Corner weights

[dogvet]

As my car weighs in at under 500kg I should be able to use 4 bathroom scales to achieve this?

If so with 3/4 tank fuel and driver in should then the LF and RF match, as well as the LR and RR,

ie balanced across each axle.

To achieve this equality altering the spring platforms is obviously necessary.

Are these assumptions correct?

Are ther any other parameters required to sort this out?

Thanks in advance

[ashaughnessy]

I won't pretend to be an expert on this but I do have some recent experience.

 

First, your car won't weigh under 500Kg with the driver in (and especially with 3/4 tank of fuel which will weigh about 40kg), and you want to get the corner weights even with the driver included, so your bathroom scales may not be enough (unless they are 150kg scales, which are quite expensive for four sets). Someone else has posted his experiences of using 8 sets, 2 on each corner. Why set the corner weights with 3/4 tank of fuel? Why not half a tank, so there is less variance between it being full and empty? For racing, you wouldn't normally have even this much, so you might do it with a quarter tank full.

 

I use four sets for weighing my car (not setting corner weights). You have to be very very careful to make sure the car is settled properly on the suspension. If you jack the car up so that the suspension goes to full droop, this pulls the front wheels in by a substantial amount. When you drop it onto the scales, this puts a very large sideways force on the scales which completely cocks up the readings. My solution was to get four squares of sheet steel, cover them thickly with grease, and put one between the tyre and the scale. Then you can lower the car and bounce the front end and the wheels will settle happily.

 

Also, I used a plank of wood on each scale to make sure the load was even on the scale. If the tyre sits directly on the scale, it will distort the scale and you won't get correct readings. I used a plank of about 6 inch by 1 inch wood, cut slightly longer than the width of the scale. The plank went on the scale, the greased square of steel went on the plank, the tyre went on the greased steel. Bounce the car several times to make sure it's level on the suspension.

 

I also used the plank and greased steel at the rear but greased steel isn't so necessary as the wheels don't draw together when the suspension droops at the back.

 

You need an absolutely level surface for accurate corner weighting. I'd be interested to hear to what tolerances this actually means.

 

Yes, you need to change the spring platform heights to change corner weights.

[philwaters]

Steve Foster, Nigel Mills and myself have a bit of practice at doing this. I can send you a spread sheet program to help if you like. you enter the weights from each corner and then it tells you waht to do at each damper.

We used two scales under each corner so as not to overload them, with a home made (by Steve) bridge to spread the load. It is good to have a freind who can wander around and take the readings for you while you are in the car.

 

Phil Waters

"Darling, DO you love the 7 more than me?"

"Driving OR Fixing?"

Caterham on the brain, Caterham around the body! wink.gif

[Blackbirdman]

DV

 

I have used the eight scale method and posted on the subject a couple of months ago. I agree with all the comments above. You will need eight scales as your average bathroom scale only reads to 120Kg. On the front of my Blackbird corner weights were in the 117-118 Kg range so six scales would have done, just.

 

To add confidence we weighed my car at 470Kg and a few days later got 471Kg on the weigh bridge at Oulton Park so it does seem to work!

 

Best of luck

 

 

 

Is it a bike? Is it a car? No it's Blackbirdman cool.gif

[Barry H]

Unless you are fantastically lucky, RF will not equal LF nor will the rears be equal. Short of moving physical weight around on the car you will never get them the same without unbalancing the wheel diagonally opposite.

 

Side to side weight and front to back weight cannot be altered by adjusting spring seats.

 

What can be altered is the balance between the wheels on a diagonal. Hence you can "move" say 5kgs to LF. At the same time of course LR, RR and RF will be affected as no weight actually moves from front to back or side to side.

 

For example consider the following:

 

LF - 130, RF - 130, LR - 160, RR - 160

 

Here the front totals 260, the rear totals 320 and each side totals 290.

 

If you add 5 to LF something similar to the following will be the result:

 

LF - 135, RF - 125, LR - 155, RR - 165

 

THe front still totals 260, the rear still totals 320 and each side still totals 290. What has changed is the diagonals; from 290:290 to 300:280.

 

So you are left with either equalising the two wheels at one end or the other ( at the cost of unbalancing further the other end) or of balancing the diagonals ( while accepting that the weight on say the two front wheels will probably be unequal.

 

It is a matter of personal preference but for the circuit the objective is to balance the diagonals as it theoretically gives similar handling characteristics on left and right hand turns.

 

I hope this makes some sense and helps.

 

Barry

 

 

[cdg]

Seems like a lot of effort to me !

 

Why not take it along to your nearest race preparation shop and get them to do it with their digital scales and proper flat patch.It will only take about 30mins. and be much cheaper than you think.

