3 wheeled bicycle, downfalls?

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yoothgeye

yoothgeye

I build stuff.
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Not a trike, I need to replace one of my tall bikes, and looking for a way to make it ever more different, I'm thinking about giving it 3 wheels, in a row, like: O O O, the front 2 will be connected with a tie rod and both be steering wheels so that no wheels will "drag" when turning. Since the cranks will be much higher than on normal bikes, I can afford the space below to do this, the 3rd wheel/tire will also help lug some of the extra weight that is in a tall bike.

Besides added unneeded complexity (remember, it's a tall bike), what other downfalls might there be to this design?

I'm thinking right off that if I am going over a bump the front 2 steering wheels may "loft" the rear driving wheel, in some situations that could get sketchy, and may cause what is referred to in cars as "bump steer."

Since chainline normally impedes a caliper brake on my tall bikes I just run a front brake, This design would allow me to run a front and middle brake or just a middle brake.

I could make the front 2 forks both suspension forks or just make the middle one suspension to keep things from getting too odd over speed bumps.

What else can all you thinkers come up with?
 
cman said:
http://turnerrecumbents.com/Products.aspx click on the tandem tag.

Sounds like the only reason besides different is for better grip at increased speed and angulation. Do it.
Click to expand...

Looks like they have no mechanism to keep from lifting the front or rear over bumps, but I think now that keeping it rigid front and back with a "shock" in the middle will help minimize that.
 
Basically only worried about the speed bump scenario, which any bump on a tall bike I am careful on, but as for going up ramps (like from road up to sidewalk) the center wheel would lift leave you on a more familiar 2 wheels, so no worried there.
 
I think your best bet would be to have 2 wheels connected on a dollie, able to rock back and forth (up and down). And maybe the extra wheel should have a king pin angle geometry that allows it to naturally just follow along like a "caster".

Absent this, the geometry is just too dynamic to keep all wheels on the ground and pointed in EXACTLY the right direction under all conditions. Because of head tube angle and trail in the fork design, the effective length of a fork, height of the frame, and wheelbase, is constantly changing as you lean to turn. I think you would need to be a rocket scientist, (or a late 19th century mechanical engineer) to design 2 forks to both touch the road and point at exactly the right angle at all possible angles of lean and turn. I predict if you proceed as you are saying; a) when your 2 steer wheels are touching 1 is scrubbing, and b) much of the time the front (or rear depending on weight distribution) will be lifted off the road.
 
now you have me thinking about how to make the front and rear steer opposite of each other .... and how easily it would be to highside something with that set-up.

maybe a long wheel base with just a front steerer would work with a tandem axle in the middle (suspension fork), like a dump truck set up or something.
 
CCR said:
now you have me thinking about how to make the front and rear steer opposite of each other
Click to expand...
As far as I can tell this would be the best way, if you have both front and middle wheel turning they will have to turn at different rates to allow for the akerman priciple, it is easy enough to work out, but basically if your center wheel is exactly at the center, it will have to turn half as much as the front wheel to avoid scrubbing.

If you go with front and rear steer, it does not matter if they turn at the same rate, that would be the best way for them to work, also if your front wheel lifted off the ground (or rear for that matter) the opposite wheel can still apply the turn for you. Not saying it would be easy to ride, or that I wouldn't avoid turning over bumps or for that matter avoid bumps all together, but it may be the best way to make it work.

Just my opinion of course... :wink:

Luke.
 
Principles and theories at work here. I am curious, but getting less curious about it under one of my tall bikes.

Reverse steer could be pretty easy to make, but on a tall bike I need less steering input, not more.
 
Ideally, the two wheels would have to turn at different angles when steering. If they are just maintained parallel to each other, they won't all be rotating about a point. As to how much difference this makes, who knows. A tandem truck has the same issue with the rear wheels and seems to work okay.
 
I really think you'd be better off building something like kenny prather did with the green monster sidehack tall bike instead of the wheels in a row ... unless im just completely misunderstanding what your trying to pull off. Would even give you a chance to play with a hack side steering rig if you feel the need.

greenmonster.jpg



i do have an idea on how to retard the steering amount between the front and second wheel but it would be a geared set-up rather than just a linkage and tie rod set-up. Kind of like a rear steer tandem with a gear box ... but working in reverse.
 
This was all just thoughts, now that I've been outsmarted with science I'll stick to my original plan, just a basic replacement for my bigger tall bike, but with a more custom frame. I'll leave off any extraneous wheels.
 
CeeBee said:
It's scary, but you actually have me thinking about how to do this.
I seem to recall an older (80's maybe?) Science Fiction or action movie that had some crazy vehicle that had several sets of wheels that articulated over rocks, other vehicles, bad guys, etc. Maybe if someone else can put a name to what I'm thinking of you could study it and make an inline version suitable for a bicycle that wouldn't shorten your life.... :D
Click to expand...

Movie was Damnation Alley
 
I think the middle wheel would just be a hinderance. Even if the front and rear were rigid, a shock in the center would probably still be too stiff to allow for the middle tire to raise enough to allow all wheels to remain in contact with the ground if you go over a speed bump. If support is an issue , just make frame changes that will get it done. Not that science neccessarily matters. Trying something might not change the world, but can't hurt it either. Everybody said a 5.5 ft fork on a tall bike wouldn't support weight at the steer tube. 190 lbs and 4 yrs later they are still wrong.
 

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