Hi chaps,

am putting the suspension together(~ for the third time!)

can anyone give me a rough procedure for setting basic geometry (ill get it properly sorted by someone after sva)

at the moment I have done the rears usuing a on meter long spirit level-

set hubs to dead vertical, then for toe in / out- measured width at the rear hubs, then used spirit level to go one meter back and measured again.

had about 3-5 mm more at the rear measurement, which im hoping is close enough not to matter!!

as for front- really not sure how to do it!

any thoughts / help appreciated!

les

i asked a similar question...Hope the people in question dont mind, but I coppied and pasted their answers for future refferance.

Suspension Basics

Designing suspension is complex and you should not really build a suspension system without a basic understanding off what is required.

However here are some basics:

Lower wishbone parallel to the ground.

Upper balljoint 5 degree behind the lower ball joint. This is caster for self centering. The actual angle does not matter too much (5, 5.5, 6 etc) but make sure they are they same on both sides. To measure the angle draw a line between the ball joint centres and when you look from the side of the car this angle is the castor. In practice it is hard to measure.

The top wishbone wants to be approx 2/3rds the length of the bottom wishbone and run downhill from wheel to chassis by about 10 to 15 degree.

When you view the wishbones from the side of the car the chassis mounts should be on a horizontal line. This will give no anti dive or squat, keep things simple for now.

Have -1 degree camber (wheel leaning in at the top)

Looking from the front, draw a line from your top wishbone mount on the chassis to the bottom wishbone mount on the chassis, the steering rack pivot should lie on this line, as a starting point to minimise bumpsteer.

If you want to get more complicated then aim for a roll centre of around 3" above ground and alter the angle of the top wishbone to achieve this.

I hope this helps,


After doing a great deal of research, we came up with a design that allows considerable fine tuning once all is done. If you look at the front suspension pics on my website, you'll notice two things: 1) the lower wishbones are pointing downward lightly (going from inboard to outboard), as the suspension is unloaded...this will lievel out when fully loaded. And 2) the inboard end of the upper wishbones are attached to plates that can be adjusted, vertically horizontally and diagonally. This allows us to fine-tune later for caster, camber, toe & anti-dive. If you do it this way, you'll be able to get it right for sure!


Aim for as much suspension travel as you can. I can never get as much as I want and always wish for more travel. However the more travel you have the harder it is to keep the wheel doing what you want (camber in roll and bump).

Longer travel also allows you to use softer springs which is good.

My car has 130mm of total wheel travel (saloon not a 7 style car)

Allan Staniforths Race and Rally Car Source book is a good starting point, then all of carroll Smiths books and finally Milliken.

John

Hiya,
based on the RS Jigtec 'bones I have fitted, I would make sure that the balljoints are at 90 degs to the line of the hub, which leans in considerably, and not the road, otherwise the ball joint will jam before the wishbones droop and fully extend the coilover.
The pictures seem to show that the upper balljoint is almost directly above the lower one. Trial fit a hub to check the stub axle is horizontal.

The distance between upper & lower wishbones dictates the length of the dummy strut. RHS's are very short (1-2 inches) mine are about 6". There must be an optimum distance, but they all seem to work OK. Just try to keep the wishbones parallel at normal ride height.

Make sure you have enough castor angle to give self centring. With my long dummy strut, I had to set the upper ball joint 20mm to the rear of the lower. DONT USE THIS FIGURE. IT WONT SUIT YOUR YOUR SETUP.
I have no idea what angle this equates to, but there are a number of reference books which may help.
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that's handy cheers

Wow,

Thanks for the reply, I think thats probably a bit too complex for me at present- Im using factory tiger wishbones, steering rack and shocks / springs. but struggling to get all the geometry right

les

So, let us put it in a WIKI-pedia!

Has some-one the room and the knowledge to make a Wiki????