Ride height setting with coilovers

I have BC coilovers installed on my 2005 Porsche Boxster S and have had it professionally corner weighed and aligned, however I am convinced they have done the usual BC setup and added about 4mm of preload and set the height with the lower adjustment rather than the spring perch.

The reason I believe this is, I had tried numerous times myself to set the droop and bump travel but always found I was running out of adjustment before I could get it where it should be, granted it was marginally off ideal therefore I ran the car as it was. The issue being that if I hit even slight imperfections in the road on the nearside it would cause a huge bang as though the suspension had hit its end stop, as I always intended on the car being fully corner weighed the company I was planning on using said to leave it and they would sort it out.

Now the car has been weighed I believe the issue I was getting was spring bind, the front weighs in at 345kg left and 358kg right, the spring rate is 4kg/mm and they are 180mm long. Therefore as an average they will compress about 88mm with the weight of the car alone, the front shock has a total travel of 130mm and a 40mm bump stop, I have never looked at how much travel is left with a full tank of fuel and myself sat in the car, which was how the car was corner weighed, but surely this means the car rides on the bump stop all the time when full with fuel, when I have looked with a 1/4 tank of fuel and me not in the car I would guess at around 2.5cm's before the bump stop would touch the shock. Using these figures I believe the shock body needs moving down by around 5cm, from previous my previous experience I believe this would not cause the wheel to foul the arch, this then means I need the spring perch to move up 5 cm's in order to keep the correct ride height, which I believe will be the equivelant to 200kg preload, therefore when the car is placed on its wheel it will compress a further 37.5mm, which is approximately 1/3 shock travel of 110mm (this is what I measured with the bump stop fully compressed).

1. As I had set the front car height bang on bah 2mm on the front left to what they have set the car to now and I was aiming for correct droop and bump travel, I am thinking I would have compressed the springs by about 5cm's (I remember it being quite a bit but this was a year ago), the weight of the car would have then compressed it a further 3.75cm's and with the remaining shock travel of at least 7.5cm's potentially all the way upto 9.5cm's if it literally squished the bump stop to nothing, the spring was compressing anywhere between 162.5 and 182.5 and I was indeed getting spring bind, does this sound plausible?

2. Is my current setup wrong, especially as viewing the shock travel with only a 1/4 tank of fuel and there is only about 2.5cm's of bump left before it hits the bump stop?

3. My thoughts are as it is used on the road with occasional track use 4kg/mm is probably right as a spring rate it just needs the spring replacing with an additonal 2-4 cm's of spring travel to stop the spring bind, my concern being 5cm's of preload seems excessive. BC offer them in 200/220 or 230mm lengths

4. The rear spring rate is 6kg/mm and 210mm travel, has a shock travel of 150mm and a 40mm bump stop (20mm when compressed with the weight of the car) and the rear weights are, left 380kg, right 393kg.

5. Any other thoughts?

Thanks

Paul

You may need to revise your understanding of how springs actually work?

It's quite difficult to follow your post, but general comments.

To confirm if it's a bump-stop or coil-bing issue, put a dab of grease, or similar, on the stop where the contact will be made, and between a few of the coils - if contact is made the grease will be transferred.

If you're running into coil bind, NO adjustment of the seat or body will prevent it - the spring simply doesn't have the length and/or spring rate you need.

Pre-load doesn't change the spring rate, it merely changes the load that is required to initiate further compression of the spring - because changing the seat position changes the relationship between the spring base and the suspension, it lifts the vehicle and people think it makes the spring 'stronger'- it doesn't.

It isn't clear, but is the "bump stop" on the chassis or on the damper shaft? If the chassis not much that can be done without careful consideration, but if the damper rod there is plenty. If the latter is the damper travel 130 + the 40 for the bump stop (without the stop is it 170?), or 130-40 for an effective travel of 90mm?

Yes, option 3/ would seem to be the way to go - but I don't get why you're so hung up on the pre-load - those damper assemblies are specifically designed to minimise "pre-load" and you certainly shouldn't be even thinking of the 50mm, or whatever, you have in mind - set the dampers to minimal pre-load of the spring (on the bench is best) of a turn or two, or a set distance such as 5mm, then fit them to the vehicle and adjust THE BODY of the damper to the ride height and corner weights desired!

