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Discussion and questions related to the course Motorsport Wheel Alignment Fundamentals
Apologies in advance as this will be a bit of a wordy/length post.
There are now several posts on the procedure about base ride height adjustment on the forum now, and I personally feel that it was only briefly covered in the course (for something so different to how everyone is instructed and a bit difficult to wrap your head around). Anyway, I'll get onto the subject of my post.
Went to start the height adjustment, coilovers off the car and springs removed. Cycled the suspension to full bump, but the tyre contacted the chassis 1" before the bump stop had even started to engage. So needed adjusting. At this point I had 370mm gap between wheel centre and arch at full droop.
So began to wind the damper out of the lower mount until the bump stop was fully engaged, and before my tyre came into contact with anything. At this point measurements were:
•Max droop - 420mm / •Max bump - 280mm
Installed the spring (knowing I would need the spring perch to be lowered in order to lower my ride height). I have had to wind both collars down to their max on the damper threads, so they're directly next to the lower mount locking collar.
I'm literally just about where I need to be with my static ride height which is 310mm, but I physically can not go any lower.
Also, this only leaves me with 30mm of bump travel and 110mm of rebound....obviously that is glaringly wrong. So my hope is that I've cocked up somehow that's obvious (to you lot anyway!). As I'm a bit confused with it all now. Haha
Now disclaimer, the car is on 4 axle stands currently and I am doing 1 corner (as none of the others have hubs on currently). So I'm replicating the car being at static ride height by jacking the lower arm up until the car starts to lift off of the axle stand. Is this appropriate to replicate the cars ride height?
I've attached some pictures trying to show what I've typed out.
If you've made it this far, thanks for reading. I hope someone can direct me in my mistake
The pictures didn't attach for some reason, maybe try and upload them to imgur or something and link them instead?
I see 2 possible problems initially. Your springs can change ride height quite easily, you can get the same spring rate, in a longer or shorter version to change the ride height by that amount. Ex, 200 in/lb 8 inches long, and switch to 200 in/lb at 6 inches long, and be 2 inches lower. Don't change this just yet. The second is with how you're simulating the static weight on the wheel.
You have the car on 4 jackstands. In your case, the rear jackstands are a fulcrum, and the car a big lever. If you set the stands for the rear, at your center of gravity, you could tip raise the front of the car with a finger. If you apply force at the lower control arm, it goes to to the spring, and the spring pushes on the body. So regardless of your spring rate, you'd still be able to lift the car with a finger. You're pushing against an unknown leverage/weight. If most/all of your weight is between the axles, and your stand on the rear axle, you're lifting the majority of the cars weight on 1 corner. https://i.imgur.com/cMGW5vY.jpg
To the same effect, the weight on the front is split between 2 wheels, as you're only lifting and testing one of them, it's seeing twice the weight to be expected even if it doesn't quite lift off the stand due to chassis flex.
If you can reupload the pictures, and maybe give us some more details on the car I might be able to ballpark the static compression for you if you're unable to put the hubs on, However reattaching them and letting the car rest on its own weight is the most accurate.
Thanks for the reply @finalreqy.
Actually now you explain that, makes perfect sense about the rear axle stands acting as a fulcrum. I was questioning myself whilst doing it. (Having 30mm of bump seemed majorly wrong)
I've put all the pictures and a video in a Google Drive folder which I'll link below. I've named the files to reflect exactly what they're showing.
As you say, best way will be to wait until all the hubs are back on, get the car back on the floor and start again.
Couple details on the car, Integra DC2 (double wishbone). Recent installation of front and rear roll centre correction parts.
So with these parts installed the recommended ride height is between 295-320mm (measured from the wheel centre to arch). Surely if my full bump is 280mm I'm only going to have 30mm bump travel at my current height of 310mm?
Confusing myself with this massively haha
Ok so some quick google searches gives me
Weight: 2500 lbs
Front Weight: (.62*2500) 1550
Front Corner Weight: (1550/2) 775
You have what appear to be 14kg springs from your 62.200.014 picture, that look to be near vertical, but to error on the safer side, I'm going to use 80 degrees from the LCA virtual, and mount 1/3rd of the way up the control arm.
From this we can see that for 25mm of wheel travel, your damper only compresses 17. ~.68:1. So for your spring rate of... 750 in/lbs, we can expect to see.
