Spot on. I think many people would benefit from your posts on the matter. I get asked a lot about this so I will be directing people to your posts as reference from now on. I think there is a lot of confusion thinking there is only 2mm of actual compression on the spring when the dampers are installed on the car, which is definitely not the case when installed on normal arms with normal bushings.
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thanks bud!

I want to try 1" of clear travel. BUT won't make any changes til late October before putting the car away. I would like to touch a 1.44.xx lap at Gingerman with the car exactly as it sits lol. I'm at 1.45. Must...touch. I'm used to the car and I like it. So I don't wanna screw with it til after this next track day.

In late October, I'll try different lengths/preloads and take more pics for peoples' info.
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Awesome. You should make a dedicated thread for this once you get the chance.

 

Here are some numbers I gathered , not sure if it's helpful but there it is:

Front

Suspension travel: 3.25 inches
Midpoint of suspension travel 3.25/2 = 1.625 inches
MR = 0.7 From OP
Inverse of MR 1/0.7 = 1.4 from OP
700lbs approximate weight per corner
Weight acting on each corner at rest is 1.4 * 700 = 980 lbs
Springs are 100N/mm (~10k) = 572 lbs/in
Compression at rest = 980 lbs / 572 lb/in = 1.71 inches
Preload = 1.71 - 1.625 = 0.085 inches of preload or 2.16mm
Ohlins recommend preload 2mm
Other recommended preload 2.5mm


**** not used in this thread ****
*MR = 0.589 sakebombgarage

Suspension travel: 3.25 inches
Midpoint of suspension travel 3.25/2 = 1.625 inches
* MR = 0.589 sakebombgarage
Inverse of MR 1/0.589 = 1.697
700lbs approximate weight per corner
Weight acting on each corner at rest is 1.697 * 700 = 1,188 lbs
Springs are 100N/mm (~10k ) = 572 lbs/in
Compression at rest = 1,188 lbs / 572 lb/in = 2.077 inches
Preload = 2.077 - 1.625 = 0.452 inches of preload or 11.5 mm

Rear

Suspension travel: 2.125 inches
Midpoint of suspension travel 2.125/2 = 1.0625 inches
MR = 0.689 from OP
Inverse of MR 1/0.689 = 1.45 from OP
700 lbs approximate weight per corner
Weight acting on each corner at rest 1.45*700 = 1,015 lbs
Spring rate is 80 N/mm (~8k ) = 458lb/in
Compression of spring at rest 1,015 lbs / 458 lbs/in = 2.216 inches, hence the bump stop riding discussion since 2.216 is greater than the suspension travel of 2.125
Preload = 2.216 - 1.0625 = 1.15 inches of preload or 29.21mm
Ohlins recommended preload 2mm to get 0.55 suspension travel
Other recommended preload 17mm to get 1" suspension travel

*****not used in this thread***
*MR = 0.579 sakebombgarage

Suspension travel: 2.125 inches
Midpoint of suspension travel 2.125/2 = 1.0625 inches
* MR = 0.579 sakebombgarage
Inverse of MR 1/0.579 = 1.73
700 lbs approximate weight per corner
Weight acting on each corner at rest 1.73*700 = 1,211
Spring rate is 80 N/mm (~8k ) = 458lb/in
Compression of spring at rest 1,211 lbs / 458 lbs/in = 2.644 inches, still riding on bump stop according to the math
Preload = 2.644 - 1.0625 = 1.58 inches of preload or 40 mm (crazy)??

 

Not interested in arguing. I've been around too long sadly. Good luck to all of you with your setup.

Do the math. Here's some hints.

8k springs compress at what rate. Convert that to inches and pounds. Take into account approximate 1.4 motion ratio and you can figure if you're riding on bump stops or not. Then figure out how much 'preload' to set to maximize compression bump travel.

Don't listen to me or anyone else online for that matter. Use the math they taught you in high school

 

LOL.

I know how MR's and WR's work.

A 450LB spring would compress 2.x"....if the car was an immovable object (or weighed 12xxLB/corner (sprung)).

But its not. It weighs like 600LB/corner (sprung). A 450 LB spring in a S2000...with a S2000 rear shock angle will compress ~1.5" til it can lift ~600LB. Then it will lift the chassis away.

Your math is bad.

