Coilover Height Adjustment Method

[plohl]

Please note; this does not include angular correction for shock orientation. This is purely looking at a weight acting on a spring with and without pre-load

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[Magpie]

Thanks plohl, nothing like pictures and formulas to explain

[kazama]

well... i think thats enough internet for me today

[plohl]

wow... those pictures are stupidly big... my bad

[hks_kansei]

Looks like I was wrong.
Still not 100% how, but meh, I’m an accountant, not an engineer.


Also, below is the formula simplified and ready for people to plug in more standard spring measurements (ie: kg/mm rates and mm preload rather than N/mm and N)

W = Weight (or load)
R = Spring rate (kg/mm)
P = Preload (mm)
C = compression (mm)

((W*9.81)-((R*9.80655)*P))/(-(R*9.80655)) = C


Figured I'd make it easier, since it threw me for a minute with the measurements in Newtons etc.

Also makes me wonder how the above took up 3 pages when the same formula can be written in a more easily understood manner in one line. (9.81 = the Gravity part of the equation, that cna be a digit since it doesn't change) and the 9.80655 etc is to convert kg/mm into N/mm... which I suspect may just be an unrounded gravity constant)

I may not be an engineer, but damn it I can still maths!

[Magpie]

lol at least we are on the same page now

It took 3 pages beacuse it is in colour and looks good. Notwithstanding plohl's response is a very good explanation.

[sailaholic]

And half of each page was a free body diagram. Engineers are tought to draw them or fail.


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[plohl]

^^I prefer to write out equations - way quicker then typing. I wasn't expecting the pictures to upload so big, so I spread it out, could have fitted it on 1 page haha.

I did it with newtons to keep it all SI, hence why spring rate is k and gravity is still in the equation.
The multiplier you have added to convert to N/mm is gravity. So if you ever see spring rates in N/mm, dividing it by 10 will give you and approximate rate in kg/mm.


p.s.
to convert lbs/in to kg/mm divide by 56
to convert kg/mm to lbs times by 56

[hks_kansei]

The multiplier you have added to convert to N/mm is gravity. So if you ever see spring rates in N/mm, dividing it by 10 will give you and approximate rate in kg/mm.

That'd make sense.

1 N/m is equivalent to 1kg on a 1m lever isn't it (I remember Newtons being something like that)
And 1N/mm would be 1kg on a 1mm lever?

[plohl]

1kg*gravity*1m = ~10Nm

Weight is a force.

Force = Mass x Acceleration, which in the above case, the acceleration is gravity acting towards the center of the earth (down).

[sailaholic]

Your talking Nm (torque) there hks not N/m. So 1Nm (it's a product not a division) is 1 Newton (100g) on a 1m perpendicular lever.


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[Gladiator]

Wow, I read this thread hoping to learn something, now I just feel DUMB.

[Magpie]

Suspension does that to you

[Magpie]

Interesting conversation with Just Jap (BC Racing supplier) today regarding height adjustment methods. The person I spoke to agreed that the method of setting limits first then using preload to adjust height is a much better way of setting coilovers up, if you have the time, tools and resources to do it right, this includes corner weighting etc. However, the BC Racing method detailed in their instructions is OK for about 90% of their users and is not wrong, just quicker and easier.

Plus since mine were out of warranty I was free to do with it as I wanted We also discussed some of the 'issues' I have had with the BC ER's, that is the lack of linear adjustment in the rebound and the design of the external canister limits height movement to an extent. The limit of movement was acknowledged and that was it (known issue). The lack of linear adjustment in rebound, it was suggested that on a heavier car it would be more linear and it may help to start a little higher (towards hard) than what would be 'normal'. Maybe this issue could be solved with custom valving, not sure and not discussed. However, all up a pleasant conversation with a person who knew their product and suspension in general.

Again the question is why are there adjustable collars (asked of me by somebody else) and I think that unless the coilover was completely customised for the vehicle then almost every manufacturer (including MCA) needs some flexibility to adjust the coilover length for a car. Even MCA state that the length is what they consider best (based on their testing and assumptions), however if needed it can be customised hence their method of adjustment takes in the ACTUALL car's suspension and setup.

So either way is not wrong, just one is easier than the other. It will be interesting to see how this turns out and if it is worth the effort. I have a feeling that I will have to compromise on ride height to ensure bump/droop are maximised. I'll measure everything up before I make any changes, take detailed notes, many pictures and do a write up for those interested.

[Locutus]

Tein did not contradict themselves. By being able to adjust both preload and lower perch at the same time, you can change pre-load without affecting ride height. Every mm you reduce the shock length, you can add a mm to preload and you will end up with the same static ride height.

The adjustable lower mount/collar is there because every car has slightly different suspension/chassis geometry. It also allows you to compensate for different wheel/tyre combos as well as modified suspension arms/chassis/panels. They are also used for corner weighting.

The manufacturer's instructions that ship with coilovers are almost always wrong because 99% of people who buy coilovers are only interested in slamming their car or reducing tyre/fender gaps and have little to no appreciation of how their suspension actually works.