Gear inch question
#27
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The upshot is that I've ordered a new crank and bottom bracket. Based on Sheldon Brown's gear calculator, that should move me from a low gear of 22.6 gi to one of 18.1 gi.
#28
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That has nothing to do with knowing which gear you are in. I really don’t think while ratios while riding and I think about gearing far more than most people do. I know what the high is and the low is but I honestly don’t think “I’m riding in the 4th out of 9 gear so that means I’m riding in the 72” gear”. I don’t think anyone does that. We generally ride by “feel” because doing calculations on the fly is just too difficult.
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This (Bicycle Gear Calculator) is my favorite resource for toying around with gear inches and development, development being in European inches. It's an invaluable resource. Also, kudos to the poster who pointed out the derailleur capacity issue.
All too often in discussions about gearing, people seem to forget that drivetrains are systems and that derailleur capacity is a thing.
For Shimano you can get all the info you need from their product information website (https://productinfo.shimano.com/#/) either from the current section, or more likely, the archive.
All too often in discussions about gearing, people seem to forget that drivetrains are systems and that derailleur capacity is a thing.
For Shimano you can get all the info you need from their product information website (https://productinfo.shimano.com/#/) either from the current section, or more likely, the archive.
#30
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Back to the original question: yes, it'll make a difference on steep hills (>12%, perhaps), or if you're touring with a load. In other words, if you run out of gears with the setup you've got, that change will give you about 1.5 extra low gears, and that's often significant.
#31
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Follow up and let us know if you feel the difference, please. I'm a high gear guy myself so it's not something I'd contemplate, but I'm always curious how stuff like this works out for people, and it might be helpful for people planning rides like yours.
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#32
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It sounds like you have a Shimano Tiagra triple set-up. I bought a bike with the express notion of changing the small chainring to a 26 tooth. I'd had success with doing that with a Campy triple (24 tooth) in the past. It didn't work with Tiagra. If I adjusted things just right, it would only work marginally. even with a Jump Stop installed, it dropped the chain way too much for my liking. Tiagra is set up to work with a limited range of chainrings in each position. In my opinion, they picked some bad choices for a triple. I wound up changing the whole crankset to a Sugino Alpina II with 48-36-24 chainrings and using a bar-end friction shifter and Alpina derailleur. I'm a shift-o-holic and I had to have STI for the rear but friction shift on the chainrings is fine (if not preferable). For the rear, I replaced the cog set (11-28) with one that has 11-34. This necessitated in my changing the rear derailleur for one that would wrap the extra chain. I used a Deore 9 speed mountain bike derailleur which has the same pull ratio as the Tiagra 10 speed road derailleur. It works flawlessly. You can't use Shimano 10 speed mountain bike derailleurs with Shimano 10 speed road shifters.
This was kind of a round-about way to do it, but I now have the bike that I wanted.
This was kind of a round-about way to do it, but I now have the bike that I wanted.
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That has nothing to do with knowing which gear you are in. I really don’t think while ratios while riding and I think about gearing far more than most people do. I know what the high is and the low is but I honestly don’t think “I’m riding in the 4th out of 9 gear so that means I’m riding in the 72” gear”. I don’t think anyone does that. We generally ride by “feel” because doing calculations on the fly is just too difficult.
Two, it also takes into account tire size, which since most bikes these days run 622mm isn't more than noise, but it you've got a 571 (26") MTB, or something with 20" like a folder or mini-velo, along with 700c bikes, it can be easier to see where they stack up against each other.
I see that a lot when someone switches from a hybrid / comfort bike, to a more sporting road bike, and complains that it's 'so hard to pedal' the new bike. They're used to using mostly 'the 6 or 7' (thanks Gripshift ) which is like a 77 or 80, so when they use the same lineup on their new bike, it's like a 100+ You can put the gear-inch tables of the old and new bikes next to each other, and easily see where they compare to each other.
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#36
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At 26-36 I get gear inches of 19.5 if I did the calculation correctly. I get rollout of 61.26 inches at 26 versus 70.69 inches at 30.
Gear ratio is .72 at 26 versus .83 at 30. At a cadence of 80 I get a speed of 4.64mph at 26 versus 5.35mph at 30.
Somebody please check the calculations.
Gear ratio is .72 at 26 versus .83 at 30. At a cadence of 80 I get a speed of 4.64mph at 26 versus 5.35mph at 30.
Somebody please check the calculations.
Otto
#37
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Well, I got my new crankset installed. Now, as soon as I start my trip, I'll update on how well it works! Thanks to all!
