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 Post subject: 3 WHEEL CHASSIS DESIGN.
PostPosted: April 19, 2014, 4:01 am 
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Hi guys, eventually got a (relatively) free bit of space so i'm starting to get a few ideas together for a mid engine 3 wheeler with bike engine. Plan is to use it for various race events, drag racing, sprinting, hill climbs.
I ' ve been building bikes for years but this will be 1st car so i'm looking for plans which anyone can recommend. I' m especially looking for front steering / suspension info.
Any recommendations or pointers would be appreciated.


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PostPosted: April 19, 2014, 10:21 am 
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I'll keep repeating it, use an older VW trailing link front end for a RT.

One big advantage is that the trailing links allow the wheel to go backwards as they go up so when you hit something so it doesn't "grab" like a normal suspension does helping to keep stability - I see this as especially relevant to one front wheel hitting a bump in a lightweight Reverse Trike to prevent "yawing". This is also one of the main reasons they were so popular in Off Road racing.


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PostPosted: April 19, 2014, 12:42 pm 
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Really, the best way is to drive the front wheels. Everyone gets all excited about light 3-wheeler, calculating the power to weight ratio. However, with so little weight on the rear tire, all it'll do is make tire smoke. (There was a really nice three-wheeler on here some time back, made in Sweden or Norway I think. For the specs it should have been a rocket, but while it made lots of tire smoke, it was never that fast. The builder ended up converting it to 4 wheels...

In any case, keep your overall CG as far forward as possible to help minimize tipping.

The real "problem" with 3-wheelers is aesthetic; it's nearly impossible to make them look really nice, though there have been a few exceptions.

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PostPosted: April 21, 2014, 2:46 pm 
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yorkshireracer wrote:
Hi guys, eventually got a (relatively) free bit of space so i'm starting to get a few ideas together for a mid engine 3 wheeler with bike engine. Plan is to use it for various race events, drag racing, sprinting, hill climbs.
I ' ve been building bikes for years but this will be 1st car so i'm looking for plans which anyone can recommend. I' m especially looking for front steering / suspension info.
Any recommendations or pointers would be appreciated.


Hey, nice to see another reverse-triker on the site. though there are a few of use who have built/are building reverse trikes, there is really rather a paucity of data regarding front end geometry for best handling (though as with all design solutions, "best" is a relative term).

I completed a scratch built revese trike (though front-engined) last january and have been driving it about 100 miles a week since march, its been a blast.

A proper double A-arm suspension works really well. as long as your toe settings are right, and you achieve for zero bump steer within your planned suspension travel, you can bomb over all sorts of bumps without any sort of stability issues. one can learn alot through mimckry, so look carefully at the front suspension design of the CAN-AM spyder, and Modern morgan three wheeler (don't bother with the older sliding pillar design, its a quaint relic, much like the old V-dub double trailing arm front ends). You can also find detailed parts layouts for the Campanga T-rex. That one might be most edifying of all.

there actually are many reverse trike designs out there, from which you could learn. ultimately though, you'll just have to pick a design and go for it. you would even do well to swipe one of the "book" locost front ends and use that. its proven, pretty much. In fact, given that you've never worked on a car design before, that is absolutely my advice: take the dimensions and geometry from the Haynes "book" locost,and either buy or build the upper and lower Kinetic control arms for Miata spindles, (I'm not shilling for Jack, its just a solid design that's easy to fabricate).

KB has a point about weight and balance, though its not nearly so dire as he claims. Since you're planning for a rear mid engine, you can absolutely bias the weight toward the rear tire and load it sufficiently to get good grip, but you'll have to make sure your rear tire is wide enough for the power you're planning to put down. making the rear tire aproximately equivalent in width to the two front tires is a decent rule of thumb though. that said, I think you should avoid a superwide rear tire with really low sidewalls. here's why: unlike cars, reverse trikes control roll stiffness at the front only, and -beyond deisgned in geometric mitigations mentioned below - this means either stiff springing, a stiff anti-roll bar, or both. but no matter what you choose, the vehicle will experience some roll, and this will tend to rotate the tire to the outside edge of its tread, lessening effective contact patch area. this must be lessened as much as possible, and the best way to do that, IMO, is a medium-width radial tire with a - minimum - 60 aspect ratio. The thing is gonna roll, let the sidewall flex at the rear to soak some of that up.

