Any tips on suspension set-up?

[The Pikey]

Without having corner weight scales what is the best way to set the suspension up? I think I want to get it 15mm higher at the rear but should I do this with my weight on the drivers seat for instance? I

 

What else do I need to do?

 

thanks

jason

[rj]

When I corner weigh my own car I load the car with ballast (sand bags) of my own weight, but I put 25 kgs horisontally at the front of the seat. When I following that compare the weights with myself in I am less than one kg out.

[Stationary M25 Traveller]

Assuming your sump is the lowest point, you want to start with getting something like 75mm clearance under there once you have played with camber, etc. Then measure gap under chassis rails just behind front wings, then look for +15mm at the front of the rear wings.

 

I did it with the equivalent of driver + passenger in the seats, using concrete blocks (with the seat bases removed).

 

See also this recent thread

 

Edited by - Stationary M25 Traveller on 13 Mar 2011 20:27:26

[Sheds Moderator]

Some while ago somebody had a get-out-of-jail-free method for flat flooring without scales. It was essentiallt (IIRC) a case of measuiring ride heights at the 4 corners and levelling it up with the right rake then adding one turn to the front right to balance up the effect of the driver's fat Aris. Needless to say it isn't perfect but the general view is it's pretty bloody close. I can't remember the full details but someone else will.

[ECR]

This is a method suggested by Peter Carmichael and posted some time ago so I'm sure he wont mind me reposting:

 

Chassis Set Up by Peter Carmichael

 

What I have done is devised a method which gives assurance that the car is

close to optimal flat floor settings. The main aim is to fix it so that the

front wheels have an even corner weighting and the rear springing is coping

with the off-axis weight of the driver. Here is how it is done:

 

When the front wheels have an even corner weighting, there is no torsional

reaction from the front suspension on the chassis. This can be mimicked by

jacking up the front of the car and supporting it on a narrow support (inch

wide chock of soft wood) underneath the front chassis 'cross'. In this

condition it is easy to support the rear of the car on the de dion tube and

see if the disconnected link from one side of the anti-roll bar lines up

with its mounting hole when the car is loaded as desired. This ensures that

the rear takes all the off axis loading and that the car runs straight and

level (at the back at least).

 

The next bit requires that your chassis is straight, which may or may not be

the case.

 

The intention is now to get the front suspension to be set up so that it

doesn't transfer any torsion into the chassis when it is running level. The

way I do this is to adjust ride heights until the ride is level having

contrived a situation where I *know* that the front is not reacting any roll

moment. While the front is still supported on its narrow support, *slowly*

jack up the rear on another narrow support underneath the lateral ribbing on

the bottom of the differential. Raise the car until you see the first signs

of daylight beneath either of the rear tyres. The car is now perilously

supported on two *knife edge* (wood block) pivot points and can rotate in

the roll axis with only very slight loadings. The car will probably be off

balance so that it rocks onto just one of the rear tyres. Jack down the

rear, move the pivot point slightly and jack up again until you have exactly

found the balance point (alternatively move some ballast from side to side

in the boot until you get a balance). The off centre jacking location

compensates for the weight distribution of the unladen car (heavier on the

exhaust side) and guarantees that the front suspension doesn't have any

torsion to react - once you have found this point, leave the rear rocking on

its balance point and jack down the front. Raise the rear a small amount

so that you can see that both tyres are clear of the ground and adjust the

front spring platforms until the front ride heights are even left to right.

 

You now have a good approximation of a bad flat floor setup. The front

corner weights will be matched and the rears will be mismatched. A more

ideal setup will involve evening up the loadings on the diagonals, but at

least the car will be running straight and level. You could do all of the

above maintaining half of the off-axis loading in the car (e.g. 35-40 kg in

the driver's seat)

 

How do you set the front to rear ride height ?