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I actually do this..... I know what gear inch I am riding at any time. It's always been a way for me to calculate mph while riding. Never had a speedometer and don't use strava or a gramin or any electronic device. I usually ride in a certain gear inch per various roads, and it's easy to spin 90 rpm on the crank because that is one second of time per 1.5 revolution per crank.
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I actually do this..... I know what gear inch I am riding at any time. It's always been a way for me to calculate mph while riding. Never had a speedometer and don't use strava or a gramin or any electronic device. I usually ride in a certain gear inch per various roads, and it's easy to spin 90 rpm on the crank because that is one second of time per 1.5 revolution per crank.
speed = π * (diameter + (2 * tire_size)) * (chainring/cog) * cadence
If you have more than one bike with more than one wheel size, you multiply the gear ratios that number of bikes. I have 8 bikes and the drivetrains are only duplicated in a couple of them. That’s at least 6 different gear ratio charts I have to keep in my head. That’s just not going to happen for me nor for the vast majority of bicyclist.
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Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
#40
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That has nothing to do with knowing which gear you are in. I really don’t think while ratios while riding and I think about gearing far more than most people do. I know what the high is and the low is but I honestly don’t think “I’m riding in the 4th out of 9 gear so that means I’m riding in the 72” gear”. I don’t think anyone does that. We generally ride by “feel” because doing calculations on the fly is just too difficult.
#41
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You and I are a lot alike. I think in gear-inches often when I ride. Folks who build and ride fixed gears learn to do this to compare how a particular setup will work for them. And, 72" is the sweet spot for me, so most of the time, I'm mentally comparing the gear that I'm in to what I would be experiencing at 72". Gear-inches are the great normalizer between all types of [road] bike riding.
When I run a multi gear cog set, it will have a combination with relatively straight chain-line that produces about 71-72 gear inches and I will spend a lot of time in that gear.
The other bike has the same 42/16 but ends up at 68” on 26” tires. I wouldn’t mind getting that one up to about 71 to 72, but not exactly sure how to make it happen.
Otto
#42
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Big difference. I haven't been out of the saddle since getting it. I may go slow, but I get there!
Last edited by kombiguy; 10-07-20 at 05:27 PM.
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#43
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I actually do this..... I know what gear inch I am riding at any time. It's always been a way for me to calculate mph while riding. Never had a speedometer and don't use strava or a gramin or any electronic device. I usually ride in a certain gear inch per various roads, and it's easy to spin 90 rpm on the crank because that is one second of time per 1.5 revolution per crank.
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#44
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Yes 13% is a noticeable difference. That happens to be the step size on the Pinion 18 speed gearbox. Since gear inches = chainwheel to cassette ratio times wheel diameter, it is really only the ratio that is important, the wheel diameter will stay constant. But convention and comparing different setups may make it convenient.
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What new crankset did you go with, OP?
I started with a 3x9 (30-39-50 & 11-32) Sora groupset on my Specialized AWOL. I swapped the rear derailleur out for a Deore 9 speed, which worked perfectly with the STI shifters (Mega 9), and put on a 12-36 cassette. That worked for awhile, until I swapped the stock drops out for Jones bars and went with full 3x9 (22-32-44 & 12-36) Deore. I'm still running that set up, but I'm a bit sick of it right now and looking to go 2x or 1x.
I started with a 3x9 (30-39-50 & 11-32) Sora groupset on my Specialized AWOL. I swapped the rear derailleur out for a Deore 9 speed, which worked perfectly with the STI shifters (Mega 9), and put on a 12-36 cassette. That worked for awhile, until I swapped the stock drops out for Jones bars and went with full 3x9 (22-32-44 & 12-36) Deore. I'm still running that set up, but I'm a bit sick of it right now and looking to go 2x or 1x.
#46
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What new crankset did you go with, OP?
I started with a 3x9 (30-39-50 & 11-32) Sora groupset on my Specialized AWOL. I swapped the rear derailleur out for a Deore 9 speed, which worked perfectly with the STI shifters (Mega 9), and put on a 12-36 cassette. That worked for awhile, until I swapped the stock drops out for Jones bars and went with full 3x9 (22-32-44 & 12-36) Deore. I'm still running that set up, but I'm a bit sick of it right now and looking to go 2x or 1x.
I started with a 3x9 (30-39-50 & 11-32) Sora groupset on my Specialized AWOL. I swapped the rear derailleur out for a Deore 9 speed, which worked perfectly with the STI shifters (Mega 9), and put on a 12-36 cassette. That worked for awhile, until I swapped the stock drops out for Jones bars and went with full 3x9 (22-32-44 & 12-36) Deore. I'm still running that set up, but I'm a bit sick of it right now and looking to go 2x or 1x.