THREE WHEELED TILTING VEHICLES

[ryanturnercom]

Does anyone have any insight on the advantages / disadvantages on tilting suspension setups? I have normally seen it on three-wheeled vehicles. Such as

http://www.maxmatic.com/ttw_moto.htm

but I am not sure if its advantageous or not. What do you guys think?

 

[GregLocock]

What problem are you trying to solve?

The narrow track 3 wheelers have to do it to stop them falling over. There is also an advantage, more generally, in tilting the sprung mass if it moves the CG inboard. Passengers may be more comfortable with a tilting body. Research has shown that drivers drive better if the body does not tilt at all.

Tilting the wheels does not seem to offer anything like these advantages, although if you start from a motorcycle then the wheels and tyres are designed to corner like that. Car tyres would work better if they are kept square to the road. I don't know which is the 'better' tyre choice, all things considered, but would guess it is the car tyre (ie flat tread) than the motorbike tyre.

Cheers

Greg Locock

 

[ryanturnercom]

Greg - I am not trying to solve a problem. I am just trying to weigh the pros and cons of a 3 wheeled craft.

I like the weight savings, the efficiency possibilities, and the fact that as long as I keep the engine displacement below 1800cc its certified,registered and insured like as a motorcycle.

Are the three wheeled vehicles stable in general regardless whether they tilt? Would a single wheel in the back have better cornering traction than a vehicle with two wheels in the rear. For some odd reason I feel that the three-wheeled design would have a tendancry to spin very easily, and get really squirely while braking and turning at the same time.

Can you take a look at this and give me your thoughts on stability and vehicla dynamics? I have ordered a couple books and am really trying to learn as much as possible.

http://www.usa-trex.com/

Any Ideas?

 

[GregLocock]

Your link is broken.

"Are the three wheeled vehicles stable in general regardless whether they tilt? " No, the narrow track ones have to tilt to keep the CG inside the axle. The wide track ones may be stable if the CG is low enough. Generally stability is an issue because the roll over track is roughly half the two wheel track.

Two wheels at the front definitely looks better (other than on bubble cars). Single wheel at the front can suffer from all sorts of evil/hilarious tendencies, eg the plastic pig, or Reliant Robin, which could roll over if you braked and steered simultaneously.





Cheers

Greg Locock

 

[ryanturnercom]

Greg, thanks for the information. The link works for me. But here is another one, this one is the official site, but has less pictures. I am worried that their design has very poor handling, but I have not been able to find any reviews that are pertinant.

http://www.go-t-rex.com/

 

[GregLocock]

What makes you think it will have poor handling? By pure guesswork it'll be a go-kart(that is a good thing). C of G is low, track is very wide. It'll get tail happy in the rain, but other than that the fundamentals look OK. The tyres are huge for its weight.

$43k

yeah, whatever.



Cheers

Greg Locock

 

[ryanturnercom]

Greg, thanks. I have just been skeptical I guess. As long as I am able to keep the CG low and centered I think I will be ok.

A friend and I are doing research on building an inexpensive street vehicle. Being three wheeled and <1500lbs the vehicle registers as a motorcycle. Which is much easier to get registered as &quot;street legal&quot;. Things such as doors, bumpers, mirrors, etc.. are not required by law to drive it on the street. Moreover the weight savings by ditching the 4th wheel and reusing motorcyle parts will be dramatic. I am also hoping that rear wheel cornering traction will be very good.

Anyway... thank you for your comments. I respect and appreciate your comments. I have read your posts all over this forum and they are invaluable. Thanks

 

[Eechols]

If you haven't check out R.Q. Riley's site (

http://www.rqriley.com/3-wheel.html)

you might want to give it a look. When I started my three wheel project that was one of the first places I started. There are many articles on three wheel handling and suspension systems as well as other design sources.

Also see:

http://www.indycycleonline.com,

http://www.geocities.com/motorcity/speedway/6755/,

and

http://www.maxmatic.com/shrike.htm

As long as it's designed properly, with the CG in the right place and proper suspension it should perform as well as any 4 wheeler. And two wheels in front seems to be the prefered configuration. With two in front the tendacy is to understeer which is deemed safer than oversteer.