 

I'm in the Midlands and use Tollbar Racing in Darley Dale (01629 735176). Michael Flounders is the man to talk to -he's also a very good friend of mine! Don't know where you're based but there are several other places that I could recommend.How much would it cost to buy 8 sets of bathroom scales?

 

Chris.

[philwaters]

This is true, but then the cost of the scales are a one hit deal, which you can use whenever you like - or more importantly - whenever you change something on the car like remove spare wheel or fit new spring or dampers etc.

You also have the satisfaction of doing the job yourself and, with no offence to any companies out there, you know the car will be looked after.... ok - who mentioned DeathStar?

You will also get a much better understanding of what effects things and can therefore bore loads of people who make the mistake of asking you about it at the pub wink.gif

 

Phil Waters

"Darling, DO you love the 7 more than me?"

"Driving OR Fixing?"

Caterham on the brain, Caterham around the body! wink.gif

[ashaughnessy]

8 sets of 120Kg bathroom scales can be had for £32 (yes, £4 each) from Argos.

 

I think it takes most places a lot more than half an hour to set the corner weights. I believe it's a trial and error process and as the springs are fiddly to get to, I've been told it takes a couple of hours or more. But I've never seen it done, so I'm not certain.

 

Barry, if I can change the corner weights from 130/130/160/160 to 135/125/155/165, then doesn't that mean I can do the reverse? If I'm lucky (i.e. it isn't guaranteed) wouldn't it be possible to start off with imbalance from side to side and change it to get near equal weights side to side? I say lucky, because if the imbalance is large enough you'll never do it, but you might. I got my car set up at Caterham midlands recently and with driver and small amount of fuel, the print out says 150/151/150/150.5, which is pretty amazing. The downside was that they had forgotten to take out the tool box full of 25Kg of lead ballast that was in the passenger footwell, but never mind :-( Anyway, I accept that this amazing equality might have been a lucky break and not necessarily achievable in all cars.

PS: Just thought about this again - maybe it isn't usually possible. I can only use hand-waving arguments, and you can't see my hand waving, so I'll leave it for others to tell me I'm wrong.

 

Anthony

 

Edited by - ashaughnessy on 11 Oct 2001 16:28:07

[Peter Carmichael]

No.

 

Rephrasing what has already been said:

 

You can only get even front and even rear corner weights if the car's center of gravity is exactly on the centreline of the car as you are setting it up (i.e. with you in it and no tools in the footwell). No mucking around with spring platforms will move the CoG a mm, so if it isn't there to start with you are playing the game of aiming for even diagonal loading.

 

If you start off with an imbalance side to side, it is because the CoG is off centre. You cannot change it. The imbalance will still be there when you finish. The example you and barry have been working with starts off with *no imbalance side to side* and ends up with no imbalance - i.e. the question is rigged.

 

I say lucky, because if the imbalance is large enough you'll never do it, but you might. I got my car set up at Caterham midlands recently and with driver and small amount of fuel, the print out says 150/151/150/150.5, which is pretty amazing.

 

I think if you had a printout from before you would find that even if the diagonals were out of balance each side would still have weighed in at 301 kg +/- 0.5 kg.

 

Sorry, but physics isn't negotiable.

 

[philwaters]

I agree, but it is a case of making the most of what you have without spending loads on moving things around in the car. I'm sorry, but I still feel good when I do the work yourself and can feel the effect. It may not be perfect but if it is better than it was before then thats got to be good - right. Even better if it costs 40 quid and you know you've made the difference.

 

Phil Waters

"Darling, DO you love the 7 more than me?"

"Driving OR Fixing?"

Caterham on the brain, Caterham around the body! wink.gif

[dogvet]

So on the basis of what has been said:

If the carhad

LF 140

Rf 130

LR 160

RR 170 then the diagonals would be 290 and 310 respectively

So to achieve as near a balance as poss by altering the relative platforms to get 300/300 would be the optimum.

Thanks to all!

[Peter Carmichael]

And you need to get the car running straight and level with these corner weights...

[cdg]

Two hours to set corner weights by a professional race engineer??

 

I can only speak from experience, but my Mallock sports libre car took 20 minutes to get as near perfect as is humanly possible.

 

I think you've been talking to the wrong people.

 

Chris.

[ashaughnessy]

cdg - quite possibly. I haven't been happy with either of the two people that have done this so far. Both have seemingly made mistakes. The first set the car dead level, which Caterham then said was wrong - the rear should be higher than the front. Caterham then got the weights even, but had done so with the lead ballast they'd forgotten to take out of the footwell.

I didn't watch either of them and don't really know how long they took, so you might be right.

Anthony

[stevefoster]

"Even better if it costs 40 quid and you know you've made the difference."

 

Yeah my £32 actually Phil!

Comparisons on weigh bridges and pro flat floors have shown that scales can be accurate enough and fun to do....

