iwannarace

What would the difference in ride height be?

Example, if I put 500lb 8" springs on my teg vs. 500lb 9" springs on the teg, would the car with 8" springs actually be 1" lower?

NVturbo

YES

B serious

iTrader: (1)

No.

The car does not have a 1:1 motion ratio.

Are these on threaded coilovers? If so...the ride height is determined by where you turn the perches to. Spring length is not relevant unless its TOO tall or TOO short to be able to adjust the perch satisfactorily.

Tyson

no difference in ride height because why wouldnt you change the perch height??? perch would be 1" higher/lower.

B serious

iTrader: (1)

This riddle is bullshit.

iwannarace

Lol, noo! This is a relevant, real-life question. For the sake of this example the spring perch is a constant/in the same position.

boxedfox

Assuming a motion ratio of around 0.7 for the front suspension of a third gen Integra, replacing a linear rate spring with a 9" free length with another 8" spring of the exact make, model, and spring rate would lower the car a little over 1.4".

That said, that is an odd question. Just out of curiosity, what are you trying to accomplish?

I ask because I vaguely remember asking myself the same weird question while trying to figure out what length springs I needed to order the last time I changed the spring rates on my coilovers.

iwannarace

Short story, just replaced 9", 450lb springs with 8", 550lb springs and trying to compensate for the shorter spring with perch adjustment.

I tripped my own brain up by wondering if under 450lbs of weight the spring will move 1"... But if thats the case and if spring rates and pearch height are constant, the diff in height between 8" and 9" springs should be 1", right?

B serious

iTrader: (1)

No.

The car does not have a 1:1 motion ratio on either axle.

You're going down 1" in spring length, but up 100LB in rate. Your new spring is 22% stiffer than your old. And you wanna keep your same ride height.

1" ÷ 1.22 is 0.82.

Turn the perch upward like 0.82". That should do 'er.

iwannarace

Haha, well it was worth a shot. Yolo and guess it is!

B serious

iTrader: (1)

I edited. Using some inferred mathematics.

boxedfox

Aah, that makes sense. I'm assuming that you meant that you were going to a 8", 450 lb-f/in spring (rather than a 550lb-f/in spring). If that's the case, yes you can just raise the perches one inch from where they were and you'll be back at the same ride height that you were before. You'll lose a bit of spring travel but I'm assuming you don't have enough shock travel to block an 8" suspension spring in a double A-arm Honda, so it should be fine.

If you did actually mean that you were going to a stiffer 550lb-f/in spring though, that doesn't apply. In theory you could calculate the weight of the corner based on known corner weights and compute how far you need to adjust the perches. But in practicality, it's not worth it. Measure your current ride height from the rockers to the ground, install the new springs and play with the perches until you get the ride height you want.

I guess what I'm trying to say is that as long as your spring has enough free length so that it won't block out before the bump stops hit, the location of the spring perch on the damper body isn't terribly relevant. Go by target ride height from the rockers to the ground, or (if you have access to scales) whatever it takes to get to a 50% cross weight.

More questions out of curiosity - What compelled you to make the change to a shorter spring?

boxedfox

FYI I'm thoroughly enjoying this. It's like one of those inane brain teasers that you can't stop thinking about even though the answer seems obvious.

B serious

iTrader: (1)

Nevermind. That does not work out unless sprung weight is 450LB.

You need sprung weight and motion ratio.

It will deflect 22% less. But deflection is dependent on sprung weight and motion ratio.

You really just need to measure spring deflection at static height.

For example, if the car compresses a 500 LB spring 2" from its free length...then the sprung weight x motion ratio is 1000LB....and you could base all your perch heights per spring rate off of that.

YOLO and guess, bruv

iwannarace

wait, isn't that a 1:1 ratio? Or, are we just simplifying for the sake of yoloing it?

B serious

iTrader: (1)

No. Your motion ratio is whatever it is. That won't change.

You're changing spring length by 1" and rate by 1.22X.

But without knowing how much weight the spring is supporting, you don't have anything to divide by 1.22 to get final deflection.

Feel?

Nah?

Fuggedaboudit

boxedfox

Yes, and to add to the fun the sprung weight on the corner changes pretty drastically with the height. You can move 25 lbs of corner weight around with a single turn of a front spring perch. But it's nonlinear - after a certain point the changes get smaller until it basically stops.

Imagine trying to sort that out in your head. It'd probably cause an aneurism.

iwannarace

It was an accident. The back had 8" springs so i assumed the front did too. It didn't. I'm too impatient and cheap to wait a week and order 9" springs so throwing the 8" springs on.

The extended top hat's should help with the lost shock travel. And it looks like the shock body has an option to mount at a lower point to help with travel too.

iwannarace

This is actually all starting to make sense. It tickles a little...

B serious

iTrader: (1)

I'm not following.

This is all actually very easy once you have spring deflection. I've done it a thousand times with 1000 successes.

Until you preload the spring PAST the corner sprung weight...everything is linear.

Imagine it thusly:

If he was replacing his 450LB 9" spring with a 450LB 8" spring, he would simply move the perch up 1" to keep ride height constant.

But he now has 22% less deflection (550LB spring). Its 8" long.

So if you move the perch up 1", the car will sit higher. The spring will deflect 22% less.

I'm not factoring motion ratio because its a constant. So it affects things....but its irrelvant in this case because its a constant.

If he knew how much the spring deflected...he'd know what to divide by 1.22.

Oldest trick in the book. Or...2nd oldest. IDK..im not very old.

B serious

iTrader: (1)

Your control arm is going to hit your shock tower if this is being done on the front axle.

iwannarace

I dont think so. The car won't be that low.

boxedfox

Haha. You know, that makes perfect sense. I did the same exact thing about 10 years ago. Ordered the wrong length springs and couldn't return them because they were custom wound (no one makes the weird 70mm diameter springs I use in the rates I need). At the time I didn't have access to scales so I literally sat there staring at the car trying to figure out how to get the ride height back to where it was when I last corner weighted it.

At least yours are only an inch shorter. Mine were 2" shorter in the rear and they would just fall off the perches at full droop. Ended up spending even more money on a set of stupidly expensive Swift helper springs just to keep them from clattering around. If you look at it now it looks like I built a badass custom coilover setup. In reality it's just a giant pile of band-aids that work well enough and I'm too cheap to fix it.

iwannarace

yep story of my car-life. One of these days I'll pay for a corner-balance. Until then I'll just whoride my biased suspension. Probably change it again in 6 months anyway.

boxedfox

I'll tell you what though, it's worth it if you ever drive your car on a racetrack. When I scaled my car for the first time it took something like 3 hours at my friend's shop to get the cross weights to anything close to 50%. But when I put it on the track it felt like a totally different car. All of the light pulling under hard braking and subtle mid-corner behaviors that I attributed to bushing deflection and alignment went away as soon as we got the corner weights right. I couldn't believe it. All we did was make ride height adjustments to all four corners of the car, sometimes in increments as small as one turn at a time.

The only downside is that it all gets thrown out of whack if you adjust your ride height drastically and the labor can be a bit expensive. Being a good friend to someone who owns a set of scales helps. Even if you don't have that luxury, still worth doing once just so you can feel what the car is supposed to be like.