BMW K bikes (Bricks)

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1Back to top Go down   New sidecar project Empty New sidecar project Sun Oct 25, 2020 9:48 am

arbalest

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This is the third time trying to post this. I had a K100 solo some time ago. What a great bike that was. I decided to hack it. It was nearly done, but the fabricator made several serious geometry errors, causing severe bump steer. I took it to another fabricator. He kept putting it off until I stopped checking on it. I couldn't take it back as I had no place to keep it in an unfinished state. It has disappeared. So....I would like to try again. The goal: a high performance sidecar with A arm front suspension (hung from the sidecar frame) and car tires all around. I found a subframe sketch that looks like what I am looking for. With this arrangement, there are no steering loads carried by the K bike frame. The only thing the headstock/triple tree is used for is a place to hang the headlight, handlebar, and steering duties. The subframe will be bolted solidly to the sidecar frame, the tug and sidecar tire set vertical, with toe adjustment for the sidecar wheel. So, is there any requirement to tie in the upper motor mounts to the subframe? The upper part of the subframe shown in the sketch will not be used. 
I am looking for input from people who know more than me. Will this work?

New sidecar project Projec10



Last edited by arbalest on Sun Oct 25, 2020 7:09 pm; edited 2 times in total (Reason for editing : link not working)

    

2Back to top Go down   New sidecar project Empty Re: New sidecar project Sun Oct 25, 2020 12:16 pm

Arlina

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Picture is not available.....


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New sidecar project Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S
    

3Back to top Go down   New sidecar project Empty new sidecar project Sun Oct 25, 2020 2:58 pm

arbalest

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Arlina wrote:Picture is not available.....
Can't click on the link? The link works on my end.

    

4Back to top Go down   New sidecar project Empty new project Sun Oct 25, 2020 3:30 pm

arbalest

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Arlina wrote:Picture is not available.....
Just tried it again....no pics.

    

5Back to top Go down   New sidecar project Empty new project Sun Oct 25, 2020 3:36 pm

arbalest

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Try it now.

    

6Back to top Go down   New sidecar project Empty Re: New sidecar project Sun Oct 25, 2020 5:56 pm

Laitch

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arbalest wrote:Try it now.
No pic, just a Google login window.


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1995 K75 81,000 miles
New sidecar project Usa-lo10
    

7Back to top Go down   New sidecar project Empty new project Sun Oct 25, 2020 6:15 pm

arbalest

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Why can't I post a photo??? Where can I put photos so I can post them here??

    

8Back to top Go down   New sidecar project Empty Re: New sidecar project Sun Oct 25, 2020 6:27 pm

Laitch

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arbalest wrote:Why can't I post a photo??? Where can I put photos so I can post them here??
Try posting using either this method or this method.


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1995 K75 81,000 miles
New sidecar project Usa-lo10
    

9Back to top Go down   New sidecar project Empty new project Sun Oct 25, 2020 7:10 pm

arbalest

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Laitch,

Thanks. Looks like I got it.

arbalest

    

10Back to top Go down   New sidecar project Empty Re: New sidecar project Mon Oct 26, 2020 3:19 pm

jbt

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I have to K-base sidecars, maybe thesesolutions will help.
I don't see why this type of suspensions would be useful for a sidecar still using the original motorcycle frame. Modern kneelers use them, but they get rid of the motorcycle chassis, they're designed around a central pole, with all elements attached on both sides. This solution with a front suspension using two superposed triangles moving around a longitudinal axis may be good for geometrical reasons: but it will imply to strenghen a lot teh sidecar chassis, meaning adding a lot of weight - weight you can't save elsewhere iy you still use the motorcyle frame. Furthermore, this weight is located at the front of the sidecar, very far from the center of gravity. It can be useful in case of sleepy front wheel in acceleration, but not good about handling.
Another concern is about the front wheel travel: it makes the width varying according to the suspension travel.  It's OK with short travels, on road racing sidecars. It's OK on a car, because both front wheels vary. But on a road sidecar, with longer suspension travel it may cause weird results in roadholding...
The alternative is to still use a twin triangle suspension system, but moving around a transversal axis.
This will guarantee the width to remain the same, and the trail issues are not a problem anymore because, forming a parallel system, the trail remains always the same.
It also permits to attach the suspension system nearer the center of gravity, using the original frame or the subframe instead of the sidecar frame. Saves weight.

Another concern about the subframe sketch you showed. Using the central stand bolting points under the gearbox is OK, this place is very solid because it's designed to support all the weight of the bike, but the points located on the engine lower case...Uh uh! This part may be not strong enough to support the efforts, and any crack will instantly drain the oil. You should better use the engine to frame junction to attach the subframe, they are much more solid. Furthermore, the tubes passing under the engine oil case will lift the whole sidecar for ground clearance reasons - and you don't wan't to have a high sidecar for roadholding reasons. A subframe around the engine is better than a subframe under the engine.

