Four wheeled bike?

This is a long story.

I will be -very- brief.

My Mom and Stepfather are very immobile. Their health varies, but neither of them can do a ton of walking, and neither could be trusted to ride a bike. My Mom cannot drive. They live in a neighborhood that would lend itself to having some personal mobility.

So, can I GRM together a free four wheeled bike? None of those PVC jobs, I was thinking of some welding pieces and parts from a few old discarded bikes and making it work for near free. Perhaps with a few donations along the way.

I have drawn up the front suspension. I figure that if I get a mountain bike fork for each side, I can maintain the suspension from that. I do not know if you can grab a generic bike wheel and only support the bearing on one side like that. Here is what I think it might look like.

Regarding the seating and the steering, I was figuring each seat would control one side, one sprocket set and derailleur set for each rear wheel. Cheap and easy. An idler gear shifting the chain over to the side where the sprockets are. Something like this:

This way the bike chain would be just like typical. Neither side would know it was attached to another bike setup. I could throw up a nice awning and some fun ways of carrying stuff and they could be done. Something to get around with and not fall off of.

I love the idea, just a silly question why not a three wheeled cart bike. They are easier to build.

So... perhaps something along the lines of this?

(4-wheel bicycles are not exactly a new idea... I found that after about 5 seconds on Google)

With each seat controlling its own side., I don't think it will track straight.

wearymicrobe wrote: I love the idea, just a silly question why not a three wheeled cart bike. They are easier to build.

I figured stability would be worth it. Were you thinking one wheel up front? I want both of them to be able to ride on it together, so the center steering would be tough.

Woody wrote: With each seat controlling its own side., I don't think it will track straight.

OK, ideas as to how to mitigate?

I like the idea, but for what you want, did you think about simply buying a used sightseeing bike from a tourist bike rental shop? Like those:

They are heavy, slow and ugly, but they are sturdy and everywhere.

Designing a bike is harder than it looks. Below is the tadpole recumbent trike I built six years ago (can't beleive this is the only picture I have of it ) I thought I would stick that together in one or two weekends, but it wasn't that easy.

If you still want to do it, here is what I've learned:

1 - Go recumbent. For people that aren't into bikes (especially the ones that are out of shape), a recumbent is a lot more comfortable. If they always have a pain in the rear whenever they use it, they won't use it long. I use my bike for hours at a time and I'm always amazed how comfortable I still am after my ride.
2 - Manage your CG well. The persons riding the bike will always be much heavier than the bike, so their position determines the CG's location. When you cannot lean into the turns, the high and location of the CG becomes really important. It's very easy to make an unstable bike.
3 - It's not the going that's hard to balance, it's the stopping. Most bike braking systems are mechanical, meaning they aren't that consistent. It makes keeping the balance quite hard. On my bike, I went with mechanical disc brakes. It took a lot of fidgeting to get the balance right, and I still need to make tiny adjustments once in a while. That's not a problem on my bike because the calipers are easily reached from my seat. For a two-seater, i'd look at hydraulic brakes from a MTB or a small scooter.
4 - Whatever steering you choose, make sure it has the least amount of scrub as possible. On my bike, I didn't make the Ackerman adjustable, and I missed it a bit. When I'm going straightish, it's not a problem, but when I turn tight, I loose a suprising amount of momentum for such a small mistake. That's frustrating.
5 - Keep the width in mine. A lot of bike paths have width limitations. Depending on where the bike is used, that could come into play.

That's all I can think of.

If these folks are as "immobile" as Tuna suggests, I don't think they'd flop down on a recumbent as low as the one above.

My recumbent was made for speed. For your folks, I'd go with a higher, and more upright position.

Also forgot to mention, get a MTB for your donor. They have more demultiplication then any other bikes out there (very usefull for a heavy bike) and the best brakes.

So how about wheels, can I mount a regular old MTB wheel with only one side supported?

I've worked in the bike industry for ~15 years, and am happy to help with suggestions and what-not.

A few things, just based on what the OP has posted so far.

1. Recumbent prob isn't the way to go, based on rider description
2. There are single sided style hubs avail that would work. Take a look at Cannondale's Lefty style suspension forks and front wheels. Not cheap, though...
3. Based on your drawings, it looks like you plan on having one drive wheel with a cassette or freewheel type cluster and a derrailluer mounted inboard. Correct? If yes, don't do that. :) That will be an engineering nightmare, and likely not very durable. Look into using a drivetrain similar to what's shown on the trike, above. Single, centrally mounted chain, driving a single speed or modify an internal 3-7 speed hub. Most trikes and quads use a single drive wheel (preferable, IMO), but you do see some that use a solid rear axle driving both rear wheels. (Off the top of my head, I don't know of anyone making a rear diff for a quad bicycle...) You can find double sided cranks that would work for the central drive. There used to be a Canadian company making them for 2 wheeled side-by-side tandems. The only real drawback is that it is a fixed system, meaning both riders have to pedal.