750(spring rate)*.68(motion ratio)=510 in/lb. This is your wheel rate. When we put 775/510(front corner/wheel rate) we would expect 1.51 inches (38mm) of static compression.
It's worth noting that I had to make alot of assumptions for this, your car almost certainty isn't 50/50 left right, there's the weight of the driver and passengers to consider, even fuel tank. If the spring is just barely captive at 420mm, I would expect your ride height to be around 370-390ish depending on which way my calculations are off.
Going lower will almost always limit travel. The damper shaft can only go down so far before it bottoms, if there's not enough room, nothing can be done without getting shorter coilovers, you're limited to 30mm if you're set on 310mm as ride height. However... That spring is monstrously stiff relative to the car, like, approaching f1 car territory. 30mm of travel is going to take alot of force to compress, 30 might be fine. Shorter bumpstops exist if needed, but they're there to prevent damage. Also, bumpstops still compress a small amount, so make sure to allow a small amount of room beyond when you compress the bumpstop to prevent damage.
Hopefully thats enough to let you keep going until you get the hubs on.
Okay, not going to lie,that took me a few attempts to understand all of the maths there. Ha
The company who manufactures the roll centre parts, along with their explanation for their recommendations can be found here (scroll down and you'll see the height/ spring recommendations):
As for the the calculations you made, seems that you were really close. I was sent a table a while ago by the company with the motion ration, and they've calculated it at 0.62 for the front and .55 rear.
The table is in the drive link below, (will have to zoom in or rotate the picture to read it)
420mm is my maximum droop. So you're saying that with the the spring just being held captive on the spring perch (bearing in mind its a 200mm spring) my ride height should be roughly 370mm? The car would have a massive arch gap at that height (about 4 inches at best guess)
So the guideline of 2/3 of damper travel being used for bump travel and 1/3 for droop isn't really achievable with my damper and ride height needs?
I only did the front, and I'd trust their .62 over my .68 guess(I also only did 1 inch of travel, they probably did the whole range). But it should be within the 30% margin of error I had. So somewhere +/- 10mm from 38mm compression is what I expect your spring to compress under the cars weight.
In this picture there's some distance for the spring to travel before its compressing at all. So, if it's still set to this, it would drop the distance between the spring and perch, and then ~38mm. If you raise it so they touch at full droop, just the 38mm compression.
The manufacturers information is far better than I expect off most aftermarket stuff, so you should be fine running with only 30mm of travel. Your springs are about 3x as stiff as the car was originally. (If they're quoting the oem ride frequency, they're wildly off if its the new one)
So, full droop at 420mm - 50mm compression(38mm really but staying safe) puts you at 370. If that gap is 60mm it should put you around at the 310mm you're targeting. 1/3rd 2/3rd will be impossible with this setup, but arguably irrelevant. You don't need more than 30mm of compression travel if you cant use it.
I'm guessing this car has a rear sway bar and none in front?
Thanks for taking the time out to help with this by the way. Much appreciated.
Apologies for coming across as a bit of a moron, but you lost me a little with the numbers in the last post. Can you clarify a couple things, just so I'm 100% sure I'm understanding correctly.
•"So, if it's still set to this, it would drop the distance between the spring and perch, and then ~38mm. If you raise it so they touch at full droop, just the 38mm compression"
Lost me a little that one, are you saying to wind the spring perch up 38mm so the spring is closer to the top mount at full droop? Surely this is just going to raise my ride height again?
•"So, full droop at 420mm - 50mm compression(38mm really but staying safe) puts you at 370. If that gap is 60mm it should put you around at the 310mm you're targeting"
Again, little confused as to what the numbers are quoting here. The 50mm compression, is that how much you expect the damper to compress with the cars weight on it on the ground (i.e. when it's at it's ride height)?
Also, what gap is 60mm? Between the top of the spring and top mount? Not sure what you mean here either.
If I were to swap the spring to a shorter one, say 180mm rather than 200mm, what would you say would be the affect? Would I be able to gain some extra bump travel whilst also achieving my target ride height?
Again, thanks for taking the time to help me out. Beginning to cause me a headache this is.
So doing anything suspension based on pictures, over the internet, comes with a healthy margin of error involved, ex I guessed a .68 motion ratio, its actually .62. So while I expect your spring to compress 38mm under the cars own weight, I used 50mm because it's less likely to cause any damage if I'm wrong, you can just lower the car an additional 12mm if I'm correct for 38.
