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Discussion and questions related to the course Motorsport Wheel Alignment Fundamentals
I have just watch the section of the course about adjusting the coilover ride height.
As said in the video I am now one of many who have been adjusting the coilovers over wrong.
I had been adjusting the bottom locking ring to gain the correct ride height I wanted and the adjusting the spring perch to gain a said amount of pre load.
So after watching this video my coilovers are miles off .
What is the best way to go about setting how much bump travel you have? As my rear wheels do catch my archs and I am guess it's due to incorrect set up?
Can I remove all springs on all 4 corners Jack up the wheels at the front and back of the car and then lengthen the shocks evenly so that at full travel there is enough clearance between the tyre and arch ? Then go on to set up ride height?
As like you I have been doing the same (surprisingly alot of people around the world even professionals do it) and after the video I also checked my tein manual which state the same as Andre (not that I was not convised already) but wanted to see if there is any recommendation there and it has all the measurements needed . So I would assume your manufactures manual should have the measurements for your coilovers. If you don't have the manual check on their website they should have somthing
Ok so took your advice and looked up the instructions for the bc coilover that I have . I am now totally confused, bc are saying the complete opposite from what I seen in the course. No more than 5mm pre load should be set and only to adjust via the bottom mount
For the ride height I took the advise in course and some info I learned before?
pre load I think it hasn’t rules but depend on proposal. Normal road of my tuning around 20mm to 40mm preload and 10mm for track but I have chosen the spring by myself. After correct the bottom mount( the piston bar inside shock should be 1/2 or 1/3 of the total travel), it has to be corrected together with spring adjusting mount. Usually ride height depend on spring, more preload means less funcation of spring. Hope teacher could note out if I understood wrong.
I also double checked with my coilover supplier (HSD coilovers from Driftworks) after watching this module and they writes that ride height adjustments should be adjusted through coilover base not the spring seat.
So I am wondering the same as you guys, what are the correct answer? I have been adjusting according to manufacturer instructions..
"Height adjustment should be carried out only with the coilover base. The spring seat should only be used to hold the spring in a captive state. Once the coilovers have been fitted and pre-load adjusted, the ride height setting should be double checked to ensure both sides are equal. To adjust the height, loosen the lock nut on the coilover base and rotate the entire coilover assembly, screwing it into the base to adjust the height downwards"
I can 100% confirm that BC's and HSD's directions are wrong! The incorrect technique of ride height adjustment is so prevalent that it's basically accepted, even by those who should know better. Here's a pretty clear video from MCA showing the principles discussed [url=https://www.youtube.com/watch?v=jjsocJxdlYA]https://www.youtube.com/watch?v=jjsocJxdlYA
When you actually understand the principles of what is happening then it becomes very clear how you should correctly make these adjustments. The only time the preload actually affects the suspension operation is with a non-linear spring rate. If you adjust the ride height with linear rate springs by using the bottom mount then you can really compromise your bump or rebound travel depending on the spring rate and the load on the suspension.
If it's any consolation I spent a large part of my career incorrectly adjusting coil overs too. This really got hammered home on one particular car where I progressively went to softer and softer spring rates and adjusted the base of the coil over to get back to my desired ride height. Each time I went to a softer spring I ended up closer and closer to the bump stop until I essentially had no bump travel available. This was the point I started rethinking what I was doing and how it affected the suspension operation.
Specifically in regard to Robin's comment about 'rules for preload' - there really aren't any. You use the preload that is required to achieve the desired ride height while maintaining the correct ratio of bump to rebound travel. In many instances with a stiff spring there will be negative preload at full extension (i.e the springs won't be captive). This can be addressed with keeper springs as it's often illegal for road use to have springs that aren't captive.
Thanks for clearing that up Andre.
I have been adjusting all wrong up until now. So as the winter season is here I Norway I'll have plenty of time to do a complete reset om my suspension and start over again.
Looking forward to next season of drifting with correct setup coilovers and alignment
I'm having some difficulty wrapping my head around this concept. So what I'm gathering is that my initial install of my Öhlins coilovers on my Honda S2000 should start with the springs set to 1mm preload, just so the springs are captive. Then install the coilovers with no spring and adjust the base height until the bumpstops are reached right before tire contact with the chassis. This then constitutes my lower limit for ride height. I should then add the spring back to the coilover, and adjust the lower perch up until I reach my desired ride height
I currently have the coilovers installed and am running into a issue with my driver's side rear tire contacting the body during extreme bump travel. So I'm wondering if the above mentioned method is what I should do, or should I just thread the shock body out of the lower mount, increasing the base height
Kurtis, I think you're right, would be great if one of the HP guys could get back with a definitive answer, but this seems to be the most logical way to go about it. It's something I've been struggling to get my head around too since actually watching the course videos (just completed them after having them for 2 years).
