I’m just in the process of singlespeeding my Cotic Escapade, built around a 39T 170mm Alfine crank and 37c tyres on 29er / 700 rims. I was thinking of a 16T rear cog, but also have 18T and 20T cogs lying around.

My commute is just over 7 miles each way, with a gradual uphill profile (one way of course!).

Any real world experiences to help me decide which cog to fit tonight? 😀

Fit the one that most suits your fitness and the terrain you will be riding.
Oh,and your bit of string is a different length to mine 😉

exactly, try the 16 and if that doesn’t work for you, try something else like the 18 or the 20 you have, or buy something else
also don’t forget to figure in raging headwinds

there is no correct answer here, it depends on you, the bike, the luggage and the terrain.

try the 16 (I think this may be a little be too easy) and experiment either way until you’re happy.

Leave the cassette and mech on and ride using a single gear both ways.

Then go up/down until you find the one that is best, use it.

Just hope for no wind on the uphill bit.

The most expensive bit is going to be the front sprocket, rear ones can be had for very little money. If you are not sure I would start with bigger rear sprockets and work down as it is easier to remove a chainlink than to add one if the frame does not allow enough adjustment to tension the different sizes.

Other than that it really does depend on too many things. Wind, tyre choice, how much you are carrying, how much you want to cruise and how much you want to race, hills, traffic lights.

I would run a bigger gear for cruising but I get stopped by lights a lot going through the centre of town. So I run a slightly smaller gear to let me pull away more easily.

I find it better to be spinning wishing I could go faster than barely able to turn the pedals uphill into a headwind after a long day.

48:18 28c

through a little playing around on an old cassette and the original 52t, i found the gear i could “only-just-massive-lots-swearing-dying” get up the hill. then translated that into a new chainring and suitable freewheel

I ride fixed (hipster what!) around 15 miles each way into London. About 500ft of climbing each way, and I run a 48/18. I wouldn’t want it any bigger but a 39/16 would do my head in. From memory my current gearing at 92 rpm puts me at about 19 mph. I say from memory as I’m normally too busy keeping an eye out for dickhead bus drivers to look at the Garmin.

I would start with the 18T and if it’s too easy go 16T and if it’s too hard go for the 20T. I am on 46/18 (68.4 gear inches) on my Genesis Flyer and it’s slightly under geared for my fairly flat commute.

50:20, 28c here for 13 miles along the north downs. It’s enough that I can get up onto the ridge in the first two miles before my legs have warmed up, but it’s getting close some mornings

Only you will really know your location and what it feels like to ride that.
39/16 on my SS road bike which may be undergeared but I built it for coming back from the pub. My flattest route around here is only 1000ft climbing in 28 mile loop so it should be fine for spinning up that.
I may change the rear to a 15 or 14. Time will tell.
SS MTB is 32/18 for winter.

I would start with the 16t as 39 / 16 is around 66 gear inches which I find ideal for road use but that is lower than a lot of people use. The 18 would be very low and the 20 would be silly (lower than I use off road in winter)

I’ve got 42/16 easy very going but very hard home. Depends on your fitness/route

Fab advice – I’ll fit the 39/16 and report back…

My commute is uphill on the way there and downhill on the way back at least!

I’m rocking a 42:16 which is a tad under-geared on the flat, but doable on Devon hills.

48:18 here for London commuting. This leaves me c 18-20mph cruising speed.

I do think it depends slightly on the set up of your bike as well as your strength and terrain. To accelerate from the lights at 48:18 means being reasonably aggressive so maybe something like the Escapade with it’s tall headtube may require a gear that’s not so difficult to get on top of.

You’ll love ss for commuting – no worries about changing down gear before the lights and junctions and you can keep an eye fully on where you’re going instead of having to think about what gear you’re in.

I’ve commuted on my SS mtb (26″) in the past, 32-16 just gets me up the 800′ 3 mile 17 percent in places main climb. The next 12 miles is mostly gentle downhill and unpleasantly spinny.
I think I’ll stick with the geared bike.

Tried it this morning on my (uphill) commute – and 39:16 was perfect!

I expected to be a bit more under-geared, but it was just right overall. I ride singlespeed (currently 30:18 on my 27.5 hardtail) during the winter, so I’ve not had to adjust much otherwise in terms of riding style.

My cruising speed on my morning / uphill commute is in the 11-16mph range, so I’ll see this evening how I do on the downhill.

Now all I have to do is build up my lightweight (geared) roadie that I’ve been collecting parts for in the last few weeks for good weather days… 🙂

interesting to hear what it’s like on the way back.
I do a 12 mile commute with 1000ft of climbing on a 39:15 fixed gear. It’s too spinny but I wanted to work on my cadence on the flats and be able to do the hills without gurning. I’m going to change the front for a 42 (just because I have one already) and see if that’s a bit less spinny – doing 140rpm downhill in traffic with one brake in the wet is a bit sketchy…

You could always add a rear brake…

A little under-geared on the way back (on the straights), but overall fine. I do live in Bristol: city of hills; so even the downhill has some uphill!!