Belt_length_calculator

	A	B	C	D	E	F	G	H	K	L	N
1
2		Brompton w/ carbon drive		w/ Veer belt & parts		w/ Veer belt & custom parts
3		in	mm	in	mm	in	mm
4	d1	16.1875	411.163	16.1875	411.163	16.1875	411.163	distance between chainwheel centers			1165.225
5		0.433	11.0	0.315	8.0	0.315	8.0	tooth pitch
6	t1	14	14	30	30	19	19	number of teeth – cog			17.14285714
7	t2	60	60	72	72	100	100	number of teeth – chainwheel			57.14285714
8		4.29	4.29	2.40	2.40	5.26	5.26	ratio
9	r1	0.96	24.51	1.50	38.20	0.95	24.19	radius of cog
10	r2	4.14	105.04	3.61	91.67	5.01	127.32	radius of chainwheel
11	r2-r1	3.17	80.53	2.11	53.48	4.06	103.13	difference in radius
12	d2	15.87	403.20	16.05	407.67	15.67	398.02	d2 - chain distance - tangent to tangent
13	theta	0.20	0.20	0.13	0.13	0.25	0.25	angle between d1 and d2
14	d3	14.62	371.42	12.28	311.91	18.29	464.56	chain wrap - chainwheel
15	d4	2.65	67.34	4.33	110.04	2.51	63.73	chain wrap - cog
16
17	d	49.0	1245.1	48.7	1237.3	52.1	1324.3	exact belt length		Standard lengths:
18		49.4	1254.0	48.8	1240.0	52.3	1328.0	belt length (rounded up)		GT2-8: 2800, 2840, 3048
19		0.3	8.9	0.1	2.7	0.1	3.7	difference (slack to be taken up)
20		114	114	155	155	166	166	teeth		GT2-14: 2800 (200t), 3136 (224t)
21
22
23									CenterTrack belts come in lengths of 113, 115,
24									118, 122, and 125 teeth
25									8-mm pitch belts: 153, 160, 180 teeth
26									http://sheldonbrown.com/internal-gears.html
27									Most current internal-gear hubs take 3-splined sprockets, interchangeable among brands
28									It is also fairly easy to modify any Shimano cassette sprocket that doesn't have a built-in spacer. These are available from 14-34 teeth. Shimano cassette sprockets have the same internal diameter as those used with internal gear hubs, but have 9 splines instead of 3. With a suitable grinder, 6 of the splines need to be removed, and the corners of the remaining three rounded off. A thin spacer washer may also be needed, because the cassette sprockets are a bit thinner than the stock sprockets.
29
30									CenterTrack Sprockets
31									60-tooth	7898-0145
32									20-tooth, 9-spline	7898-0152
33									Belt (12 mm, 115 teeth)	9255-0877
34
35
36									CDX sprockets
37									60-tooth	7898-0031
38									20-tooth, 9-spline	7898-0032
39									Belt (12 mm, 115 teeth)	9255-0829
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