# what sized chain ring and sprocket?



## jonny jeez (8 Dec 2015)

Hi guys. I ride a few bikes,mostly a 9speed Shimano and a single speed from trek (district)

I adore both but want something in-between.

The Shimano is fast but a bit fragile for winter rides...the district is tough as old boots but a little slow for the speedy sections of a commute...and a bit pretty for winter...more of a summer city cruiser.

So, I plan to pick up a cheap hack from foffa or BLB but want something harder to climb and something that wont spin out at 20-23mph. The district spins out at 16-18mph.

I don't understand gearing...any suggestions on chain ring and sprocket sizes?


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## GGJ (8 Dec 2015)

What gearing is on your single speed?


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## midliferider (8 Dec 2015)

In very simple terms, devide the number of cogs in the front by the number in the rear. Lower the number, easier to climb hills.
Example:
Front 32, rear 32 = 1
Front 40 rear 20 = 2
gear ratio of one is easier to climb than 2.
But lower the ratio, slower the speed and you are spinning fast with slow movement on flat.
Does that make sense?


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## dave r (9 Dec 2015)

Gearing is an individual thing, whats suits one may not suit another, 46 x 18 67 inch gear and 48 x 18 70 inch gear are both good gear combinations to use as a starting point, ride the gear and see how it feels and if you feel you need to change it change it up or down as required.

http://cycleseven.org/bicycle-gear-inch-calculator


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## 3narf (9 Dec 2015)

Your single gear is always going to be a compromise. It's not possible to get a gear that you won't spin out on occasion, which you'll still be able to shunt up any kind of hill. 

There are people on here who advocate 52x16, for instance. I don't know how fit or strong you are, but I do a lot of single speed cycling and to put it mildly, I'd struggle with that.

Best to find the sweet spot that will give you good acceleration at the speeds where you spend most of your time. It's very subjective; I love 46x17.


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## raleighnut (9 Dec 2015)

http://www.sheldonbrown.com/gears/

If you use this but swap to MPH at RPM it should give you an idea of what to use.


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## al-fresco (9 Dec 2015)

I'm a geriatric living on the Welsh border and I find 42 front, 16 rear to be a good compromise for the local hills and plains.


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## totallyfixed (9 Dec 2015)

52x16? Yes, right, jolly good. Presumably it is pan flat and the wind never blows. Only ever ridden socially with one other who was riding a big gear and he was walking up the hills, seemed a bit pointless.


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## midliferider (9 Dec 2015)

al-fresco said:


> I'm a geriatric living on the Welsh border and I find 42 front, 16 rear to be a good compromise for the local hills and plains.



42, 16 on hills.
Either you are superfit or your defintion of hills and mine is totally different.


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## 3narf (9 Dec 2015)

midliferider said:


> 42, 16 on hills.
> Either you are superfit or your defintion of hills and mine is totally different.



I wouldn't have thought 42 x 16 to be too outrageous as a compromise for hilly roads...


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## derrick (9 Dec 2015)

I ride 48 x 14 round N London way not to many hills some can be a bit hard, but i still spin out going downhill, I think it's a case of trial and error, You can pick up cheap fixie cogs so not really a problem, And as long as you have horizontal drop outs you will not have to many problems with chain length, A good start point would be 48 x16 then go from there.


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## al-fresco (9 Dec 2015)

midliferider said:


> 42, 16 on hills.
> Either you are superfit or your defintion of hills and mine is totally different.



It always amazes me what you can do when changing down isn't an option! I find I can cope with 1 in 7 (about 14%?) for brief periods and a shelving climb over 2 or 3 miles is part of my normal ride to the pub. If I'm plunging into darkest Wales I'll use a geared bike.


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## totallyfixed (9 Dec 2015)

Yes, it is amazing what you can do, up to a point. Comparing what different folk ride on t'internet is a bit like the age old piece of string question. Much more interesting to meet up and ride together in the real world.


