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Gear inches and commuting questions

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Old 02-17-09, 08:04 PM
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Gear inches and commuting questions

I have my 8-speed bike set up so the highest gear is 102.4 in and after that comes 90 and 77.5 in. I am in those top 3 gear most of the time. BTW, I am not a spinner.

So my questions are:

What is your top gear inch?

I noticed that most SS bikes are geared around 60-65 inches. Isn't that way too low?
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Old 02-17-09, 08:29 PM
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Originally Posted by NEXUS View Post
I noticed that most SS bikes are geared around 60-65 inches. Isn't that way too low?
In most cases, probably.

On my FG, I have a 42x15, which is 75 inches. That's pretty normal I think.

On the geared bike I'm almost always between 61 and 92 inches. I'm not sure I've ever even been in the highest gear I've got, and I know I've never been in the granny gear.
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Old 02-17-09, 08:39 PM
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71 gear inches on my FG commuter and 116.5 on my road bike (53x12), which I rarely need on the commute.
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Old 02-17-09, 08:44 PM
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My Worksman cruiser is 52 gear-inches, approx. Yes, that's low. Going up hills, it's handy, though, and good for 15 mph or better on the flats. I discovered a lot of it is just what you're used to.
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Old 02-17-09, 08:52 PM
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Originally Posted by NEXUS View Post
I have my 8-speed bike set up so the highest gear is 102.4 in and after that comes 90 and 77.5 in. I am in those top 3 gear most of the time. BTW, I am not a spinner.

So my questions are:

What is your top gear inch?

I noticed that most SS bikes are geared around 60-65 inches. Isn't that way too low?
To answer your latter question: No, not really. Depends on where and how you ride. And what you want to get out of it. I spent most of the fall and winter riding my FG at 41x16 or 67 g.i. Forces me to spin like a madman to do 20mph. But when the spring races come and the pack surges from 24 to 28, I can spin the middle of the cassette, then drop a cog and boom, smooth acceleration.

That's the plan, at least.
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Old 02-17-09, 08:58 PM
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70 seems to be the midpoint for ss gearing... I run single gearings as high as 76 and 81 on my lighter ss and fg machines and go as low as a 58/65 on my fixed touring bike that has a double stepped fixed hub.

My work bike usually runs a 63/75 since I run downtown where it's flat and my biggest issue is high winds and severe winter weather where that lower gear is wonderful. There is one hill that I occasionally have to climb and can do it with the 75 and even the 76 gear inches... at 22% it's a walk up with 81 gear inches.

My geared road bike tops out at 107.5 and low of 54.

So basically... gearing will have a great deal to do with where and how you ride and with a single gearig you have to compromise so that you can handle the worst stuff you encounter.
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Old 02-17-09, 09:18 PM
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27~75 gear inches is about all I need.

60 GI would be about ideal for me. can hit 40km/h should I need it, but with a really ideal 28km/h @ 100rpm range.
not too tall at stop and go, yet tall enough to keep up with city traffic by hitting 35km/h
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Old 02-17-09, 09:24 PM
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Originally Posted by NoRacer View Post
According to Sheldon Brown's Gear Inch Calculator http://www.sheldonbrown.com/gears/ :

Gear chart using Gear Inches

For 27 inch (nominal) tire with 170 mm cranks
Most people are running 26 inch mtb or 700c tyres although 27 inch tyres seem to be making a bit of a comeback as a lot of old bikes are getting pulled out of the garage and being put back into service.

A 27 inch tyre will increase your gearing a little over a 700c with the same chain ring and cogs.
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Old 02-17-09, 09:27 PM
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Originally Posted by AEO View Post
27~75 gear inches is about all I need.
60 GI would be about ideal for me. can hit 40km/h should I need it, but with a really ideal 28km/h @ 100rpm range.
not too tall at stop and go, yet tall enough to keep up with city traffic by hitting 35km/h

40km/h = 25mph. I don'tthink you can do that with 60 G.I. since you would need to be spinning at around 140RPM!
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Old 02-17-09, 09:37 PM
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or this calculator: http://www.panix.com/~jbarrm/cycal/cycal.30f.html

wheel size is your rim diameter + (2 * tyre height)
on most slick tyres you can pretty much assume height = width.
example:
a 700c wheel with 28mm tyres would be 622 + 2 * 28, which is 678mm in diameter
a 26" wheel with 1.5in tyres would be 559 + 2 * 1.5 * 25.4, which is 635mm in diameter
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Old 02-17-09, 09:38 PM
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Originally Posted by NEXUS View Post
40km/h = 25mph. I don'tthink you can do that with 60 G.I. since you would need to be spinning at around 140RPM!
some people can really spin.
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Old 02-17-09, 09:41 PM
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Originally Posted by NEXUS View Post
40km/h = 25mph. I don'tthink you can do that with 60 G.I. since you would need to be spinning at around 140RPM!
I bet he can.

He's a whippet.
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Old 02-17-09, 09:49 PM
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Originally Posted by NEXUS View Post
40km/h = 25mph. I don'tthink you can do that with 60 G.I. since you would need to be spinning at around 140RPM!
With youngish legs and proper training perfectly possible. Per my understanding some track racers routinely go higher than that. In "The Dancing Chain", third edition it is mentioned that one rider behind a race car with wind break for the rider was doing about 186 cadence at the record speed that he reached, about 240 KPH.

