Flat Floor Setup

[ChrisR]

After fitting a set of Avo, courtesy of Freestyle(Great Service), I am trying to set up the preload and ride height. Using the £3.99 Argos scales technique I have balanced the front end no problem.

 

However I have a 20kg difference between the rears. The Offside, not surprisingly being heavier. The rear rideheight is not much higher than the front (8mm) so I intend to increase the preload on the nearside rear. Will this upset the "Balance" obtained at the front end? If so could someone guide me as to the correct procedure for balancing not only the fronts but the diagonal weights as well.

 

Even just balancing the fronts has made a Huge difference.

 

It has been mentioned a number of times in posts about the 7 being very particular about front rear pitch, but not which way round it works? If the rear is too high does this induce more oversteer?

 

Thanks

 

Chris Rowley

Yorkshire

[philwaters]

Not sure your 'starting' point in terms of handling.. but I found last year that my car was a bit tail happy/unstable..

I raised the rear by 5mm and it all went away... why do I always find these thing out at the end of the year!

 

Phil Waters

You mean you can drive these?

I thought it was just there to polish 😬

[Joe 90]

Adjusting the rear balance moves weight across the front axle in the opposite direction. The only way to get perfect weight balance front and rear is to also move real weight around. The best you can do otherwise is to share the mismatch, 10kg front and 10 kg rear. Adjusting the ride height moves the centre of gravity up and down, and also moves the roll centre. This has a significant effect on the car balance, which is much more significant than a small weight imbalance.

 

99,977 miles so far

[ECR]

Below an article that I wrote for LF a few years ago. It might answer some questions.

 

Corner Weights and Flat Floor Set-Ups

 

One of the important items that should be checked when trying to optimise the handling

characteristics of your Seven are the corner weights in order to ensure that each tyre is

carrying its proper share of the overall weight of the car. This can be done by one of the

many Seven specialists who advertise in Low Flying or with the right equipment and plenty

of patience you can do it yourself. Because I am interested in how my car does what it does

so well I recently attempted the job myself but whichever route is taken, this article should at

least give you some understanding of the subject.

 

Firstly what is corner weight ?

The corner weights of a car are the weights which you would see if you placed a set of

scales under each wheel whilst the car was on a flat level surface with the driver sitting in the

car

 

In order to understand the subject of adjustment it will help if you have a grasp of the

concept involved. Imagine for a moment that you drive your car into the garage and

someone has left two 1” thick planks of wood on the floor exactly corresponding to the

positions of your front offside and rear nearside wheels when at rest. When you get out of

the car all four wheels are still touching the ground (surprise surprise !) although the front

offside and rear nearside are actually 1” higher from the floor than the other two. What has

happened here is that the front nearside and rear offside wheels have dropped by 1 “ to

touch the floor and in so doing the weight that was exerted on their springs by the vehicle

has been reduced. Because the car still weighs as much as it did when we started, if the

weight on two wheels has reduced then it follows that the weight on the other two wheels

has increased. You can liken the car to a four legged chair which in the above example has

had two legs shortened by a clumsy carpenter and now has most of the weight of the

occupant resting on its two longest legs. It will pay to think a little about these two examples

before moving on.

 

 

On a Seven the corner weights and the ride height (which is the distance that the bottom of

the car is above the surface of the road) are adjusted by moving the platform on the shock

absorber upon which the road springs sit. You should take note that when you are adjusting

the ride height this way you are automatically changing the corner weights as well and vice

versa..

 

It should be said at this point that in order to easily adjust your corner weights you need to

have adjustable spring platforms on your shock absorbers. This adjustment is usually (but

not exclusively) carried out by screwing the spring platforms up or down the threaded

outside of the body of the shock absorber. Some Sevens are fitted with non adjustable

platforms and whilst it is possible to adjust these (by fitting purpose made shims under the

springs) it is not very practical.

 

In order to successfully carry out corner weight adjustment certain conditions must be met.