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## Milkfloat (9 Dec 2015)

First dibs on the District now that you have decided it is unsuitable.


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## jonny jeez (9 Dec 2015)

3narf said:


> Your single gear is always going to be a compromise. It's not possible to get a gear that you won't spin out on occasion, which you'll still be able to shunt up any kind of hill.
> 
> There are people on here who advocate 52x16, for instance. I don't know how fit or strong you are, but I do a lot of single speed cycling and to put it mildly, I'd struggle with that.
> 
> Best to find the sweet spot that will give you good acceleration at the speeds where you spend most of your time. It's very subjective; I love 46x17.



Okay so this might suit me as I am pretty strong and manage hills in a pretty high gear...small hills that is.


GGJ said:


> What gearing is on your single speed?


I've no idea I afraid



midliferider said:


> In very simple terms, devide the number of cogs in the front by the number in the rear. Lower the number, easier to climb hills.
> Example:
> Front 32, rear 32 = 1
> Front 40 rear 20 = 2
> ...



So do I need a a 40 20 to cruise at 20mph without spinning out?


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## jonny jeez (9 Dec 2015)

derrick said:


> I ride 48 x 14 round N London way not to many hills some can be a bit hard, but i still spin out going downhill, I think it's a case of trial and error, You can pick up cheap fixie cogs so not really a problem, And as long as you have horizontal drop outs you will not have to many problems with chain length, A good start point would be 48 x16 then go from there.


Good point


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## jonny jeez (9 Dec 2015)

raleighnut said:


> http://www.sheldonbrown.com/gears/
> 
> If you use this but swap to MPH at RPM it should give you an idea of what to use.


Now that is what i was looking for, just to get a good start...thanks


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## totallyfixed (9 Dec 2015)

jonny jeez said:


> Okay so this might suit me as I am pretty strong and manage hills in a pretty high gear...small hills that is.
> 
> I've no idea I afraid
> 
> ...


Without wishing to complicate things, everyone has different maximum cadences.


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## jonny jeez (9 Dec 2015)

totallyfixed said:


> Without wishing to complicate things, everyone has different maximum cadences.


This is very true and I guess my comfy cadence is around 70 with a max of 90ish...before I feel like I am bobbing out the saddle (never actually measured my max cadence but I know what I am happy cruising at so have just added a bit here) I know we are supposed to ride at around 85-90 but I tend not to and select a higher gear...generally

I suppose I am looking for a ratio that allows me to reach 21mph with a cadence of 90rpn...on normal sized rims


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## totallyfixed (9 Dec 2015)

This is where riding fixed is a little different, your maximum cadence rises with experience, having short legs and short cranks helps a bit too, which I don't.


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## dave r (9 Dec 2015)

totallyfixed said:


> This is where riding fixed is a little different, your maximum cadence rises with experience, having short legs and short cranks helps a bit too, which I don't.


Its strange how it can work, I'm vertically challenged and always descend better on short cranks. I'm running fixed, a Genesis Flyer, on a 46x18 and 170 cranks and run at 19-20 mph on the flat at about 100rpm cadence and start to get uncomfortable descending above 30mph.


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## Texan (9 Dec 2015)

i am also vertically stunted but need to post this as i need 5 posts to buy some goodies,hope you don't mind

*Mod note:* I hope you realise that's cheating! Just as well I've got a sense of humour....


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## raleighnut (9 Dec 2015)

Texan said:


> i am also vertically stunted but need to post this as i need 5 posts to buy some goodies,hope you don't mind
> 
> *Mod note:* I hope you realise that's cheating! Just as well I've got a sense of humour....


Nip onto SC&P and post nobber a few times in different threads, should be easy.