4/ - are you saying the rear is riding on the 'bump-stop'? have they been correctly set-up with minimal pre-load and height/corner weight adjustment on the body, not the spring seat?

Gord,

Thanks for the reply, I wrote this in a slight rush so sorry for it being confusing.

Essentially last winter I replaced my suspension for BC coilovers with the intention of using a suspension tuner to corner weight the car and do a road/track alignment on it. As I was going to be travelling for a couple of hours to said place, I wanted the alignment and suspension to be as close as possible whilst also hopefully giving myself the satisfaction and knowledge on how to set them up correctly.

The issue I had was that if I set the suspension as per BC's instructions with just 4mm of preload and adjusting the height with the body it was sitting more like 2/3 droop and 1/3 bump.

So I did a lot of research and adjusted the damper body down to approximately 1/3 droop and 2/3 bump and raised the car with the lower spring perch, whilst making sure that if the suspension was to fully compress nothing would touch. At the time I wasn't a member of this site, however after watching the tutorial on here they also say that this is the correct way to set the coilovers. The issue being when I drove the car, if the front nearside wheel hit sharp but small imperfections in the road it would cause a very loud bang as if the suspension had maxed out it's travel. I am now believing this was spring bind rather than the shock body hitting the top mount.

To clarify some of your points/questions:

1. I understand that preload on a linear spring does not adjust its rate and if I adjust my lower spring perch up by 5cm this equates to 200kg of load, this is lower than the weight of the corner of the car and will compress further when put down on the wheels.

2. The bump stops are on the shaft not the chassis.

3. The front damper travel is 130mm - 40mm for the bump stop= 90mm prior to the bump stop compressing, I found the bump stop would compress 20mm prior to it lifting the car, which = around 110mm of total travel.

4. I believe the suspension tuner has set a low preload probably about the same as BC at around 4mm and then adjusted the height using the damper body rather than the spring. What I believe this means is, as the corner weights in at around 350kgs on a 4kg/mm spring and with say just 4mm of preload, the damper and spring when holding the weight of the car will drop by about 71mm this means that out of a total damper travel of 110mm there is only 39mm of bump travel left. I believe this to be true, from visual inspections there doesn't seem to be much travel left in the damper and the front bump stops are always touching the top mounts, the final thing is if I am pushing on on roads I have occasionally felt the car bounce as if the suspension has bottomed out.

5. I believe the rear is pretty much setup correctly, it might not be exactly 1/3 droop and 2/3 bump but it's close enough and the bump stops don't reach the top during normal road use. I simply included this in case the information was needed.

Ok, I have just been looking through some of the old posts and Andre posted a video a while back about MCA suspension, it confirms that you adjust your height with the lower spring perch. I just looked on their website and they say that droop should be no less than 45mm, where as I was under the impression you want 1/3 droop and 2/3 bump, this would mean as I have 110mm of travel after the bump stop compresses I should be aiming for 37mm, or is it a case of ignore the bump stop as 1/3 of 130mm total damper travel equates to 43mm. So what exactly should I be aiming for in regards droop?

Just to clarify how I intend on setting the suspension travel:

1. With the tyres on and the springs removed set the car at the required ride height

2. Adjust the shock body to the required droop travel (what ever that might be, 1/3 total travel or no less than 45mm)

3. Now check that when the damper is fully compressed the suspension/tyre does not contact anything, if so adjust it so it doesn't and unfortunately this is just compromise you have to take

4. Put springs back on and using the spring perchs adjust the ride height to where it needs to be.

Just been in the garage and measured the current spring length with the car in the air and it is around 172mm, therefore both preloads on the fronts are set at around 8mm, I also reckon the maximum I could raise the spring perch would be another 20mm before it would run out of threads on the damper body.