Firstly, all weighing must be done on a flat level floor (which is where the term “Flat floor set

up” comes from) This is because readings taken on a non level floor will wrongly understate

the weights taken at the high end of the car and overstate the weights at the other end (think

of the car parked on a 45% hill, the weight over the rear wheels will be a lot greater than if it

was parked on the flat) Second all weights should be taken with the driver in the car and

with an average load of fuel. Third you should ensure that all suspension pivots are correctly

adjusted and that they are not stiff or binding. With this in mind also wind your shock

absorber rebound adjustment to fully soft if this is possible on your units. Fourth you should

disconnect any anti roll bars as any pre load (caused by twists in manufacture or wrongly

adjusted drop links) will affect the corner weights. Next, make sure that your tyre pressures

are correct (this will affect ride height) and finally wire brush and lubricate the spring

platform threads on the shock absorber bodies (it makes the job a lot easier).

 

You should first of all set the ride height of the car by adjusting the spring platforms.

Different people have different points at which they check their ride height measurements

and any ride height discussion is valueless unless you define these positions. I used a point

between the heads of the bolts holding the engine mountings at the front of the car and a

point just in front of where the rear mudguard fixes to the body (by the front A frame bolt)

but you can use whatever points you like as long as you record the positions ready for the

next time you set the ride height

 

You will find that adjustment is a lot easier if you jack the car up to take the weight off the

springs, oh, and please invest in or borrow some proper c spanners, using a punch to move

the spring platforms is slow and leaves very unsightly marks on the adjusting nuts (or the car

body when you slip !)

 

Adjust these heights to your own requirements (to be equal on both sides of the car) bearing

in mind that you need to be able to drive over speed ramps in the supermarket car park as

well as around Brands Hatch! The rear height as advised by Caterham in their build manual

should always be about 15mm higher than the front whatever the measurements. After every

adjustment you should roll the car forward and backwards and bounce the suspension in

order to settle the car to its true position. Having set the ride height (with the driver in the car

remember!) you can now start to adjust the corner weights

 

First you need a method of weighing the car. If you are related by birth to Mr and Mrs

Fatwallet buy a set of corner weight scales from someone like Demon Tweeks. This will

make the job very easy as you weigh all corners at the same time. More realistically you will

buy or borrow a Pace or ADA type corner weight gauge which although not as accurate as

corner weight scales will suffice with careful use for most needs. I know that the use of

bathroom scales is sometimes suggested (and in fact my first attempt at corner weighing was

done with just such apparatus) but I can say from experience that it is not very satisfactory

as the scale mechanisms tend to seize up if any sideways loads from the suspension is put on

them.

 

My Pace Gauge was not supplied with any instructions but as with all equipment there is a

right and a wrong way of using it. You should insert a thin stiff card under the wheel to be

weighed, place the gauge (which is basically a lever on a post with a weight read out dial)

under the wheel rim and carefully lever the car off the ground to a point where the card can

be just slipped out from under the wheel (like a feeler gauge). Note the weight reading, then

roll the car forward and backwards and bounce the suspension in order to settle the car to

its true position. Repeat this four or five times on the same corner and average your readings

in order to get a more accurate result. Repeat this procedure for all four corners.

 

Having got your starting corner weights recorded you now need to decide what weights you

would like to see when the job is complete (your ideal finishing weights). Here in order to

make things a little easier to follow I will give a working example

 

Recorded starting corner weights:

Front left .... 150lbs(A)

Front right .... 165lbs (B)

Rear left .... 185lbs©

Rear right .... 197lbs(D)

 

From these figures you can establish that the total weight of the car and driver is 697lbs

(A+B+C+D) you can also establish that 45.2% of the overall weight is on the front wheels

by the following arithmetic: Total weight on the front of the car of 315lbs (A+B), divided by

the overall weight of the car and driver of 697lbs. Likewise you can establish that 54.8% of

the overall weight is on the rear wheels by the same method. Total weight on the rear of the

car of 382lbs (C+D) divided by the overall weight of the car. (As a check on your

arithmetic the two percentages when added should give 100. If not stay behind after lessons

!)