I posted pics for evidence. How do you explain the 1.53" of compression that I'm actually SHOWING via pics??

Lemme explain thusly using arbitrary weights:

You're using a lever to magnify 600LB of force into ~1200LB of force.



There is a 450LB spring between your lever and the object you're lifting.

So you're putting 1200LB into the point where the spring touches the lever.

The object you're lifting weighs 800LB.

800LB of that 1200LB is used to compress the spring 1.77". (800/450 = 1.77).

Once that happens, the 800LB object you're lifting will start to lift. The spring will not compress further. Because the spring is already pushing back with 800LB.

You have 400LB of force left over. (1200 - 800 = 400). That additonal force that you created with the lever will now LIFT THE OBJECT a certain distance based on your lever motion.

Springs make shitty load transfer devices. They're always stealing from you

 

I don't believe that Serious meant offense to you, he was being blunt and was using useful information to add to the knowledge bank for people like me who don't have the slightest clue about the math involved with this process. I don't mean to jump in without useful info but i just had learned a lot in the posts yesterday and don't want to see this get derailed. I race formula Ford's i was a mechanic for a little while but by no means have the technical understanding of these specific cars yet. My friend who i grew up with that i own the car with is the brains, i just happen to be faster around the track then him so he always sets me up perfectly when i give him feedback while i'm lapping. We grew up together, know just how to speak to each other which helps our success.

I just appreciate both of your input and would love to see more of it.

 

Please explain why you can't set spring preload on the car. As long as the shock is at full extension, there should be no difference. Right? Jack up the car and let the control arms droop. Use a pry bar to confirm the shock is extended 100% and you should be good to set preload.

 

Yes. You would need to fight bushing bind and sway bar bind to make sure the shock is fully extended.

BUT...

How do you know the shock is fully extended? Did you run out of weight on the prybar? Are you sure?

Push down on a prybar. Now take measurements. Not so easy, is it?

I guess I understand doing it this way to make small adjustments because maybe it beats removing the shock.

But why would you want to do it like this for the initial measurement? What purpose does it serve?

Doing it on a bench is error proof. For the initial setting...the shock is ALREADY out of the car. Why load it in and then fight with it??

As far as making adjustments to preload after the shocks are already loaded:

I recommend that if you're not confident in your ability of keeping track of spring lengths and doing the math while you fight bushing bind and use a prybar....then just take the shock out and re-set your preload so you know its correct.

If you are confident, then re-adjust away (I mentioned this above).

 

Thanks B again for explaining that, never really thought about the bind but now that you explained it , it does make sense. Never thought so much about suspension till these past few days and it was interesting to read all this

What are your thoughts about trying to target the mid point of the shock travel while at rest like the OP was trying to do ? From the math that I was able to replicate that the OP used the front came out around 2 mm which matches the Ohlins recommindation but the rear was way off, but you mentioned 17mm will give us the 1" at rest .

Also did you cut the rear dust cover, I read on several reviewers did not ?

 

Holy awesome responses guys! Thank you for all the info!

I followed ohlins instructions for installing by the book, and plans to see what happens after a weekend at the track.

 

*WHOOPS! I said 17mm to create 1" of clear space. I meant 12mm!!


The amount of shock travel YOU want for YOUR purposes is an individual component.

With Öhlins' recs, you have 0.6" clear travel in the back. Need more because you're constantly engaging bumpstops? Add more preload.

LETS SAY you want an inch of clear travel:

Put 0.4" worth of energy into the spring. In other words...preload the spring until it can lift your corner by 0.4" additonal.

Here:

Use 2mm as your 0 point because its easy.

2mm of preload causes 1.53" of compression on my car.

447 x 1.53 = 683LB.

The car (including the COSINE factor) is pushing 683LB into the spring.

Ignore the 35LB of existing force from the 2mm of preload. Remember...we're currently using 2mm as 0.

To get your 1" of clear travel, you want the spring/shock to only compress 1.13" (1.53 - 0.4 = 1.13).

So....you need the spring to push back a certain amount more force.

447 x 1.13 = 505LB.

683-505 = 178LB.

You need the spring to have 178LB MORE preload force.

10mm = .39".

.39 x 447 = 175LB (close enough to 178).

10mm (additional) + 2mm (initial) = 12mm TOTAL.