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PostPosted: Sun Oct 12, 2014 8:45 pm 
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I have spent 5 years doing research testing and developing on our new trike conversion system. Up to now I have used a double wishbone layout and focused heavily on keeping the toe consistent throughout normal suspension travel in order to prevent bump steer. While this has worked and cornering,tire wear and stability has been exceptional I am now looking into unequal a-arm layouts thinking of maximizing our cornering adhesion characteristics. My main concern here is keeping the bump at minimum. I am using dual tie rods which hook directly to the steering arm as this configuration does not allow for a rack and at present there is no provision for Pittman arms etc.
The question I have, is there much advantage to unequal a-arm vs equal arm suspension to warrant further testing? At present our trikes out corner the native pre-converted units by a fair degree and I am unsure if the inclusion of negative caster during body lean will translate into a legitimate increase in cornering proficiency.

I welcome any and all advice.

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PostPosted: Sun Oct 12, 2014 9:30 pm 
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PostPosted: Sun Oct 12, 2014 10:59 pm 
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Do you mean camber? Try to sound less like an advertisement, it seems to be getting in the way of expressing yourself.
:x

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PostPosted: Mon Oct 13, 2014 2:38 am 
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Very good question, if I'm understanding it right.
Endeavor wrote:
Up to now I have used a double wishbone layout <snip> I am now looking into unequal a-arm layouts
You're aware that "double wishbone" and "unequal a-arm" mean the same thing? Since the '30s "double wishbone" implies non-identical wishbones. The only application I can think of where equal a-arms (or equal wishbones) makes any sense is 2F1R trikes.
Endeavor wrote:
My main concern here is keeping the bump at minimum.
When most of us tinkers are designing 2F1R, our main concern is keeping the CG inside the lines joining the tires' contact patches, and with relatively high CG vehicles like yours, that means minimizing the risk that the rear wheel will overtake the front wheels. With modern high performance street tires, I think it's unlikely your trikes would get through a quarter of a spin before they flipped over--I'd think your main concern would be avoiding oversteer, and...
Endeavor wrote:
...maximizing our cornering adhesion characteristics...
...is not going to be the same thing as maximizing your cornering adhesion. Ideal "characteristics" are those that leave the operator on the trike (rather than vice-versa) and in control, and an imbalance of front wheel adhesion vs. rear wheel adhesion could compromise those characteristics.

Since you tell us your trikes already...
Endeavor wrote:
...out corner the native pre-converted units by a fair degree...
...perhaps you should tell that to everybody else too and leave well enough alone, performance-wise. Equal length a-arms (wishbones) promote understeer, so your current layout is probably enhancing stability. It offers the same benefit as the original Morgan three wheeler front suspension (sliding pillar) in keeping the camber angle of the front tires equal to body roll, and thus equal in camber to the rear tire, which makes the vehicle more predictable when one gets into the spooky stuff near the limits of tire adhesion. Since you can't improve camber in the rear, think twice about improving camber in the front; you risk having a vehicle that "lets go" in the rear faster than the driver/rider can correct.
Endeavor wrote:
I am unsure if the inclusion of negative caster during body lean will translate into a legitimate increase in cornering proficiency.
I think it will demand a legitimate increase in cornering proficiency. I think your riders will need to be more proficient than they need be with equal length a-arms/wishbones (or control arms, as they're commonly called on automotive design/discussion sites such as this one). Were I to license your design, I'd be more interested in how normal people handle it on normal roads than in how racers handle it on racetracks, and I think other potential licensees will feel the same way.
Endeavor wrote:
I welcome any and all advice.
Robert Riley's book Alternative Vehicles for the 21st Century would be $49 well spent. He has extensive and well illustrated explanations of three wheeler dynamic stability. Were I you, I'd pay particular attention to the areas where he disagrees with you about trike design...they're too many to list, but the 2F1R/1F2R--understeer/oversteer issue is one of them.

[EDIT: I googled it. http://www.rqriley.com/alt-car2.htm 2nd Edition, Published by Society of Automotive Engineers (Oct. 2003)
SAE Stock Number - R227]

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PostPosted: Mon Oct 13, 2014 3:44 am 
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I am not sure about this in a trike application. We sort of head down the set up route with unequal length wishbones to avoid positive camber gains in a turn , with a trike your roll is in the opposite direction because of the way you pull/lean the bike over to the inside of a bend. It would appear to my addled brain that for this application you would want the shorter arm at the bottom. I will now put my brain back in the pickle jar and try to fathom this one out.

Bob

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PostPosted: Wed Oct 15, 2014 9:49 am 
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JackMcCornack wrote:
Equal length a-arms (wishbones) promote understeer, so your current layout is probably enhancing stability. It offers the same benefit as the original Morgan three wheeler front suspension (sliding pillar) in keeping the camber angle of the front tires equal to body roll, and thus equal in camber to the rear tire, which makes the vehicle more predictable when one gets into the spooky stuff near the limits of tire adhesion. Since you can't improve camber in the rear, think twice about improving camber in the front; you risk having a vehicle that "lets go" in the rear faster than the driver/rider can correct.[[EDIT: I googled it. http://www.rqriley.com/alt-car2.htm 2nd Edition, Published by Society of Automotive Engineers (Oct. 2003)
SAE Stock Number - R227]


Oh. My. Gawd. OMFG, Jack...reading this, I'm having an epiphany about what the B-3 suspension geometry is doing, with regards to the remaining dartiness in its handling/steering.

I can see it...I can see what its doing. OMFG.

Jack thanks, this is pure gold.

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