Gear ratio

pete236uk

I have a on fixed my riding is not to hilly but mostly rural with some town work I would like to use this as training etc any suggestions on gear front and rear I think the back is 19 and front 50 but will double check
any help

mushi123

I use 48/18 (commuting in London 10 miles each way) and I have a hill to climb at the end of my commute. If you really wanna fly maybe get a 48/15.

NorwegianBlue

What tyre size are you using?

I remember an increasingly heated pub discussion over gearing, where it became apparent after about half an hour that one rider was running Spesh Fatboys (1.25" MTB slicks) and the other was running 700x28c Contis. So for the same ring/sprocket ratio the latter's gear was about 9% higher than the former's. Since the argument had been along the lines of: "You can't possibly pull 48/16 up that hill!" "Yes I can you must be soft." It was kind of important that one rider was talking about a gear of the order of 73 inches and the other about 80 inches.

The classic "medium gear" of 72 inches is a good place to start depending on the terrain. On a 700x23c tyre this is 49/18.

Greenbank

46x17 on 700x25c is 71.4"

NorwegianBlue

There's somebody who uses Sheldon Brown's gear calculator...

Greenbank

It just so happens to be what I have on my fixed.

AndyGates

50:19 is what I ride generally, a nice comfy 68-69".

NorwegianBlue

I ride 42/16 which equates to 68-69 inches. It's pretty hilly up here in the foot hills of the headlands and it's a bit much in places, any lower though and the downhills would be murder.

I chose the 42 tooth ring because my chainset gave me the choice of a 42 or a 52. With the chainline right the 52 tooth ring would have fouled the chainstay.

One supposed benefit of running a smaller ring and sprocket and therefore less chain is lower weight. Personally I can't see it, but a friend of mine who used to ride fixed time trial used to insist on starting with a 12 tooth sprocket and working from there to keep the weight down as much as possible. Given that he would run a 46 tooth or larger chain ring I think his legs were somewhat stronger than mine!

bobajobrob

NorwegianBlue wrote:

One supposed benefit of running a smaller ring and sprocket and therefore less chain is lower weight. Personally I can't see it, but a friend of mine who used to ride fixed time trial used to insist on starting with a 12 tooth sprocket and working from there to keep the weight down as much as possible

...and the flipside of that is that a larger sprocket/chainring should give more wear. Another thing is aesthetics, larger chainwheels look better on larger frames, and vice-versa. I ride 48x18 (about 70"), which I gather is very common for general purpose use. I have a 20t freewheel on the other side for hilly rides and off-road.

NorwegianBlue

Back in the day when variable gears weren't allowed in the TDF it was common to run a fixed on one side and a freewheel on the other. Fixed for going up the hills and freewheel for comming down. Of course we don't have anything quite like le col du Galibier here in the Pennines.