"Lost me a little that one, are you saying to wind the spring perch up 38mm so the spring is closer to the top mount at full droop? Surely this is just going to raise my ride height again?"
You're correct, that would raise your ride height. The spring only takes the weight of the car when it's in contact with both upper and lower perches. If you wind the spring up so it's always in contact with the upper perch, we should see 420mm(max droop)-38mm(static compression) of the car on its own weight. The static compression of the spring is simply the weight of the vehicle, on a spring.
The spring will only compress while its in contact with both perches. If the spring isn't in contact with the upper perch, the car will drop until it is in contact with the spring, and then 38mm.
The 60mm is just a guess at https://i.imgur.com/oi2lUuX.jpg distance. Between the upper perch and top of the spring. I guessed 60mm, simply because it would put you at approximately the correct ride height. I expect the damper to compress 98(60+38) and the spring to compress 38mm once it's in contact with the perch.
If you left everything the same, from being at 310mm ride height, and went from a 200mm to 180 spring, you'd drop to a 290mm ride height and have 10mm of bump available. However, you'd be able to raise the lower perch up 20mm and have the same ride height, but no longer be bottomed out on adjustment should you wish to go lower(or for corner balancing). This isn't really worth considering unless you run into issues with with lack of adjustment.
I've had plenty of headaches learning this stuff. Just set it max low, measure the gap between the upper perch and the top of the spring. Subtract it, and 38mm from your full droop(420) and that should be your ride height with the weight of the car on the suspension.
Edit: I messed up. Damper movement is subject to the same motion ratio as the spring(for coilovers). If that gap is 62mm we'd expect the wheel to move 100mm, and then the 38mm compressing the spring. (I cheated the numbers for easy math on .62:1 motion ratio)
Okay think I'm following you now. Really need to get the hubs back on pronto and get some measuring done!
Hypothetically speaking, using your educated measurements, we're saying that in order to achieve my ride height of 310mm I need to have both my spring perch and locking collar would down fully. Like in the following picture: https://drive.google.com/file/d/1CDF2Cprn12hv3pzlPbYu5zUNDiCAGc1h/view?usp=drivesdk
And the gap between the top of the spring and upper spring perch is 62mm, like in the following picture:https://drive.google.com/file/d/1C7vOP2xQqLP8272GV6PZ9Y8_cRyGXEGm/view?usp=drivesdk
I'm going to need a helper spring at least 62mm in length in order to take up that space at full droop?
Judging by that scenario, would I be right in saying that the 180mm springs will be beneficial in order to get that fine tuning of ride if I do need to go lower than 310mm ride height? As I'm currently missing that ability with the spring perch at maximum low. Whilst also giving me an extra 10mm of bump travel?
Sounds like you're starting to piece it together.
Yes, you'd need a helper spring longer than that gap to take up the freeplay in the suspension(if it matters). You have the weight of the car keeping that spring in place. If you can lift the inside wheel, it might become free(lifting a wheel is often a roll bar issue, and might still keep it captive). But having a spring off come off its perch is an issue if it happens. Under normal driving you should be fine.
I miss calculated and forgot to calculate motion ratio on the damper(sorry). If that gap is 62mm at full droop, the wheel will move 100mm before the spring is in contact, then the 38mm from the cars weight on the spring, making your ride height 288mm. If that gap is.... 31mm, the wheel will compress 50mm, then an additional 38mm from the weight of the car, put your ride height at 322mm. You can adjust the gap by moving the spring up or down and measuring it at full droop.
Being as low as possible on your adjustment isn't inherently a bad thing. If you corner balance the car(or take it in for someone to do it) You might end up with 312 instead of 310 ride height because they needed that adjustability. Simply being balanced will make a bigger difference than 2mm of ride height will. This isn't an f1 car where 2mm is a huge change.
Changing to 180mm springs, of the same rate, and corrected to the same ride height, wouldn't gain you any bump travel. The bumpstop, ride height, and damper limitations decide that(I'm sure there's an exception to that statement out there somewhere). If you want to fine tune the car, beyond what you're already doing, small changes to ride height is the wrong place to look. You can change springs to affect roll stiffness, and in turn over/under/neutral steer characteristics and see much bigger changes than allowing yourself an extra bit of adjustment lower.
I'll be on the safe side and order some helper springs and perch adapters if I do need them with my final settings.
Final question (for the time being), I can get the helpers in 100mm free length. The perch adapter measures in at 5mm and the fully compressed spring comes in at 8mm.
