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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 04-24-08, 10:08 AM   #1
ralphm2k
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Gear Inches question

I'm upgrading my drive-train. Right now I'm @ 72 gi's (48/18) - and I have no problems with that, but I want to go a bit faster and spin a bit slower. My daily ride is mostly flat, but it gets windy sometimes and my house is on a hill.

My shop guy suggested I go up to 81 (48/16). I decided not to and went one size down from his suggestion (46/16). So when my stuff comes in, I'll be @ 77 gi's.

I'll probably throw a 17 cog on the other side for windy days and that will be 1 more gear inch from where I'm at now. I'm just curious about the consensus of whether 5 gear inches is a significant jump on a fixed gear.

I'm also shortening my crank length form 172.5mm to 170 btw.
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Old 04-24-08, 10:19 AM   #2
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77 isn't bad for flatlands. You should be able to man up and handle it.
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Old 04-24-08, 10:25 AM   #3
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I ride ~77 now and it's not bad after you get used to it, especially in a basically flat area.
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Old 04-24-08, 10:29 AM   #4
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You'll have fun with that.
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Old 04-24-08, 10:32 AM   #5
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A 48:16 on 700:25 tyres is 79 gear inches.

I'd run a 17/19 to get 66 and 75 gear inches which would be pretty much perfect and barring that would run an 18 on the flip or that 19 if you can handle a 3 tooth change in your dropout.
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Old 04-24-08, 10:50 AM   #6
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A 48:16 on 700:25 tyres is 79 gear inches.
I'm going by this, I guess it's a rough estimate...

http://veloroutes.org/tools/...

Thanks all.
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Old 04-24-08, 10:55 AM   #7
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I use Sheldon Brown's gear inch calculator as it is a little more specific as it accounts for crank length and a great number of wheel sizes / tire combinations... it is still not dead on as tyres withing a certain size range still vary a little.
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Old 04-24-08, 11:03 AM   #8
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I use Sheldon Brown's gear inch calculator as it is a little more specific as it accounts for crank length and a great number of wheel sizes / tire combinations... it is still not dead on as tyres withing a certain size range still vary a little.
?

Crank length should never have any impact on gear inches.
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Old 04-24-08, 11:06 AM   #9
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I use this, which gives skid patch analysis and all sorts of good stuff.

According to it, I've got 75.7 gear inches running 49x17 on 700x23s. It works well in the wind and relatively flat terrain I encounter most days. I switch to the 19 on my Dingle cog every once in a while for a little more spin or if I'm tired.

I'd say you're in a good range.
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Old 04-24-08, 11:13 AM   #10
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I use this, which gives skid patch analysis and all sorts of good stuff.
Neat!
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Old 04-24-08, 11:18 AM   #11
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?

Crank length should never have any impact on gear inches.
It affects gain ratios.

Some folks use this instead of calculating gear inches.
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Old 04-24-08, 12:12 PM   #12
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You will probably be fine, but spinning builds character.

It seems to me that your plan involves changing both your ring and sprocket. I would consider 48/17 as a compromise. I am not sure what size tries you run, but for 23s that works out to be around 74GI.
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Old 04-24-08, 12:23 PM   #13
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Neat!
Yeah, I thought so... even though I've never skidded nor do I plan to, it's good to know I've got 17 lovely patches, or 34 if I unintentionally develop ambidextrous skidding ability.
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Old 04-24-08, 12:49 PM   #14
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Yeah, I thought so... even though I've never skidded nor do I plan to, it's good to know I've got 17 lovely patches, or 34 if I unintentionally develop ambidextrous skidding ability.
I can skid.. but not effectively enough to stop myself in a pinch. My left fool likes to pop out of my clip too.
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Old 04-24-08, 12:53 PM   #15
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I can skid.. but not effectively enough to stop myself in a pinch. My left fool likes to pop out of my clip too.
Might want to reevaluate your strap setup (tighten them a tad, or get doubles... maybe your clips are even the wrong size).
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Old 04-24-08, 01:08 PM   #16
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On windy days I far prefer to work hard at at too low a cadence into the wind and fly with it without being spin limited (for me ~160rpm) than to fight the wind with a good ratio and spin out when it's on my back. I've never flipped my rear wheel to my lower available ratio even on the windiest of days. Just a thought.

5g" will be very notable.

Al
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Old 04-24-08, 01:13 PM   #17
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You will probably be fine, but spinning builds character.

It seems to me that your plan involves changing both your ring and sprocket. I would consider 48/17 as a compromise. I am not sure what size tries you run, but for 23s that works out to be around 74GI.

I am.
My old drivetrain is 3/32. I ordered a 1/8 crankset and chain on-line - thinking I could use my old 18 tooth cog. I initially was going stick with a 48 tooth chainring. I bought my wheels @ my LBS and had them thow a 16 tooth cog on it (after a discussion about ratio's and he guy @ the shop saying could get away with using my old cog). When I got home with my new wheel-set, I decided using the old cog might not be such a good idea. - and after thinking about the 48/16 ratio, I changed my order to a more reasonable (to me) 46/16.
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Old 04-24-08, 01:16 PM   #18
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Might want to reevaluate your strap setup (tighten them a tad, or get doubles... maybe your clips are even the wrong size).

The clips are the right size. My technique sucks. When I pull up, I have to think about not having my toe pointed down.
I might look into doubles. Those Soma 4 gate clips are sexy.

Last edited by ralphm2k; 04-25-08 at 07:03 AM.
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