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View Full Version : Any ideas on incoporating an internally geared hub?



theTman
09-20-2009, 08:12 PM
I just bought the vigilante instructions and I decided I wanted to go with an internally geared hub so I can have more than just one gear ratio since I live in an area that I need to climb some hills, and the bike will be rather heavy. I was thinking of putting in this one. http://www.shimano.com/publish/content/global_cycle/en/us/index/products/0/nexus/product.-code-SG-8R36.-type-.html Even if I spoked it to the wheel I wouldn't be able to get the chain to the gear. Does anyone have any ideas on how to do this, or an easier way using a regular derailleur?

PeterT
09-21-2009, 07:39 AM
Tman,

If you double team a 16 & 23 sprocket to your Shimano hub, then you can use your crank sprockets to drive the internal geared hub, via the 16 sprocket on the right side of the hub, this gives you the nine gears, and with the 23 joined to the left side of the hub, drive your rear wheel with an attached 14-20 sprocket (your choice) on the rear axle.
e.g. pedal crank has 24, 32, 42 and hub has 16 sprocket (Mechanical advantage (MA) has hub turning 24/16=1.5x faster, 32/16=2.25x faster, & 42/16=2.66x faster)... 23 sprocket is now turning at 1.5, 2.25 & 2.66 x pedal crank. This is in turn driving your rear wheel, with e.g. 23/16=1.44 MA.

Add these two ratios together, and you have the following MA 1.5 + 1.44 = 2.94. This means that you are now driving your rear wheel 2.94 times faster than you are pedaling, and your 9 speed hub is acting as a geared axle.

If you use closer geared sprockets, i.e 23 & 21 , then your ratios wont be as high e.g. 23/23 = 1, 23/21 = 1.1
etc. which is still acceptable for getting your rear wheel turning.

However don't go over the size of your drive sprocket or you will start reducing your final drive e.g 23/28 = 0.82 and you could find yourself pedaling up trees! :jester:

PeterT

John Lewis
09-21-2009, 08:00 AM
I think the easiest way to do it would be to use the hub as a mid drive. I think I've seen some examples of that in the forum so looking back through the posts may be profitable as would a google search on mid drive. I think that is essentially what Peter is suggesting.
You will probably need some good low gears to get moving and for hills. I always think it's better to be geared a bit low. On my commercial trike the highest gear is 120 gear inches but there is simply no way I can push it except down a good hill. It would have been more sensible to have topped at 90 or 100.

John Lewis