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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 06-18-09, 06:29 AM   #1
Trance
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(a different type of) gear ratio question

hey guys, hows it going?

i have a different question on fixed gear conversions. at the moment i ride an old road bike, predominately in the gears 42x15 (73.6 inches) and 42x13 (84/.9 inches).

I did a Respiratory Exchange Ratio test at University and found that i was working my aerobic system with the 42x15, but not in the 42x13, which used muscular power. i had a test ride at a local bike shop of a fixed gear, and thought of changing my back wheel (needs replacing anyway) to a fixed. bike mechanic says it'll cost less for the fixed wheel, sprocket, and chain anyway; i can do the rest myself.

I've heard that its easier to run faster sprockets on fixed gears, as theres more mechanical power in the bike due to no deraillers and a straight chainline, and heard similar contradicting arguments.

from experience, would i be all right to train my heart on a 42x13 instead of a 42x15 if i converted to fixed gears?

my cranks are 170 and wheels are 700C if that makes any difference.

cheers guys
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Old 06-18-09, 06:35 AM   #2
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Points for a very educated post.
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Old 06-18-09, 06:51 AM   #3
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42x13 is a beastly gear. I wouldn't run that anywhere that isn't complete flat.
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Old 06-18-09, 07:19 AM   #4
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I don't think 42:13 is that high but I do think if you are trying to get a more aerobic workout, you should spin somewhere in the mid 70 GI. 42:14 would give you 81 GI which is a little high for these purposes, so I would go with the 15t cog. I won't pretend to be an expert in nutrition and training, but from the knowledge I have gleaned about cadence and cycling, this is more in the range of GI that will train you to spin better. Obviously you don't want it so small that you are spinning out constantly, but you want it to be low enough that you are able to spin out.

One relevant question would be though if you have to take any practicalities into consideration, such as ... is this simply for training rides or is this ratio also intended for commuting, running errands, etc?
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Old 06-18-09, 08:09 AM   #5
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cheers for the replys guys.as to the question though, i also wondered about this, and therefore a flipflop hub, however, the price factor and the fact that my dropouts are angled (horizontally, but a bit upwards) tell me i shouldprobably stick with just one.i do train mostly, but i also like to get across the suburbs of the sydneyscape quickly to see girls and the such. will that create a problem with the 15 tooth?also, will the 15 tooth be "much" easier to pull if i go to a 15 tooth fixed? (due to chainline and such)
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Old 06-18-09, 08:11 AM   #6
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I think the important part of making a decision is what type of riding you are going to be doing most often. If you are riding in the city with lots of stop and go definitely go with the 42x15 but if you are going to be out in the country more where you can ride without having to stop as often and you feel comfortable with the 42x13 then go with that.

Personally I would go with the 42x15 because I would rather spin than mash
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Old 06-18-09, 08:33 AM   #7
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sounds like to me that you should get a heart rate monitor. If you are using strength, you are still training your heart especially if its anything longer distances. Your heart rate is still elevated with pure strength exercise such as weight lifting (its just that the heart rate isnt elevated long enough to have significant effect).

I highly recommend getting a heart rate monitor for training as this will give you hard data on your training level as well as progress. As a last point, its better to train with several gears as well as different terrain. This makes it more difficult for the body to adapt thus making better endurance/str increases. Hope that helps
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Old 06-18-09, 08:33 AM   #8
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Whereabouts in Sydney do you ride?

The bike part of my commute is from Rhodes to Canley Vale via Parramatta and I do that on 65 gear inches. I would consider that run to be reasonably flat but I wouldn't really want to go much higher ratio.
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Old 06-18-09, 08:36 AM   #9
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65 GI sounds incredibly low, don't you think? For flats?
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Old 06-18-09, 08:37 AM   #10
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Trance:

If you're that curious about the difference between how much more "efficient" a FG is than your geared bike, it is always an option to not route your chain through the deraillers and run your bike as a single speed in the gear combination of your choosing. The chainline might not be dead perfect, but the differences there will be really negligible.

I'm guessing either way, if you're liking 72GI on your geared bike, you're not going to be jumping up to 88GI on the FG just because "the drivetrain is more efficient".
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Old 06-18-09, 09:27 AM   #11
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all right, cheers guys its something to consider for the future. someone told me it wouldnt be a big deal to go from a 15 tooth to 13 tooth, so i might just try the 15 then see whats up.

johan, i study sports science at Uni, and am trying to get my heartrate down down down. thanks for the info though, that reminds me; i need new batteries.. the reason for the concept you explained (fwiw) is that the three energy systems dont run independently of each other; only a highly trained athlete can use purelyaerobic energy without musclar power

i ride around moorebank/liverpool /chipping norton lakes (great scenery) often at relative high heart rates, but just broke a brake lever off and rear wheel (spokes and rim) today. i can still ride on the hood, but the rear wheel (a 6 speed) might be quicker replaced by a fixed gear wheel. guess the money problem is why i'm curious..

Last edited by Trance; 06-18-09 at 09:31 AM.
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Old 06-18-09, 09:55 AM   #12
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if you really want to go fast, a fixed gear isnt the way. however, a fixed gear can make you fast. a big gear will allow you to go faster on a fixed gear now, but training on a lower gear and working to be able to spin bigger and bigger gears will increase your speed and stamina on any bike much more with time. with efficiency, a larger setup with the same ratio will be more efficient.
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Old 06-18-09, 10:18 AM   #13
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Quote:
Originally Posted by Johan13 View Post
sounds like to me that you should get a heart rate monitor. If you are using strength, you are still training your heart especially if its anything longer distances. Your heart rate is still elevated with pure strength exercise such as weight lifting (its just that the heart rate isnt elevated long enough to have significant effect).

I highly recommend getting a heart rate monitor for training as this will give you hard data on your training level as well as progress. As a last point, its better to train with several gears as well as different terrain. This makes it more difficult for the body to adapt thus making better endurance/str increases. Hope that helps
I was going to say something along these lines too. In regards to an actual workout, you'd be better off buying a cheap Polar and a used rear wheel to replace your broken one. It wouldn't be a bad idea to try and utilize more than the two gears that you currently use.
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