asl
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| posted on 9/5/09 at 04:53 PM | |
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Suspension set up
Hi. Is there an idiots guide on how best to set up the suspension? I have not touched it since I bought the car but the back 'looks' a bit
high. It drives ok but obviously if there is an easy method to set up correctly I would quite like to do it. Alternatively is there somewhere in
Surrey I can take it to to get it set up properly? Thanks
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mad-butcher
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| posted on 9/5/09 at 05:15 PM | |
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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.
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 setup" 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. (it is a good idea to
slacken off to finger tight any suspension rubber mounting points in order to ensure this). 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. It is also possible to use
cheap bathroom scales providing you do so in a way that ensures that their mechanisms do not bind due to sideways movement of the suspension.
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 150Kg [A] 165Kg [B] Front right
Rear left 185Kg [C] 197Kg [D] Rear right
From these figures you can establish that the total weight of the car and driver is 697Kg (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 315Kg (A+B), divided by the overall weight of the
car and driver of 697Kg. 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 382Kg (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 315Kg
divided by 2 which is 157.5Kg) 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 362Kg (B+D) and so your front right ideal finishing
weight will be 45.2% of that (163.6Kg) and the rear right ideal finishing weight will be 54.8% of it (198.4Kg) Carrying out the same arithmetic for
the left hand side of the car gives an ideal finishing weight for the front left of 151.4Kg and the rear left of 183.58Kg
Now compare your recorded starting weights [As] with your ideal finishing weights [Af]
Front left 150Kg [As]
151.4Kg [Af] 165Kg [Bs]
163.6Kg[Bf] Front right
Rear left 185Kg [Cs]
183.5Kg [Cf] 197Kg [Ds]
198.4Kg [Df] Rear right
You will notice (given my very clumsy rounding of decimal places) that all corners are 1.5Kg out with two corners being light and their diagonal
opposites being heavy.
Now if my corner weights were within 1.5Kg 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 1.5Kg. Move to the other wheel on the same axle (front left) and wind its platform up to increase the weight by 1.5Kg. Now work on the corner
diagonally opposite the last corner and wind the spring platform down to reduce the weight on it by 1.5Kg. Move to the other wheel on the same axle
and wind its platform up to increase the weight by 1.5Kg.
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 !
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gordon h
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| posted on 9/5/09 at 05:42 PM | |
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now thats what you call an answer.
bec is best but going to try sabb 2.3 turbo mk
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mr henderson
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| posted on 9/5/09 at 05:48 PM | |
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quote:
Originally posted by gordon h
now thats what you call an answer.
To type all that in 22 minutes is good going. Perhaps MB uses one of those voice to text programs?
John
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asl
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 posted on 9/5/09 at 06:34 PM | |
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Wow, that is some answer!! Thank-you very much. Is there anywhere I can take the car to in Surrey that would do this for me??
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r1bob
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| posted on 9/5/09 at 06:39 PM | |
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Bloody hell !
i spent 60 sec's checkin my tyre pressure's off i went
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mad-butcher
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| posted on 9/5/09 at 06:47 PM | |
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do it yourself, scales about £3.00 a set @ tesco
appologies I think for size of pic.
 
Rescued attachment corner weight setup.JPG
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Hellfire
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| posted on 9/5/09 at 07:03 PM | |
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I thought I'd read all that somewhere before 
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mr henderson
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| posted on 9/5/09 at 07:08 PM | |
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quote:
Originally posted by Hellfire
I thought I'd read all that somewhere before
Now we know Mad Butcher's actual name!
John
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mad-butcher
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| posted on 9/5/09 at 07:41 PM | |
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Someone sent it me in word format so I had no idea were it came from originaly
appologies and credit to original author
tony
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Ninehigh
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| posted on 9/5/09 at 08:43 PM | |
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quote:
Originally posted by mr henderson
quote:
Originally posted by gordon h
now thats what you call an answer.
To type all that in 22 minutes is good going. Perhaps MB uses one of those voice to text programs?
John
Nah that'll take 22 minutes to get it started!
When you're using 2 scales per corner I take it you combine both readings?
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asl
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| posted on 10/5/09 at 07:08 AM | |
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Hi. Just one more question..... I will follow the instructions to corner weight it but how low do you guys set the suspension. Do you run up at one
height for road use and then lower it for the track?
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procomp
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| posted on 11/5/09 at 06:51 AM | |
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Hi
Setting the geometry is what needs doing first. Then the corner weights as any adjustment to the geometry will require re setting of corner weights.
Then if keen enough what makes the biggest difference to the ride quality is having the dampers matched and setting in a working range. No point going
to all the effort of corner weighting and then having dampers that are 50-80 Lb out of balance.
