fixed gearing

Mark Alexander

I am currently running a 70" gear 48X18.
I am looking to spin more for getting away from the lights and there are some hills around here.would a 46 or 45 make much difference? :?

demmerson

Mark Alexander wrote:

I am currently running a 70" gear 48X18.
I am looking to spin more for getting away from the lights and there are some hills around here.would a 46 or 45 make much difference? :?

It would be cheaper and easier to fit a bigger sprocket rather than a smaller chainring. 48x19 will give you a gear in between 46x18 and 45x18 which will be enough of a change to make a difference on hills in my experience. Depending on your dropouts/track ends you should be able to get away with that without messing about with altering the chain length. If you've got a double sided hub you can leave both 18 and 19 in place.

robbarker

I run 46/18 and it's fine for medium hilly. I think I have 22 going spare if you want to try it Mark, possibly a 20 as well - fell free to drop across to my workshop or send me a PM if you want to work something out.

NorwegianBlue

48/18 to 45/18 would be the same as changing from 40/15 to 40/16. So if you have a geared bike with a 53/39 chainset and 15T and 16T sprockets on the cassette that would be close enough to give you a feel for the change.

It is a noticable change, but I'm assuming you're living somewhere in the Bridgend area from the links in your sig and I remember it being pretty hilly north of there. As such I don't think dropping from 70" to 66" is that much of change. Here in the south Pennines I like a 63" gear, 48/20, and I think the terrain round here is probably similar.

Of course it does depend on our comparitive levels of fitness and riding styles, but if you are anything like me you shoul give 63" a try.

billy whippet

I ride 46 18 and 44 17. 46 18 is a good gear - wouldn't really want it any shorter, it's the 'classic' gear

Mark Alexander

robbarker wrote:

I run 46/18 and it's fine for medium hilly. I think I have 22 going spare if you want to try it Mark, possibly a 20 as well - fell free to drop across to my workshop or send me a PM if you want to work something out.

Thanks for the offer Rob. After riding out of Cardiff on longer than 'around town' rides I have decided to keep the 72" gearing 48x18. I cn still feel my calves!

redddraggon

So 48/18 a goodish gear then?

I'm eventually getting around to putting the finishing touches to my langster - not planning on doing anything too hilly with it though, shortish rides around Chester/NE Wales avoiding the steep stuff.

Mark Alexander

I find it great. better than 48x17 it is more suited to training than to commuting as I don't race to work

stickman

48:22 was mentioned, with a 46 chainring what sprocket would be used to equal that ratio?

Monty Dog

Nearest would be a 21 sprocket - not a common size tho

stickman

Thanks.
Is there an easy way to learn how to work out ratios, or is there a chart anywhere on the web?

flashes

I think this is what you're after...................

http://sheldonbrown.com/gears/

demmerson

stickman wrote:

48:22 was mentioned, with a 46 chainring what sprocket would be used to equal that ratio?

I find the easiest way to compare various chainring/sprocket combinations is just to divide the chainring by the sprocket rather than mess about with mysterious gear inches. 48/22 = 2.18 so the equivalent with a 46t chainring is 46/2.18 = 21.1.

stickman

flashes + demmerson, thanks, that's some useful stuff

GarethPJ

demmerson wrote:

stickman wrote:

48:22 was mentioned, with a 46 chainring what sprocket would be used to equal that ratio?

I find the easiest way to compare various chainring/sprocket combinations is just to divide the chainring by the sprocket rather than mess about with mysterious gear inches. 48/22 = 2.18 so the equivalent with a 46t chainring is 46/2.18 = 21.1.

There's nothing mysterious about gear inches, all you do is take the figure you just worked out and multiply it by the diameter of your tyre. It's a useful figure for comparisons between different bikes. If you have different bikes with different tyres (as I do) then you can't simply compare the ring/sprocket ratio.

One of my bikes has tyres with a diameter of 26.7" another sports tyres with a diameter of only 25". So 42:16 on the former would be a 70" gear. On the latter you would require a sprocket with one tooth less or a ring with three teeth more to achieve the same gearing.

ridgerider

I am being a bit lazy here (cannot be bothered to go on Google!), but I have been wondering...

My wheel has a circumference of about 2m
My gearing is 46:17

That means I must pedal about 2.5 wheel circumferences for every rotation of the chainring...which would mean a gearing of about 5m, or 15ft, or 180".

So how come gearing figures are down in the 60"-70" region?