 

The front should be set so that you have enough energy absorption ability in

the suspension for 99% of the situations you expect to encounter. This does

depend on tyres. I have done no analysis on the bump steer at the front in

relation to ride height so I just go for something high enough that my sump

stays safe most of the time. I think you should aim to have at least two

inches clear space underneath the front of the sump. The rear is something

of a mystery to me with the Watts linkage. A good starting point would be

to follow the book's advice and have 35mm more clearance under the rear. I

think with the current spec dampers you can go significantly lower than this

without experiencing problems with ground clearance and the Watts linkage

should prevent you from developing too much understeer. If you do get

understeer, raise the rear and see what sort of effect it has.

 

Once you have done the flat floor thing, you can adjust both of the rear

spring platforms in step without altering the flat floor settings. The same

goes for the front.

 

(The big assumption in this lot is that you don't have a corkscrew deformed

chassis).

 

 

[Shaun_E]

I have used Dave Jackson's simple method and when I finally put the car on the scales it was very close to perfect.

1. Set front lower wishbones parallel to the ground (and therefore equal number of turns) - you can modify this if you don't like the resultant ground clearance.

2. Add desired rake - 15mm is a good start (measured from the chassis to the ground at the front engine mount and the leading edge of the rear wing)

3. Add 3 or 4 turns to the rear drivers side - roughly takes account of the driver's weight.

[Jason Plato]

kept me good since about 2001 😬

 

slight addition to the above

 

Make sure your front and rear spring pairs are the same lengths +/-2mm. Obviously the rear pair are longer but you know what I mean

 

set the sump height first - I go for 79mm without the driver.

 

This should also equate to the front wishbones being parralel to the ground - if not then choose if you wnat to achieve sump height for safety or reduced bump steer with parralel wishbones....

 

Then count the threads or measure the spring position on the front dampers and ensure that hey are exactly equal on left and right sides.

 

Then measure the rake from under the front engine mount on the chassis and under the front leading corner of the rear wings under the chassis. Obviously you need to make sure the ground is level for this bit but its not realy crucial. I go for 15mm rake with std rear springs or 10mm with 200lb rear springs (I use these for slicks to cut the understeer).

 

Then count the threads on the rear dampers as you did on the fronts and equalise both sides, then add 3 threads in ride height for the drivers rear (effectivly jacking up the drivers rear corner to account for the lard in the seat), for drivers over 90Kg add 2 more threads.

 

Note - if your making significant changes to the front ride heights (+/-10mm)then you might want to consider getting the tracking checked

 

In fact I did put it on the scales after doing the above and to our shock it was equal across the fronts and about 17Kg heavier on the drivers side. Just what I was hoping for. If you are going for cross diagonals then my method doesnt work. Personally I prefer equal fronts as without physically moving weight - ie battery, DS tank and small fuel tank into passenger rear of the boot then you will always be trying to overcome the fixed problem of driver sitting over the rear wheel ☹️

 

Sorted ........ cup of tea cheif 🤔

 

 

Edited by - Dave Jackson on 14 Mar 2011 09:04:46

[Eugene]

These may help...???

 

Suspension and The Round Bits

 

and

 

Sticking to the Black Stuff

[Jason Plato]

trouble with Peters method is that the chassis is realy floppy and could be slightly twisted - as he says on the diclaimer at the end . The theory is spot on for a totally rigid chassis.

 

My method is also a comprimise , but it does account for chassis floppiness to some degree.

 

I dont like cross diagonals as the car squirrels under braking and locks a single front wheel sooner than the other (before Pendennis comes along)

[The Pikey]

All great info and I'm going to give Daves methot a try now.

 

thanks

Jason

[Sheds Moderator]

The method described by Dave is very close to the one I was alluding to earlier, I knew someone would be along with proper details rather than some vague half-addled recollections .

[Wrightpayne]

Dave,

 

you forgot to mention your test procedure - jam the brakes on at 50mph and if both fronts lock up at the same time then

 

Ian