Three wheels and a helluva lot of fun

Posted on July 31st, 2007 in Aerodynamics,Economy,Handling,Opinion,Power,Suspension by Julian Edgar

As I write I’m getting over a cold. I am well enough to be mobile but not well enough to work. Well, that’s what I tell myself anyway.  

As many of you will know, I am becoming more and more interested in lightweight vehicles. One of my cars is a Honda Insight – amongst the lightest of all production cars on the road – and I find the downsides of its design usually quite minor. (If I need to carry more than two people, I take Frank the Falcon.)  

Now the Honda might be light, but it still has four wheels when surely three would be enough. Using a tadpole configuration (two front wheels and one rear) would also allow the car to be nicely streamlined, something that would be helped by a front mount engine and front wheel drive. That way, the classic teardrop shape for low aero drag would be much easier to implement.  

The starting point for such a car would be a FWD half-cut, say a Mira or Suzuki 660cc 3 cylinder turbo. Use the complete driveline, subframe, steering and front suspension and brakes, add on a tube frame chassis and then run the single rear wheel and suspension from a motorbike.  

Swing axles defended…

Posted on July 24th, 2007 in Opinion,Suspension,Tyres by Julian Edgar

milliken-car.jpgI’d no sooner finished writing A Disappearing Suspension Technology than I came across something that goes a long way to explaining the reason that swing-arm suspension was used by such hugely respected engineers like Porsche and by companies like Mercedes.

The magazine article is on a very interesting car produced by one of the all-time greats in suspension theory. The designer of the car was Bill Milliken and the premise was that by using narrow tyres running a huge amount of negative camber, very good cornering grip would be able to be obtained.

Now there’s a lot more to his car than just that (by clicking on the magnifying glass you can enlarge the article scans enough to print/read them) but the narrow tyres/huge neg camber is a very short summary.

The tyres being used by Auto Union and Mercedes pre-WWII race cars were similar in width to current big motorcycle tyres and so would have been far less susceptible to loss of grip through lifting of the flat tread of the tyre that would otherwise occur through negative camber. In fact, the lateral thrust from the camber achieved by the swing-arms would, as the Milliken car shows, have made a major contribution to cornering grip.

It makes me think that a lightweight car running low pivot point swing-arm (or semi-trailing or leading) suspension and motorcycle tyres could develop a lot of grip while maintaining an ultra lightweight suspension, in turn giving a very low unsprung weight and low total vehicle mass. And the narrow wheels and tyres would also give far lower rotating inertia, improving acceleration and braking still further…

Suspension behaviour, the VE Commodore and hybrids

Posted on July 14th, 2007 in Hybrid Power,Opinion,Suspension,Technologies by Julian Edgar

107787_4mg.jpgThe other month I found myself commuting 160 kilometres each day, most of that on two, three and four lane freeways. When everyone’s travelling at basically the same speed, it’s an ideal opportunity to look at the suspension behaviour of other cars. For several kilometres of bumps, you can literally eyeball from close quarters the front or rear wheels of a car travelling at 100 km/h.

One of the interesting things is watching the front dynamic camber variations. Theory says that you want a neg camber increase in bump, primarily to keep the outside, loaded tyre closer to vertical as the car rolls. But theory also says that this dynamic camber increase is pretty well impossible to achieve with MacPherson strut suspension, unless the steering axis inclination is radical (which in turn brings other problems).

And can’t you just see it in action when you watch adjoining cars!

On my local roads, the (pre VE) Commodores and nearly all Japanese and European small cars have front wheels that just move up and down. But watch a Falcon, or any of the European cars with double wishbones, and you can see clear dynamic camber variations.

And the same thing applies at the back, except this time the wheels just moving up and down are those connecting to torsion beam rear axles (FWD cars) or solid rear axles (RWD cars). On cars with multi-link or wishbone suspensions, the camber change is quite obvious to the eye. Of course I’m not talking about much variation – perhaps a few degrees. But you can still see it.