I will not comment on bathroom scales
Cheers Matt
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mr henderson
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| posted on 11/5/09 at 07:45 AM | |
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quote:
Originally posted by procomp
I will not comment on bathroom scales
Well if you won't, I will-
Bathroom scales are an intelligent and practical alternative to the expensive electronic equipment used by firms who charge for their services, and
who are therfore able to recover the initial outlay.
As anyone who has dieted will tell you, they are surprisingly accurate, maybe not in an absolute sense, but comparatively, and that, of course, is
what is needed here.
I would suggest that anybody who doesn't want to pay a professional firm to do this for them, especially if it is a developing project and may
need to be done several times, that they invest in 8 scales. £10 each will get you something quite decent, althought they can be had for less.
Make sure you get the old fashioned spring type, electronic units are likely to turn off or reset themselves.
Then, test them. Make sure they are all reading the same. Put them on a hard surface, makes sure they are not rocking, step on each one. If one or
more is out, take it back and change it for one that is ok.
Then, when you've got 8 scales all reading the same, set them up as in the (oversize  ) picture above.
Put your car on them, and simply add the weights at each pair of scales. Don't be concerned if on any particular pair there is a marked
difference between each scale in that pair, that will just be the effect of the connecting board and the position of the tyre relative to it. The
combined weights will accurately tell you the weight of that corner compared to the others.
John
[Edited on 11/5/09 by mr henderson]
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procomp
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| posted on 11/5/09 at 08:15 AM | |
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Hi
And just how many people who have done it with bathroom scales have then back to back checked it with a set of race scales. The answer is not many i
bet. Those that have where left wondering why they bothered. The thing with corner weighting is it is either right or wrong. And that means being very
accurate.
PS most companies only charge £30 for a quick corner weight setup.
Cheers Matt
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mr henderson
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| posted on 11/5/09 at 08:24 AM | |
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It's not a question of whether any test procedure is accurate or not, it's a question of whether it is accurate enough.
The bathroom scale method, if done carefully and on a flat surface (which would be needed for any method) is indeed accurate enough.
How much any particular company might charge may also not be relevant to somebody who doesn't have a convenient method of getting the car there,
or where there may not be such a company within easy reach.
So, anybody who thinks they might benefit from the batchroom scales method, and who is able to ensure a flat surface, or at least 4 pedestals which
are level to each other, should go right ahead
John
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procomp
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| posted on 11/5/09 at 08:40 AM | |
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Hi
Only goes to show you simply do not understand what is actualy needed with corner weighting. "accurate enough" Is not accurate. It needs
to be done absolutely right other wise it's wrong. That means getting to with in 0.5 KG. Not the nearest 5kg.
I can not be bothered to argue with you again. But it is simply either right or wrong.
PS anybody who is taking it even slightly seriously would find people with in an hours drive who could do the job both accurately and with knowledge
to see other benefits at the same time. As it's not just about shifting the numbers but many other factors should also be taken into account to
gain the full benefit.
Cheers Matt
[Edited on 11/5/09 by procomp]
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mr henderson
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| posted on 11/5/09 at 12:22 PM | |
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quote:
Originally posted by procomp
Hi
Only goes to show you simply do not understand what is actualy needed with corner weighting. "accurate enough" Is not accurate. It needs
to be done absolutely right other wise it's wrong. That means getting to with in 0.5 KG. Not the nearest 5kg.
Your words there clearly show that it is you who does not understand, on several different levels.
First, all engineering is done to a tolerance, things are not right or wrong, they are either within limits or they are not.
Then you go on to say 5kgs is wrong but .5 kgs is ok. So which is it? .5kgs sound like a tolerance to me. In any case, if you weren't tying to
show off your electronic scales you would know that decent bathroom scales could indeed resolve .5 kgs and this can be easily tested and
demonstrated.
quote:
Originally posted by procomp
I can not be bothered to argue with you again.
I'm glad to hear that. I, however, will make the effort to argue with you every time you attack the products and suggestions of other
manufacturers and well-meaning posters here.
Cheers
John
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Frosty
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| posted on 11/5/09 at 12:57 PM | |
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I've got to agree with Procomp here. Whilst bathroom scales will give a rough idea on the weight of the corner, I think you're far better
off just measuring the compressed length of the spring versus the uncompressed length to find out the weight on that corner (sprung, at least).
The variables in the spring rates will be far less than those encountered trying to spread the load of each corner over 2 scales, when each scale will
have its own tolerance and accuracy anyway.
You won't really be able to work out what your weight split from front to rear is, but you'll be able to get both sides pretty accurate to
each other by measuring.