 

Now for the clever bit ! If the car was a single seater with all components (including the

driver) placed on the centre line of the car then both front wheels should be set to the same

weight which is exactly half of the total weight sitting on the front wheels (in the example

above 315lbs divided by 2 which is 157.5lbs) However in a Seven the driver sits to one

side and so the centre of gravity of the car is also offset to that side.

 

In order to cope with this, the total weight on the right hand pair of wheels should be split

45.2% to the front and 54.8% to the rear to establish your ideal finishing weights. In my

example the total weight on the right hand side of the car is 362lbs (B+D) and so your front

right ideal finishing weight will be 45.2% of that (163.6lbs) and the rear right ideal finishing

weight will be 54.8% of it (198.4lbs) Carrying out the same arithmetic for the left hand side

of the car gives an ideal finishing weight for the front left of 151.4lbs and the rear left of

183.58lbs

 

Now compare your recorded starting weights with your ideal finishing weights

Recorded Starting Ideal finishing

Front left ... 150lbs(A) 151.4

Front right ... 165lbs (B) 163.6

Rear left ... 185lbs© 183.5

Rear right ... 197lbs(D) 198.4

 

You will notice (given my very clumsy rounding of decimal places) that all corners are 1.5lbs

out with two corners being light and their diagonal opposites being heavy.

 

Now if my corner weights were within 1.5lbs first time out I would definitely leave them

alone, but as you are doing the job yourself you must be a bit of a perfectionist so start with

a heavy corner (in this example front right for instance) and wind the spring platform down

to reduce the weight on it by 1.5lbs. Move to the other wheel on the same axle (front left)

and wind its platform up to increase the weight by 1.5lbs. Now work on the corner

diagonally opposite the last corner and wind the spring platform down to reduce the weight

on it by 1.5lbs.

Move to the other wheel on the same axle and wind its platform up to increase the weight

by 1.5lbs.

If you adjust all corners instead of trying to work on just one or two you will avoid dramatic

ride height changes (remember that altering the spring platforms also changes the ride height

!). The secret with this work is not to adjust too much at once, a little on each corner is the

way to go

 

When all adjustments have been completed check both your corner weights and ride height

(just to be sure !) and refit your anti roll bars one at a time. Check the corner weights again.

If they have changed you either have a twist in the anti roll bar which must be straightened or

if that is not possible adjust the mountings so the pre load can be removed or in the case of

bars with adjustable drop links one of the links is too long.

 

The result of all this work (given that all other parts of the car are functioning correctly !) is

that you will be able to take both right hand and left hand corners with the car behaving

predictably.

 

Finally and most importantly corner weight work like this gives you a perfect armoury of

technical excuses with which to baffle your friends when your driving is not up to par !

 

Roger Swift

 

Next in the series: Quantum Physics an exploration.....

 

With recommendations and acknowledgements to “How to make your Car Handle by

Fred Puhn

 

Ex Chairman Roger

[Nifty]

Chris,

 

Give Mark Hicks of Anglia Sevens a ring on 07814 477964

He flat floored Nick Woods car yesterday evening and in the past he's done it for Jacques Villeneuve, Mark Blundell ..............

[Nick Woods]

Seconded

 

Mark has made a huge difference to the way my car feels, and what he doesnt know about setting up suspension probably isnt worth knowing IMHO. 😬

 

Nick

P8MRA - Red and Black 1.6K supersport, back on the road at last. See pictures of it being rebuilt here

[Tricky]

Roger,

 

Thank you for the detailed explanation.

 

Tricky

[Steve-B]

roger thanks very much. Miraz was out with me yesterday when we went to Silverstone, and he mentioned that more progressive / stiffer springs need to be added onto more powerful 7's such as ours as well.

if one was on a tight budget which i am just now, would i be better checking the weight distribution beforehand 🤔

 

 

Steve

210Bhp SV-VHPD click here to see our pictures....

 

Edited by - w1scb on 17 Mar 2003 09:10:39

[Lawrence_Z]

Roger

YHM

 

Lawrence