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Qwendolyn
03-17-2008, 03:50 PM
I made the plunge to fixed gear a week ago, and was hoping for some advice about gear ratios. Just now I've got it set up with 48/16 (6.18 gain ratio, 81 inches)

I can get up all the hills I need to, and I'm not really used to spinning away like I am now on the flats and downhills. So was thinking I am probably fine with what I've got. But then I was looking around a bit on the 'nets to see what other people use and it seems that I may have too high of a gear. --Bad for knee health etc.

Advice?

mizake
03-17-2008, 04:39 PM
I made the plunge to fixed gear a week ago, and was hoping for some advice about gear ratios. Just now I've got it set up with 48/16 (6.18 gain ratio, 81 inches)

I can get up all the hills I need to, and I'm not really used to spinning away like I am now on the flats and downhills. So was thinking I am probably fine with what I've got. But then I was looking around a bit on the 'nets to see what other people use and it seems that I may have too high of a gear. --Bad for knee health etc.

Advice?

that personally seems a bit high to me as well. i'm running 44:16 right now and much more experienced people (dean @ bike central to name one) feel that even that's a little too much. however, try out that ratio for a while and if it works for you, i wouldn't change it. everyone's got their own comfort level re: fixed ratios.

Dillon
03-18-2008, 12:31 PM
I run 46:17 which is about the same as mizake. 81 seem high but I ride up to OHSU a lot so.. I'm sure it adds more stress to the knees. You'll get used to spinning fast. Maybe try buy a cheap used chainring and try out a smaller gear. Also if you do any skidding the 48/16 only skids in one area since most people always lock up their legs in the same place. Here's a little gear calc that I like to use.
http://software.bareknucklebrigade.com/

Qwendolyn
03-18-2008, 02:20 PM
thanks for the tips.

that chainring is brand new and it would seem a shame to throw it in the parts bin and go get a used one.

what i'll probably do is get an 18 tooth cog to put on the flip flop... but i'll see how i feel about the current set-up after another week or so.

toddistic
03-18-2008, 07:31 PM
out a 17t cog on instead of 18. You'll get more skid patches - in fact you get 17.

A skid patch is how often (on average) you skid your tire in the same place.

To figure it out use this handy dandy chart:

http://rideyourbike.com/images/skidspots.jpg

Its based on reducing your chainring and cog as a fraction so a 48x16 gear ration gets 3 patches because 48 / 16 reduces to 3/1 thus 3 patches but more than likely you only skid with your lead foot forward so it's more like 2 or 1 depending on how you start pedaling.

A 48 / 17 (which is what I use) gets 17 because 17 cant reduce against 48.

Anyway, hope that makes sense.

Qwendolyn
03-18-2008, 08:11 PM
I think there may be a theorem buried somewhere in those charts.

How's this...

Lemma 1: If p is not prime, then don't try to prime factor it in traffic, because you really should be watching the road.

Lemma 2: If p is prime, then put it on the rear cog and go ride. The bike is not gonna ride itself.

Theorem: If you don't remember very much number theory, one good place to post snarky theorems is on the internets!
Proof: See above. Which is what we were to have shown. QED, etc.

Corollary: Those look like useful charts, it's just that I'm a bit of a poser and this is my first fixed build and I can't skid yet but hey I've only been on the bike a week and I'm having fun (imagine crack-cocaine on two wheels only you can't coast) and having fun is what it's all about.

fetishridr
03-18-2008, 11:33 PM
try a 42 18 to work your spin on. thats 65 inches. 100rpms at 15 mph.
you can climb anything, and learn to spin 150 rpm on the down hills.
Yes, riding fixed is hard on your knees. rocking a racing gear or anything close will severely stress your patella.
try 70 inches or so if you dont want to spin so much.

Schrauf
03-23-2008, 07:05 PM
I'm just impressed that someone can have no problem climbing hills with an 81" gear. Wow. I would be walking a lot. Although if you never ride in the West Hills or other long climbs, maybe it is doable.

Qwendolyn
03-25-2008, 08:52 AM
I'm just impressed that someone can have no problem climbing hills with an 81" gear. Wow. I would be walking a lot. Although if you never ride in the West Hills or other long climbs, maybe it is doable.
It's just a commuter bike. --12 miles a day maximum. And yes, I definitely take MAX through the west hills.

huss
03-25-2008, 10:16 AM
I ride 48-16, wouldnt want to spin any faster going down hills. It gives you a nice cruising speed 18-22. Ok some hills are a pain in the ass, like Mt Tabor. Now thats good fun....:D

I've rode to the coast from Eugene, couple steep spots but made it...:cool:

Just depends how fast you like to spin, I like speed more, I'll attack the hills as they come.:rolleyes: