16 replies to this topic

[mariner]

Three wheelers have two big weight advantages - saving a corner's worth of tyre, wheel, hub and brake, plus no need for any torsional rigidity so only beam (+ safety) strength for chassis. 

However, the roll resistance is much reduced to about half the two wheel axle width.

 

Three wheelers can be two wheels front, one rear ( Morgan, CanAm , Heinkel) of one front, two wheels rear ( Reliant, Bond).

 

Conventional wisdom seems to be that two front wheels are best as the weight braking and going into corner is “ thrown” onto the front so the thing will tip over with only one front wheel.

But I that really true?

 

Weight will be transferred from wheel to wheel on any vehicle but it doesn’t physically move in the car so it can’t be “ thrown forward”. As there is only one pair of wheels to resist roll any lateral weight transfer must happen across that axle, be it at front or rear.

 

A single front wheel would have a slight advantage on turn-in as it is not using any grip to generate  lateral force so it can just give steer angle inputs.

 

It is true that most high performance three wheelers have used two front, one rear wheel but that is mainly because you can use the complete mechanical assembly from a high power motorbike – engine, gearbox, swing arm and transmission , and rear weight transfer adds to traction.

So is there some inherent handling advantage of two front vs one front wheel layout on a three wheeler?

 

 

[BRG]

Of course the two front wheel layout is better - it is simple physics.  When braking and entering a turn, the centre of gravity shifts forward and to the outside of the turn.  If there is a wheel there (as there is in a four wheel vehicle) , then all is well,  If there is no wheel there (as in the one front wheel layout) then there is nothing to stop the inevitable toppling action.  Many drivers of Reliant three wheelers can bear this out.  It is no surprise that the three wheelers with any racing pedigree were two front wheel layouts such as the Morgans which were regularly and enthusiastically competed in the 1930s.   In recent years, there have been races on UK short ovals for Reliants which have been demolition derbys as car after car rolled over.

 

It also the reason (in my opinion anyway) why the Deltawing concept was never going to work.  I know it had four wheels, but the front ones were so close together that it was essentially a  three wheel layout.  Any success that design had (and there was not much of that) was because it was always running with a massive weight advantage.  The original Le Mans design had a smallish engine but also weighed half the minimum weight of the LMP1 class that it was allowed into.  So its power to weight ratio was about the same as the genuine LMP1s, yet the Deltawing was slower that all the LMP1s and most of the LMP2s, which I put down to slower cornering because of the wheel layout.

[mariner]

I understand what you are saying but in reality  the centre of gravity doesn't move at all - it can't because it is function of where the vehicle  components are. Braking etc, doesn't  make the engine slide towards the front or back., the weight transfer is purely dynamic and depends on wheelbase, track and total corner spring resistance 

 

I suspect there is some benefit in two front wheel but it isn't just weight thrown "thrown forward so it tips" A strong rear AR b0 ar would fix that.

 

 

i think  it is the distance from the two wheel axle to the CG which matters because if the CG is well forward ( like a Reliant) the inside wheel will lift and yes it tips over .

 

However if I built a three wheeler with a transverse power pack at rear or a Porsche flat six out the back it may never tip over 

Edited by mariner, 06 April 2024 - 09:46.

[BRG]

You may have a point about placing the engine at the rear but I reckon that is just reducing the disadvantage rather than achieving an improvement over a two front wheel layout.

 

 

 

versus

 

 

Pretty sure which one I would rather be driving!

 

[Nathan]

I would want the 2 up front for braking and managing the grip of the steering tires at the limit.  

[Canuck]

As an individual that grew up riding various off-road trikes including the deathly 250R, I can assure you that a single front wheel, speed and a direction change are not your friend. It is in fact much, much worse if there is traction that prevents you from drifting the rear as your steering input. Yes, childhood stupidity and driving beyond our abilities / conditions, but the physics of (you) rolling into that space between the single front wheel and where there should be the outside front wheel remains.

 

Also, it seems to me that you want at least as wide a front track as the rear, if not slightly wider for "better" handling but that's just something stuck in my head from somewhere.

[Greg Locock]

You may remember in one Arnie SF film he drove a single wheel at the front trike. This thing was a serious design, I think by Robert Riley. (it was , the trimuter https://3-wheelers.c...interview1.html) It suffered the same problems as any other single wheel at the front trike - linear range oversteer, terminal oversteer, and a tendency to roll over when braking into a corner. Riley switched to tadpole config for his later designs.

 

Here's some smartass having a look at the trimuter. https://www.eng-tips....cfm?qid=157681

Edited by Greg Locock, 06 April 2024 - 23:05.

[Canuck]

From Greg's link.

Greg Locock: last thought...

Greg Locock: further last thought...

Greg Locock: more last thoughts...

etc...

Greg Locock: if you want to send me some data...

 

That question got it's hooks in good

 

I'll bite - what was the reasoning for front-single on the solar builds?

[Greg Locock]

Aero and packaging. Our wind tunnel (fibber, plank of plywood on a roof rack and a bunch of water tube U manometers and a 1/5 scale model) results showed that twin front spats accelerated the air under the car more than single front spat. The steering spats for a wheel that steers have to be wider than the non steering spats. The shape of the body was a fairly flat wing that tapered towards the edges, it would have been harder to incorporate room for the suspension travel with two front wheels. All 3 wheels were mounted to a rigid triangular frame that was then used to suspend the body. This guaranteed perfect wheel alignment.

