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Old 02-01-06, 05:10 AM   #1
geebee
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How to fit twin rear wheels?

I would like to setup the rear end of a bike I am building with a wheel setup similar to the Tomahawk.
But I will need drive to both wheels to allow cornering at speed, I was wondering if anyone had any thoughts on the best way to achieve this?
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Old 02-01-06, 06:54 AM   #2
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find a hub with lots of holes (like one of those 90+ types). then crisscross the spokes between two hubs. don't tighten the spokes until you've inflated the tires, because the tires will push the rims apart and over stretch the spokes.

oh, and keep the valves 180 degrees from one another for balance. or maybe 120 degrees, with a reflector between them.
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Old 02-01-06, 08:49 AM   #3
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That motorcycle uses independent suspension for each wheel. You could try something similar so that the inside wheel can move up during a turn, while the outside wheel stays down. Perhaps something similar to Connondale lefties adapted as seatstays.
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Old 02-01-06, 04:36 PM   #4
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Forgot to mention that I would like the chain to drive between the wheels if possible, not essential but would be nice.
i want to use a couple of innova 3" tyres that fit on standard 20" bmx rims so lots of tyre over hang on the sides.
I like the idea of independent swing arms but it would require buying another couple of bikes for parts and I suspect spring tension would have to be spot on to work.
Thanks all keep the ideas coming.
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Old 02-17-06, 12:45 PM   #5
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Two hubs mounted on the same extended axle, with two single cog free wheels in the center. Then use two chain rings and chains. One free wheel would have to be spun on backwards (not a problem) but I imagine you could get the two very close this way. More than close enough for your 3 inch tires.
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Old 02-17-06, 02:34 PM   #6
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You could also get a trike rear end and chop it down so you had just enough axle sticking out on either side of the center to fit the tire overhang and chain. No suspension, but it would probably be a lot easier to make.
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Old 02-17-06, 03:47 PM   #7
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Quote:
Originally Posted by AlmostTrick
Two hubs mounted on the same extended axle, with two single cog free wheels in the center. Then use two chain rings and chains. One free wheel would have to be spun on backwards (not a problem) but I imagine you could get the two very close this way. More than close enough for your 3 inch tires.

Where this gets complicated is in how you run the chain.
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Old 02-17-06, 04:06 PM   #8
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http://mnhpva.org/Meetings/Nov_04/pages/01.html and the next few pages, shows a leaning trike. It has two swingarms linked by a bellcrank, the big rectangular aluminum bar.

It rides just like a two wheeler. It doesn't need to drive both rear wheels, as the weight is always evenly distributed between the rear wheels. The shaft on the 5th photo is his first attempt at a lockout mechanism for holding it up at stops.

If you were to always ride it like a bike, the swingarms could be right next to each other. It seems to me that with a bit of fooling around, you should be able to get wide tires to within about 1.5"-2" of each other. The bellcrank could be much smaller and lighter. Especially if the swingarm pivots were at the top of the swingarms and short tie rods linked the bottoms to a bellcrank under the frame.
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Old 02-17-06, 04:13 PM   #9
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Quote:
Originally Posted by halfbiked
Where this gets complicated is in how you run the chain.
Your frame would need an offset bottom bracket. (driven off a BB/crank in the regular position) That or you could put a chain ring on each side, but then you'd have to space the wheels further apart, which it sounds like you don't want to do.

Last edited by AlmostTrick; 02-17-06 at 05:20 PM.
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Old 02-18-06, 09:16 AM   #10
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You would need to start with a Starley Differential.First invented in 1877.Differentials(chain pull type)were used on Harley 3 wheelers and other 3 wheel motorcycles.I think there were some 3 wheel mo-peds--that might be a source--maybe those old honda 3 wheelers might have someting to look at.This will be a major piece of work---good luck---sam
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