FAQ - Suspension - Coilover Ride Height Setup Guide

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campbellju

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Introduction
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This one is for V who asked for 10 pages :wink: :D
Apologies if this makes people's heads hurt as its taken me quite a few years to understand the concepts and I too had to read it a few times and I wrote it :shock: . I write it with the usual disclaimer that it could all be complete nonsense so don't blame me if you damage your car.

I won't attempt get into what the precise settings should be but will say how it can be done at home for free. This help is not designed for setting up race cars but it will help the average daily driver better optimise their car's suspension. It will take about 8 hours and this is why very few shops you take the car to wil do it properly.

The guide doesn't really cover roll centres much and doesn't go near camber, toe, bumpsteer to name a few, I might do these in the future when I next get 4 hours spare!! All are interlinked and I've found the SR20forum and Sports Compact Car magazine both excellent sources of information.


Why bother, what does it do?
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Most people know that rasing and lowering your car will lower the Centre of Gravity (CofG) Rasing and lowering your car will also change its roll centre (RC) front and back. This is a major topic in itself but in short, the height of your RC at the front and back will dictate the size of the lever acting on the CofG and in turn the amount of roll/weight transference. This can be used as another tool to adjust the understeer/oversteer balance of a car. By adjusting, your ride height side to side and making the geometry symetrical, you will improve the weight balance but primarily it will better locate each ends roll centre towards the centre of the car.

Corner weighting is similar in philosophy but attacks the problem from a differnt angle. With simple corner weighting, you will have balanced static loads but the geometry may not be matched giving a non central RC. As soon as the car rolls, your dynamic load will change as the levers acting on the RC are different lengths. With ride height balancing, the RC should be more central but you can't be certain of the static loading on the wheels.

The two are closely related and if you're going to corner weigh the car, this should be done after you've set the ride height up. Once the car is corner weighted, then you will need to balance the ride height again from opposing corners to make the suspension geometry symmetrical again. If you do both, given our car's weight distribution, I bet you'll have to come up with a compromise anyway. Like I said, this guide is not meant for setting up racecars.

Tools
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Builders Spirt level (1-1.5m)
3m long piece of flat, straight true wood
50cm ruler
Coilover supplied spanners
A few pieces of board (plywood, MDF) of varying thicknesses
Your own body weight in Sand, Rubble, sinks :wink: :wink: ,bricks etc.
Car jack/axel stands

Setting up the area
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-You need to put the car on a relatively flat surface the flatter the better.
-Put your long flat straight piece of wood in line with the side to side and front to back wheels of the car. Put the spirit level on top and see how much your level is out.

-Jack up corner of the car and put under it pieces of board until the you level the floor all round underneath the tyres. If you are lazy or its to difficult, at least make sure the side to side levels are balanced. My garage floor had 10mm drop at the front and a 5mm drop at the back on the same side.



-Once your floor area is setup, mark out where you put the boards and note down how may boards you used. If and when you come to setting camber, you must have a flat surface and being able to quickly set it up again in the future saves hassle.

Setting up the car
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-Insert your virtual self into the car. I put an old sheet over the seat and then put in a 40kg Belfast sink, A bag of sand and a bag of cement as they were to hand.

-


-Check your tyres pressures are what you typically use, if they are out it can make a 5-10mm difference in ride height. At this point, I measured my overall wheel size front and back and found that 35psi front and 33psi rear made them equal. This might be 36/32 or 38/36 but you will need more air in the front of the car as its taking more load.
-As a quick check, go round the car and see how many fingers you can get under each wheel arch to look at the difference.
-To do it properly you should really remove the ARB's from the suspension so all sides are independant but in practice I found this was nothing a good bounce and moving forwards and beackwards etc couldn't solve.


Measuring the ride height
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-As I don't have any specialized equipment, I took 2 different measurements to improve my accuracy. As time went on I become more accurate but still used the second one for a check.
1. Measure from the centre of the wheel to the centreline of the arch
2. Measure from your now level floor to the to the centreline of the arch

The first measurement is what you're working with but the second measurement is easier to take. This is all quite a rough science when you look into the detail but try to be accurate to at least 5mm.
-WRITE IT DOWN!! Sounds obvious but you'll find yourself repeating the process about 10 times whilst balancing the heights and analysing your own data is important.
-When you jack up each corner, note down the number of turns on each coilover as this is critical in balancing out the ride height.




Adjusting the ride height
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The aim is to make the rdie height on the front and back equal on both sides.

TOP TIP - Start at the front first.

You probably won't be able adjust the ride height with out jacking up the car so basic saftey first and remember to use axel stands, even though it might only take 5 minutes of adjustment a time.