With that 13mm total thickness, am I correct in saying that will raise my ride height again by 13mm? (310mm to 323mm)
So will I need to lower my bottom spring perch another 13mm again when using the helpers? Or will it not affect my height again?
If 310mm is the lowest possible ride height with the perch adjustment, those helpers will raise your ride height by 13mm, same as sticking a 13mm spacer on top of your perch. To be technically accurate it will more like 13.5mm, they're still springs and take force to compress. So you'd have to lower it to get back to 310. This isn't an issue if you're not at the limit of your adjustment.
So I've finally got the car back on the ground and have been setting up the base height a corner at a time.
You were right Robbie, up on 4 axle stands I wasn't seeing the cars true bump compression, can cycle the suspension properly with the car on the ground now.
So the rears are pretty much perfect, bump stop engages before the tyre contacts the arch and at my required ride height the springs are held captive at full droop.
Fronts are (as suspected) a little worse. I have a 2" gap between the top of the spring and the upper spring perch at full droop, so will be buying some helper springs.
Question I have is there a rule of thumb, or specific calculation into the spring rate I should be looking at for the helper springs?
The ones I am looking at come in a variety of rates ranging from as low as 4 lbs/in all the way up to 280 lbs/in.
Also second query, would utilising bumpstop spacers/packers be advisable? I've wound my damper so far out of the lower mount to ensure the bumpstop engages before the tyre contacts the chassis, that the I now have the bare minimum amount of threads I'm comfortable having inside the lower mount now -1".
If I use a bumpstop spacer could I essentially then wind my damper back into the lower mount the equal amount of distance as the spacers? Say 10-20mm, as the bumpstop will now engage earlier.
People are gunna start to hate me if every post requires use of a calculator.
The spring rate for stacked springs is 1/k1 + 1/k2 = Keq, where Keq is the equivalent spring rate of the whole thing, k1 is the first spring, and k2 is the 2nd. So, for 2 100 lb/in springs, 1/100 = .01 | 0.01+0.01=0.02 | 1/0.02 = 50. While cool, and useful somewhere where you expect to spend part of the race on the helper spring(rally cars landing over a jump for example) you can use this to have different stiffnesses based on how far into droop you are. This is only applicable until the helper spring compresses all the way becoming effectively infinitely stiff. So you're just at the main springs spring rate.
For you, you already have the correct springs for your car, go for a low rate helper spring so it's fully compressed anytime the cars under its own weight. Leave the larger spring rates to the rock crawlers or rally cars. (4 lb/in springs are also way cheaper than the other options).
Having the bumpstop be the first point of contact is always benefical, if you need spacers/packers, or a longer bumpstop to do that, I would highly suggest it.
I think you're correct regarding the bumpstop, I'm just rephrasing in case I misinterpreted what you meant. Threading the damper in will lower the damper, and spring perches with it(you can correct for that). If you lower it 20mm, you'll need a 20mm longer bumpstop to engage at the same point(if ride height is the same). You'll also technically have 20mm more compression travel, it's just the bumpstop will prevent it. If you want earlier engagement of the bumpstop, you'll need a longer one than what you're threading the damper in by.
To clarify if you're a little confuse by stacking springs.
In the example given, each spring would compress 1 inch for a force (load) of 100 lbs. However, if you use two springs and compress the pair by the same 1 inch, each is only compressed by a half inch and the force required (load) is only 50 llbs.
Conversely, for a load of 100lbs, each will compress by 1 inch giving a total of 2 inches of compression.
So, it should be clear the new spring rate is 50 lbf/inch.
I appreciate the maths, will be handy for in the future if I need to alter the setup.
I didn't even realise that the 4lb springs were quite a bit cheaper to be honest, I'll probably just go with those then seeing as I imagine it will only be in extension when I jack the car up.
My current bumpstop measures in at 66mm long and is progressive, ramping up from 6lbf to 400lbf at full compression.
What you've said regarding the length of the bump stop Vs the amount the damper is wound into the lower mount is exactly what I had in my head.
I think I'll try and get hold of some bumpstop packers then (hard to find in the UK it seems) and try and get the coilover wound down into the lower mount whilst having the bump stop engage earlier (balancing act of getting the perfect ratio I bet).
At present with the car in the air the wheel has roughly 120mm of droop travel from its static ride height, so the front end looks more akin to an airborne rally cars suspension when at full droop. Haha