It would reallly hurt to come off a bicycle at that speed! Maybe why the last several speed record riders I have seen photographed were shown wearing motorcycle racing leathers.

Gear inches choice and cadence are highly individual and vary widely depending on rider condition, type of bike and terrain in the riding area.
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Old 02-17-09, 09:57 PM
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Originally Posted by NEXUS View Post
40km/h = 25mph. I don'tthink you can do that with 60 G.I. since you would need to be spinning at around 140RPM!
The only time I can do that is going downhill on the fixed gear bike, and my legs are just along for the ride.
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Old 02-17-09, 10:17 PM
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I have spun my fg out to 160 plus rpm on some downhills (running 81 gear inches)... you do not want anyting to go wrong at that speed and you must keep putting a little power to the pedals.

And I have old legs.
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Old 02-17-09, 10:20 PM
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What is your top gear inch?
48 x 11 = 116.8 gi


I noticed that most SS bikes are geared around 60-65 inches. Isn't that way too low?
Mine's geared 44 x 18 on both the fixed and free sides. That's 64.5 gi and it's not too low. My round trip commute is 25 miles and covers 2000' of elevation gain with 3 climbs of 1 mile or longer.
Average cruising speed of 18.5mph puts me at a comfortable 95 RPMs.
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Old 02-17-09, 10:54 PM
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Originally Posted by Sixty Fiver View Post
I have spun my fg out to 160 plus rpm on some downhills (running 81 gear inches)... you do not want anyting to go wrong at that speed and you must keep putting a little power to the pedals.

And I have old legs.
That would put you at over 100mph! Did I ever tell you about the 1,200 pound catfish I once caught? It jumped back in the water while I was fiddling with the Polaroid.
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Old 02-17-09, 11:31 PM
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Originally Posted by NEXUS View Post
That would put you at over 100mph!
If he said it was on a 700c tire...

I happen to know that Fiver's got a 20" fg folder somewhere in his stable, and I'm willing to put money down that it was this bike he topped 160rpms on.

120rpm on a 20 incher running 81gi is only 29mph. 160rpm would be somewhere around 38mph.



Maths are fun!
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Old 02-18-09, 12:27 AM
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Originally Posted by NEXUS View Post
That would put you at over 100mph! Did I ever tell you about the 1,200 pound catfish I once caught? It jumped back in the water while I was fiddling with the Polaroid.
Math is fun...

It also works out to 40 mph / 61 kmh on a 700c road bike...

My friend was chasing me on his road bike and said he had never seen anyone pedalling so fast and clocked me at 40 mph before he chickened out and hit his brakes.

This applet rocks and makes math easy.

http://software.bareknucklebrigade.c...it.applet.html

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Old 02-18-09, 12:50 AM
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Gear inches are determined by chainring teeth * wheelsize / cog teeth.

X gear inches at Y rpm is always going to yield Z speed.

Getting 81 gear inches on a folder with 20 inch wheels requires a 53:12 combination and that requires some pretty high end parts... only Phil Wood makes a 12 tooth fixed cog and it needs a special lock ring.

You could always run a 61:14 to get the same gearing...
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Old 02-18-09, 12:56 AM
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Originally Posted by Sixty Fiver View Post
I have spun my fg out to 160 plus rpm on some downhills (running 81 gear inches)... you do not want anyting to go wrong at that speed and you must keep putting a little power to the pedals.

And I have old legs.
Finis...

After this Kessel run I hit the bottom of the hill and as soon as I stopped I dropped my chain... I discovered later that I had bent the chainring.

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Old 02-18-09, 03:34 AM
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I am running 283 gear inches all the time
62t crank
7t cog
32 inch wheel




knock knock.
this is the world speed record forum, isn't it?
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Old 02-18-09, 07:44 AM
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Originally Posted by tatfiend View Post
With youngish legs and proper training perfectly possible. Per my understanding some track racers routinely go higher than that. In "The Dancing Chain", third edition it is mentioned that one rider behind a race car with wind break for the rider was doing about 186 cadence at the record speed that he reached, about 240 KPH.
As reported in the New York Times the following day, Frank Murphy covered the measured mile in 57.8 seconds on a bicycle with a 104 gear inch drivetrain. For the math challenged, that's just over 200rpm at the cranks.

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PS - This happened on June 30, 1899.

PPS - Frank (a.k.a. "Mile-A-Minute") Murphy gave roller riding demonstrations where he spun over 300rpm.
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Old 02-18-09, 07:46 AM
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I can't break the 200rpm barrier. I max out at 197rpm on the trainer thus far.
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Old 02-18-09, 08:10 AM
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I have my 8-sp bikes set up with gears ranging from 28" to 86" or so. I don't use the top two gears very much; only on a good downhill. When I do, I often get up to 35 mph, occasionally over 40. The fastest speed I can remember seeing on my mileage computer was 47.2, but I was younger then (it was 1983!).

I can spin 160 rpm easily enough, but don't know my maximum.
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