No googling the answer

meagain

There are a number of different ways of "measuring" gearing. That which gives say "70"-80" (gear inches?) equates to the diameter of the front wheel on an ordinary ("penny farthing"). That which relates to distance travelled is a "gain" measurement.
There are others!
All explained on Sheldon Brown as I recall.

GarethPJ

Ridgerider wrote:

I am being a bit lazy here (cannot be bothered to go on Google!), but I have been wondering...

My wheel has a circumference of about 2m
My gearing is 46:17

That means I must pedal about 2.5 wheel circumferences for every rotation of the chainring...which would mean a gearing of about 5m, or 15ft, or 180".

So how come gearing figures are down in the 60"-70" region?

No googling the answer

I don't think you quite understand gear inches. It's dead easy. Gear inches could be defined as the diameter of the wheel who's circumference matches the distance you travel for one complete turn of your cranks. Calculated by multiplying the outer diameter of your tyre by the number of teeth on your chainring and dividing by the tooth count of your sprocket.

So assuming you have a 2m circumference to your wheel the diameter would be 636mm or 25" (1.5" tyres on a 559 rim?) 46:17 would therefore give you:

25" * 46 / 17 = 68" (thats kind of rough, given that you were rough about the wheel size)

Easy when you know how.

Gear inches are not a complete comparison of gearing between different bikes, but they do allow a rough comparison for different wheel tyre sizes.

When comparing gearing between two bikes most people completely ignore the factor of tyre drag. Imagine two bikes, one with a 700x23c slick tyres at 100psi and the other with 26x2.1" MTB tyres at 40psi. Both have 42/17 gearing and 170mm cranks. The gear inches are the same, the gain ratio the same, but the former will probably feel undergeared unless climbing a reasonably steep hill. The latter will feel like it's carrying a much higher gear. I run roughly 53" off road and (depending on the bike) 63-72" on road. You may think the lower gear off road is mainly to deal with steeper climbs. It isn't. It's to deal with the increased tyre drag, especially in muddy conditions. Road sections aren't much fun when you have to spin 95rpm just to maintain 15mph!

Dickie

I use this.

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

Dickie

I use this.

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

GarethPJ

Forgot to mention that knowing your gear inches will give you an easy speed/cadence calculation. Simply divide 336 by your gear inches and you get the crank rpm at 1mph. Once you've got that figure it's easy to calculate cadence from speed, so you don't need some fancy computer to know your cadence just something for £3.99 from Aldi.

OK so it's not something you could do on the fly if you have thirty gears, but if you've only got one it's pretty simple to do in your head.

ridgerider

Thank you all.

I love maths!

mz__jo

Gear inches have stayed in common use because they give figures in the range 25-100 for most common needs, it's not really anything to do with nostalgia for penny-farthings. Try working in "metres developpement" which is in theory more useful and in practice so cumbersome that all the french riders I know simply refer to the ring/sprocket ratio. I have never bothered working out the exact wheel diameter (until recently when I got an mtb), I have always used 27 and 26 as wheel sizes and compensated in my head.
If you are old enough to have a slide rule, working out the different combinations with the same gear size is easy, one setting gives you all. (Now I have progressed an spend hours on Sheldon Brown's gear calculator
Cheers Jo
PS I like 48x20 and 44x18 as gear combinations on fixed although these days it's 42x18 with a freewheel

GarethPJ

I agree completely, gear inches endure because they make it easy to compare gears. I currently own bikes with tyre diameters from 24.4" to 27" and in the past have had tyres as small as 20" so working simply on the ring:sprocket ratio would meaningless.

Imagine two riders talking about their ring to sprocket ratio one has 53:18 and the other 42:16. Pretty obvious which is the higher? Then you learn that the former has 650x25c tyres and the latter 700x23c, now which is the higher gear and by what proportion? That's where gear inches are useful and it's an easy calculation given a basic pocket calculator or a slide rule and a rudimentary knowledge of tyre sizes.

I don't bother with Sheldon's gear calculator because I find the calculations fairly easy given my old calculator, but mainly because I don't have a PC in the garage and I can't be bothered to walk back down the steps to the house (especially in cleats) to calculate gearing.

mz__jo

The metric gear development could be as useful as inches (more useful even) if only they would work in decimetres to give a figure which was easier to understand - but then the French have never been into making things easier to understand (or at least that's my opinion after 18 years living here). Who would want to ride a bike to three decimal places??
Cheers Jo