If you raise the front right, it will push down the back left. If you do the back first as I did, you will find as soon as you start balancing the front, it all goes wrong. As the front is much heavier and uses stiffer springs, any changes you make there have a far bigger influence on the rear than the other way round.

The actual adjustment of the suspension is quite obvious and will depend on your specific coilover manufacturer but you normally turn a large nut that raises or lowers your spring platform.

Say for example your front left is 10mm higher than your front right. If you lower your front left spring platform 10mm. You will probably now find it is 7mm below the right now rather than even. So a few pointers from my experience.

1. The car and springs act like a big see-saw. If you drop the right 10mm, the left will go up 10mm. So if you want to lower a side 10mm, lower it 5mm :wink:
2. The CofG will not be central to the car so you'll find insetad of being 5mm, you might need to drop the car 6mm to get the other side to rise 4mm and make it even again.
3. The manufactureres springs will not be perfect and could be as much as 10% different in spring rate. (Like I said, the more you look into the detail, the more you realise its a rough science, especially when you're talking about dynamic rather than static settings)

After each change you make NOTE IT DOWN. I can't say how important this is, if you don't you'll be forever chasing round the corners of the car raising and lowering bits as the car see-saws between each setting.
ALSO, after each change move your car forwards and backwards and bounce all 4 corners a few times so the suspension can settle.

-On the Tein's a turn on the spring platform equates to about 2mm in ride height difference.
-In the end I got the front balanced with an additional 2 turns on the front off compared to the front near.
-You should now be able to lower the car level to whatever setting you want. If you want to drop the car about 10mm, take 5 turns from each spring platform.

-Once you've done the front, you will find the back might be slightly better or a lot worse. Probably the latter.
-Repeat the same process on the back as you've just done on the front. I found my rear near needed an additional 6 turns compared to the rear off. This implies there is more weight on the near and thers is, its my 80Kg of Sink, sand and cement. It is obviously having a greater effect on the rear springs then the front's which are stiffer.
-Now lower or raise the car in an equal amount on each side to the desired level.

Again, if you have lowered a corner, its opposing corner will rise. So all you've done is finished the first pass.
-As the front has the biggest influence, check its ride heights again. Before making any adjustments, consider all the other corners. If you assume that the springs are roughly similar, the car will be better balanced with the least difference across front or back spring platforms. Otherwise you might find the front right is over compensating for the back left that means you have to overly raise the back right...... Still with me :? .

-This is a minor detail and is really where you need corner weighting to help out but doing this will help.

-After you've made your single move :lol: on the front suspension. Check the rear again and see what is wrong.
-Again, by looking through all your notes and readings, you should be able to make a single move on the rear to balance it out too.

I make it sound simple but this process took me over 8 hours of fiddling. The more you adjust, as long as you write it down, the more you start to see patterns and get a feel for whether you need 2 turns up on the front left or 1 down on the right.

Once you've got your front and rear "side to side" balanced with as little differnce between them, you should be able to raise and lower the car as much or as little as you want whilst it still remains balanced 8)

If you now want to lower the car 10mm all round, take 5 turns off every spring platform. Its worth a double check measure but within reason, it works extremely well.

Important Considerations
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1. When you lower a car, you will increase its camber. This can be a good or bad thing.
2. Lowering a car can make the front severly toe out and the rear severly toe in. If you don't compensate you will kill your tyres and ruin the cars feel/handling.
3. Lowering a car can reduce its CofG but past a point, our suspension will make the difference between the RC and CofG increase. This means that past a point, the car will be more inclined to roll rather than less, even though the CofG has gone down.

In general, less is more with our car's geometry and a drop of 15mm to an absolute max of 50mm is best. The Tein's go down to 60mm and at this level, the lower control arms all round are nearly horizontal, so any roll will induce positive camber. Tein have done this for out and out race cars running super stiff springs where suspension travel is minimal. These are not really for road cars and though the situation could be improved by running more camber to start with, it is a bit like fixing a leaky boat with a bigger bilge pump.

For reference
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Nissan specify a wheel centre to body distance of:
365mm front 375mm rear

Whiteline specify a 40mm drop all round over standard
325mm front 335mm rear

My current specification is given for reference, I am still not happy with these yet either so I only give them for ideas. My gut feeling is it still needs to go up another 5-10mm all round but I'm struggling to get decent camber at the moment so as always its a compromise. Also, its what suits me, my car and my driving style that is differnt to other peoples car's, roads/tracks and driving style so don't flame me if you do something different.

Setting Front near front off rear near rear off
Wheel to body 330m 330mm 345mm 345mm
Floor to body 606m 606mm 621mm 624mm
turns 7 9 16.5 6

End result
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Inner peace, the world in union and a balanced car:



Jim
 
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