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Chain length stuff
I use old Torpedo hubs on my bikes, which these days have rather
short rear forks. It is always a problem when I change to a different rear sprocket, to find the right chain length so that the rear axle is still within the fork length. With these hubs, the chain has to be tight. Is there a formula for calculating the length between the bottom bracket and the rear axle for a given chain length and number of teeth on the sprocket? Or, better still, the change in that length when I change to a sprocket with a different number of teeth? That would tell me how many chain links I have to add or subtract when I change to a different sprocket, so as to still be within the fork travel. I thought along the lines, if I add one tooth, I must add one chain link (pair), but that doesn't work, probably because an extra tooth also changes the sprocket's diameter. As an aside, I have a small collection of these hubs and they are now about 70 years old. When I get one, it is usually rusty, but when I open it up, it is perfect inside. They don't make them like that any more. -- Dieter Britz |
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#2
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Chain length stuff
On Sat, 20 Mar 2021 08:07:52 +0000, Dieter Britz wrote:
I use old Torpedo hubs on my bikes, which these days have rather short rear forks. It is always a problem when I change to a different rear sprocket, to find the right chain length so that the rear axle is still within the fork length. With these hubs, the chain has to be tight. [...] Sorry, I found a good site that tells me all I need to know. -- Dieter Britz |
#3
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Chain length stuff
On 3/20/2021 3:07 AM, Dieter Britz wrote:
I use old Torpedo hubs on my bikes, which these days have rather short rear forks. It is always a problem when I change to a different rear sprocket, to find the right chain length so that the rear axle is still within the fork length. With these hubs, the chain has to be tight. Is there a formula for calculating the length between the bottom bracket and the rear axle for a given chain length and number of teeth on the sprocket? Or, better still, the change in that length when I change to a sprocket with a different number of teeth? That would tell me how many chain links I have to add or subtract when I change to a different sprocket, so as to still be within the fork travel. I thought along the lines, if I add one tooth, I must add one chain link (pair), but that doesn't work, probably because an extra tooth also changes the sprocket's diameter. As an aside, I have a small collection of these hubs and they are now about 70 years old. When I get one, it is usually rusty, but when I open it up, it is perfect inside. They don't make them like that any more. There's no simple rule. Fit the chain on your bike. Also, and this is important, don't over tighten your chain: http://www.yellowjersey.org/chainchk.html All the various components are nearly but not exactly round and concentric, such that chain tension varies as the system turns. A chain tight spot will greatly increase bearing wear at hub and crank. With minimally one inch of frame slot adjustment, you can achieve proper chain tension. There are half links for 1/8" chain if you feel one would be helpful: http://www.yellowjersey.org/photosfr...t/HALFLINK.JPG -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
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