Coilover Height Adjustment Method

[Magpie]

Following on from a discussion in another thread. How do people change the ride height on their coilovers?

There are a few schools of thought, one is to use pre-load (after setting up the suspension geometery) ala MCA's method or setting pre-load then adjust height via extending/retracting the coilover body ala Megan/BC.

Tein http://www.tein.com/products/features.html even state, but is contradicting itself:
Full Length Adjustable -
Vehicle ride height and spring pre-load can be adjusted independently. Ride height is adjustable in two ways: a. adjustable shock length, and b. adjustable spring seat.
a. The lower mounting bracket can be adjusted, thus changing the overall length of the shock, and therefore altering the vehicle's ride height. This also allows the user to determine suspension travel and droop.
b. The adjustable spring seat allows for independent adjustment of spring pre-load without affecting vehicle ride height.

[corners]

I created a thread a while ago

viewtopic.php?f=30&t=57628

[Magpie]

Oooops missed that. I guess what I'm trying to get started is how people on here actually do their coilover adjustments and has anybody actually done the MCA method from scratch? I understand that the MCA's are sent out ready to bolt in with only adjustments to the pre-load for height. Or in general do people just set and forget?

[plohl]

I have played around with both shock length and spring pre-load. These have always been minor adjustments. Any adjustment to spring pre-load will affect the ride height.

I think for what most of the active people do on this forum it doesn't really matter how they do it.

I'll be trying the MCA method at some point - hopefully soon.

[project.r.racing]

i dont know what the MCA method is. but having installed 50 plus coilovers so far, the method for me is the same. and all from factory would've required up to 20mm adjust (excluding height adjustment) to work properly on a car. JICs, D2s, BCs and YSRs.

match front and rears. see if lengths are different, if so adjust.
install.
see if heights are different, measure and adjust.
done.

[hks_kansei]

I would have thought it to be as simple as set your necessary preload, then set the height.

Same as with a carby, set the mixtures, then set the idle speed (mixtures can effect idle speed, but idle speed can't effect mixtures)

[Magpie]

The MCA method is here http://mcablog.com/?p=409 and its premise is to find the correct position for your base (bottom mount) and then use pre-load to set height. Others like Tien/BC and others have the pre-load set first then the base is adjusted for ride height.

Do people prefer to adjust height using pre-load or adjusting the shock length?

[hks_kansei]

I thought the whole point of being able to adjust pre-load and height separately was to be able to tune the suspension better?
If you're supposed to adjust via pre-load only, then why do any companies bother with the cost of making adjustable bottom perches?


I'm not as versed in suspension settings as some people, but my understanding is that pre-load changes the amount of force needed to initially compress the spring.
ie: a un-captive spring needs more force to compress 10mm from rest, than one with 10mm of preload wound on.
(do correct me if any of that is wrong by the way)


All I can think that pre-load adjustment can help with is to keep it so that the bump stops act at a normal height (ie: wind the spring perch right down, the shock body sits closer to the bump stop. Travel is reduced, but it will hit the stop before the car bottoms.
If you wind the bottom perch (ie: shorten the shock body) right up it may reach a stage where the car still has 2inches of shock/bumpstop travel, but only 1 inch of ground clearance (so the bottom smashes into the road before the car touches the bump stops)

But that's only at the extremes of adjustment, and I'd argue if you're adjusting to either extreme, comfort/handling etc aren't high on the priority list.

[project.r.racing]

i dont see anything in the MCA write up about using the pre-load to adjust height. i think some people are reading it incorrectly. i see them adjusting the pre-load for maximum shock travel and gain in bump/droop.

[plohl]

If the shock length is set, adjusting preload will change the ride height.

I think manufacturers may have started adding the independent adjustment to account for people lowering the cars large amounts. As in, really low would mean you had very limited bump travel and unnecessary amounts of droop. It's just a theory....

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[kazama]

it also gives more options. manufacturers probably started adding them because over time things improve

[Magpie]

hks_kansei the springs are what supports the car's weight, not the absorber. Think that with a 8kg/mm front spring that has 240 kg of weight on it will be compressed 30mm. If the spring has 5mm of preload the weight will compress it the further 25mm to get to 30mm in total. If you put 30mm of preload the 240kg of weight will not change the spring length from its pre-loaded length.

My understanding now is that the bottom perch adjustment is to maintain the suspension geometry so that bump is fully used just before it hits the car body. By using the bottom mount to change ride height there is the possibility that things will hit, as in my case and I replaced the bumpstops and used packers to compensate for the wheel hitting the body. It would appear that I went down the path well worn, but it is not the BEST solution.

Either method acheives the same result. The bottom perch can adjust ride height as can using preload, but what gives the best result, at least to me, it is the one that considers the bump/droop and hitting parts of the body as part of the solution.

[hks_kansei]

hks_kansei the springs are what supports the car's weight, not the absorber. Think that with a 8kg/mm front spring that has 240 kg of weight on it will be compressed 30mm. If the spring has 5mm of preload the weight will compress it the further 25mm to get to 30mm in total. If you put 30mm of preload the 240kg of weight will not change the spring length from its pre-loaded length.

I didn't mention the shock supporting any weight, only the shock's position as having an effect on suspension travel (ie: when the shock body hits the bump stop it has no more travel)

With your sums, assuming a linear rate spring, would the spring not compress 30mm extra in both examples? regardless of pre-load?

ie: for every 8kg it compresses 1mm.
With 5mm of preload it essentially has 40kg of load on it at all times.
If you then put 240kg of weight on that spring, it shoudl still compress 1mm for every 8kg, so 30mm compression on top of that. The equivalent of having 280kg on the spring.
5mm + 30mm = 35mm total compression from free length (but only 30mm change during usage, since the pre-load remains static)



It doesn't really makes sense that an 8kg/mm linear rate spring would only ever compress to a maximum of 30mm shorter than free length.
By that reasoning, if you put 30mm of preload on a spring with a 240kg load you end with no spring movement, and have the same effect as if you just welded a steel rod in place of the springs.

[Magpie]

This is getting complicated.

The spring will have a free length and a compressed length. If somebody could supply these actual measurements it would be appreciated.

For argument say the free length is 300mm and the compressed length is 200mm and the rate is 8 kg/mm. Therefore the spring can be compressed 100mm and this will take 800kg of weight to do it. Therefore if 5mm has already been used or 40 kg there is only 95mm or 760 kg of weight that can be put on that spring before it is fully compressed. Hence if 240kg of weight is put on that spring it would cause 30mm of compression however 5mm has already been used by the preload hence the sping compresses another 25mm and the total compression on the spring is 30mm and the total weight on the spring is 240kg.

Anybody confused?

[sailaholic]

Hks Not quite, my understanding is

The spring only moves once the wight placed on it overcomes the preload placed on the spring

So at 0 preload
80kg give 10mm deflection to rest. So car now has 10mm of sprung suspension droop if the car weighs 80kg per corner

5m pre load
40 kg takes up the preload, 40kg pushes the car down 5mm. Car now has 5mm of sprung suspension droop at 80kg per corner

10 mm pre load
80kg take up pre load, no suspension movement. Car has no SPRUNG suspension droop. The wheel might droop further based on movement but it's not controlled by the spring.

10mm pre load
80kg takes up preload. 40kg dynamic loading give 5 mm of suspension bump from static but still no droop travel from static.

Keep in mind that be weight of the car acts in the opposite direction (downwards) on the spring compared the force of the preload (upwards).




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