Inches ?
SME
Posts: 348
Hope this is the right forum!
It's a simple question.
I have a cycling app that measures gearing in inches. I've also seen some other reference to gearing in inches in these forums.
What are 'inches' when referred to in cycle gearing, and how do they relate to, say, gear ratios ie. using 50 a chainring and an 11 sprocket?
Steve
It's a simple question.
I have a cycling app that measures gearing in inches. I've also seen some other reference to gearing in inches in these forums.
What are 'inches' when referred to in cycle gearing, and how do they relate to, say, gear ratios ie. using 50 a chainring and an 11 sprocket?
Steve
0
Comments

================
2020 Voodoo Marasa
2017 Cube Attain GTC Pro Disc 2016
2016 Voodoo Wazoo0 
Gear inches is another way to express gearing, which uses the size of chainring, sprocket, wheel and tyre  so the calculation doesn't account for crank length. It derives from the high wheel 'Ordinary' bicycle  the only way to vary the 'gear' on one of those is to change the size of the wheel.
If you want to convert from one to another, use a calculator as above. Both are valid methods  like pretty much everyone who rides fixed, I use inches. Others use ratios.0 
It's how far, in inches, a bike will travel for one complete revolution of the cranks.0

Thanks all.
Am going to go and play with the app now to see if I can work out what gears I'm in at certain times in the ride.
Cheers,
Steve0 
I find considering gears by ratio much simpler and easier to compare than inches myself0

Ber Nard wrote:It's how far, in inches, a bike will travel for one complete revolution of the cranks.
No. That is progression.
See above about the ordinary wheel.
When fixed wheelers get together, we do like to compare our inches.
(67 most of the time, have geared up to 71 for some longer rides)0 
As one of the aforementioned fixie riders, I spend unhealthy amounts of time on http://www.bikecalc.com/ looking at different inches but also very useful is cadence at speed which adds a bit of context.0

