2F/1R rollover tendency > Solution?

[JimmieD]

Hi guys!

Couldn't find a forum section for 'Weird Stuff' so I'm tossing this here    Just about finished with final design & ready to start fabbing up a 2F/1R 3 wheel vehicle for street, trails & offroad. Vaguely, very vaguely, similar to a Morgan 2 wheeler, at least in general chassis layout. Roughly 140-175hp 4cyl w/ 5 speed, about 1000 - 1,100 lbs. Bunch of good reasons for going 3 wheeler, but that's beside the point.

So, these 3 wheelers have a potential to flip over in a really hard fast turn. Chassis can't load to the outboard rear wheel 'cause it isn't there, only having the single central mounted rear wheel. Just like a 4 wheeler lifts the inside wheel on a hard turn, 3 wheeler has the same loads, but nothing for it to feed into, so chassis wants to roll instead of flexing.

Scratching my head 1/8 awake this a.m. and sat looking at an overhead view drawing, had one of those 'Hey, wait a minute...' moments. You guys have played with all kinds of stuff and some really expert minds here, so what do you think:

Similar to how a wheelie bar is used on a dragster, why couldn't I add a mini wheel at the outboard rear corners of chassis, at a height from ground that would only contact when chassis was in a position to flip? Of course using a small wheel/tire assembly stout enough to handle the loads, can you see any reason it wouldn't work? It would be almost completely covered by rear bodywork.

Seems it should all react similar to having a normal wheel there, except center rear wheel is fully in contact and is taking most of the side loading, with mini wheel only preventing rollover. Only used as safety measure and instantly back off a little when reaching point of contact.

Think it would work?

[chrishallett83]

As far as I can find, http://en.wikipedia.org/wiki/Campagna_Corporation don't have a problem with rolling over.



Neither do http://en.wikipedia.org/wiki/Can-Am_Spyder.



I would imagine that three-wheeled chassis stability requires fairly different balance and suspension geometry to a four-wheeled vehicle, ideally you'd need the front track fairly wide and the rear roll-centre as low as possible, right? And the grip balance so the rear tyre tends to slide rather than edge into the bitumen and grip, high-siding you into the road-side shrubbery?

Maybe there is a book on the subject in your favourite technical bookstore?

[JimmieD]

Thanks, Chris!

T-Rex is similar all right. In general I haven't heard of problems with flipping those. I chased around a bunch of forums and did months of research and unfortunately the tip-over was mentioned a few times. When you finally reach the limits there's nothing to prevent the inner wheel lift so the chassis just keeps lifting and apparenly it all happens very fast, maybe too fast to back off.

I definitely agree it's probably a non-issue, but thinking I'd hate to find out the hard way? Figured it wouldn't hurt to add some insurance, but yeah, not even sure it's a problem I'd ever have to deal with.

May experiment with the bare chassis w/o bodywork & see what happens.

[Boostinjdm]

A front sway bar is a must.  I would also move the front wheels back slightly.  The less acute your triangle is, the harder to roll it over.

The golden ratio comes to mind, only tweaked a little.

[fabr]

my only thought about an outboard "training wheel" is what happens if that small tire snags a pothole?

[JimmieD]

Thanks guys!

Front track near 60", wheelbase 84"-87", very low COG. I've beat the measurements to death and that's the best possible from what I can see, but just maybe I can pull another 9" out of wheelbase. Planning on a 48" x 48" cabin/seating area, maybe slightly different when I actually build, possibly take 6" out of that too.

Yes, I have a front sway bar, couldn't figure out if that would actually help or not, confusing to me. I plan on [famous last words] using aerodynamics to advantage, maybe even tunnel effect but that's only good at speed. Hopefully low mount spoilers would help keep things planted?

On the potholes, I dunno, not likely on pavement where I'd be driving but could be interesting. Figuring on some spring loading? Attach a strut like a lever angling downward/rearward, wheel at end point, spring to press down on lever. I know there's a tech name for it but it escapes me right now. Almost like a girder front end in reverse.

Wide open to ANY suggestions! Never done a 3W before....  :-\

[Nutz4sand]

With two extra wheels wouldn't it be a five wheeler?

I say make it a quad and be done with it.

The reverse three wheeler thing is just a fad I feel. I would like to see one race against a two wheeler bike and and a car to prove it can be fast in the corners. 

[JimmieD]

From a U.S.A. perspective I would somewhat agree, but otherwise it's doing pretty darned good for a fad: starting in the late 20's to early 30's and going very strong ever since in Europe. I was just amazed at the number of 3W that have been mfd. & sold to the public!

http://www.3wheelers.com/azlist1.html

Far as a race 2W to 3W no doubt a bike would always have an advantage, but the same goes for 2W to 4W races on a twisty course. Acceleration is maybe a tie, power to weight being equal, but possible advantage to 3W for superior traction off the line. I think my design will offer the best traction overall of any layout, 2W, 3W, or 4W.

I suspect that except for the pushing the ultimate limits to rollover a 3W and 4W would generally be very close on handling, but the old Morgans and other 3W regularly mopped up on any 4W for years in what we'd call offroad courses in the USA.

I'm building off a Dodge Omni drivetrain, 2.2L, 5 speed, tube frame to accomodate the stock K member & stock suspension at front. Used a Mopar V8 distributor & converted it to the 4 cyl. to eliminate computer control, changing stock computer carb to side draft Webers, adding cam & fab headers so maybe 150 or so hp, more or less.

I think I've figured out 3W drive with a limited slip in front, need to look closer at stock config. to see if my plan to drive single rear wheel will also work. If it's mechanically possible that means driven wheels hitting 3 different tracks for traction, so lots better than a 4WD that only hits 2 tracks. Planning a wide rear tire & slightly narrower fronts on mine.

