Gearing on a fixie/single speed

[rb58]

I probably should know this, but I don't! And if I had a logical mind I could probably work it out, but I don't!

If a single speed bike has 48 chain ring and a 16T freewheel, does that represent the same gearing as when running on a 48 chain ring, and 16 rear sprocket on a bike with 'normal' derailler type gears?

Thanks

 

[raindog]

yes

 

[wheres_my_beard]

yes

+1 (somethings) The ratios stay the same (3:1), as are 36/12, 39/13, 42/14 45/15

Is that the ratio you plan to ride?

 

[Zoiders]

From a dead start - yes.

Once it's up and running at a good cadence though the flywheel effect starts so the effort needed to keep it spinning will seem easier at times.

I wouldn't be recommending 48x16 for a toe in the water for fixed, sure you see some stupidly large gear inches on the likes of Fixed Gear Gallery that people claim to ride brake-less but they tend to get pushed to the coffee shop a lot instead of actually being ridden.

 

[DrSquirrel]

I reckon 48x16 (39x13 in my case) @ 79.5inches is pretty good for mostly country roads with a bit of town work. Personally I wouldn't want to be messing around in town with that, although anything lower with hills will suck for descending.

 

[rb58]

Thanks. What ratio would you recommend as a starter? I'm more of a spinner than a grinder normally.
Cheers

 

[DrSquirrel]

What sort of terrain are we talking about? A lot of town work etc?

Too low, you will end up spinning... which you might like, but going down a hill the cadence isn't as nice as if you were doing the same on the flat. And too high you'll have to put a lot of power in to get moving.

Get whatever is on the bike, and work from there? As a start, 39x15/42x16 (68-69inches) would be fine, though that is 96rpm @ 20mph, 145rpm @ 30mph

http://www.machars.net/bikecalc.htm

 

[fossyant]

For a beginner - maybe 70" - depends upon your general fitness. I have 70" and 74" (fixed fixed hub) - spend first week or so on 70" then went 74". Upped to 77" after two years - only because I wanted a new spangly Chain Ring. My commute is OK, although the 77" is hard work on the last mile home - 8% hill. That said, fixed are OK going up, much better than you would think. Flat commutes you could use bigger.

77" gives me a good 25 mph on the flat at 110-115 rpm (my most efficient power vs rpm), and about 33 downhill without spinning out/setting my pants on fire ! 74" I was blowing at 25 on the flat at 125 plus RPM..

 

[brockers]

Thanks. What ratio would you recommend as a starter? I'm more of a spinner than a grinder normally.
Cheers

I'd say if you're moderately conditioned you'd be fine on 42x16 around Bexley (I think that's the London courier's weapon of choice), but there's no shame in going lower. Seem to remember reading that many fixed Audaxers choose 42x17 but then they're logging 100 miles plus. It's horses for courses really.

See what gear you're in on the steepest hill you'll encounter (on your geared bike) and go from there. That said, I put 42x18 on my fixed just so I can grind up Star Hill (at the bottom of Poll Hill near Otford if you know it). On my geared bike though, I find I need at least 34x21 to get up it ! So you tend to force yourself up hills in a bigger gear than normal because you've got no choice. Not particularly good for your knees in the long term though.

 

[Deleted member 1258]

Thanks. What ratio would you recommend as a starter? I'm more of a spinner than a grinder normally.
Cheers

I'm running 46 x 18 on 165 cranks, gives me about a 68 inch gear, I use Sheldon Browns Rabbit gear calculator for checking gearing.
http://software.bareknucklebrigade.com/rabbit.applet.html
If you are just starting out with fixed a gear in the 68 to 72 inch range usually makes a good starting point, once you've put in a few miles you'll have a better idea what gear you want.