You will notice that the third wheel, in most cases, is an automotive type, because motorcycle wheels are designed for leaning into a curve.

Good luck and be sure to keep everyone informed on your progress.

Edwin E. Echols

 

[ryanturnercom]

Thank you, those links area great. I have already contacted the shrike guy. But the prefabbed indy cycle looks really cool. thanks for the post

 

[Slowzuki]

I have seen a comparison of a 3(2 in front) vs 4 where the 3 wheel stability was found to be quite poor if the design is not adjusted. Note that comparison was for static tilt table rollover.

The height of the cg obviously plays a role but it also the fore aft location of cg will have a large effect too.

The rear has no means to resist a roll moment and the rear roll centre is on the pavement. If you have a high rear mounted cg you will generate a large roll moment when cornering.
Ken

 

[ryanturnercom]

Point well taken,
Most of the designs on the web have a very low stance in the front, but end up using a motorcycle rearend.Leaving the motor relatively high and toward the rear of the vehicle.

I am sure the entire frame would have to be designed around a solid suspension model, which would most likely put the engine low and centered. Unlike most of the cages welded to a motocycle that I have been seeing.

I would be really interested in seeing any direct comparisons between the 3 and 4 wheeled vehicle dynamics. Do u have any links or documentation? I am not completely sold on a 3 wheeled design and am weighing my options.

 

[Slowzuki]

I'm afraid I can't find it in any of my documents and I know it did not get into dynamics.

Thinking of the basic oversteer/understeer characteristics, throttle on oversteer could get interesting. I'm curious how hard the car could be pushed/ how comfortable it would be pushing it.

 

[ryanturnercom]

We are as well. As u had mentioned a couple posts earlier... the rear would have no means to resist roll, but it has no means to create roll either, some believe this may lead to a larger contact patch in the rear - giving it better traction through high g turns. I believe it may be beneficial that there is no 4th wheel which is unevenly weighted, and no extra chassis torque either.

I have really no idea on how a properly designed 3wheeler could possibly handle. But Im very curious and getting closer and trying to do research to see if I could get a 3wheeler to handle similiarly to a 4. As there are many advantages to the 3wheeled design.

 

[Slowzuki]

Ryan,
How do mean the rear would have no means to create roll? I could not get the links above to work but I have seen other tilt body 3 wheelers.

Does this 3 wheeler lean the body based on the forces acting on the body?

Most are at a function of the angle of steer. This cannot keep the contact patch inline with a force vector (gravity+cornering forces) from the cg and therefore will have roll moments generated most of the time. For every steer angle and road banking, one speed would give zero roll moment, the rest of the time the roll moments exist.

 

[gsflier]

the rear would have no means to resist roll, but it has no means to create roll either?????????

I believe the rear end would produce a roll moment based on the fact that the instantaneous roll center is at road level and all of the mass above that point would create a roll (torque)in a corner. It would however not have the ability to resist the moment and would contribute to the roll-over tendency. The front end would have the job of resisting the entire roll moment of the vehicle but with only a portion of the vehicle's weight. The instantaneous roll center of the entire vehicle is a mixture of both axle moments averaged together with the appropriate weight ratio of each axle. More accurately put there would be a line drawn connecting both roll centers and in this case would most likely not be parallel to the ground plane. Gary

 

[PTwizz]

Further to gsflier, the line connecting the front and rear roll centres is referred to as the roll axis, and the vehicles behaviour in roll is dependant on the CG location relative to this line.
Vehicles of this format usually have the CG as low as possible an biased toward the front, in an effort to maintai some cornering stability. Unfortunately, this gives only small weight transfer under acceleration, leading to the tail happy nature under power. For this reason, front drive trikes are far easier to design and set up.

PT

 

[GregLocock]

Tricyclists might like this site,

http://scg.levels.unisa.edu.au/solar_commuter/

Cheers

Greg Locock