Long story short, it may be easier and cheaper to buy a used quad, as a previous poster mentioned. Building one would be way more fun, though :)

tuna55 wrote: So how about wheels, can I mount a regular old MTB wheel with only one side supported?

Most quick release style bike wheels only have a 9mm axle, so probably not strong enough. How much weight do you need to support?

wpcouch wrote: I've worked in the bike industry for ~15 years, and am happy to help with suggestions and what-not. A few things, just based on what the OP has posted so far. 1. Recumbent prob isn't the way to go, based on rider description 2. There are single sided style hubs avail that would work. Take a look at Cannondale's Lefty style suspension forks and front wheels. Not cheap, though... 3. Based on your drawings, it looks like you plan on having one drive wheel with a cassette or freewheel type cluster and a derrailluer mounted inboard. Correct? If yes, don't do that. :) That will be an engineering nightmare, and likely not very durable. Look into using a drivetrain similar to what's shown on the trike, above. Single, centrally mounted chain, driving a single speed or modify an internal 3-7 speed hub. Most trikes and quads use a single drive wheel (preferable, IMO), but you do see some that use a solid rear axle driving both rear wheels. (Off the top of my head, I don't know of anyone making a rear diff for a quad bicycle...) You can find double sided cranks that would work for the central drive. There used to be a Canadian company making them for 2 wheeled side-by-side tandems. The only real drawback is that it is a fixed system, meaning both riders have to pedal. Long story short, it may be easier and cheaper to buy a used quad, as a previous poster mentioned. Building one would be way more fun, though :)

wpcouch wrote:

tuna55 wrote: So how about wheels, can I mount a regular old MTB wheel with only one side supported?

Most quick release style bike wheels only have a 9mm axle, so probably not strong enough. How much weight do you need to support?

I was planning on having two MTB rear wheels mounted in the back, each driven by their own chain with an idler (two sprockets keyed on a shaft) mounted midway so the crank centerline would be inboard of the wheel centerline, but Woody had said I may have tracking issues (although these guys are not going to be flying down the roads in this thing, so I am not sure how big of a deal this is). The benefits being that either or both could pedal as health/energy allows. Also, it means I have to engineer nothing except the idler shaft.

If the shaft through the wheel isn't strong enough to be supported from only one side, I'll just put a fork on each end and mount some sort of mud guard so it looks like it was there on purpose. I can't see spending money just for that feature.

I wonder whether the happy medium is to have a "tadpole four-wheeler"... That is, four wheels, but go ahead and put the rear wheels in line with the cranks.

As noted above, you'd need to pay attention to where the CG winds up, and it's possible of course that this won't work for reasons of stability, but it should provide better stability than a tadpole trike while vastly simplifying the drivetrain.

We built a soapbox derby car a few years ago which used two kids' 20" front ends cut free from the rest of the frame and welded to our structure. I don't remember exactly how we figured it, so I'm guessing we mostly got lucky that it didn't have major Ackermann, scrub, or flop issues. It was also a one-seat recumbent trike with a rearward weight bias, so that may have hidden geometry issues.

Bicycle wheels certainly put up with lateral loads, but that's not how they experience their heaviest loads. I believe there are some garden carts that use BMX mag type wheels with one-sided hubs. Like this. Not sure if there's a more economical version; when googling for that, I also saw replacement wheels, but they were ridiculously overpriced relative to the cost of a whole cart.

Wasn't there a pedal car plan set in the back of every issue of Boys' Life? Guess that's probably changed in the last 30 years. They might not even have the vacuum cleaner powered hovercraft plans anymore...

As folks have suggested above, I believe one person will need to control brakes and steering, and getting that stuff to work evenly will be important and a bit fiddly. OTOH, I'm guessing that these folks will probably be pedaling this thing SLOWLY... any hills in their neighborhood?

Don't even try to use a bicycle wheel in a one side supported manner. Like wpcouch said, most have a 9mm axle, which is just too small even for a single seater. I know they have some HD MTB wheels with 12mm axles, but those are pricey. For a two seater, I would look into scooter wheels.

I used these wheels on my bike. They come with crappy tires, and even crappier 1/2" ID bearings. The bearings didn't last one season, but once I replaced them with good sealed bearings, I haven't had problems since. Those wheels might work, but I think they would be at their limit.

If you want both wheels to be driven, I'd just look into a Peerless differential axle. Something like this.

They aren't too expensive or heavy, and they are available in a lot of sizes. But you loose the rear sprockets/derailleur/tensioner assembly.

I want this thing to be stupid easy and cheap, given two donor MTBs, I was literally thinking that the brakes on each MTB would remain on forks over each wheel and would be actuated by one handlebar. The passenger side would get a handle to hold onto, but no steering or braking. Both sides would get pedals powering their respective side, and the aforementioned idler shaft would put the riders inboard of the footprint.

I was planning on having two MTB rear wheels mounted in the back, each driven by their own chain with an idler (two sprockets keyed on a shaft) mounted midway so the crank centerline would be inboard of the wheel centerline, but Woody had said I may have tracking issues (although these guys are not going to be flying down the roads in this thing, so I am not sure how big of a deal this is). The benefits being that either or both could pedal as health/energy allows. Also, it means I have to engineer nothing except the idler shaft. If the shaft through the wheel isn't strong enough to be supported from only one side, I'll just put a fork on each end and mount some sort of mud guard so it looks like it was there on purpose. I can't see spending money just for that feature.