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## 3narf (10 Dec 2015)

jonny jeez said:


> This is very true and I guess my comfy cadence is around 70 with a max of 90ish...before I feel like I am bobbing out the saddle (never actually measured my max cadence but I know what I am happy cruising at so have just added a bit here) I know we are supposed to ride at around 85-90 but I tend not to and select a higher gear...generally
> 
> I suppose I am looking for a ratio that allows me to reach 21mph with a cadence of 90rpn...on normal sized rims



If you _ are _ bobbing up and down, your saddle might be a bit low...


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## ayceejay (10 Dec 2015)

Another question - are we talking about a single speed freewheel or a fixed wheel. If single the downhill won't be a problem so select a ratio for the flat and uphill. the problem is that freewheels are not so readily available as fixed cogs.


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## ozboz (23 Dec 2015)

When I get my old 28' frame up and running it is my intention to use this as a single speed , I was wondering the same for me , on my road bike I can comfortably ride on the big ring and mid on the rear , in a reply earlier it was said if you have no option to change then somehow you will manage , I will go with that at first , it will be a heavy bike by today's standards so I will have to compensate for that in some way


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## zigzag (26 Dec 2015)

i would suggest using big ring up front and then select the rear cog/freewheel accordingly. this way you will have more options if you want to have a higher gear, also big chainring feels a bit smoother and the chains last longer (but the whole setup adds a bit of weight, if that's important). when i ride single speed i usually have 52x16 gear as it gives me comfortable cruising speed of 22mph at 85rpm, hills are fine as long as they are not super steep. i used to gear down to 52x20 to work on spinning technique, but these days just use my geared bike with cadence sensor for that, keeping the cadence at around 110rpm.
i would recommend 52x18; you'd be going at 19mph at 85rpm.


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## Ian H (26 Dec 2015)

It's down to individual experience, but higher cadence is generally considered better. I'm happy at 90-110" and can manage in excess of 150 on downhills (it used to be well over 200, but I'm older than I used to be). I'm also in Devon, where there are HILLS, so factor that into my advice.


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## nuovo_record (28 Dec 2015)

The flat lands of Cambridge aren't a problem for a 52 front, but I'm now using a 48x19 which is quite nice.


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## fossyant (28 Dec 2015)

46 x 16 should be nice cruising at 20-24 mph - the gear I (used) to ride.


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## biggs682 (28 Jan 2016)

Just finished building a single speed using parts from the spares box so ended up with a knee popping 39 x 15 set up , much prefer something like 52 x 18 and a lower cadance


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## Pennine-Paul (28 Jan 2016)

biggs682 said:


> Just finished building a single speed using parts from the spares box so ended up with a knee popping 39 x 15


Err 39x15 is only 68"! Do you mean 49x15?? 
I used to run 84" (48x15) on flat routes without any problems,one of my colleagues used to run 52x12! that is knee popping gearing!


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## Smurfy (29 Jan 2016)

biggs682 said:


> Just finished building a single speed using parts from the spares box so ended up with a knee popping 39 x 15 set up , much prefer something like 52 x 18 and a lower cadance


39x15 = 18.6mph @ 90rpm on 700x25 tyres
52x18 = 18.6mph @ 81rpm on 700x25 tyres

39x15 = 14.5mph @ 70rpm on 700x25 tyres
52x18 = 14.5mph @ 63rpm on 700x25 tyres


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## biggs682 (29 Jan 2016)

Pennine-Paul said:


> Err 39x15 is only 68"! Do you mean 49x15??
> I used to run 84" (48x15) on flat routes without any problems,one of my colleagues used to run 52x12! that is knee popping gearing!



no 39 X 15 is correct



Smurfy said:


> 39x15 = 18.6mph @ 90rpm on 700x25 tyres
> 52x18 = 18.6mph @ 81rpm on 700x25 tyres
> 
> 39x15 = 14.5mph @ 70rpm on 700x25 tyres
> 52x18 = 14.5mph @ 63rpm on 700x25 tyres



using spares from spares box and knee popping due to amount of spinning


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## bonsaibilly (2 Feb 2016)

Can't you count the teeth on each cog? BB


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