So basically I believe I am correct in thinking the tuner has set the preload to low, granted it is slightly higher than what BC recommends but not high enough to prevent the piston from travelling excessively, by my calculations: 8 x 4 = 32kg of preload, the average weight on each front is around 350kg's, therefore 350-32=318 kg's (Load which actually compresses the spring further), 318/4 = 79.5mm of travel on the damper piston, this only leaves 10mm of travel prior to touching the bumpstop and around 30mm before the bumpstop is fully compressed, this would be with a full tank of fuel and myself sat in the car.

I have 3 options for longer springs from BC, 200, 220 or 230 mm, currently 180 is fitted, my thoughts would be as I have at most 20mm before running out of threads on the body to get the 220, this should give me 55-60mm of height adjustment (20mm currently remaining threads plus the additional 40mm of the new spring).

Or should I set the required droop/bump ratio ensuring nothing catches and then calculate how much the damper has actually lowered then order the relevant spring length that will raise the car back to the desired height?

In order to do either method I need to know am I aiming for 1/3 droop (See my previous post above for 2 different aims of 37mm or 43mm) or no lower than 45mm of droop, or even another iteration that perhaps I haven't found on the internet yet lol.

Also would I be better off setting the ride height and alignment with half a tank of fuel and my weight? In my head this means the difference between max and min fuel has a smaller effect on the setup in regards geometry and height. If I was to do the setup with half a tank I would be more inclined to aim for a droop of around 45mm or possibly higher.

Any thoughts?

I still suspect there are aspects where things are at cross purposes, I'm having a little trouble visualising everything, but in general...

Philosophies differ on setup of the springs - I'm firmly, when possible, of the minimal pre-load of the spring by adjusting the spring perch, and the adjustment of the ride height by adjusting the damper body in the lower mount, and that is what every "dual thread" coil-over says - but others do have different views - if it works for them then it's all sweet.

Regardless, it may help if you consider it this way.

For any ride height, the top mount is going to be a fixed height from the floor, as it is fixed to the chassis it moves with the ride height.

You decide on ride height A, this means the top mount has position B above the ground. Because there is some movement of the suspension the bottom mount for the coil-over on the suspension will be height C above the ground.

Holding the vehicle's chassis in position are the springs which are applying an upward force on the top spring mounts D, and a downward force on the bottom seat E - at this point you may be considering a diagram would be a good idea ;-)

Between the seats D and E there is the compressed length of spring F - the length of this will depend on the initial spring free length and spring rate, which I may come back to later.

The position of the spring seat E will be a height above the that depends on the spring, and we will call that height G.

Now, if you're still following it, you can see that ultimately A, the ride height depends on the height of G, the spring seat - assuming the same spring is used. if G is raised 25mm then A is also raised 25mm because F is the same.

Getting back to the adjustments, traditional coil-overs have a single threaded adjustment ring for the seat E, and by adjusting this upward the top seat D is also moved upwards to keep the sme spring compression - this also has the draw-back that it limits the droop from the nominal ride position - this is IMPORTANT, especially as droop is one of your concerns, and in more extreme cases, where a too short and/or too soft spring is used there may be almost no available droop before the pre-load is reached which limits further travel.

To counter this, and reduce the number of springs required, mostly length, a dual thread damper assembly was invented, this separates the ride height adjustment from the preload position. This has two big, related, advantages and two big disadvantages - the latter being additional mass, and people who don't understand the whole concept screwing things up by adjusting the spring, not the body.

The advantages are that any spring, provided it fits within the adjustment range, can be fitted to the coil-over with the minimum pre-load to allow full travel under both compression and extension - droop! Before, with the conventional design, one would need to have a variety of spring lengths for each rate, to allow full travel of the dampers - or either limit extension from high levels of preload or use supplimentary springs/spacers to increase the effective distance F, of the spring, and use clearance/helper springs to prevent the spring becoming unseated if the spring used for the ride height wasn't actually pre-loaded.

In your case, there seems to be several things going on?

You are running out of compression travel and either bottoming out the spring or hitting the damper bump stop. What you need to do is prevent the spring coils running into a bind condition if that is the problem - this can ONLY be remedied by using a longer spring of the same rate, +20mm could be sufficient, but longer could be fine with some additional preload at the cost of a little droop. If the damper body is hitting the stop, and coil bind isn't the issue, you need to lower the damper body in relation to the bottom spring seat E. With traditional designs this is where you say ****, because you need to buy a new damper with a reduced distance from the top of the body to the bottom mount - BUT because you have a dual thread damper with a means of adjusting the relationship of the damper's top to the lower mount all you need to do is screw the body down to a point where the stop still works (to prevent the piston bottoming hard in the body if it doesn't have a hydraulic stop), and the spring seat up the same amount.

