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Category: Bicycles

Fixed with Vertical Dropouts

So I've been meaning for some time now to figure out a method for finding properly fitting chainring combinations to use on a fixed gear with vertical dropouts. This guy from the point83 forums claims to have one. Does this look reasonable to all you math/bike types?

OK, basic math...
Add the number of teeth on your chainring and on the rear cog. Take the total, and look it up.

40 = 0"+/- 1/2"
41 = 1/8" +/- 1/2"
42 = 1/4" +/- 1/2"
43 = 3/8" +/- 1/2"
44 = 0"+/- 1/2"
45 = 1/8" +/- 1/2"
46 = 1/4" +/- 1/2"
47 = 3/8" +/- 1/2"
48 = 0"+/- 1/2"
49 = 1/8" +/- 1/2"
50 = 1/4" +/- 1/2"
51 = 3/8" +/- 1/2"
52 = 0"+/- 1/2"
53 = 1/8" +/- 1/2"
54 = 1/4" +/- 1/2"
55 = 3/8" +/- 1/2"
56 = 0"+/- 1/2"
57 = 1/8" +/- 1/2"
58 = 1/4" +/- 1/2"
59 = 3/8" +/- 1/2"
60 = 0"+/- 1/2"
61 = 1/8" +/- 1/2"
62 = 1/4" +/- 1/2"
63 = 3/8" +/- 1/2"
64 = 0"+/- 1/2"
65 = 1/8" +/- 1/2"
66 = 1/4" +/- 1/2"
67 = 3/8" +/- 1/2"
68 = 0"+/- 1/2"
69 = 1/8" +/- 1/2"
70 = 1/4" +/- 1/2"
71 = 3/8" +/- 1/2"

As you can see, it repeats. Here's the notion, For each tooth you add, you "remove" a 1/4 of a link of chain (assuming you don't change the chain length and could actually remove 1/4 of a link). So if you add 4 teeth, you need to add a link to your chain. Pin to pin is 1/2", averaged out on both top and bottom is 1/8" and there you go.

So, if you know your dropout to BB is 14.5" center to center (BMX in this case), you can run a gear combination where the total number of teeth equals 40, 44, 48, 52, 56, 60, etc. The difference in length due to the chainring being larger than the cog is not worth calculating. Besides, chains wear.

posted by graham Email | 02/08/06 | 08:16:57 pm | 26 views | math, Bicycles | 9 comments


Which Frame Should I Use?

It's definately a better frame, but is the LeMond too regular, do you think?


posted by graham Email | 01/21/06 | 12:07:49 am | 5 views | random, Bicycles | 1 comment


Spyker Bicycle = WTF?!!!1!!!

I honestly never expected the Colnago/Ferrari bikes to be outdone in terms of exorbitance, but I think this bike may have accomplished just that. It's $12,000 and change, a city bike, and has leather grips. Click on the image for hi-res photos of the thing.

posted by graham Email | 12/26/05 | 09:59:23 pm | 7 views | random, Cars, Bicycles | Leave a comment


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