# Gear inches

Discussion in 'Australia and New Zealand' started by Owen, Jan 20, 2007.

1. ### Owen Guest

I have this utterly boring book with a snipit of interesting technical information as a footnote. Quoting;

The calculation of gears is an abiding legacy of the Ordinary (A penny farthing) ...Take the diameter of the rear wheel, mutiply this by the number of teeth on the chainwheel...divide the result by the number of teeth on the rear sproket...you have gear inches.

So, counting the cogs I have;

Chain wheel Cluser
48 13

<snip> <snip>

28 34

which for a 27 inch wheel gives me a range of 100 to 22 inches. It is the 22 inches which interests me as that what I use to stuggle up hills just before getting off to walk. After 6 years of social/group riding, I have *never* heard anyone talk of gear inches, although when thinking about a Rohloff hub, it seems it would be a useful measurement.

So I was just wondering if the more profession riders that read this group sit around at night sipping their beer and talking about gear inches, or is it a purely pommy thing from whence this book came? (maybe it's gear centimeters these days?)

TIA

Owen

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2. ### jur New Member

Joined:
Feb 2, 2005
Messages:
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It still is a used concept, especially when considering a singlespeed bike. What number is a useful number for SS? I had a 77GI; many people run approx 70GI.

Or talking loaded touring: A useful range might be 30-90GI, just what a 11-34 cassette can give if you only have a single chainring as on a folding bike.

Or as you suggest, with an internally geared hub it gives you nice insight about choosing the sprocket and chainwheel size to end up with useful range.

The other units used are meters development (wheel circumference used instead of diameter) or Sheldon Brown's gain ratio, incorporating crank arm length. The one which seems to be in widespread use is GI.

3. ### John Henderson Guest

Owen wrote:

> I have this utterly boring book with a snipit of interesting
> technical information as a footnote. Quoting;
>
> The calculation of gears is an abiding legacy of the Ordinary
> (A penny farthing) ...Take the diameter of the rear wheel,
> mutiply this by the number of teeth on the chainwheel...divide
> the result by the number of teeth on the rear sproket...you
> have gear inches.
>
> So, counting the cogs I have;
>
> Chain wheel Cluser
> 48 13
>
> <snip> <snip>
>
> 28 34
>
>
> which for a 27 inch wheel gives me a range of 100 to 22
> inches. It is the 22 inches which interests me as that what I
> use to stuggle up hills just before getting off to walk. After
> 6 years of social/group riding, I have *never* heard anyone
> talk of gear inches, although when thinking about a Rohloff
> hub, it seems it would be a useful measurement.
>
> So I was just wondering if the more profession riders that
> read this group sit around at night sipping their beer and
> talking about gear inches, or is it a purely pommy thing from
> whence this book came? (maybe it's gear centimeters these
> days?)

I don't know about the professionals, but I started talking
about gear inches back in the 70's because that was the only
way you could make gearing understood.

I still think and talk that way, although Sheldon Brown thinks
the writing's on the wall:
http://www.sheldonbrown.com/gain.html

My 7-speed internal hub gears are set up (by chainwheel and
sprocket size) to give me a gear-inches range from 31.38" in
first to 95.80" in 7th.

John

4. ### Friday Guest

Owen wrote:
> I have this utterly boring book with a snipit of interesting technical information as a footnote. Quoting;
>
> The calculation of gears is an abiding legacy of the Ordinary (A penny farthing) ...Take the diameter of the rear wheel, mutiply this by the number of teeth on the chainwheel...divide the result by the number of teeth on the rear sproket...you have gear inches.
>
> So, counting the cogs I have;
>
> Chain wheel Cluser
> 48 13
>
> <snip> <snip>
>
> 28 34
>
>
> which for a 27 inch wheel gives me a range of 100 to 22 inches. It is the 22 inches which interests me as that what I use to stuggle up hills just before getting off to walk. After 6 years of social/group riding, I have *never* heard anyone talk of gear inches, although when thinking about a Rohloff hub, it seems it would be a useful measurement.
>
> So I was just wondering if the more profession riders that read this group sit around at night sipping their beer and talking about gear inches, or is it a purely pommy thing from whence this book came? (maybe it's gear centimeters these days?)
>
>
>
> TIA
>
>
> Owen

I think it's still used in racing. For a long time junior track riders
weren't allowed to have greater than 100 inch gearing to protect their
knees. I don't know if that rule still applies.

Friday

5. ### Gemma_k Guest

"Owen" <[email protected]> wrote in message
news:[email protected]
> After 6 years of social/group riding, I have *never* heard anyone talk of
> gear inches, although when thinking about a Rohloff hub, it seems it would
> be a useful measurement.
>
> So I was just wondering if the more profession riders that read this group
> sit around at night sipping their beer and talking about gear inches, or
> is it a purely pommy thing from whence this book came? (maybe it's gear
> centimeters these days?)
>

If you head down to your local velodrome again it's the only gearing
language spoken.....and can't see it dying out anytime soon (rollout
measurement in metres seems less 'meaningful', although that is what the
juniors are restricted by)

Gemma (90inches is my favourite gear)

6. ### Gags Guest

"Gemma_k" <[email protected]> wrote in message
news:[email protected]
>
> "Owen" <[email protected]> wrote in message
> news:[email protected]
>> After 6 years of social/group riding, I have *never* heard anyone talk of
>> gear inches, although when thinking about a Rohloff hub, it seems it
>> would be a useful measurement.
>>
>> So I was just wondering if the more profession riders that read this
>> group sit around at night sipping their beer and talking about gear
>> inches, or is it a purely pommy thing from whence this book came? (maybe
>> it's gear centimeters these days?)
>>

> If you head down to your local velodrome again it's the only gearing
> language spoken.....and can't see it dying out anytime soon (rollout
> measurement in metres seems less 'meaningful', although that is what the
> juniors are restricted by)
>
> Gemma (90inches is my favourite gear)

Only last week I made up an excel spreadsheet to plot gear inches of all
possible combinations of Chainrings (48,49,51,53,54) and cogs (14,15,16)
that I got with my track bike.....This gives me a range of 81 to 104.1
inches. I am currently running 81 inches on my road fixie but I am not sure
how this translates to the track.....hopefully I will be able to get out
next week for my first ride on the new bike.

Gags

7. ### Joel Mayes Guest

On 2007-01-21, Owen <[email protected]> wrote:

> So I was just wondering if the more profession riders that read this group
> sit around at night sipping their beer and talking about gear inches, or is it
> a purely pommy thing from whence this book came? (maybe it's gear centimeters
> these days?)

I had several long conversation re. gear inches yesterday & today, most likely
'cause I've redone my postie bike as a single speed with a 22t chainring and a
19t cog on the rear. for a grand total of 30ish gear inches.

The tiny chainring on the large bike garners a bit of attention (and I
almost get two of the require chain lengths from a single store bought
lenght of chain)

Cheers

Joel

8. ### Bleve Guest

Gemma_k wrote:

> Gemma (90inches is my favourite gear)

You must be racing indoors

9. ### Boostland Guest

"Gags" <[email protected]> wrote in message
news:[email protected]
> "Gemma_k" <[email protected]> wrote in message
> news:[email protected]
>>
>> "Owen" <[email protected]> wrote in message
>> news:[email protected]
>>> After 6 years of social/group riding, I have *never* heard anyone talk
>>> of gear inches, although when thinking about a Rohloff hub, it seems it
>>> would be a useful measurement.
>>>
>>> So I was just wondering if the more profession riders that read this
>>> group sit around at night sipping their beer and talking about gear
>>> inches, or is it a purely pommy thing from whence this book came? (maybe
>>> it's gear centimeters these days?)
>>>

>> If you head down to your local velodrome again it's the only gearing
>> language spoken.....and can't see it dying out anytime soon (rollout
>> measurement in metres seems less 'meaningful', although that is what the
>> juniors are restricted by)
>>
>> Gemma (90inches is my favourite gear)

>
> Only last week I made up an excel spreadsheet to plot gear inches of all
> possible combinations of Chainrings (48,49,51,53,54) and cogs (14,15,16)
> that I got with my track bike.....This gives me a range of 81 to 104.1
> inches. I am currently running 81 inches on my road fixie but I am not
> sure how this translates to the track.....hopefully I will be able to get
> out next week for my first ride on the new bike.
>
> Gags
>

Here are some gear charts I modified from the cycling NSW ones, I added a
Inch gear table as I am a trackie and somehow I can't bear to for go my
years of talking in inch gears.

< http://users.g-node.com.au/boostlinux/Gear_Charts.xls >

Here is one you can easy print out on a A4 for use at the track

< http://users.g-node.com.au/boostlinux/Gear_Charts.pdf >

On Newcastle 200 meter track I usually ride a 88.7 inch gear, but as I don't
currently have a 46 chainring for my new Miche cranks I am using 88.2

I am entered into the Sydney cup on wheels next weekend and will probably be
using a 94 to 96 inch gear as the Dunc Gray indoor timber track is quite
fast.

< http://www.nsw.cycling.org.au/files/Races/2007/07011/07011.htm >

10. ### Bean Long Guest

Owen wrote:

> So I was just wondering if the more profession riders that
>read this group sit around at night sipping their beer and
>talking about gear inches, or is it a purely pommy thing from
>whence this book came? (maybe it's gear centimeters these days?)

From what I can tell, track riders still talk almost entirely in gear
inches. They want to know how far each pedal stroke will take them
rather than the specific tooth number I s'pose.
--
Bean

"I've got a bike
You can ride it if you like
A bell that rings
And things to make it look good
I'd give it to you if I could
But I borrowed it" Pink Floyd