 

here's our (their, nothing to do with me) third bite at the wing shaped car, I think the aero on this one was by an ex ferrari aero guy. 

 

As you can see the packaging room is limited at the front corners we could have got around that by burying the suspension in the spat,-but the aero was far more important.

 

here's the photo of the guts of the thing, I think they've gone to independent suspension (and hence a load bearing structure)

 

 

I've asked my research minions to find a cutaway drawing of the original car, let's see if it is still around.

[Joe Bosworth]

Here in Australia our posties for the most part deliver their mail in 3 wheelers with a single wheel in front.

 

There are two major problems. One, they carry substantial weight of mail in bag hanging off the front of the handle bars;

Two they have a sunroof well above their heads and mostly over the length of the vehicles.

 

I have a neighbor who has been delvering mail for a number of years as well as being a regular 4 wheel motor cycle rider of even more years.

He assures me that they tip over with great regularity.  They dare not turn while going over a curb or the like.  The castor on the single front wheel results in the front

falling below the center line of the vehicle and drops the center of gravity at the same time with the easily expected results.

 

The problem becomes worse when they must turn around in a drive way due to post box location and becomes even worse when being chased by

an un-friendly dog.  He and his supervisor have regular disagreements on the results.

 

Regards 

[Greg Locock]

Single wheel at the front ATX motorbike trikes were a good way of killing farmers, that's why we went to quad bikes, which are slightly less lethal.

[BRG]

And interestingly, the motorcycle/scooter industry now offers a number of 3-wheel models - all with two front wheels.  Now a firm favourite for camera bikes on pro-cycling races due to their extra stability.

[GreenMachine]

Single wheel at the front ATX motorbike trikes were a good way of killing farmers, that's why we went to quad bikes, which are slightly less lethal.

 

Very slightly.  AIUI there were another couple of fatalities in the last month or so. (EDIT) Another two this last weekend, per Aunty.

 

And interestingly, the motorcycle/scooter industry now offers a number of 3-wheel models - all with two front wheels.  Now a firm favourite for camera bikes on pro-cycling races due to their extra stability.

 

EXTRA stability        What were they using before?  Yes, I know, 2-wheel motorbikes (TdF at least).  They should have jumped straight into something like a Smart or a Jimny,   I imaging the road real-estate they occupy is a concern there, mixing with bikes etc, but it won't be long before the  job is done with drones I imagine.

Edited by GreenMachine, 08 April 2024 - 00:57.

[mariner]

Well, you have all convinced me that for practical road three wheelers two front wheels are better than one.!

 

However, I have say, politely, that I am not convinced that two front wheels vs one front wheel is better in vehicle dynamics terms.

 

I say that based on racing sidecar outfits. They are clearly three wheelers with just one front wheel. They have track, by regulation less than a Reliant so should tip easier but they don’t do a “Reliant tip up “ on track. I have searched for “sidecar racing crashes” on YouTube and no examples of “Reliant tip up”.

 

In fact they can lap the Isle of Man TT circuit at almost 120 mph , hairpins included.

 

They have a Laden power to weight ratio of nearly 500 bhp/tonne versus 70 bhp/tonne for a Reliant.

 

They have wide slick tyres so much more grip than any narrow tried Reliant.

 

So with way more power and grip but less track they should tip up like the photo at the  first corner but they do not??

 

btw the sidecar outfits are very interesting 

 

Edited by mariner, 08 April 2024 - 08:39.

[BRG]

 

Well, you have all convinced me that for practical road three wheelers two front wheels are better than one.!

 

However, I have say, politely, that I am not convinced that two front wheels vs one front wheel is better in vehicle dynamics terms.

 

I say that based on racing sidecar outfits. 

I suggest you Google "Sidecar racing" and then click on 'Images' as I just did, and see how many show a three wheel combination with only two wheels touching the track.  And a loony hanging over the edge in a desperate attempt to defeat the laws of physics.  The discipline of sidecar racing is a triumph of engineering that has gone a long way towards negating the clear disadvantage of the single front wheel layout.  But still cannot overturn the physical laws that rule the universe.  The only reason sidecar outfits aren't two front wheel layout is because the regulations don't allow it.

[gruntguru]

CG is strongly biased to the rider side which avoids the topple-under-braking effect.

CG is also at a similar longitudinal position to the extra wheel so cornering with that wheel to the outside does not significantly bother the F/R weight distribution.

[Lee Nicolle]

 

Well, you have all convinced me that for practical road three wheelers two front wheels are better than one.!

 

However, I have say, politely, that I am not convinced that two front wheels vs one front wheel is better in vehicle dynamics terms.

 

I say that based on racing sidecar outfits. They are clearly three wheelers with just one front wheel. They have track, by regulation less than a Reliant so should tip easier but they don’t do a “Reliant tip up “ on track. I have searched for “sidecar racing crashes” on YouTube and no examples of “Reliant tip up”.

 

In fact they can lap the Isle of Man TT circuit at almost 120 mph , hairpins included.

 

They have a Laden power to weight ratio of nearly 500 bhp/tonne versus 70 bhp/tonne for a Reliant.

 

They have wide slick tyres so much more grip than any narrow tried Reliant.

 

So with way more power and grip but less track they should tip up like the photo at the  first corner but they do not??

 

btw the sidecar outfits are very interesting 

 

 

A racing sidecar has the chair wheel near the centre,, and the swinger is moving all over the thing to keep it balanced. So an entirely different scenario  with moveable balast. You can always tell the sidecar crews,, they limp! Road race or speedway.