed with a trailer... SO i am looking to convert the bike with brakes to a 6 -7 speed. I would ideally like to have a single front chain ring, and just one bar end for the rear derailleur.

What is the largest cassette you can have in the rear while only having a single chain ring in front?

How is your 7-8 speed set up?

I don't see why you couldn't go all the way up to ten speed- although the higher you go the more you cross the chain. Maybe someone else can explain if that somehow causes problems. I'd probably personally go with 7 speed myself, 8 at the most. how wide are the dropouts? That might have more impact on what you can fit back there.

A guy at the local co-op runs a 1x9. Could probably do a 1x10 if you wanted to.

I run a 1x8. Building a 1x7 for the wife.

I've got a burley solo trailer and I pull my four year old. It's not that much extra work, really. The burley is really nicely balanced and once you're going it tends to stay going. ymmv....of course it's always fun to talk about new gear, and get new gear....don't you really want to a new bike to go with that new trailer? ; )

Sorry. I didn't pay attention to the title. I see you are building a new bike.

I'm guessing that hub spacing is going to be your limiting factor. There isn't really a limit on how low of gears you can put in the rear in relation to your front chainring. However, if you are limited to 7 speeds (which I am guessing that your rear hub spacing will dictate), you won't be able to buy a 36-tooth cassette; I think you can get a 34 tooth in 7 speed, and for sure 32, but am not positive. Honestly, a 36x32 should be plenty for hauling a kid (until they are ready for the tag-along) in a relatively flat area, while giving you a decently high gear at 36x11 or 12.