Discussion points, I'll return to this later, if there's any interest.
Not sure I follow André's reasoning - seems his problem was that he wasn't increasing the spring lengths to compensate for the increased compression softer springs have under the same load. Free (unloaded) spring length is IMPORTANT, and has to be considered with the spring rate!
In a perfect word, we'd have a wide selection of spring rates and each in a range of lengths. however, it isn't usually financially or practically viable for most of us to have this option.
This is a bit "granny... egg", but may be timely.
Any spring rate is the force (lbs or newtons - NOT kg) require to compress, or extend (which we won't concern ourselves with, in context), a spring by a specific distance (inches or mm - cms is a horrid measurement, and shouldn't be used, IMO) from the free length (no forces applied to it). For a constant rate spring it will compress at a constant rate of x distance for y force, until the coils make contact with each other and the force increases immensely. ie 2x compression needs 2y force, 3y force will compress it 3x distance, etc. This is IMPORTANT!
Now consider the basic coil-over design. The top spring retainer/collar is relatively fixed in relation to the chassis via the eye. The vehicles mass is applying a force (load) to the spring through the top collar which the spring is resisting. With the vehicle at rest that specific force applied by the spring to resist the load will be the same regardless of the spring rate, compressed length, or whatever - this is IMPORTANT!
Following on those, for the same ride height different springs will compress different amounts or, more correctly, have different compressed length. This is IMPORTANT.
Because the compressed lengths are different, and the top collar position is consistent, the only way to adjust the spring to compensate is by moving the bottom collar.
With conventional coil-over designs with a single screw adjuster for the spring, this would usually mean pre-loading the spring - effectively giving it a head start, or backing it off and using an additional short spring that is basically used to prevent the spring becoming unseated. THIS IS IMPORTANT, and I'll return to it.
With the coil-over design that has both the adjust ment for the coil AND an adjuster that allows the main body to be moved up and down in relationship to the bottom mounting eye. or strut body, it would seem to solve all these problems - and it does to some extent. The ride height can easily be altered without messing around with the spring seats, or the spring rates and/or lengths, but it isn't perfect. While the need may be removed for helper springs or pre-loading, because the bottom collar can be adjusted on full extension to 'just' take up the free length, there may still be insufficient adjustment in the body thread, and it may run out of compressive travel if the spring is too short and/or soft - on the other hand there's a much smoother transition to the unloaded state.
OK, the important bit - spring length. this seems to be largely overlooked but it can have some quite serious affects on the suspension characteristics. If the spring is too short, especially if it's soft, it can result in very short suspension travel from free length to coil bind, excessive preload - or rather a very high lower perch as André found - long clearance/anti-rattle/anti-displacement springs which may mean poor suspension control in droop, etc. If the spring free length is too long for the damper travel, there will be a sudden change in effective spring rate as the damper tops out, and there may be problems if it needs to be lowered further.
With the correct spring rate and length, and pre-load or helper springs,you should be able to get the best balance of travel and ride height, within the constraints of the rest of the suspension. Note, you may even find you benefit more from the main spring being a little softer, with the 'helper' actually being of a higher rate.
Forgot, many coil-over manufacturers and suppliers will have different top spring collars, with different distances between the fixed collar to the mount - if available, these can help with positioning the spring relative to the damper top mount, if coil-bind or topping out is a problem with the springs required for the travel and rate for the application.
Hi Gord, I think you've possibly missed the point of the post and gone a bit too far into the details. What was mentioned in the course wasn't really about varying spring lengths, it was more about setting the correct height of the vehicle for a given spring length (no matter how long it is) and how to set that height in the correct manner. Yes if you stick with off the shelf springs you may not end up with what you class as the desired height for the car so may need to look at alternative spring options, but that really is another subject and is way more technical than what was discussed.
Off the shelf springs come with a variation in height suggested by the manufacturer say 20-50mm lower than OEM ride height - this is what the subject touched on, how to set those heights and the correct way to do it.
If you want to lower/raise the vehicle outside the suggested manufacture variation, then yes, you'll need to look at different spring rates, lengths etc.