Re: [doc] Front springs

[Martin Gutkowski - DMC Ltd <martin@xxxxxxxxxxxxxx>]

Hi All (esp Mark)

I've driven a lot of DeLoreans now, and more than one with old front 
springs on the rear. I also have moderately lowered rear suspsnsion on 
my own car, by about an inch with Grady's (former) shock setup.

1) Front springs on the rear make the rear too low IMO, in fact 
sometimes lower than the front. Anything lower than where the control 
arms are level is a bad idea IMO.
2) On my own car I've eaten 2 sets of back tyres in 10,000 miles thanks 
to the lower setup (toe-in is correct and although I'm a fan of 
wheelspinning, so is Chris H and he's done more miles on one set :-) 
I've got adjustable lower links on my other car and the wheels sit 
noticably straiter at the back.
3) A softer ride on the rear makes an unbelievable difference to the 
ability to lose the back end, in a similar, but more predictable way as 
loose trailing arm bolts do. I've recently had two cars in at the same 
time - one Stage 1 and one Stage 2. The Stage 1 car (less powerful) was 
far too tail-happy. The difference was front springs on the rear, and I 
can vouch for the rest of the suspension on both cars, and both had the 
same set of pirellis.
4) In playing with the adjustable suspension we do, you can make the car 
thoroughly dangerous (but a great drift machine, if you're into that!) 
by stiffening up the front and softening up the rear. It's quite surprising.

"

The rear suspension uses the 'Second Order Lever' It has its fulcrum and effort(spring) in opposite ends and the load in the middle, just like a wheel barrow set up.

The front suspension uses the 'Third Order Lever'  The fulcrum and load are at opposite ends this time with the effort(spring) is in the middle, such as a shovel.

"
I'm not entirely sure how you can apply lever principles to the rear 
suspension because as I see it, there isn't one. The weight of the car 
is passed directly to the hub carrier at one end of the lever. The other 
is just a pivot. There's no multiplication involved unless you look at 
the angle of the spring/shock which in this case is only non-vertical to 
get it out the way of the tyre, hence needing a slightly stiffer spring 
than if it were vertical, at a ratio exactly proportional to the angle 
of the spring/damper compared to the vertical (at a guess, but it's 
probably as near to no difference as makes no odds). That's "moment of 
forces" stuff and Newtonian physics, IIRC, but it's a while since I did 
my A-level Maths and Physics!).

The front suspension is a second order lever, although dealing with a 
multiplication of effort rather than a division of it.

You're absolutely correct that all other things being equal, the rear 
spring can be weaker for the same effort, given the geometry. 
Unfortiunately all other things aren't equal because someone had the 
bright idea of plonking the engine over the back wheels :-)

http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0017416.html

Martin



Nick Tomlinson wrote:

> 
>  I personally tried the front springs on the rear trick, but this resulted in too wallawy, too soft a ride for my liking. Just a basic test like pressing down on the bodywork showed this.
>





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