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Recumbent What IS that thing?! Recumbents may be odd looking, but they have many advantages over a "wedgie" bicycle. Discuss the in's and out's recumbent lifestyle in the recumbent forum.

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Old 12-10-05, 09:45 PM   #1
FarHorizon
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Rear wheel steering?

Out of curiosity, has anyone made a front-wheel-drive recumbent with rear-wheel-steering? It would seem that having the drive train concentrated in the front of the bike (where the power is developed) would be more efficient than having to route a mile of chain to the rear wheel.

What are the physics of rear wheel steering? Would such a bike be rideable? What type of geometry would be needed to provide adequate rear-wheel-trail for stability? Does anyone make such a contraption?

The steering would probably need to be under-seat, with an offset tiller bar used to move the rear "fork." The idea is intriguing...
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Old 12-10-05, 09:55 PM   #2
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Couldn't a setup similar to USS for a LWB be used?
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Old 12-10-05, 10:05 PM   #3
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Quote:
Originally Posted by Dchiefransom
Couldn't a setup similar to USS for a LWB be used?
Pardon my ignorance - What's "USS?" I'm presuming it's "Under-Seat Steering?" If so, then yes - that's exactly what I suggest in my original post (just not in those words).
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Old 12-11-05, 10:17 AM   #4
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Quote:
Originally Posted by FarHorizon
Pardon my ignorance - What's "USS?" I'm presuming it's "Under-Seat Steering?" If so, then yes - that's exactly what I suggest in my original post (just not in those words).
As far as I know the use of rear steering has been used and is still used by some recumbentfans. How it works I don't know however.
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Old 12-11-05, 11:22 AM   #5
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I've seen pics of one or two RWS trikes. With a trike, balance isn't a problem. The problem with RWS is that getting it to go where you want is not intuitive, making them extremely difficult to ride & nearly impossible to balance. Even as trikes they required massively-stretched wheelbases to bring the weirdity down to a manageable level. Havng FWD is not a problem, though. Zox does it, Barcroft Dakota does it, Cobrabike does it... You can even get a kit from Cruzbikes that converts a dual-suspended mountain bike into a FWD bent.
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Old 12-11-05, 04:01 PM   #6
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I had some similar thoughts, and it turned out my friend built just such a bike a few summers ago. He said it was extremely difficult to control, and he barely managed to ride it down the block. Nevertheless he thought that it could be improved a lot by adjusting the geometry.
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Old 12-11-05, 04:22 PM   #7
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Quote:
Originally Posted by the homealien
I had some similar thoughts, and it turned out my friend built just such a bike a few summers ago. He said it was extremely difficult to control, and he barely managed to ride it down the block. Nevertheless he thought that it could be improved a lot by adjusting the geometry.
I suspect the villan is trail. The angle of the steering mechanism should lead the contact point of the wheel (as it does in all diamond frame bikes). If one reverses a conventional fork to create a rear-wheel-steerer (RWS), then one is trying to "push" the contact point of the wheel ahead of the steering axis. This would make for EXTREMELY difficult control!

For a successful RWS mechanism, the "head tube" would need to be oriented forward and down in the direction of travel (just like it is on a diamond frame bike). Then the trail induced by the steering mechanism itself would stabilize the bike (just like it does on a diamond frame bike), and the entire bike should have stability equivalent to a normal front wheel steerer.

This is all theoretical at this point... I really don't want to get into frame building, but I'd very much like a front wheel drive recumbent. I asked in the frame builders forum if anyone custom built recumbents and got told, essentially, "why bother?"
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Old 12-11-05, 04:26 PM   #8
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It was probably hard to ride cause no matter how hard we try we still use steering to balance. You'd have to learn to ride a bike all over again.
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Old 12-12-05, 03:18 AM   #9
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There have been several rws trikes, they all appear to suffer control issues particularly at speed ie. dangerously unstable. Great concept but falls down in execution, at least thus far.
Google you will find lots of info.
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Old 12-12-05, 11:09 AM   #10
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The problem with RWS is that you can't just point the front end where you want to go. Instead, you have to point the rear end away from where you want to go. While you might think the two are the same, they're not. It's a whole different paradigm.

As I pointed out earlier, FWD and FWS are not mutually exclusive. Personally, I like the concept of FWD. There are two styles of FWD, 'moving bottom bracket' such as the Cruzbike, and 'fixed bottom bracket' in which the chain twists as the front steering/drive wheel is turned. Although there are limits to the amount of twist the chain can handle, FBB is actually pretty efficient in normal use. The MBB style has the advantage of being somewhat no-hands-rideable, but the disadvantage is that pedal steer is tremendous, so pedaling hard causes control problems.
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Old 12-12-05, 11:36 AM   #11
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Are there differences in efficiency between moving bottom bracket and fixed bottom bracket? Doesn't the chainwheel gnaw at one's ankles with the moving bottom bracket?
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Old 12-13-05, 09:11 AM   #12
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Hi, first time poster here. Here is my latest Moving Bottom Bracket bike that I have been working on for a while. It is front wheel drive/ front steer:

atomBLASTER

Since the BB swings with the steering, no, the chainwheel does not contact my leg.
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Old 12-13-05, 10:32 AM   #13
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A few years back I saw a diagram of a front wheel Drive recumbent bike and the pivot point was two rods connected over the head and below the seat so when the biker wantes to turn all he did was pull left or right . But I think what is wrong with front wheel drive systems is that there is poor traction .
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Old 12-13-05, 11:38 AM   #14
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AS you turn you twist the axis of your feet versus your hips. I don't see how you could pedal and turn at the same time.
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Old 12-13-05, 12:03 PM   #15
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Keith,

I think the answer to you question is that most turning on a bicycle (especially at speed) involves minute direction change; at most a couple of degrees. Because of this, turning is not a problem. Most direction change at any speed is done by leaning, mostly.

