Two-bicycle, side-by-side, quadricycle tandem

I'm thinking of buying two cheap ladies mountain bikes and lashing them together like the "granny
bike". My better half can't ride a bike, and my arferitus makes getting on a permanently upright
bloke's bike impossible (you should see me getting on and off my MTB Anyway, I was thinking of 2'
2" between the frames (leave 2" between the handlebars anyway) and I haven't a clue yet what
Ackerman angle to incorporate into the steering (around 40 degrees between the two steering arms at
straight ahead?) What minimum specs should I look for in the two bikes? I suspect alloy rims,
stainless spokes, and would steel or ally frame be more robust where I clamp the cross ties on the
headstock and rear downstays? Any suggestions greatly appreciated.

Moosh

 

"Moosh" <[email protected]> wrote in message
news:[email protected]...
> I'm thinking of buying two cheap ladies mountain bikes and lashing them together like the "granny
> bike". My better half can't ride a bike, and my arferitus makes getting on a permanently upright
> bloke's bike impossible (you should see me getting on and off my MTB Anyway, I was thinking of
> 2' 2" between the frames (leave 2" between the handlebars anyway) and I haven't a clue yet what
> Ackerman angle to

MR SPOKES BIKE HIRE Barrine Drv Acton 2601
(02) 6257 1188

I believe these are the details of an outfit on the shores of Lake Burley Griffin here in Canberra.
They hire out just the thing for you - 4 wheels, two pedallers and one steerer. Maybe they could
tell you where they source them from.

Steve

 

On Mon, 12 May 2003 10:12:02 +1000, "Steve_Robertson" <[email protected]> wrote:

>
>"Moosh" <[email protected]> wrote in message
>news:[email protected]...
>> I'm thinking of buying two cheap ladies mountain bikes and lashing them together like the "granny
>> bike". My better half can't ride a bike, and my arferitus makes getting on a permanently upright
>> bloke's bike impossible (you should see me getting on and off my MTB Anyway, I was thinking of
>> 2' 2" between the frames (leave 2" between the handlebars anyway) and I haven't a clue yet what
>> Ackerman angle to
>
>MR SPOKES BIKE HIRE Barrine Drv Acton 2601
>(02) 6257 1188
>
>I believe these are the details of an outfit on the shores of Lake Burley Griffin here in Canberra.
>They hire out just the thing for you - 4 wheels, two pedallers and one steerer. Maybe they could
>tell you where they source them from.

Much obliged, Steve.

I did a search, and he sure gets a lot of publicity, but I can't find a picture. I want to build
this myself for economy reasons, so I just need a few hints and tips.

Moosh

 

Hi. Interesting exercise. A modern " Sociable". May I ask how you intend to join the two frames? Mig weld in some cross tubes?Ensuring that both frames are sloping out from the vertical about one or two degrees. Provision for toe-in adjustment of the front wheels. With independent rear drives, the stronger rider will affect the steering direction. Could be great fun, picnicing by the lake with your lady friend. Keep us informed? Cheers.

 

On 16 May 2003 00:30:13 +0950, Paul A. <[email protected]> wrote:

>Hi. Interesting exercise. A modern " Sociable". May I ask how you intend to join the two frames?
>Mig weld in some cross tubes?Ensuring that both frames are sloping out from the vertical about one
>or two degrees. Provision for toe-in adjustment of the front wheels. With independent rear drives,
>the stronger rider will affect the steering direction. Could be great fun, picnicing by the lake
>with your lady friend. Keep us informed? Cheers.

Thanks for your thoughts, Paul.

The kit that is available from Canada comprises an aluminium "girder" between the head tubes clamped
on with U bolts; a triangulated pair across the rear seat stays; and an adjustable tie-rod between
two steering arms clamped to the stems.

My thoughts are that aluminium with U bolts is a bit harsh on the bike tubing, and so I will try for
the main braces, very strong and light pine planks with semicircular grooves that will fit the tube
diameter cut across the ends of these planks (beams) and clamped with U bolts around "gaskets" of
similarly grooved pine pieces.

Why do you suggest leaning the two bikes out? Camber? I was thinking of leaning slightly in if
anything for perhaps slightly more cornering stability.

How much toe-in at straight ahead do you suggest? I was going to try a 40degrees Ackerman angle
(angle between the steering arms at straight ahead.)

As I will be effectively "Captain" I don't believe I will have serious problems with "power steer".
I may alter the brake levers so that I have control of both fronts, and my "Stoker" has control of
both rear brakes when I give the command

How did you know I had lakes and picnics in mind?

Of course there is a supermarket a few km along the cycle path from our home, and a large plastic
crate strapped between the rear wheels will serve this well. A small trailer may be added at a
future date.

 

"Moosh" <[email protected]> wrote in message news:[email protected]...
> On 16 May 2003 00:30:13 +0950, Paul A. <[email protected]> wrote:
>
> How much toe-in at straight ahead do you suggest? I was going to try a 40degrees Ackerman angle
> (angle between the steering arms at straight ahead.)

I was enquiring of one of the engineers where I work about the correct angle for ackerman steering
and was told that as a rule of thumb the steering arms should point at the centre of the
differential. Presumably if one doesn't have a differential or it is not located in the centre then
this means the centre of the rear axle.

I cannot vouch for this information but he was quite a knowledgable engineer and most of the
information from him was good however he was not an automobile engineer. To me there is a logic in
this as the idea is to turn the front wheels so their turning circles always coincide on a line
drawn through the rear axle so you would think the correct angle would have something to do with the
rear axle. As I say I don't know but it would seem a good starting point.

 

On Sat, 17 May 2003 13:56:33 +1000, "Cody" <[email protected]> wrote:

>"Moosh" <[email protected]> wrote in message news:[email protected]...
>> On 16 May 2003 00:30:13 +0950, Paul A. <[email protected]> wrote:
>>
>> How much toe-in at straight ahead do you suggest? I was going to try a 40degrees Ackerman angle
>> (angle between the steering arms at straight ahead.)
>
>I was enquiring of one of the engineers where I work about the correct angle for ackerman steering
>and was told that as a rule of thumb the steering arms should point at the centre of the
>differential. Presumably if one doesn't have a differential or it is not located in the centre then
>this means the centre of the rear axle.

Yes, this is apparently a good place to start, but I believe it is quite a rough approximation. I
was thinking of setting it to my best approximation, and then rollong it slowly over a lot of sheets
of paper set out on a flat area. They should theoretically not move at any lock. Anyone have a
better suggestion, other than see how fast the treads wear?

>I cannot vouch for this information but he was quite a knowledgable engineer and most of the
>information from him was good however he was not an automobile engineer. To me there is a logic in
>this as the idea is to turn the front wheels so their turning circles always coincide on a line
>drawn through the rear axle so you would think the correct angle would have something to do with
>the rear axle. As I say I don't know but it would seem a good starting point.

Yep, thanks for that, Cody.

Moosh