 

I have a great picture of Phil W (65kgs) sitting in Nigel's car pretending to be Nigel (~100kgs) with a sack of salt and gallons of oil on his lap to make up the weight while Nigel was under the car doing the adjustment and I read off the scales and checked them against the spread sheet...

 

I am not quite sure what the wife thinks about our car clinc weekends.....?!

[philwaters]

Much appriciated your £32 investment is too, Steve smile.gif.

 

Yeah salt and Oil were ok, once moved off a certain area!!!

 

Phil Waters

"Darling, DO you love the 7 more than me?"

"Driving OR Fixing?"

Caterham on the brain, Caterham around the body! wink.gif

[Graham Perry]

Providing you don't want the tracking done, it should only take an hour at the max. Thats what Hyperion charged me ie £50, and the car is far better as a result.

[Blatman]

I'm prob'ly gonna go the bathroom scales route too ('cos I'm only a poor Westf1eld owner...) but rather than mess around with greased plates and such, I'm gonna construct four "platforms" from some 4x1 and 4x2 (my lifeblush.gif). I *should* be able to just roll the car off and on the scales, whilst bouncing it on the non delicate wood bits........

[philwaters]

You can get away with just one slide plate, just to take the droop out of the front suspension when you lower the car back down. Without this you might end up putting too much sideways force on the scales at the front.

 

Again - I can send you the excel spreadsheet if you like.

 

Phil Waters

"Darling, DO you love the 7 more than me?"

"Driving OR Fixing?"

Caterham on the brain, Caterham around the body! wink.gif

[Peter Carmichael]

Now that the Sevens list archive is for subscribers only, I think a repost on Blatchat is appropriate:

 

THE DIY FLAT FLOOR SETUP WITHOUT A FLAT FLOOR:

 

To set up your car with even front wheel weights 'a la flat

floor'.

 

* find a flattish piece of tarmac;

* set the spring platforms exactly equal at the front;

* [...snip]

 

I have a simplification to my previously stated process that will give

you a near perfect flat floor setup without any special equipment. This

is because a Caterham comes ready fitted with a handy suspension

alignment gauge. Follow these simple instructions:

 

* support the rear of the car with the de Dion tube on

axle stands;

* release the handbrake (just in case the cable tension

does something odd);

* remove driver's side rear wheel and disconnect the

anti-roll bar link;

* make sure that the two anti-roll bar links are adjusted

to the same length, left and right;

* now, jack up the front of the car centrally, underneath

the cross, placing a one inch wide strip of softwood longitudinally

between the jack and the cross to produce a powder coat friendly

knife-edge bearing - the front of the car should be able to rock from

side to side and cannot now transmit any torque into the chassis;

* load up the car with your chosen payload... (driver

only/driver and passenger/driver and half passenger);

* now raise or lower the spring platform at the driver's

side rear corner until the anti-roll bar link is perfectly aligned with

the hole in the anti-roll bar - rocking the rear of the car helps to

settle the suspension;

* re-attach the link, put everything back together, drop

the car down and you're done.

 

Using this method, it will be possible to work out the various settings

of this single spring platform that conform to several load conditions.

You will then be able to switch between optimum settings for

driver-only, passenger and driver or any other chosen setting from one

adjustment. I recommend marking up the threads on the spring platform

so that you can record settings and subsequently replicate them at will.

Tip-ex is very good for this sort of marking.

 

All presuming that your chassis isn't twisted...

---

and.

 

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 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).

---

[Blatman]

Now that the Sevens list archive is for subscribers only

 

I was getting around to e-mailing Dave or Nigel, but you've answered (another) of my questions. Any idea why they've made it subscribers onlyquestion.gif

[Mike Bees]

I don't think there was anything sinister about it, Steve (who started & runs the list, purely for fun - strange chap) moved it all over to a new server, new software etc. I'm pretty sure that you can subscribe but choose not to receive mail, so you can just browse online if you want.

 

Mike

[paul.davis]

Like Blackbirdman I also used 8 scale systems with planks to spread the load of 580 kilos. With the help of an experienced friend I learned:

1. Try using hardboard to set up four flat patches using a builder's spirit level before doing anything else

2. Get the rake right approximately before starting, say 14mm up at the back with front suspension struts parallel to ground

3. Use Homebase non electronic scales £3.99 - no switch on problems and zeroing is easier. (Also with 2 kg of Oulton Park Weighbridge)

4. Peter is right - this is all about diagonal balances. Work out total weight on each of two wheels on each side and front and back, and then play with the diagonals.

My car with me in it was roughly 52% weight on RHSide and not far off 49/51% front to rear without spare wheel and half a tank. This was a surpise but the De Dion and LSD diffrential is a heavy unit - and me too!

 

Paul

 

Zeeeeeeetec . . .

[Blatman]

Mornin' Mike.

 

Thanks. So it's subscribe and lurk these days thenblush.gif