That said, you may still find you need to make some compromises to get everything to play nice, if the damper body assembly is too long.

From all you've said, and assuming I've followed it correctly, you need longer springs of the same rate, the pre-load on the springs to be set to a minimal value (maybe 5mm or a full turn of the seat adjustment) with the damper body at full travel - if there is a suspension droop stop, check strap, or whatever use that instead of damper full travel - this will give you the most droop.

Then fit the coil-over assembly and set the ride height as desired using the adjustment of the damper into the bottom mount assembly. This should maximise the compression travel. If you have more compression than desired, such as tyre-body contact on heave compressions, use a longer and/or harder bump stop over the shaft - some will use different stop materials, shapes, etc, as a tuning aid or auxiliary spring.

Gord,

I think we are getting each other confused.

For example you say that you prefer to apply 5mm of preload and to adjust the lower mount to set the height, but then later say that I should adjust the body damper to gain the bump travel I require and then to use the spring perch to regain the height - You are running out of compression travel and either bottoming out the spring or hitting the damper bump stop. What you need to do is prevent the spring coils running into a bind condition if that is the problem - this can ONLY be remedied by using a longer spring of the same rate, +20mm could be sufficient, but longer could be fine with some additional preload at the cost of a little droop. If the damper body is hitting the stop, and coil bind isn't the issue, you need to lower the damper body in relation to the bottom spring seat E. With traditional designs this is where you say ****, because you need to buy a new damper with a reduced distance from the top of the body to the bottom mount - BUT because you have a dual thread damper with a means of adjusting the relationship of the damper's top to the lower mount all you need to do is screw the body down to a point where the stop still works (to prevent the piston bottoming hard in the body if it doesn't have a hydraulic stop), and the spring seat up the same amount.

This statement here is actually applying preload to the spring to achieve the desired ride height and damper travel, because if you were to now lift the car off the ground the spring will no longer be preloaded with the 5mm as previous and will have what ever distance you wanted to gain in travel as preload.

I have uploaded some drawings to explain the following, basically I have drawn 5 dampers in different states to try and explain what I mean and what I think you are saying, all of them have the same spring rate of 5kg/mm and is 12cm's long, the damper body is 10cm's long and the damper piston has 8cm's of travel, the car has a desired ride height of 10cm's and weights in at 350kg's per corner, also for simplicity I have ignored bumpstops and I have not applied any preload to make the maths simpler, obviously I would not set mine up like this.

Damper A:

This has no preload applied to the spring and the car is in the air.

Damper B:

This is damper A and the car has now been placed on the ground

350kg/5kg-mm=7cm of compression of the spring and damper piston

8cm-7cm=1cm (available damper travel - actual damper compression=remaining damper piston travel)

12cm-7cm=5cm of remaining spring compression

Damper C:

Apart from there being no preload on the spring in the drawing and mine having around 7-8mm, this is exactly the scenario my car is in as a lot of manufacturers tell you to set them this way and this is also annoyingly how the suspension tuner has set mine and charged me for the pleasure. I also believe this is how you are advising is the correct way to setup a dual coilover system, as you can clearly see by adjusting just the base adjustment the damper piston travel remains the same at 1cm and the car now rides at the correct height. The only way I could now add damper piston travel with out adding preload would be to fit stiffer springs, therefore the spring would compress less and I would gain bump travel at the expense of comfort and handling.

Damper D:

Is the same as Damper A however now has 3cm's of preload added which equals 150kg of load (30mm x 5kg), therefore for the first 150kg of load the spring and damper piston does not compress and then the remaining 200kg's will compress the spring and piston damper. This is also what I believe you were saying in the text included above.

Damper E:

Is damper D but with weight on the wheels, as you can see the 200kg's/5kg-mm=4cm of compression of the spring and damper piston. This is the way that MCA, HP Academy and a few other sources I have seen say to set the suspension, the key thing of doing it this way is to ensure that no part of the wheel assembly/suspension comes into contact with the chassis when under full compression. If it does it means you have to adjust the base adjustment down ie damper body up to prevent this from happening and then lower the spring perch to achieve the required height. I stand to be corrected, but the bottom adjustment was designed so that companies like BC could use damper bodies of roughly the correct size therefore saving costs not having to design and build shocks for each vehicle type, we then use the adjustment so that we can dial in the required bump/droop travel whilst preventing damage to the car by setting the damper position so it prevents wheel contact with the chassis.

As for my spring bind issue, I was only getting this when I was trying to set the suspension as per damper E and this was a year ago prior to the suspension tuner doing his work. I now need to calculate the required spring length so that I can fit it and then set it up as per Example E, however in order to do that I need to know what the ideal droop/bump ratio is, I have sent an email to HP Academy and one of the tutors is going to have a look at this thread and I am hoping will be able to answer this question once and for all.

Hi Paul,

I'll try and keep this simple and avoid confusion. While adjusting ride height at the lower mount is very common, it's also not the correct way and can artificially limit your available suspension travel. MCA have done a great job explaining why so I won't rehash it. Please read this https://mcasuspension.com/spring-seat-adjustment-method/

Adjusting the ride height via the spring seat requires that the bump/rebound travel and relationship has been correctly set via the bottom mount. This becomes iterative if you intend to make significant ride height changes but most don't so the bottom mount is kind of set and forget. This is all covered in significant detail within our wheel alignment course if you need more info.

My general rule of thumb for the bump/rebound relationship is 2/3 in bump and 1/3 in rebound. While it would be nice to always have perhaps 45 mm of droop travel, this may not always be possible with some dampers. A bit of personal preference comes in here and it becomes a balancing act between insufficient droop travel allowing a wheel to lift, or insufficient bump travel requiring a stiffer than ideal spring or constantly contacting the bump stop - Ultimately neither situation is ideal so we have to pick the compromise that we're happiest with and understand the implications.

Slightly off topic but I'd suspect 4/6 kg is quite soft for something that is going to see the track. I have no experience with a Boxter so I might be missing something here.

I'll get back to you later, Paul, when I have printed those images off.

As I said, opinions differ, the MCA suggestion limits the potential droop, especially with too short springs, but it's an option many chose.

As Andre said, some things are going to be fixed - where the bottom mount is on the suspension, and the top mount on the chassis/body, through the desired wheel travel, and whatever one does with the damper/spring relationship has those limitations in fully compressed and extended (droop) mounting points - plus any other suspension, steering, transmission, etc, components that may further restrict packaging.

It just needs one of the components chosen to be too far out and it will be impossible to work around it and it will need to be changed. The most common is the spring.

With a big enough budget, one could get very close but, for us mere mortals it's down to trying to find the best compromise within our budget.

The two main things (excluding steering/suspention/chassis/body component interference, etc) mechanically limiting travel are -

The springs - too short and they will unseat before the damper reaches full extension, too long and they can't extend fully because the damper can't extent far enough to unload them, plus there is a higher risk of coil binding.

The dampers - too long and either the piston will bottom out in the body or the top of the body will hit the underside of the top seat, limiting compression but too short and overall travel will be limited because the extension will be limited. Note, assuming a rough corrolation with 'length' and travel.

In theory the greatest travel will be obtained when the spring is barely pre-loaded, travel being the difference between free length and coil-bind, which is why I would suggest that is done and the ride height is adjusted by the damper body in the lower mount. The disadvantage is that if the spring is too soft and/or short the top of the damper body can hit the underside of the top seat and/or shaft bump travel limiter(s) - the usual band-aid is to adjust the spring seat up on the damper body, and lowering the damper body into the bottom mount, this increases the damper to top seat clearance but at the same time it limits the droop available. This isn't a problem with the first method, but a problem with the wrong spring length and/or rate being chosen for the application - a good approximation can be made of the actual load on the spring(s) from how compressed it is from the free length and the rate.