marcusjb wrote:Ber Nard wrote:It's how far, in inches, a bike will travel for one complete revolution of the cranks.
No. That is progression.
Well I never!
I remember asking the same question of someone I assumed to be wiser and that was the answer I got. Seemed to make sense so I never questioned it again.
Live and learn...0 
(I originally thought exactly the same)
Progression or development is what you're referring to.
Just to give you some ideas of what they feel like:
Typical fixed gear is somewhere between 65 and 75 inches  so a reasonable cruising gear, able to go along at 30ish kph and get up anything but the steepest of hills usually.
Track riders are typically in the 90s (that's why they take a huge effort just to get moving).
Top end of a road bike with silly little 11 tooth sprockets is 120ish inches (i.e. massive!)
Bottom end of a touring bike's range might be low 20s.
I would have no comprehension of what ratios are etc., but can instantly work with inches. It's the same if someone talks about gears (particularly on their fixed wheel bike) and just gives me the actual tooth count ("I'm on 47*16"), I'd have no idea whether that is high or low or whatever without a calculator.0 
MarkusJB wrote:Top end of a road bike with silly little 11 tooth sprockets is 120ish inches (i.e. massive!)
I always thought this was a massive gear to. Until I read about one guy who could bimble along all day at 40RPM in such a gear, even on climbs of upto 6%. Apparently, the only time he even needed to get out of the saddle, was when he had something to say.....
47/16 gives a ratio of 2.93 to 1...(ish) compared to 4.545 to 1 for a 50/11 set up.0 
Well, think I've got it now.
So if I'm bumbling up a hill on a 34 front and 32 rear, that's nearly 1:1
So a 700 wheel (given about 2100mm circumference) would equate to around 82inches in gearing speak.
Thanks for all the explanations,
Steve0 
SME wrote:Well, think I've got it now.
So if I'm bumbling up a hill on a 34 front and 32 rear, that's nearly 1:1
So a 700 wheel (given about 2100mm circumference) would equate to around 82inches in gearing speak.
Thanks for all the explanations,
Steve
34/32 on a 700/25c wheel/tyre is a 28inch gear. http://www.bikecalc.com/gear_inches
An 82inch gear would be pretty tough going on any thing that could remotely be called a hill.0 
Nope. It’s the diameter of the wheel multiplied by your ratio. A typical road bike tyre is a bit under 27" tall, so your 34T×32T ratio would give you about a 28" or 29" gear.
Ratios are meaningless without knowing the wheel size. Since bicycles (and trikes, recumbents, etc.) have a huge variety of wheel sizes, gear inches are a useful shortcut for describing and comparing gears.0 
OnYourRight wrote:Nope. It’s the diameter of the wheel multiplied by your ratio. A typical road bike tyre is a bit under 27" tall, so your 34T×32T ratio would give you about a 28" or 29" gear.
Ratios are meaningless without knowing the wheel size. Since bicycles (and trikes, recumbents, etc.) have a huge variety of wheel sizes, gear inches are a useful shortcut for describing and comparing gears.
Well I'm confused now :oops:
Why would it be the diameter? If the gear in inches is the distance travelled for one full pedal rev, the formula would be:
(chainring teeth/sprocket teeth) x wheel circumference (in inches)
where wheel circumference is pi x diameter. I'm missing something!0 
Alex99 wrote:Why would it be the diameter? If the gear in inches is the distance travelled for one full pedal rev, the formula would be:
(chainring teeth/sprocket teeth) x wheel circumference (in inches)
where wheel circumference is pi x diameter. I'm missing something!
It is not the distance travelled for one full crank revolution (which is the development).
When bicycles were of the ordinary/highwheel/pennyfarthing style, the cranks were attached directly to the wheel without gears. Wheel size was very important (and variable) because the bigger the wheel, the faster you could ride, but the maximum wheel size was limited by your inseam. So wheel diameter in inches was a key specification that everyone knew for their bicycle.
When the safety bicycle became popular, gear inches were used to describe their gearing in a way that was intuitively understood by people who had ridden ordinary bicycles, i.e. the effective wheel diameter.
Today that remains the case. ‘Gear inches’ is a specific term whose definition is what it is. If you want to use inches to describe development you must clarify that (but why would you want to? The conventional unit of development is metres).0 
OnYourRight wrote:Alex99 wrote:Why would it be the diameter? If the gear in inches is the distance travelled for one full pedal rev, the formula would be:
(chainring teeth/sprocket teeth) x wheel circumference (in inches)
where wheel circumference is pi x diameter. I'm missing something!
It is not the distance travelled for one full crank revolution (which is the development).
When bicycles were of the ordinary/highwheel/pennyfarthing style, the cranks were attached directly to the wheel without gears. Wheel size was very important (and variable) because the bigger the wheel, the faster you could ride, but the maximum wheel size was limited by your inseam. So wheel diameter in inches was a key specification that everyone knew for their bicycle.
When the safety bicycle became popular, gear inches were used to describe their gearing in a way that was intuitively understood by people who had ridden ordinary bicycles, i.e. the effective wheel diameter.
Today that remains the case. ‘Gear inches’ is a specific term whose definition is what it is. If you want to use inches to describe development you must clarify that (but why would you want to? The conventional unit of development is metres).
OK, got you. Thanks0 
Development is probably a more sensible way than gear inches to compare gearing, but few Englishspeaking people have an intuitive feel for development. I know that a gear of 8 m development is vaguely large, but I don’t know more than that. Whereas I know exactly how a 68" gear feels. So it would be tricky to change.
Many things have this legacy baggage. See digital camera sensor sizes for a total minefield!0 
Formula for gear inches is : ( [tire size x 2] + rim diameter size) x by gear ratio(number of chainring T divided by number of rear cog T)
eg 23mm tyre on 700c* rim and 50T front 25T rear = ([2 x23mm] +622mm) x 2
So 668mm(26.26 inches) x 2 = a 52.52 inch gear
For a 34/32 cog set up on the same wheel : 26.26 x 1.0625 = 27.9 gear inches
For a 50/11 cog set up on the same wheel ; 26.26 x 4.4545 = 119.4 gear inches
Gear inches are useful more as a relative measure of one gear to another, than as an absolute measure.
* 700c rim is a bit of a misnomer as the diameter is actually 622mm.0