Ed MD

8 full turns equals 1 inch, approx. 3mm/full turn. Ed

mark kibort

you are talking about the "motion ratio". its about 5:1 with our cars. 1" on the shock perch is going to be 5" of ride hight change. So, one full turn , if its 3mm on the shock perch, will be about 1/2" on ride hight. There are some spring factors that can make this more or less. if you just drop one side, you are lessing the pressure on that wheel, and lightening that side. so, the drop would be less, as the spring would be uncoiling a bit.

mk

pscottjr

I guess that I am asking about change in ride height for one of full turn of the adjustment ring. See pictures below. (These picture are from an earlier post on ride height adjustment - I am sorry I do not have the original posters name)



Are Mark and Ed are saying basically the same thing? One full turn of the adjustment ring I don't believe is 3mm on shock perch.

Mark is saying a 3mm change on the shock perch changes the ride height 1/2" and Ed is saying approximately 4 turns changes the ride height 1/2". So I guess approximately 4 turns = 3 mm change on the shock perch and 1/2" in ride height.

RyanPerrella

I can tell you that 5 turns and 6 turns didn't do much for me. I still want to drive the car and then measure again before continuing to lower it.

I will update the heights after i put a few miles on it and settle the rear.

mark kibort

What i am saying is that ignoring spring pressure, there is a 5:1 relationship. what ever that distance you move the purch up or down, the ride hight should be 5x that. however, as i mentioned, there is also a relationship of the spring pressure pushing the car up more or less depending on corner balancing.

mk

RyanPerrella

yeah Mark i wasn't debating any of that. I had also read that 1 turn is 3mm in ride height. So i needed to pull out 20-30 mm and i thought i would start low and continue to lower it until i get to the correct height.

Oddly the rear shocks have about 4-5" available to have the lower shock mount at? WHY? Is this for anyone that decided to mini tub their 928 and jack the rear end up? Why is there so much adjustment in the rear? Where the car is now (@ 200mm ride height there its about 80% down towards the bottom, just thought that was odd.

Okv

The rear also needs to settle.

Just completed mounting my new suspension, finished the ride height adjustment today.
Noticed that when jacking the rear end, adjusting down some, lowering the car again - then it sits higher than before jacking and adjusting.
Only a few meters movement back and forward I think is enough to make it settle.

mark kibort

good question. as it is now, my race car is at 110mm front and 135 rear and the rears are max all the way down the last thread. the fronts still have a lot of adjustment down. conversely, the stock stuff was maxed out in front and the front was still at 155mm, while the rear could have been dropped to the ground (to your point)

mk

jon928se

Its nowhere near 5:1

At the front it is near 2:1 ie move the perch 1mm the car moves 2mm.
At the rear is around 4:3 ie move the perch 3m the car moves 4mm.

jon928se

The thread pitch on the shocks is 1.5mm
thus 1 turn on the front shock adjuster perch by 1.5mm and moves the car by 3mm (2:1 ratio at the front)
and 1 turn on the rear adjuster moves the car 2mm (4:3 ratio at the rear)

RyanPerrella

Little update after going for a ride

Before adjusting I measured LF 164.5 RF 166.5 (FRONTS ARE GOOD!)

LR 198 RR 202 (REARS NICHT SO GUT!)

So I decided I would start slow and just adjust the left side 5 turns and the right side 6 (to try and even out the 4mm difference side to side)

Well after going 5 turns on the left and 6 on the right and driving only 3-4 miles i brought the car back in and remeasured and got.....

LR 186 RR 192

So my left side in 5 turns went down 11.5mm, right side in 6 turns went down only 10mm. WHY? Well i just assume the right side hasnt settled completely yet, which would also lead me to believe that the left side may also drop some more.

I think I will go another 4 or 5 turns on the left side and go another 4 or 5 +1 more or the right to even them out side to side.

Also when i next have the RF wheel off I will turn that adjuster 1 turn to try and get rid of the 2mm difference. But if i am going to be that picky about 2mm i should be in the drivers seat and have someone else measure it if i am going to be so exacting.

Below is a picture of all the tools needed to do ride height adjustments and measuring.

A set of dial calipers. I figure most all DIY'ers have a set of these

The C spanner wrench from 928GT.com Only $9, works great.

A telescoping magnetic pick-up tool to shot actual height (telescoping allows you to need only 1 measuring tool as opposed to many at different lengths) This tool is pretty tight so that when you extend it, it holds and doesn't drop or move. I think i got this at autozone for < $5

HAVE FUN!

jon928se

Ryan

before you go further adjusting and potentially chasing your tail trying to get it correct, check that the spring perches are in the same position relative to the shock body on both sides (count the number of threads showing) . RF and LF should be near the same and RR/LR should be near the same.

It is possible to get the ride height correct yet have most of the cars weight on just two diagonally opposite wheels - this causes "very strange" handling.

928 springs are normally matched well enough side to side that you can get the corner weights balanced enough for road driving without actually weighing the corners just matching the perch hights side to side.

RyanPerrella

Jon,

Not quite sure i understand what you mean by lining up the perches. I assume your talking about the indent in the perches which the end of the wound spring slips into. I am not quite sure i understand how your describing how these should be aligned.

Do you have a picture perhaps?

Also, I am simply trying to DROP the *** of the car. It started out around 200mm and I want to get it in the 175 range, thats the reason i am adjusting the ride height. I would then get it aligned

I think you did bring up a good point again about corner balancing. I would like to do this.

If your setting up a car do you follow these steps in this order (this would make sense to me)

1) set ride height to general specs and to get to the height you want.

2) corner balance car with driver and 1/2 tank full of fuel

3) have 4 wheel alignment

Would you corner balance (Adjust ride height) the car before or after getting an alignment?

Charley B

Ryan, where are you measurering your height at? If that is a current picture in your avatar, it sure doesn't look that high.

jon928se

Sorry my bad - Everywhere I said Perchs I really meant the adjusting Nuts. The point being that if you have equal numbers of thread showing under the Nut on both sides of the car it will be reasonably well corner balanced.

Starting from 200 you need to wind the rear adjusters down approx 18mm (=12turns) to get to 175mm (25mm lower ride height = move the nut down the shock by approx 25*3/4=18mm )

Alignment last always. Changing the ride height changes the camber at the rear and changes Toe Camber and Caster at the front - toe most dramatically.

Would I corner balance ? - I'ld start with Ride height with half a tank of fuel but no driver. This should give you reasonably well balanced corners because 928 springs are reasonably accurately manufactured and matched.

Then put the driver in and see how much effect that has on ride height (you'll need to drive it after adding the driver before rechecking)
I guess it will be very little (On my SE with Billies and Eibachs I can't reliably measure the difference - but I am all of 140lbs wet through) If it is measurable I guess there will be more difference at the rear than the front as the rear springs are softer.
You would then need to take out the difference based on the amount of movement between no driver - with driver. Say the front went down 3mm with driver you would need to adjust the front drivers side nut up by 1.5mm (=3mm change in ride height) or 1 turn. Say the rear went down 4mm you would need to move the rear drivers nut up by 3mm (=4mm change in ride height) or 2 turns. This should bring you back reasonably close to the correct heights with the driver in the car and if you then weighed the corners without the driver in the car the corner weights should have remained equal.

Stating the obvious you can't corner balance for matching weights side to side with the driver in the car because he doesn't sit in the centre of the car - His weight will be proportioned something like 9/32DF, 3/32PF, 15/32DR, 5/32PR. So with the driver in the car you would need to set the corner weights accouting for the difference - so Front Driver side (DF) would need to weigh 6/32 x driver weight more than PF and DR 10/32 more than PR.