Doesn't mean the other methods won't work, I just don't think they're necessarily the 'right' way to go about it.

One potentially big issue is that just as hitting the bump stop is usually to be avoided because it's a sudden change to a much higher net spring rate at the tyre, so is the sudden change to zero spring rate when the spring hits the pre-load point on extension. Depending on the springs and ARB this may not be much of a problem cornering as the ARB may still be holding the spring off the inner spring's 'pre-load' point, by transferring loads from the outer, but if cornering over an uneven surface, or a crest, it may make that end much more 'twitchy' because not only may the inner tyre be subject to rapid changes in load around the limits of travel, but if the bumps are sufficient to allow the spring to 'top out', the outer will be further compromised via the ARB - of course, there are many other factors, but if excess "patter" or understeer under those conditions is something difficult to nail down, might be worth considering?

Hi Gord,

There's many areas of suspension where there's various opinions but no black and white. Despite the number of people who adjust the ride height by the lower mount, and coil over manufacturers who advise the same, this is absolutely NOT the correct way to do so. Doing it in this way simply ensures that for a given ride height your ratio of bump to rebound travel, and in turn the available bump and rebound travel, will be defined by your spring rate.

'As I said, opinions differ, the MCA suggestion limits the potential droop, especially with too short springs, but it's an option many chose.'

Let's examine your statement. Using MCA's and HPA's recommended method does not limit droop travel. As I mentioned in my original reply, the droop travel, bump travel, and relationship between the two is the first thing you set by using the lower mount. This is done irrespective of spring rate or spring length. it's simply a case of taking measurements from your desired ride height and setting the lower mount accordingly. From there you fit the spring and adjust the spring perch to achieve your ride height. If you do this then by definition the droop (and bump) will be whatever you decided it to be when you set the lower mount.

Your approach is common and before I really sat back and thought through what was happening I'll admit I also used to set ride height using this technique. Where it really became apparent that this technique is flawed is on our first GT86. This ran BC coil overs setup as per their recommendation (minimal preload on the spring, set the ride height at the lower mount). The front strut in particular on the GT86 is very short and this exaggerated the issue I noticed which was that we moved progressively to softer springs while doing some testing. In the end the car suffered terminal understeer and was a complete dog. Reason being was because each time we went softer in spring rate the car naturally sat lower and in order to correct this I wound the lower mount down to get back to my original ride height. The problem of course is each time I did that I reduced the available bump travel to the point that eventually the strut was sitting on the bump stop with almost any bump travel at all. Ultimately this technique would have also allowed the wheel to contact the inner guard/chassis if it had hit a bump hard enough to compress the bump stop sufficiently which is clearly dangerous.

In short, adjusting ride height at the lower mount will affect your available bump and rebound relationship and can result in the potential for wheel to chassis contact in many cases. Adjusting it at the spring platform on the other hand preserves the bump to rebound relationship (see first post for notable caveat and the need for an iterative approach for large ride height changes) and ensures that you will never have contact. The usual argument for using the lower mount is the misconception over 'spring preload' which is not relevant for linear rate springs

Andre, Gord

Thanks for all the help, I have decided I am going to set the height with half a tank of fuel and me sat in it, then set the droop to 45mm, this would mean with a full tank of fuel it will have around 40mm of droop and empty it will be about 50mm, this would leave between 60-70mm of bump travel before the bump stop is fully compressed, this will be set as per Andres instructions, this was how I tried to do it at the very beginning and I believe this to be the correct way. I also believe with the pot holed roads here in the UK, setting it in this way rather than to 1/3 droop will hopefully stop the suspension fully extending and causing issues as Gord suggested. As a guess this will also require me to fit longer springs to prevent spring bind.

I will then drive the car to see if I am having issues with the damper extending to it's end stop when going over pot holes or undulations and potentially add more droop if required. Once I am happy that the height is correct I have a local garage who have said they will check and reapply the alignment that the suspension tuner did for me.

Once again thanks for all the inputs, I will try and remember to come back on in a few months to say how it's going, as Andre pointed out I am also questioning if the spring rate is to soft, but until I get the travel aspect sorted it is to early to tell.