[Boostinjdm]

Now hold on a sec,  front wheel drive?  I wouldn't worry about a roll over.

And the point of a sway bar is to keep body roll to a minimum which will be a problem with a three wheeler. 

[Nutz4sand]

Acceleration is maybe a tie, power to weight being equal, but possible advantage to 3W for superior traction off the line. I think my design will offer the best traction overall of any layout, 2W, 3W, or 4W.

I think I've figured out 3W drive with a limited slip in front, need to look closer at stock config. to see if my plan to drive single rear wheel will also work. If it's mechanically possible that means driven wheels hitting 3 different tracks for traction, so lots better than a 4WD that only hits 2 tracks. Planning a wide rear tire & slightly narrower fronts on mine.

Neither of the above make any real sense to me. I am not sure you have contemplated how the forces are going to be applied in real life. 

[JimmieD]

3W against 2W, might have a race here:

http://www.brudelitech.com/

I don't know for sure on possible rollover, but have read reports of it with a 3 wheeler. I agree the front drive should lower the tendency, that's what I'm hoping.

"Acceleration is maybe a tie, power to weight being equal, but possible advantage to 3W for superior traction off the line. I think my design will offer the best traction overall of any layout, 2W, 3W, or 4W."

"I think I've figured out 3W drive with a limited slip in front, need to look closer at stock config. to see if my plan to drive single rear wheel will also work. If it's mechanically possible that means driven wheels hitting 3 different tracks for traction, so lots better than a 4WD that only hits 2 tracks. Planning a wide rear tire & slightly narrower fronts on mine."


Neither of the above make any real sense to me. I am not sure you have contemplated how the forces are going to be applied in real life." 

The first traction reference is comparing 2 wheels to 3 wheels. Bike may sit there burning while the 3 wheel drive is already gone.

I'm hoping to be able to use 3 driven wheels, not sure it can be done though. If it can then it would be better than 2 or 4 wheels regarding traction. With 4 wheels there's left side wheels & right side wheels, and whatever road surface they ride on. If the front wheel on one side didn't get traction then the rear probably isn't going to either. But with 3 wheels there's a 3rd road surface to get traction on in the center of vehicle, plus the right & left, so it seems you'd have better traction offroad. At least that's what I'm thinking.

[Boostinjdm]

With 4 wheels there's left side wheels & right side wheels, and whatever road surface they ride on. If the front wheel on one side didn't get traction then the rear probably isn't going to either. But with 3 wheels there's a 3rd road surface to get traction on in the center of vehicle, plus the right & left, so it seems you'd have better traction offroad. At least that's what I'm thinking.

That's not how it works....

If you are going to do all wheel drive then it would be best to start with a car that has it.  Like an 88-91 honda civic wagon.   The front is driven directly from the tranny like a normal front wheel drive and the rear is driven by a drive shaft.  No external transfer case.  Your front an rear ratios have to be spot on or they will fight and that's wasted power.

[Nutz4sand]

That's not how it works....

If you are going to do all wheel drive then it would be best to start with a car that has it.  Like an 88-91 honda civic wagon.   The front is driven directly from the tranny like a normal front wheel drive and the rear is driven by a drive shaft.  No external transfer case.  Your front an rear ratios have to be spot on or they will fight and that's wasted power.

I agree. And thats why it does not make sense to me.

Just cause a tire is not behind a tire in front of it does not mean its gonna have more traction either.

[fabr]

Still gonna be predominately at a disadvantage as far as traction is concerned due to the single rear wheel. Just curious, but why you wanting to do this?

[JimmieD]

I'm talking about all wheel drive, all the time. One front and the rear wheel are directly coupled, the other front is independently driven, but through a limited slip. The ratios are all identical, unless I slightly overdrive the rear, common in 4WD vehicles. The limited slip will prevent the steering & handling from getting too squirrely.

The 3 separate wheels are all seeking traction on 3 different parts of road surface. That is an advantage over trying to get traction on 2 parts of road surface, just like a 2WD limited slip has advatage over a single leg differential 1WD. Even in slushy ruts or wallows where front wheels both lose traction the single centered driven rear would be on higher & drier ground, getting traction. Many 3WD do very well, even offroad, with only the single rear wheel driven.

My front drive will be the nearly stock Dodge Omni setup, but limited slip to give traction to both front wheels. The rear will be driven off one front. Disc brakes on all 4, with those made for a car weighing 3 times as much, so killer brakes.

I am building for several reasons, first because I want to. Also it is cheapest to register and insure, as a motorcycle, plus I beat all SMOG regs, very important here in California. I can easily build the whole machine for way under $1,000. A stock Omni can knock down 41-44 mpg easy, at around 3,000lbs or so. I figure on something like 75+mpg with 1/3 the vehicle weight & good aerodynamics.

It will be a multi-use vehicle for most any road surface and moderate offroad, and should be good in snow, sand and mud. It will have extreme acceleration, crazy top speed if I wanted, very aggressive handling, excellent for the steep & twisty mountain roads here. It could pull my small popup trailer for long trips, with incredible mileage. It will seat 2, look good, handle great with incredible  acceleration, handle most any terrain and all with far more than good mileage and be exciting to drive. Complete parts cars are readily available for $200-$300. The tranny I'm using is a direct boltup to the VW 4 cylinder diesel. I've got a spare turbo and can intercool it and have strong power & torque, and bring the mpg's up around 100mpg if I drop in a diesel.

I can't see any reason NOT to build it