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I am in the design phase of a can am style trike and had some thoughts on suspension and wanted some feedback.
The rear wheel will have positive camber with any lean, it is inherent in the basic design. Therefore I don't want much if any camber gain in the front or it will cause a dangerous oversteer condition. I am planning on using miata front hubs and very long (16") A arms in a parallel, almost equal length configuration. This will result in a ground level roll center and a large roll moment, which will require a stiff roll bar. My question is what if anything am I missing. Any input will be appreciated.
Thanks in advance.

You are missing that a RT naturally understeers, seems strange but it's true. A single front wheel is of course the opposite.

Unless you're really concerned about weight, go for a VW front end, has distinct advantages, the best bit being the suspension's ability to go backwards and roll over bumps smoothly and effecting longitudinal stability less on a RT.

Strange, yes. True, no.

Actually, I agree with cheapracer. Let's all vote and get the truth that way. Or maybe someone could explain why a RT naturally understeers. Or maybe give some examples. Nah. I like the vote idea better.

There are far too many unknown factors for any type of definitive over/under steer analysis to exist, even regarding only steady state cornering. Vehicle dynamics just can't be oversimplified that far. But because this is obviously going to be a RWD reverse trike, there is at least a greater possibility for powertrain induced oversteer.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

So your vote is...?

That "a RT naturally understeers" is incorrect simply because it is a blanket statement based entirely on assumptions. There is no more guarantee that a 2F1R or 1F2R trike will have a natural propensity towards oversteer or understeer, than there is a 2F2R vehicle will have a natural propensity to be perfectly neutral.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Youre right, there are too many variables to determine how any particular RT will handle, but the operative word here is "naturally". Weight transfer up front means the front tires won't have max grip for their load, while the rear, without any weight transfer, will. Of course anyone can come up with a thousand scenarios where that isn't true, but we're not talking about specific scenarios.

What exactly makes the specific assumptions required for your scenario to remain valid any more 'natural' than those required from any other scenario? Front vs rear weight transfer effects are but one single factor, which is nowhere near enough to determine anything regarding overall 'natural' tendencies for even a single given vehicle, let alone tying it to an entire genre of vehicles that differ wildly in both design and execution. The whole point I'm trying to make being that there simply is no such thing as "naturally" occurring tendencies without relating it to an explicit set of conditions and constraints.

If you wanted to say "some RT's naturally understeer", "many RT's naturally understeer", or "RT's can be made to naturally understeer", then you would have a completely legitimate point...But going beyond that, turns it into nothing more than a fallacy.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Sorry Justin, I guess down here in Marin county we have our own ideas about what's natural. I think we can agree that weight transfer is natural, and that friction is natural, and I don't think I made any other assumptions besides that, other than the number of wheels in front and the number in back. If I did make any other assumptions, I apologize, that was not my intention.

I think Nick was kidding about the voting thing and support of Cheap's conclusion.

I think we are not considering that at lateral loads of this level would result in roll, meaning naturally some camber gain or less lost compared to the rear. While we talk about front transfer and rear transfer, there is also diagonal, since the cg is between the ends rather than on either end, so the inside is transferring to the outside front and the rear.

I've driven the 1f2r atvs that were banned in the 80s, trike converted touring bikes, and even taxied heavy aircraft. They all understeer except for the atv, which would throw you long before you got to that point.

Justin made my point that a blanket statement shouldn't be made, even if the source of the statement is well known.

From this Road and Track test of the Trex 1400:
http://www.roadandtrack.com/car-reviews ... -rex-1400r

"Even with the relatively small 205/45R-16 tires up front vying with a monstrous 295/35R-18 rear (which is actually equivalent to two 147.5-mm tires) the front provides way more grip than the rear could ever wish for, making for a playful oversteer-prone design."

Regarding reverse trikes in general, I also found this article where a fellow tested a variety of machines:
http://www.telegraph.co.uk/motoring/new ... -test.html

Lots of physical effects are natural, like the above noted body roll. Yet weight transfer as described leading to umdersteer would at least seem to be assuming that the rear tire didn't have a noticeably higher area loading than the front tires to start with.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

To actually answer your question (I knew I was forgetting something), I think it would be very hard to give you any definitive answers. However if you're looking to reduce any propensity that you design might have towards oversteer, then a minimal front camber gain and a stiff (relatively speaking) front sway bar both seem like reasonable choices. If you're really trying to limit camber gain, one thing to watch out for is that caused by caster. By using Miata spindles you may not be able to get enough mechanical trail without also having more caster, and the associated camber gain when the wheels are turned, than desired for your particular design goals. But there is only one way to find out for certain how well your specific idea will or won't work. The comment about using a VW front suspension is also not a bad alternative that could potentially even reduce the amount of engineering effort required to get to a final product, if it can be made to cooperate with the rest of your design.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Here's a Video describing the Morgan 3 wheeler's handling dynamics, as well as the Caterham 7's
http://www.youtube.com/watch?feature=player_embedded&v=htI3weS49cc

From Autoblog
http://www.autoblog.com/2013/05/30/morg ... #continued

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Ahh; gitty up!

It is not a conclusion, it is a fact of dynamics, go get the multiple SAE papers on it.

The Deltawing is living proof of it and very well explained by the engineer in a Chris Harris video getting around.

What you are refering to induced sliding through wheelspin.