When setting the bump/rebound, make sure it is done at normal ride height! Also consider when the bumstops engage.

Bumpstops add to the spring rate, and for a rear wheel drive car increasing the front spring rate will increase the oversteer potential of the car when cornering. When in a straight line the bumpstops (depending on amongst other things horsepower) should stay constantly engaged to prevent a porposing type effect.

I was having an issue with the handling of my naturally aspirated MX5 (when it had BC ER's) where in corners it was going to oversteer, especially when changing directions quickly.

A suggestion was made by a very experienced suspension person (Murray Coote) to check the bumstops and adjust them. The logic is if you have 60mm of damper travel in bump with 10 kg springs the weight will have to increase by 600kg before you run out of damper travel. For my MX5 that would imply that I would be putting over 850kg on a front wheel!

Whilst damper pots can be noisy, the change between normal stock bumpstops (purple) and cut down (green) is obvious! By the way the car was more predictable and faster!

I have since changed from the BC's and now running custom valved Shockworks dampers with custom bumpstops. The shockworks whilst not having as many 'clicks' as the BC's have helped take seconds off my lap times!

I did this note a while ago when on Team Racepak, hopefully it may help with the logic I used to solve the problem.

Facebook Article

Video of car with Shockworks dampers installed, not my PB (58.18) but close enough. Car is a naturally aspirated MX5 NA6 (Miata) with a BP motor.

Lap of Queensland Raceway (Sprint) with damper pot data

@Andre.Simon, could you please advise on how to set up the lower (non spring - the one securing strut position in the hub) perch of the coilover given the desired ride height. I did go through the course (likely two) covering the subject, but it's always about the spring preload (lower spring perch) and not about the strut assembly length.

Should I just follow the manufacturer (Ohlins) recommendation, even though I'm running a different preload settings (+-15mm from their recommendation)?

It seems to be somewhat of a chicken and egg kind of a problem...

Thanks

Hi Alex,

Are you running a single spring with a linear rate or a non linear setup?

Also you say ohlins has made a setting suggestion, do you know if that is specifically for your car or a generic setting guide that they suggest for their coilovers? For example the BC's I fitted suggest something around 5mm of preload and don't give a suggestion on the bottom perch as they use that to set the height of the car which is user preference.

Hi, Paul

I'm running linear springs front and rear. Rear also has a helper spring (added by me).

Ohlins recommendations are for my particular platform (981 Cayman), but if I follow those my front is laying on the ground, while rear stays on approximately OEM ride height. I had to raise front to clear my driveway and lowered rear a little as well. I was doing so mostly with the lower spring perch (adjusting preload).

After raising my front I lost the most of my droop travel, and had to dial it back a notch - my ride improved substantially after that. Still, rear has way more droop than the front and I'm concerned if I don't have enough compression there. It rides well though but I'd rather support my feelings with math and exact setup technique.

Ohlins does provide recommendations for both: spring preload and coilover length. Not quite sure what their recommendations are regarding adjusting the ride height, but I'm afraid they do recommend to adjust the coilver length, rather than spring preload. After watching suspension setup courses on this website that's not something I want to follow.

I did ask Ohlins about the strut travel length and which part of it is the bump stop travel. I believe I might need that in my exploration.

ok so I am assuming the rear helper spring is the type that you can squash with your hand and you have installed it in the rear to keep the spring captured as you have had to lower the spring perch.

my suggestion would be to do the following:

1. remove one front and rear spring and their bumpstops and loosen the lower collar at the hub

2. remount the dampers into their top mounts

3. Measure the length of the damper travel, this could be the visble length of the fescalised portion or it could be shorter if internally the damper stops it from compressing fully, to find out jack the wheel carrier up with the wheel off and see how much is left visible.

4. put the wheels back on

5. lower the car to the correct ride height you want, obviously the corners that do not have the springs fitted will need to be supported as the springs are no longer there. There are specific points porsche tell you to measure from and personally I adjust my height the same amount front and rear from the stock setup, the reason being this will adjust your rake and can cause handling problems if you go to far from stock (Under/Over Steer), you might be able to get the stock height settings off the internet if you don't know what it was prior to fitting the coilovers.

