I need help with a fixed gear I'm planning for a gift. I’m currently cleaning up my fixed gear to give to my step son for a college commuter and would like some advice. Here is what I have:

Schwinn world sport frame conversion with Surly flip-flop rear hub re-spaced to fit the 126mm rear drop outs with a 20t Surly cog and lock ring. The crank is an old Shimano bio-space with a 39t single speed ring. My current setup has a straight chain line.

Here are the questions:

Should I change the gearing? He lives in a less hilly town and is in better shape.
Should I add a freewheel on the other side of the flip-flop hub? I have read that they are not very useful and can be hard to get a good chain line on a flip-flop…

Let me know what you thinks

Thanks
Kevin

Only thing that springs to mind is that he would probably want a bigger gear. The cog is probably fine - I'd just throw on a bigger chainring.

I have a 42t that had the same BCD. Is that big enough? Also he has never riden a fixed gear....

Maybe a bigger gear. I would get a different cog though, unless your surly is an 05 model (Surly cogs have a very narrow thread section and are known for stripping hubs). You can get a Dura Ace cog for about $15.
https://www.sheldonbrown.com/gears/ - this was helpful to figure out gearing.
Personally I like 46x17 in San Francisco. It is a very personal thing though. Your step son will probably be playing with the gearing no matter what is on the bike when he gets it.

About the freewheel. I had one on my bike on the flop side for months. Never used it. Took it off. I sure don't miss it.

Hope this helps!

The exact gear ratio will vary a bit depending on whether it has 700c or 27" wheels. Use Sheldon's gear calc and aim for something in the 65" to 72" range. It may take him a little while to get into it, but it's really not a hard gear to push and a few weeks of riding or so should recondition most reasonably fit folks.

As for ring or cog, well that's really up to you.

Oh, and no freewheel. It's just not worth it. The only time I've even wanted a different gear is on my mountain bike. I ride many miles to the trailhead and a higher road gear would be nice. Actually up until just tonight I had the worst of both worlds--A gear that I felt was too slow on the road and too tall for climbing...kinda sucked. Now at least I have the magical 2.0 gear ratio. In the spring I build up a flipflop and throw on a smaller track cog for good road speed.

He's probably going to want 52x20 if there aren't any significant hills around. A 52t ring should be easy to find. It's about equiv. to 42x16 if a new cog is cheaper. In flat, flat Chicago 52x20 is too spinny, but it should be okay if there are rolling hills.

Mind you this all depends on him as a rider. But I am not particularly strong and ride 44x16 on the flats.

forget the free wheel.

So it is a Biopace crankset with a normal circular chainring right? I am asking because I have the opportunity to get a nexus biopace crankset but thought it would be a bad idea.

The nexus biopace cranset is normal mtb bolt diameter. Chainrings are interchangable. I have mint steel biopace rings if anybody wants.

I'll hold out for cherry.

Yes, biospace 165mm crank with a new round chain ring.

Thanks for all the in put. Looks like I'm going send as is along with a new ring and cog(instead of buying a freewheel) to change after he gets use to the fixed gear idea...

I think a 20T cog is "huge"- the 39 chain ring is fine if you have the right cog, although it appears some people might be a bit insecure about running a smaller ring in front, but since you already have a 42, I'd put it on.

A 39X14 actually gives a plenty steep ratio (steeper than the 46X17), but a 42X 16 might fit all occasions.

Frankly, a nice setup is to have both a 14 and 16 and a 39 and 42 and mix and match according to mood.

I adapted a biopace crank for a single speed and found I had to grind away at it a little bit to get a regular chainring to sit right. But maybe there's some crucial detail I was missing...