I wouldn't be overly concerned with tracking on this. NO trike/quad tracks all that well!

You would need to use the rear stays of a frame, vs a fork to mount the rear wheels. Front hubs have as OLD of 100mm, vs 135mm for rear hubs. The bonus is you will already have the proper derrailluer mounts on the frame ready to use.

Troll CL for a couple of 26" comfort bikes to use as donors. If you can afford it, go with a major manufacturer (Trek, Specialized, Giant, Cannondale, etc.) Quality of build and materials will be much higher.

wpcouch wrote:

I was planning on having two MTB rear wheels mounted in the back, each driven by their own chain with an idler (two sprockets keyed on a shaft) mounted midway so the crank centerline would be inboard of the wheel centerline, but Woody had said I may have tracking issues (although these guys are not going to be flying down the roads in this thing, so I am not sure how big of a deal this is). The benefits being that either or both could pedal as health/energy allows. Also, it means I have to engineer nothing except the idler shaft. If the shaft through the wheel isn't strong enough to be supported from only one side, I'll just put a fork on each end and mount some sort of mud guard so it looks like it was there on purpose. I can't see spending money just for that feature.

I wouldn't be overly concerned with tracking on this. NO trike/quad tracks all that well! You would need to use the rear stays of a frame, vs a fork to mount the rear wheels. Front hubs have as OLD of 100mm, vs 135mm for rear hubs. The bonus is you will already have the proper derrailluer mounts on the frame ready to use. Troll CL for a couple of 26" comfort bikes to use as donors. If you can afford it, go with a major manufacturer (Trek, Specialized, Giant, Cannondale, etc.) Quality of build and materials will be much higher.

Sorry, I call that thing in the back a fork too, I get it, I was naming it wrong.

OK, So I cut up two 26" MTB.

I weld the stays to the back of the frame and weld the neck of the front fork to the front of the frame.

I engineer a steering system to actuate that through a steering shaft and mount a dummy neck&handlebar combo near the driver, paying close attention to Ackerman.

I mount a clever bellcranky way to actuate both sides brakes at the same time through the existing levers which get mounted on the drivers handlebars.

I leave the back derailleurs (how does anyone spell that word without spellcheck? on the stays. I leave the front derailleurs on the bottom brackets, and just space this all out on a frame. The front chain will drive an idler, moving the rearward chain inboard by a foot or so.

Good?

Sounds like I need two full bikes, one extra stem&handlebar and two extra bottom brackets for the idler. Some chain would be the only thing to buy other than hardware for the steering arrangement.

In reply to tuna55:

Sounds about right, although, for simplicity's sake, I'd leave it at one drivetrain. Or, at the very least, eliminate the front derailleurs (I still use spellcheck, and I've been spelling it for years.)

Go-cart front end.

tuna55 wrote: I leave the back derailleurs (how does anyone spell that word without spellcheck? on the stays. I leave the front derailleurs on the bottom brackets, and just space this all out on a frame. The front chain will drive an idler, moving the rearward chain inboard by a foot or so. Good?

Also, keep in mind, the drivetrain must be on the rider's right (or, at least, on the rider's right side of the wheel) due to the rear hub/freewheel design.

It sounds like a golf cart is the ideal tool for this application.

The bike will realistically not get ridden.

wpcouch wrote:

tuna55 wrote: I leave the back derailleurs (how does anyone spell that word without spellcheck? on the stays. I leave the front derailleurs on the bottom brackets, and just space this all out on a frame. The front chain will drive an idler, moving the rearward chain inboard by a foot or so. Good?

Also, keep in mind, the drivetrain must be on the rider's right (or, at least, on the rider's right side of the wheel) due to the rear hub/freewheel design.

Good call. The idler will allow this to not be a huge deal since the two idlers can be different lengths and mounted slightly differently.

wvumtnbkr wrote: It sounds like a golf cart is the ideal tool for this application. The bike will realistically not get ridden.

Before falling ill less than two years ago, my Mom ran several miles each day for fun after performing a 2 hour aerobic routine inside. My Stepfather doesn't do that much, but less than a decade ago trained for and successfully ran a marathon in Rome along with other events.

These aren't couch potatoes, they are just sick. They will pedal if they can be assured they won't fall over and such.

Sweet!

I may have been speaking from personal experience. I have got my parents a kayak, bicycles, a wii console, anything to get them up and moving.

Nothing works.

I am glad that your Mom seems more athletic. Good for her!

Silly question...

Why not just weld two bicycles side by side. Like literally put them 2 feet apart and weld some tubes between them?

The only thing to worry about then is steering. Use one of the handlebars to steer and hook up a linkage so it steers the other one as well.

Am I missing something? Hell, you could even make a bench seat and pount it a little further back if you wanted something comfy-er