Quoting Alan Dahl <alandahl@mac.com>:
> On Monday, June 9, 2003, at 11:31 AM, Henry Chea wrote:
> > - Does anyone here have solid experience with the effect of weight
> > distribution,
> > regarding both front/rear balance and polar moments? What's your
> > advice on
> > optimizing this and things to avoid?
>
> I am not an engineer but I would assume that something approaching
> 50/50 weight distribution with the expected usual driver and fuel loads
> would be best (if it's meant to be optimized for racing then you might
> not include a passenger in your calculations).
>
> With respect to polar moments I would also expect that the closer the
> weight is to the CG the better since it would reduce polar movement. I
> used to have a 1978 MG Midget which added 35kg high-impact bumpers to
> each end of the car. When I removed the bumpers the difference in the
> way the car handled was amazing, much more stable and easy to control.
>
It is a popular notion that lower polar moments is better, but I brought up this
issue because I've also heard some arguments against going too far with lowering
this. Basically, lowering the polar moments makes it easier to change the yaw
of the vehicle. But theoretically if the polar moments are reduced to near
nothing, then it becomes too easy to change the yaw of the vehicle, and the car
may become prone to snap spinouts. I've heard this is especially true if the
weight balance is not 50/50. I wonder, at what point is reducing the polar
moments going too far? Does anyone have experience with cars that were prone to
snap oversteer?
In our car design, the weight balance is currently between 40/60 and 35/65
front/rear. If I place the radiator in the front it helps with weight
distribution but increases polar moments and overall weight. If I place the
radiator just in front of the rear wheels, it worsens the weight distribution
and lessens the polar moments and overall weight. I'm trying to figure out
which is better, and I think that placing the radiator at the front will be
better.
> > .....snip.....
> > - What design elements in cars you've driven do you find particularly
> > clever or
> > well-done?
>
> In my opinion being clever is not as important as sweating the details.
> Every aspect of the car should be examined to see if it's as close as
> possible to the ideal. Make sure that the suspension characteristics
> are well-designed and the rest will follow.
>
Our car is designed as a true sports car, which means that some things like
luggage space and passenger comfort are compromised but performance things like
the suspension and engine are given top priority within cost. The front
suspension uses double A-arms with nice, long arms. The rear suspension
currently uses double A-arms but I will probably change this soon to trailing
arms so that I can extend the rear diffuser forward. Fortunately we have all
sorts of computer simulation tools to refine everything from suspension
geometries to crash safety to gear ratios. We also have a wind tunnel with a
rolling ground for aerodynamic refinement. Therefore we should be able to have
the vehicle pretty well tuned even before the prototype is built.
> ....snip....
> > - If you were going to design an affordable sports car with the
> > intention of
> > buyers using it as a weekend racer, how would you design it?
>
> Light weight is the most important thing, followed by reliability and
> affordability. Once again the MX-5 is the class of this segment. My
> ideal car would start with the MX-5's platform but strip off all
> non-essentials while adding about 50 hp. The result would be a
> front-engine/rear-drive sports car weighing 1900 lbs with about 190 hp,
> great handling and fantastic reliability. Build something like that and
> people will beat a path to your door.
>
Can the MX-5 really be made that light? Using an MX-5 as a platform to build on
could be a good idea, but we hope to be able to design a less-compromised
suspension and aerodynamic package with more aggressive styling. I'll
definitely take a closer look at the MX-5 in any case!
> Here in the USA Dodge recently showed a prototype of the 1900lb, 250hp
> "Dodge Razor", expected to cost $14,500 if actually produced. Something
> like this, even at $25k would be wonderful:
> http://www.edmunds.com/news/autoshows/articles/48583/page026.html
>
This car caught our attention too. It's interesting to see how American car
co's can come out with performance cars at such low prices, such as the Dodge
SRT-4. It's also interesting that here in the european market, such cars would
not even be considered for purchase from the sporty crowd because no one wants
to be seen in a dodge or honda.
We've also noticed that many car co's are coming out with prototypes and
starting production of niche cars, specifically in the light affordable sports
car area. We hope to beat them in this area.
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