Low speed, sharp turns do cause the *inner* leg to sort of bow and the *outer* one to stretch, but it's no big deal, and is very easy to learn.

Tom Traylor has a website for his MBB FWD bikes, check it out:
Tom Traylors Moving Bottom Bracket Front Wheel Drive Bikes
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Old 12-13-05, 12:51 PM   #16
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Aren't there some established manufacturers who use front-wheel-drive? I thought I'd seen some.
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Old 12-13-05, 01:13 PM   #17
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Quote:
Originally Posted by FarHorizon
Aren't there some established manufacturers who use front-wheel-drive? I thought I'd seen some.
Yeah, but many of them have a unique gearing mechanism that keeps the BB fixed, while still allowing a full turning ability.
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Old 12-13-05, 01:18 PM   #18
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There are several FWD bent manufacturers I can think of. All of these bikes are are "twisting chain", not Moving Bottom Bracket like my bike. There are drawbacks and benefits to both designs.

Zox in Germany produces several FWD models.
zox bikes

And until he went out of business recently, Reynolds Weld Lab made some of the nicest custom Titanium twisting chain bikes.
Reynolds

And Barcroft makes at least one FWD bike, the Oregon:
Barcroft
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Old 12-13-05, 03:46 PM   #19
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As I mentioned before, another FWD maker is Cobrabikes

Twist chain (Fixed Bottom Bracket)
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Old 12-16-05, 03:52 AM   #20
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Quote:
Originally Posted by FarHorizon
Are there differences in efficiency between moving bottom bracket and fixed bottom bracket? Doesn't the chainwheel gnaw at one's ankles with the moving bottom bracket?
There are efficiency losses in twisting the chain so the moving bottom bracket bike has an edge there. The fixed bottom bracket bikes usually (although not alwasy) have an extra drive side pulley further adding inefficiencies.
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Old 12-16-05, 03:54 AM   #21
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Quote:
Originally Posted by FarHorizon
Out of curiosity, has anyone made a front-wheel-drive recumbent with rear-wheel-steering? It would seem that having the drive train concentrated in the front of the bike (where the power is developed) would be more efficient than having to route a mile of chain to the rear wheel.

What are the physics of rear wheel steering? Would such a bike be rideable? What type of geometry would be needed to provide adequate rear-wheel-trail for stability? Does anyone make such a contraption?

The steering would probably need to be under-seat, with an offset tiller bar used to move the rear "fork." The idea is intriguing...
http://wannee.nl/hpv/abt/e-index.htm
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Old 12-16-05, 08:07 AM   #22
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Quote:
Originally Posted by meb
There are efficiency losses in twisting the chain so the moving bottom bracket bike has an edge there. The fixed bottom bracket bikes usually (although not alwasy) have an extra drive side pulley further adding inefficiencies.
I'm not sure that a MBB has the edge in efficiency. After all, a significant amount of energy must be used by the upper body in order to counteract the inherent pedal steer, which would otherwise cause the front wheel to track back and forth with each pedal stroke. I'm told that doing so becomes second nature, but the energy expenditure still exists; and the only alternative is to limit power output. OTOH, idler pulleys are usually quoted as worth about 1% loss apiece, so figure losses for a 2 idler FBB system at 2% plus the twisting loss which is only significant at slow maneuvering speeds. It's hard to say which has better efficiency, since the upper body stuff will be hard to quantize.
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Old 12-16-05, 08:38 AM   #23
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Although my bike is MBB FWD, I'm also not sure it has an edge in efficiency. Theoretically it does, but as BlazingPedals states, it is hard to quantify the losses incurred due to the "unorthodox" nature of riding this type of bike. On my bike, I have rather large, Bachetta-type nandlebars on it which helps to counterbalance the forces induced by pedaling. A good spinning technique also helps to smooth things out.

All the "winning" bikes at Battle Mountain are pretty much twisting chain. I believe there are two reasons for this.

1) It is difficult to fit a MBB bike into a streamliner shell
2) MBB bikes "weave" as they go down the road. There is a slight "side to side" motion that is incurred by the pedaling forces. Not something you want when you're trying to set speed records.

However, in light of all this, when planning to build a FWD bike, I decided that MBB was good for what I wanted: a light, speedy bike with really quick steering and good climbing capability. I'm not out to set any speed records, and I didn't like the idea of all the pulleys/mid drives/etc... And I also read that you cannot back up a twist chain bike without the chain coming off. Something that everyone does in the "real" world. That seemed like it would quickly become a hassle.

Here are some pics:
atomBLASTER1
atomBLASTER2
atomBLASTER3
atomBLASTER4
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Old 12-16-05, 08:05 PM   #24
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Good job on the bike, atombikes. I have a question. It looks like you welded part of the boom to your stem. How do you get it apart, ie to change the headset? It seems like a clamp arrangement at the stem would be easier to maintain, although perhaps harder to make in the first place.
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Old 12-19-05, 07:46 AM   #25
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Thanks for the nice comment.

The bike does have a separable boom. In this pic you can see the quick release, and you can *kinda* see the socket head cap screw at the clamp location around the steerer tube.

clamp
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