gear inch calculator

[nomdeplume]

Can someone please explain in simple language 'gear inch calculator' as I wish to change my chainwheel to a smaller one and need to calculate the number of teeth?
Thanks.

 

[Rohloff_Brompton_Rider]

sheldonbrown.com/gears


http://xldev.co.uk/bgc.html

This is not just for Brompton just click the non Brompton option

 

[2Loose]

"Gear Inch Calculator" - is used to work out how many inches the bike will travel in one pedal revolution when using cogs with specific number of teeth.

 

[gaz]

"Gear Inch Calculator" - is used to work out how many inches the bike will travel in one pedal revolution when using cogs with specific number of teeth.

Actually it is a measurement of how big the wheel would need to be if you wanted the same gear on a penny farthing

 

[byegad]

Kgear by Kinetics of Glasgow, download from site, is pretty good with several hub gears listed including the SRAM Dualdrive. And yes it gives the equivalent size of a Pennyfarthing or 'Ordinary' wheel that gives the same gear. Multiply by pi for distance travelled per revolution, the answer will be in inches

 

[Minotier]

Drive/chainring teeth divided by Driven/rear sprocket teeth multiplied by Wheel diameter.

Eg 50/13X27 = 103.84 inches.

Simplex.

 

[derrick]

Why would one need to know this ?

 

[Rohloff_Brompton_Rider]

Why would one need to know this ?

Why doesn't everyone need this?

 

[derrick]

Why doesn't everyone need this?

Explain.

 

[Rohloff_Brompton_Rider]

Tomorrow, off for a night ride

 

[Rickshaw Phil]

Explain.

I'll have a go.

Knowing about gear inches is an excellent way of comparing gear ratios between bikes, as it takes gearing effects from the size of the wheel into account, or for working out what you'll end up with if you try alternative parts.

For example: When I was looking to upgrade my Raleigh from a freewheel to a cassette, by working out the gear inches for each gear combination I knew what I already had in terms of ratios and could look at how alternatives compared before spending any money.

On the old set up (28-38-48 tooth front, 13-34 tooth rear, giving 22.2 to 99.6 gear inches range) I was pretty happy; with the lowest gear I could wind my way up almost anything locally and with the highest, 25mph was still a comfortable speed to pedal at. (downhill, with a following wind.)

For the new set up I didn't really want higher gearing, as what I had seems to suit me, so after looking at the options settled on a 22-32-42 tooth chainset with an 11-30 cassette. This looks a very different spec but I've ended up gaining slightly at each end of the range (19.7 to 103 gear inches), kept similar spacing in the middle gears and have got rid of the big jump between 1st and 2nd on the rear, which wasn't always ideal.

Having been able to work it all out beforehand I now have a bike that I'm very happy with.

 

[Rohloff_Brompton_Rider]

^ this.

Knowing your gearing is important, especially if you ride; a fixed, a ss, a Brompton, a unicycle or climb lots and lots of hills.

 

[derrick]

^ this.

Knowing your gearing is important, especially if you ride; a fixed, a ss, a Brompton, a unicycle or climb lots and lots of hills.

I do ride fixed, i just tried a few differant rear cogs till i found one that suits me, knowing how far a certain size cog will take me over one revolution is all very well but if your legs can't pull that gear it's not really a lot of use.

 

[Rohloff_Brompton_Rider]

If you knew your gearing you wouldn't have had to guess or try other cogs.

 

[albion]

I go by ratios.

And if you consider that a mountain bike tyres ride like treacle, your average pleasure ider like me finds it far easier thinking in front/rear ration.
So 50" has little meaning whereas a 13/32 will also relate well.