The bathroom scale method just looks far too error prone to me.
Henderson you say that it's just a case of getting it close enough, but I'm not sure if you could get within 10kg of what cornerweight
scales could. If you did, it's more down to lottery than skill because there are so many variables involved.
Also with the "close enough" comments, what procomp is saying is that the difference between 0.5kg, and say 10kg of accuracy is multiplied
where it really matters.
Let's say your corner weights at the front are 10kg out because of inaccuracy, if you brake at 2g then you are actually going to see a lot more
than a 10kg difference between the two, and you'll be locking one up before the other.
I think corner weighting is one of those things that just needs to be done properly, and unfortunately it costs a lot of you want the satisfaction of
doing it yourself to a good standard.
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MikeRJ
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| posted on 11/5/09 at 01:03 PM | |
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quote:
Originally posted by mr henderson
As anyone who has dieted will tell you, they are surprisingly accurate, maybe not in an absolute sense, but comparatively, and that, of course, is
what is needed here.
You are talking about the use of a single set of scales, where repeatability and relative accuracy are more important than absolute accuracy.
What's needed here are many sets of scales (8 at 2 per wheel) that require those same attributes, but also all scales have to have a very close
tolerance i.e. they must all read the same with same weight applied. That is a far more difficult target to achieve from scales thrown together in
China.
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mr henderson
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| posted on 11/5/09 at 06:00 PM | |
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quote:
Originally posted by Frosty
I've got to agree with Procomp here. Whilst bathroom scales will give a rough idea on the weight of the corner, I think you're far better
off just measuring the compressed length of the spring versus the uncompressed length to find out the weight on that corner (sprung, at least).
The variables in the spring rates will be far less than those encountered trying to spread the load of each corner over 2 scales, when each scale will
have its own tolerance and accuracy anyway.
You won't really be able to work out what your weight split from front to rear is, but you'll be able to get both sides pretty accurate to
each other by measuring.
The bathroom scale method just looks far too error prone to me.
Henderson you say that it's just a case of getting it close enough, but I'm not sure if you could get within 10kg of what cornerweight
scales could. If you did, it's more down to lottery than skill because there are so many variables involved.
Also with the "close enough" comments, what procomp is saying is that the difference between 0.5kg, and say 10kg of accuracy is multiplied
where it really matters.
Let's say your corner weights at the front are 10kg out because of inaccuracy, if you brake at 2g then you are actually going to see a lot more
than a 10kg difference between the two, and you'll be locking one up before the other.
I think corner weighting is one of those things that just needs to be done properly, and unfortunately it costs a lot of you want the satisfaction of
doing it yourself to a good standard.
Your argument seems to depend on your opinion that inexpensve bathroom scales are not accurate.
Theproblem with that argument is that if the scales are indeed accurate, then the argument fails. I have experimented with bathroom scales over the
years, and my findings are that the ones I have tried are indeed accurate. Maybe the ones you have tried haven't been. But that doesn't
mean that the method is faulty, only your choice of equipment.
So where does that leave us? I guess it leaves you using purpose made corner weighting equipment and me managing very well with my bathroom scales, if
and when I choose to invest in another set (I don't have any at the moment).
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procomp
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| posted on 12/5/09 at 03:09 PM | |
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Hi
So if your going to spend £80 on scales and then make some run up ramps. Why not just go half way and get a simple guage that would be a darn sight
more acurate than the TEHY MIGHT BE ACURATE aproach.
Cheers Matt
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mr henderson
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| posted on 12/5/09 at 05:52 PM | |
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quote:
Originally posted by procomp
would be a darn sight more acurate than the TEHY MIGHT BE ACURATE aproach.
Here we go again.
I've already explained how the scales, if carefully chosen, and tested, will indeed be accurate. I'm sorry if that peeves you, when you
are trying to extol the benefits of people taking their cars to people who charge for setting cars up (actually I'm not sorry really ) but
this is the Locostbuilders forum and discussing ways of getting good results without simply paying others to do stuff for you is what this forum is
all about.
John
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procomp
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| posted on 12/5/09 at 06:33 PM | |
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Hi
You really are a Pratt. I was trying to help you get accurate results rather than guess work. At an affordable price.
End off
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mr henderson
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| posted on 12/5/09 at 06:51 PM | |
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quote:
Originally posted by procomp
Hi
You really are a Pratt. I was trying to help you get accurate results rather than guess work. At an affordable price.
End off
No you weren't you were trying to promote your car setting up business.
I wasn't going to say that, obvious as it was, but when you start in with the insults you must expect to have things pointed out that you
don't want to hear.
John
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