I'm trying to adapt Locost rear suspension (4-link, solid axle, as in the book 2nd edition) to a Honda CX500-based trike.

The drawing shows how a short, triangulated subframe (red) would extend the CX500's frame (black) rearward, and where the four links (magenta) would attach.

My question is: Would the angle of the links be enough to keep the rear axle centered left-to-right, or would some sort of Panhard bar also be needed?

And if one's needed, where would it mount to on the trike frame?

Thanks.


[Edited on 22/2/05 by carcentric]

[Edited on 22/2/05 by carcentric]

Hi Doc you will definitely have to have some type of lateral location and I think that your mounting of the shocks on the links is a very bad idea . Also if you are using a live axel then you will have a very high unsprung weight sit uation . You would do much better with an independant rear from say a searia but befre yo start you had better check that your output shaft is rotating in the corect direction . You could however avoid all of that problem by puting two wheels at the front ! adapying the locost front suspension design and then you would have really distinctive trike and better braking to boot
best wishes
Iain

Hi again Doc
If you were to make the two lower links into a triangle with the apex meeting the center of the diff with a ball joint like a Cateringham it may work, still don't like the shocks on the links though .
best wishes
Iain

First, the reason I picked the Pinto rear axle - the ratio is 3.08:1. I also have a complete BMW 320i rear suspension (subframe, trailing arms, diff, axles, brakes), but the ratio on that one is 3.45:1 which will require huge and heavy 215/70x16 tires to get the same gear/tire overall ratio. I haven't found any lightweight IRS diffs in the 3.08:1 range - ones with those ratios tend to be from V8 sedans (e.g., Mercedes).

What's the problem you see with having the bottom of the coilovers bolted to a crossbar between the top two links? That's the way a lot of cars have their front suspension (except sideways, of course). Since the crossbar in my design would be welded to the top two links, it acts like a no-flex anti-swaybar (without which the seat and front frame will lean OUT in turns).

I agree you get better handling and braking with a 2F1R trike than with a 1F2R layout, but this is a chopper-esqe putt-around trike for this retired codger and the missus.



BTW, rule of thumb for shaft drive bikes: If the shaft is along the right side of the rear tire (viewed from rear), the shaft will turn the same way a car shaft does. If the shaft is along the left side, you'll need to flip the diff to get several speeds forward. Works with the Honda CX500 (right side) and Yamaha XS1100 (left side) anyway.

[Edited on 18/2/05 by carcentric]

Hi Doc
I just worry that there are high loads from the shocks on a piece of 25x 25 rhs (asuming that is what you are using ) but I supose you balance that against the extra structure needed to mount them to the axel housing . Glad to hear that you will not have trouble with shaft rotation direction . any way you should consider my sugestion for the lower links becoming an a arm as it is probably be the most elegant way to do the suspension . I have seen several trikes done here with car diffs and often they are done as rigids , relying on the tyres for suspension , I'm not sugesting that this is a solution for you though. by the way you will have to work out the correct spring rate if you mount your shocks as sugested by the drawing.
I have had a C X my self and liked the bike infact my brother has three of them a good "Codger bike"
here is an amusing trike , with codger
Best wishes
Iain
Rescued attachment startrike.jpg

quote:

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Originally posted by niceperson709
Hi Doc
I just worry that there are high loads from the shocks on a piece of 25x 25 rhs (asuming that is what you are using ) . . . . any way you should consider my sugestion for the lower links becoming an a arm as it is probably be the most elegant way to do the suspension . . . .
Iain

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What if you triangulate the rear of the trailing arm. It might put a loading on your front pickup points though.
Rescued attachment trikeaxle.jpg

Hi Doc
What I was sugesting is that you replicate the susupension set up of a Cateringm / lotus that is two side links and the lower one is an a arm mounting at its apex on the center off the diff housing at the bottom. Thus the lower a arm allows up and down movement but no lateral movenent but the ball joint allows each side of the diff to go up and down to follow road surface . if you conect the two links with angle iron as you sugest you are efectively making that ito a single swing arm and it will fail to give you any proper supension or it eill fail from fatiuge .
I have included a very rough drawing of what I am suggesting . I hope that is a bit clearer .
Best wishes
Iain
Rescued attachment Image1.jpg

I appreciate the sketch, niceperson709, thanks - it made your suggestion clear and confirmed my interpretation that it would look like a "W" from above. My only reservation is that I'd have to weld another connector to the diff case (not impossible resistance to overcome).

The bigger issue is letting one side go up when the other doesn't (e.g., over a bump). When that sort of "roll" is allowed in a trike, the seat and frontend leans OUTWARD in a turn (dangerous and awkward feeling). A trike fares better when something acts like an extremely stiff anti-swaybar to keep the seat and front frame straight up and down. The tradeoff is that the wheel that doesn't hit the bump is also pushed up (rougher ride, but flat in cornering - see URL below for better description).

So, I think if I add a center mount under the axle, it will be the same bushing style as the ends get rather than a swivel-ball mount.

http://www.krebskustomcycles.com/no_lean.htm


sketch above shows outward weight transfer in a LEFT turn

[Edited on 23/2/05 by carcentric]

Hi again Doc
I only sugested that you use aball joint at the apex because Cateringhams find that there is some strain on the casing with locost like bush but you would not be looking at long travel susupension say no more than a couple of inches total so a bush would work fine , I have riden sidecars so I do understand the effect you talk about It can be disconcerting and really it is somthing you largely have to live with to some extent . Good luck with it and I look forward to seeing the final out come :
best wishes
IainD

Yes, 10 full months have passed since I started this thread and I've still not cut a single piece of tubing.

But I have taken the feedback above to heart and think I've found a solution to the "Panhard needed?" question. To wit: using a Datsun 210 (aka B310) rear axle assembly with its 4 unequal, unparallel links (and Subaru air shocks for springs).

When viewed from above, the links are angled in similar fashion to those recommended above by niceperson and others, and that arrangement would seem to negate the need for a Panhard rod. Am I correct?


COLOR CODE:
Turquoise = Datsun and Subaru parts
Red = Fabricated subframe
Blue = Propshaft (made from 914 axle)

If the drawing is blurry, it's probably been reduced in size to fit your screen. Just put your cursor over the drawing and when the Expand icon pops up in the lower right corner, click it to see the full size drawing.

[Edited on 27/12/05 by carcentric]