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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 08-20-10, 04:31 AM   #1
Triple8Sol
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Smaller cog. Should I go from 46t to a 47t or 48t chainring?

Currently I'm running a 46x18 setup for hills, just because it's what I started with when I first started riding fixed 3yrs ago. It was ok at first but the weak 67.2 GI became annoying with how it tops out on flats (let alone downhill). I couldn't stand it so I picked up a cheap 15t take-off that I came across, but the 80.7 GI was too extreme for me on even moderate hills, so I went back to the 17. It's unbearable now, so trying to figure out what to do.

I'm gonna try out a 17t cog b/c it nearly doubles the skid patches, from 9-->17. I still need to be able to tackle moderate hills, but want to better keep up with friends on geared bikes on the flats/downhill.

Not sure if the 71.2 GI would be enough of a change for me? Or should I go with a 47t that makes it 72.7 GI or a 48t 74.3 GI?

Last edited by Triple8Sol; 08-20-10 at 04:36 AM.
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Old 08-20-10, 04:53 AM   #2
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I have no idea on how strong you are and your ability to get over hills, so I will base this on my personal experience.

I spin a low gear at 68 GI, which is perfect for my liking, I get up hills with ease, I learned to spin down hill. I live on a hill, and learning to spin was a fun experience. With that said, I can also go at a modest speed on the flat with not too much effort, I could just spin faster if I wanted more speed. I've tried 46/17 before, but it was slightly too high for my liking and because I love to spin down hill with my ratio so I changed it back.

Try to see how the 46x17 is like first, if you don't like it, move up a tooth on your chain ring. Cogs are generally cheaper to buy than chainrings, having a few cogs to play around to find your ratio is helpful.

Last edited by Squirrelli; 08-20-10 at 04:57 AM.
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Old 08-20-10, 06:52 AM   #3
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Maybe get a front triple with a rear cassette and two derailleurs.
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Old 08-20-10, 07:14 AM   #4
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I think your first mistake is trying to keep up with people on geared / freewheel bikes on downhills. Not gonna happen. All my life I've never exceeded 70gi on any of my road FG bikes, even though I race 90+ gi on the track. My gearing is based on the worst climbing / headwind conditions that I encounter, a minimum acceptable cadence of 60rpm under any circumstances, and 90+ rpm on the flats in calm conditions. As to optimal sprocket choices for skid patches, not an issue for me cuz I hardly ever skid.
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Old 08-20-10, 10:02 AM   #5
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there is not much difference between the 46 and the 47. Unless you are just fine tuning, go for the 48. You may be bettter off (and its cheaper) just to get a 16 tooth cog. I ride a 48x16 [correction: 42x16] on the street - puts me at 100rpm at 20mph - that is a good ballance for me.

leave the chain ring at 46 and get a cog that gets you where you want to be.

(your post is a little confusing. You went back to the 18 or to the 17?)

Last edited by chas58; 08-20-10 at 02:48 PM.
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Old 08-20-10, 10:07 AM   #6
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^^^100rpm puts you over 20mph

either try different cogs or practice spinning faster, or both
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Old 08-20-10, 10:12 AM   #7
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I ride a 48x16 on the street - puts me at 100rpm at 20mph
By my calculation, that gear ratio at 20mph should put you closer to 85rpm, assuming you are using 700x23c tires. I have a FG with 42 x 16 and 700x23c tubulars, and at 20mph I show about 100rpm, which I find to be a very comfortable cadence for extended riding.
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Old 08-20-10, 11:50 AM   #8
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No one here can tell you what is the best gear ratio for you. For starters, get a good chainring that (1) allows numerous skid patches and (2) puts you in the range of reasonable gear ratios when paired with typical sized cogs (15t-18t). Odd numbered chainrings tend to be best, like 47t or 49t. Then buy a few cogs and start experimenting. You may find that there is no best gear ratio. I regear my bikes frequently, depending on the situation.
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Old 08-20-10, 02:46 PM   #9
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Oops - I have a 42x16 for the street. ~100rpm and 20mph. Works great for me. That is the reference point I was trying to provide.

(The track bike has the 48t chain ring, and is 5-8 mph faster at a given rpm, depending on the cog I'm using at the time)

Last edited by chas58; 08-20-10 at 02:51 PM.
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Old 08-21-10, 02:29 PM   #10
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Originally Posted by TejanoTrackie View Post
I think your first mistake is trying to keep up with people on geared / freewheel bikes on downhills. Not gonna happen. All my life I've never exceeded 70gi on any of my road FG bikes, even though I race 90+ gi on the track. My gearing is based on the worst climbing / headwind conditions that I encounter, a minimum acceptable cadence of 60rpm under any circumstances, and 90+ rpm on the flats in calm conditions. As to optimal sprocket choices for skid patches, not an issue for me cuz I hardly ever skid.
I can't help that the few friends I have that are into cycling all have geared bikes, while only a small handful are fg/ss. Keep up may be the wrong term, but at least not have to work so damn hard the entire time to keep from falling too far back. I don't ride super steep hills much anymore, so that's why I can now give up some of that climbing ability and compromise for some more top end.

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there is not much difference between the 46 and the 47. Unless you are just fine tuning, go for the 48. You may be bettter off (and its cheaper) just to get a 16 tooth cog. I ride a 48x16 [correction: 42x16] on the street - puts me at 100rpm at 20mph - that is a good ballance for me.

leave the chain ring at 46 and get a cog that gets you where you want to be.

(your post is a little confusing. You went back to the 18 or to the 17?)
I went back to the 18t cog. Have a 17t on the way. Although I see alot of bikes come with a 48x16 stock setup, that won't work for me. Prob too high GI and only 1 skid patch just won't work.

I pretty much agree with all your logic here. When the new cog arrives, I guess I'll try running it with the current 46 ring first and see how that feels. I'll prob know better at that point whether I want a small change to the 47 or a bigger jump to 48. I was just hoping to get a new ring ordered as well and install it all at once.
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Old 08-21-10, 04:02 PM   #11
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I ride in san francisco and I am currently using a 46/17 set up. Perfect for me because I get my patches and seems to be a moderate balance between spinnin out and maintaining speed without working too hard. 70 - 73 GI is a good bet in general if you are in hilly terrain.
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Old 08-26-10, 09:16 PM   #12
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Installed the new cog today and went for a quick spin. The 46x17 actually feels pretty good. The +4 GI is noticeably harder on the hill climbs, but still very manageable. Also much better going back downhill, than before. I'm still debating what chainring to go with, so I'll prob ride a bit more and hold on on the decision for now.
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