6. Now the car is at the height we want it to drive at we need to adjust the height of the damper by twisting it in/out from the hub so that it is around 1/3 droop/rebound(How much the car will compress it with its weight) and 2/3 bump travel (How much is left for when we are driving and compressing the suspension) from some research I have done the minimum recommended droop is 45mm but andre covers his views on this above. What I will say is this purely depends on your car and this might take a few attempts to get right, there are few factors you need to take into account which I will cover below.

7. once you have set the damper to the correct position, put a jack under the lower control arm and jack it up until the damper is fully compressed, we are now looking to see if the wheel is going to fowl the wheel arch/liner, if it does then you will need to extend the damper out more to push the wheel away. If it doesn't fowl the liner then later when driving the car and it doesn't appear the damper is extending to its limits (you will hear a loud bang) when hitting say pot holes or other deep depressions in the road you have the potential to retract the damper slightly and give yourself more bump travel, it is a balancing act you don't want to go to far either way.

8. now put the car back in the air refit the bump stops and springs to the front and rear dampers.

9. copy the damper positions to the otherside of the car.

10. using the lower spring perch set the height of the car and you should now have the correct damper travel, ride height and if you were to hit something and fully compress the suspension the bumpstop will do its job and save your car from having it's tyre pushed through the fenders.

Although I am confident that this is the correct way of setting these kind of coilovers up, I will caveat this by saying at this moment in time I have still not actually driven my car yet due to life getting in the way, I have also had to buy longer springs for the front in order for this to work as the ones provided by BC were not long enough, hopefully the Ohlins ones are long enough for you and you shouldn't need the helper springs.

Hopefully that makes sense

Thanks, mops.mad.house, this is very thorough, well put down and all makes sense (at least for now). Appreciate your help and time spent to write this up!

I did add helper spring on the rear to have more adjustability, since the recommended preload was just 2mm and I wanted to lower my rear a little bit with lower spring perch.

According to Ohlins support, total shock travel on the front (model 5P80) is 74mm, while on the rear (6P80) it is 114mm. This explains a much longer droop travel on the rear (which I was concerned about). I can probably leave my ride height setup alone for now. Yet to do corner weight balancing though.

For 981 owners with Ohlins R&T

- on the front my current droop is about 27mm

- rear droop is about 37mm

- lower non-spring perch (coilover length) is +-10mm from the recommended settings.

- front ride height ~10cm

- rear ride height ~12.5cm from the fender to the rim

PS: This is a f-ing rocket science, honestly!

Alex,

No worries and I wouldn't say it's rocket science just that there is a lot of misleading information on the internet and from the manufactorers themselves which just leads to confusion.

Just curious do you know the spring rates on yours? As your damper travel is less than mine I hope the roads in the US are smoother than the pot hole ridden UK roads lol, as we are coming out of winter the amount and severity of the holes are rediculous at the moment.

On a positive note for my car hopefully it will be back on the road in the next 2 weeks, the alloys have been painted however one has had to go back for a touch up, I have 4 new tyres on route, so fingers crossed I can get this setup finished, get the car MOT'd and I will be able to drive it again.

I will then tweak the height if neccesary and once happy bang it in for an alignment.

For anyone that is interested here is an update of how the adjustments have turned out.

As per the other posts, I installed a springs that are 40mm longer in the front and then tried to set the damper lower adjustment so that when the car is at the ride height I want the damper can only travel enough to prevent the wheel contacting the car and have around 45mm of rebound. As it turned out, to prevent the wheel contacting the car at the original ride height it was around 50mm of rebound, so after driving the car I have now raised the front by 10mm to give me the extra rebound. I have also raised the rear by 15mm to give me extra rake.

I had the car out this weekend with a full tank of fuel. On some really bumpy country roads, the front left which has always been the side that has had the worst issue still had about 5 - 10mm clearance before the bump stop would touch the top mount.

I'm happy with the results, it's just a shame I have had to do so much research and adjustment to the suspension to get this result especially after taking it to a suspension tuner who in my opinion set it wrong.

My forum membership runs out in 3 days so I won't be able to reply after this, I would just like to thank those that have taken the time to help me out.