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Old 12-02-2009, 07:33 PM   #1 (permalink)
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Old 12-02-2009, 07:48 PM   #2 (permalink)
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I don't know if this is of value to you, but if you change the wheelbase of a car (as in, mount the single rear tire fore or aft of the previous axle's center) you also change its effective ackermann geometry which may lead to undesired handling. Worth noting, anyway.

Ackermann steering geometry - Wikipedia, the free encyclopedia

that is all I have to contribute at this time.
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Old 12-02-2009, 08:29 PM   #3 (permalink)
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morgan 3 wheel cars - Google Search

The Morgan 3 wheeler.

I am considering the same configuration, primarily because in Virginia it is considered a motorcycle.

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Old 12-02-2009, 08:36 PM   #4 (permalink)
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Narrower track-

pro: allows more slender bodywork

con: less stability. You especially want the heavy end of the vehicle to have the wider track for better stability.

Rear drive wheel on tadpole trike:

pro: simplicity; perhaps lighter?

con: less traction. Yes, traction is better when the heavy end of the vehicle has the drive wheels. You do NOT want the single wheel end of a trike to be the heavy end. However if it is a fair weather, low power vehicle traction isn't as much a factor.
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Old 12-02-2009, 09:20 PM   #5 (permalink)
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Quote:
By tadpole trike you mean JUST THE BOTTOM RIGHT pic am I correct , EXCLUDING the top right pic?
Tadpole is ANY trike with the single wheel in back. Axle track has nothing to do with it.

Quote:
Why exactly wouldnt you want most of the weight more towards the rear tire on a trike?
Er.... cuz you might tip over?



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Old 12-02-2009, 09:44 PM   #6 (permalink)
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How safe what is? I need to know where the Cg is.

We haven't spoken of altering the wheelbase so why would "wheelies" and stoppies become an issue?
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Old 12-02-2009, 09:49 PM   #7 (permalink)
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I really don't think I can comment within your format, and I don't think you should even believe all you "know" already. There are, unavoidably, several factors you have to learn to consider at once. Over-simplification can make you feel sure of yourself, until you try to drive your creation.
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Old 12-02-2009, 10:24 PM   #8 (permalink)
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Sorry, I should have included your "Because I already know less drag from less tires , less weight from the front axle and rear axle and missing tire/wheel." specifically. I didn't call you a know-it all. Since tire drag is almost linear with load, changing to a single tire gives only ancilliary drag benefits, which are then mostly or wholly overcome by other considerations to restore all the original performance in a comparison.
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Old 12-02-2009, 10:24 PM   #9 (permalink)
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Ok, I'll save my physics post and explanation of stability and handling for a later time... I'm not sure I want to post it after reading this page.

It's a pretty simple tenet, really... when you're trying something new, you abandon what you "know", and relearn everything. It's a safer bet that way that noone gets hurt, and you don't waste money, time, and possibly yourself.

If I see this thread turn back into something desirable for this forum, I'll post what I've saved.

EDIT: Removed the section clarifying what Bob posted.
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Old 12-02-2009, 10:35 PM   #10 (permalink)
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cornering stability and tire loading. A reverse trike has the ability to swing-ass, rather than tip on it's face, like delta trikes.

Both right side pics were tadpole trikes.

I can't think of an instance where you'd want the front track width thinner than the rear, because under heavy loading, the vehicle wants to move fore and in the opposite direction of the curve which you're following. There is a fine line between stability and rolling over.

Imagine that there is a straight line between the center lines of the rear and front hubs on the side opposing a curve. The closer to perpendicular the moment angle is to that line, the less stable you're going to be as far as rollover performance. Traction performance is exactly the opposite. The best available compromise is a 45* angle to that line at maximum angle, which is with the two available lines parallel to each other. (each line between left and right sides), which means that the track widths should be equal, or very close to it.

The reverse (tadpole) trike design is inherently stable when the weight is about 70/30 with the front tires bearing the most load, approx 35% per tire, and 30% on the back tire. If the layout of the reverse trike is a right triangle, with each tire 90* from the next, this places the moment angle on the hardest cornering exactly parallel to the front tire opposite the curve, which lifts the back tire. In this case only, you'd want more than 30% of the weight on the back tire, maybe 40-45%. Most of these designs are not right triangles, though, rather closer to Isosceles, meaning that only two sides are equal.

This would place the track width more narrow, closer to the lower right image, which gives greater chance for rear end swing if the weight isn't properly balanced. Of course, proper balance means a trade-off for traction on the drive tire. The fix for this would be to place ballast weight on the rear tire, and maintain a FWD drivetrain, with two driving wheels, which completely changes the handling characteristics.

Keep in mind, that everything in this post assumes that you're coasting through a curve, with only angular load on the rear tire, not accelerating or braking.

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