I have to K-based sidecars:
New sidecar project K100_c17
New sidecar project K100_c16
This one uses a Side Bike front end, designed for the Yamaha XJS900. It also uses a sidecar steering wheel, but this doesn't matter here.
New sidecar project Img_2180
The front end is very light and simple. Note the subframe design: the upper fixation is bolted on a plate welded near the fork axle: it's the only attachment that needs welding.
Then a tube runs around the engine both side, providing fixation to the front end, and re-using the engine to frame points.
Note that this solution implies to re-route the exhaust system, under the engine, that implies to have a high motorcycle to preserve ground clearance. I did not designed it, but if I had, I'll chose another option, with lateral exhaust, to lower the bike.
Handling and maneuvrability are excellent, but I can't tell you if it is because of that front end design or because of the steering sidecar wheel.

My other sidecar is a K1 using a double triangle suspension system:
New sidecar project 20170312

New sidecar project 20170311

Also a french design, made by BCS, Benoist Constructions Spéciales.
It uses 2 triangles, moving around two transversal axis, attached on a module that is not fully integrated to the bike nor sidecar frame. This because it was an aftermarket modification, the sidecar was originally designed with an Earles fork, but it was not satisfying and was modified.
The steering system is complex, quite hard to turn! But the stability this system provides is extraordinary. May the road be bumpy, it does not matter, the trajectory the sidecar follows remains absolutely unchanged. You can ride without hands on the bars, it won't move.
The front wheel is prone to understeer when accelerating frankly (franticly!) on wet roads. I think this is due to a lack of weight on the front end, but also to the fact that the front wheel is very far away trom the bike (because of the aftermarket mod, the front module is not well integrated). But I have to test a new tyre before concluding, this one is old and not very sticky anymore.
I'm afraid I have no pictures about the subframe design on the K1.

    

11Back to top Go down   New sidecar project Empty new sidecar project Mon Oct 26, 2020 7:23 pm

arbalest

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Thanks for your input. I really like the look of the transverse control arms. My original thinking was to essentially build a three wheel car. Build a flat chassis that would carry the engine and sidecar and carry all the suspension loads. The only reason for the motorcycle chassis is to hold the gas tank, seat, with the headstock carrying the stock triple tree to have something to mount the headlight to and carry the steering linkage. Looking at the subframe sketch, I see your point about using the smaller mounts to the oil pan.

    

12Back to top Go down   New sidecar project Empty Re: New sidecar project Tue Oct 27, 2020 5:54 am

jbt

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Car solutions are not always adapted for a sidecar design, its behavior is not identical.
Many builders have tried their own design, the actual trend tends to focus on an independent structure supporting the front end, the sidecar itself and attachments to the subframe. But it may be only for legal and homologation reasons: the builder just have to pass tests for one standard sidecar, and then can fit any motorcycle on it.
Some have developped a whole specific chassis: Krauser with the well known Domani : 
New sidecar project 1990-Krauser%2BDomani-3

It still used a transversal axis, even if roadracing sidecar designs from the same builder had both solutions:
New sidecar project 29595224-910893182452753-8264890693312892960-nNew sidecar project 5900287821_7954a31d2c_b

Another example is the RSC Scalene, made by Hechard, french manufacturer:
New sidecar project 99734b_394af54608304045a5cbf131f0c6c996~mv2_d_1503_2048_s_2
I think (not sure) that this one has a front end moving on a longitudinal axis: but the design of that sidecar is very unique (its designer is a racing car engineer): it's very long (2 meters from wheel to wheel), very narrow (1.45m), the sidecar wheel is steering and placed forward, and the offset of the rear wheel is superior to the front wheel (the sidecar leaves three separate trails on the ground).
I'm not sure that more than 2 were ever built...

A lot of sidecar builders, in France and Germany, had converted to double triangle front end, but most (all?) of them use a transversal axis design, even on the most radical designs such as the Ruko Vector.

Even the Side Bike Zeus, probable the most car-like sidecar ever built (with the Corda) uses a transversal axis for the front end suspension:
New sidecar project S1-voyage-au-coeur-de-l-olympe-408439
Yet its design would easily have allowed to anchor the triangles laterally, and knowing its engineer, he has choosen the best technical solution for its sidecar.

Speaking about the Corda:
New sidecar project Chassi11
New sidecar project Corda-001-web
I'm no sure, but it seems that the front end is, like the others, transversal.

 Vogel, in France made a 3WD chassis, using also transversal axis, but this may be due to the use of Citroen 2CV components: New sidecar project 1189629189 New sidecar project 1189629222New sidecar project 1189629159

I have to go to visit a friend of mine, one of this days, Jean Louis Damois, who builds sidecars https://www.dj-sidecars.fr/, he's a neighbour, I'll ask im if there's a technical reason why almost nobody uses a longitudinal axis.

    

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