fore-aft locaion of the CG has little effect on tippiness (EDIT: umm, actually, yeah, it kind of does, see Acerguys post below. Far be it from me to gratuitously misinform ;-) ), though CG height and roll center location do. Comparitively, a CG far above the roll center will roll/tip more, and CG below the roll center will roll less. on a car, it is usually accepted that for best handling, the roll center axis should incline upward from front to rear, with the rear roll center higher than the front. this is fundamentally impossible on a reverse trike, because the rear roll center will always be at the intersection of the rear tire centerline and the ground. designing the front suspension such that the front roll center is enough below ground to maintain the automotive roll center axis paradigm will only exascerbate tippiness.

in my case, since I chose a 6 inch ground clearance as best for daily driving, I have both a really high roll center at the front, and I've sprung the thing rather stiffly. Roll is minimal. in the interest of full disclosure, I do experience camber loss in roll, but the thing still rails around turns in a most pleasing style.

its important to remember that you're not designing either a car or a motorcycle, and the reverse trike requires applying a different set of design rules to best fit its specific dynamics.

But, ultimately, the best advice, really, is to look at successful reverse trike designs, and mimic those. have fun!

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The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.


Last edited by robbovius on April 22, 2014, 8:20 am, edited 1 time in total.

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PostPosted: April 21, 2014, 3:03 pm 
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The "direness" of tipping can be pictured graphically.

Draw lines on the floor between the three tires. Locate where the CG will be, and imagine a string hanging from the CG with a weight on it. The string will swing with the cornering force, and if and when it points at the line drawn between the tires, the vehicle will tip. It's a great illustration why the CG on a three-wheel car should be kept both low and forward... or, just use really skinny tires so you can't build up any cornering force...

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Both available from https://www.lulu.com/


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PostPosted: April 21, 2014, 3:57 pm 
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Or watch videos of Jeremy Clarkson driving a Reliant Robin.


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PostPosted: April 21, 2014, 6:12 pm 
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Some side car boys used to race Austin minis with the body and rear wheels replaced by a single wheel. Front wheel drive of course. Quite stable if you make use of variable CG (i.e. the monkey)


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PostPosted: April 21, 2014, 7:05 pm 
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KB58 wrote:
The "direness" of tipping can be pictured graphically.

Draw lines on the floor between the three tires. Locate where the CG will be, and imagine a string hanging from the CG with a weight on it. The string will swing with the cornering force, and if and when it points at the line drawn between the tires, the vehicle will tip. It's a great illustration why the CG on a three-wheel car should be kept both low and forward... or, just use really skinny tires so you can't build up any cornering force...


From the R.Q. Riley website: Image

And an interesting paper from the American Solar Challenge: http://americansolarchallenge.org/ASC/w ... 060811.pdf

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PostPosted: April 21, 2014, 8:45 pm 
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http://reversetrike.com/plans-built.html

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PostPosted: April 22, 2014, 8:16 am 
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Acerguy wrote:
[And an interesting paper from the American Solar Challenge: http://americansolarchallenge.org/ASC/w ... 060811.pdf


I read thru that to the last paragraph, and was surprised to find that rear wheel weight for a reverse trike was recommended to be 33-36%, and that's right about where mine is.

KB, given Acerguys info, I admit to being incorrect about the effect of longitudinal CG placement on tippiness. live and learn eh? ;-)

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The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.


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PostPosted: April 22, 2014, 8:18 am 
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nick47 wrote:
Or watch videos of Jeremy Clarkson driving a Reliant Robin.


comedy gold, right there.

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The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.


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PostPosted: June 15, 2016, 2:53 pm 
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Joined: March 26, 2012, 1:53 am
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robbovius wrote:
...fore-aft locaion of the CG has little effect on tippiness...


The way I think of it is, lateral weight transfer is only from one front wheel to the other, regardless of where the CG is.

So the higher the % of weight on the front wheels to start with, the more lateral g's it takes before lifting a wheel.

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