Free Height Of Springs (Mm) Needed To Suit Bilstein Sleeve Height Adjustable Coilovers?

[THENIG]

I've been sifting through the suspensions forums for some time now but still haven't found the information I'm after.

Car in question.

4door R32 with 25DET engine & box (2WD)

Front has 34GTT 310mm discs & calipers (heavier than standard)

Rear has 32 GTR alloy hubs/uprights. (lighter than standard)

17x9" 33GTR wheels & tyres

Kerb weight is around 1450kg from memory.

I haven't taken it to a weigh bridge yet or determined what the sprung/unsprung mass is at each wheel but I will if I need to.

I've Bought a set of Bilstein shocks for a 32 GTR to match the GTR hubs in the rear.

I understand the fronts are shorter than Gtst 2WD, how much shorter I don't know.

Shocks are getting re valved by a Bilstein specialist here in melbourne who is going to fit some height adjustable Bilstein sleeves to each shock to make it easier for spring selection without getting custom springs made and getting it wrong. Also should help with 'dialing out' the height variation of the front shocks GTR into Gtst 2WD.

Things I have nailed down:

I've settled on 500lb. springs in the front @ 355mm ride height front (hub centre to guard)

350lb. rear @ 345mm ride height rear (hub centre to guard)

Inner coil spring dia. is 65mm.

Things I need to nail down:

Need to pick a free height of spring from a catalogue like one in the link below from king springs:

kingspring prosport catalogue

Can anyone shed some light or give me some advice on what the free height of the springs should be to get close to what I'm after or is more information needed?

Would prefer to get it right the first time but im expecting to have to change the springs either front or rear once before I get it right.

I see people using a 8" or 10" front spring but not sure on if they are using the circlip to adjust height.

Cheers

Rob

[djr81]

On the assumption you have an aftermarket top and are not recycling the old Nissan ones.

Front 8" should be fine in the front.

Rear 10" should also be ok.

That is what I am using on my R32 R but as you can see the spring rates are lower than yours. Typically you use a shorter spring for a higher rate.

If you are worried about it get the shop to machine an extra groove into the shock body below the two you have.

Do you happen to have dyno graphs for the shocks? Be very interested to see these if they are available.

[THENIG]

On the assumption you have an aftermarket top and are not recycling the old Nissan ones.

I will have to check if the strut tops are going to be changed in the process, I haven't specifically asked for them to be replaced.

Any real benefit?

Front 8" should be fine in the front.

Rear 10" should also be ok.

Do you remember the spring rates you used at this length? Even if they are in kg

The next size down from 8" (203mm) is 180mm. I'm not sure if the higher spring rate will compensate the 20mm free length.

That is what I am using on my R32 R but as you can see the spring rates are lower than yours. Typically you use a shorter spring for a higher rate.

If you are worried about it get the shop to machine an extra groove into the shock body below the two you have.

Do you think I will have to run helper springs to keep them captive with that high a spring rate?

Do you happen to have dyno graphs for the shocks? Be very interested to see these if they are available.

I will get hard copies and post up a scan of the cards when I get it all sorted.

Cheers

Rob

[djr81]

I will have to check if the strut tops are going to be changed in the process, I haven't specifically asked for them to be replaced.

Any real benefit?

Yes. Definately so. The available travel without them is hopeless with 65mm springs. There is a whole thread on this somewhere. See photo showing the difference for the two tops. Obviously the bottom of the shock will be at the same point. So the remaining travel is shorter.

Do you remember the spring rates you used at this length? Even if they are in kg

The next size down from 8" (203mm) is 180mm. I'm not sure if the higher spring rate will compensate the 20mm free length.

My rates are variously 5, 5.5kg/mm front & 4, 4.5 and 5 rear.

Work out your unsprung weight per corner. Divide it by the spring rate. Then add this number to the fully compressed spring height. The difference between the result and the unloaded spring length is how much spring travel you have available. It will be a small number of the order of 50mm for the front.

Note that shock travel and spring travel are two different things.

Do you think I will have to run helper springs to keep them captive with that high a spring rate?

No. Maybe at the front but I doubt it. Even if you do it is no big deal. Bit of a case of suck it and see.

I will get hard copies and post up a scan of the cards when I get it all sorted.

Cheers

Edited February 7, 2012 by djr81

[Mr. Untouchable]

I would recomend getting the aftermarket tops as drj81 mentioned, mine atm is sitting in the garage with the nissan tops, theres stuff all travel, put it this way i didnt even bother testing it, i have had some bushes made up to suit the 10mm bilstein shafts and the ISC tops (15mm) I think dj mentioned this in another thread.

cheers

[THENIG]

Thanks for the advice guys, I can see what you mean after seeing the two side by side.

I found your previous thread on this topic here.

Lots of useful info on this.

I will email ISC for a quote on a set of front and rear non pillowball strut tops for 65mm ID springs.

Im guessing you guys have already done your research and found ISC to be the easiest/cheapest place to get them?

I can get some bushes made up at work to the specs you have given on in the other thread.

Where abouts did you guys buy your Eibach springs from?

Anyone know what the difference is in length of the front shock absorbers GTR vs GTst?

[djr81]

I will email ISC for a quote on a set of front and rear non pillowball strut tops for 65mm ID springs.

Im guessing you guys have already done your research and found ISC to be the easiest/cheapest place to get them?

I couldnt find anyone else selling them without spherical bearings to be honest.

I can get some bushes made up at work to the specs you have given on in the other thread.

You may also want to replace the washer ISC provide - the one that fits under the bottom conical rubber. The Nissan item wont fit inside a 65mm spring. I got some plate & had it drilled 10mm on the ID & cut 60mm OD. Then plated for extra bling. Gives the shock bump rubber something solid to smack against.

Where abouts did you guys buy your Eibach springs from?

Anywhere - you can get them anywhere.

Anyone know what the difference is in length of the front shock absorbers GTR vs GTst?

Fully extended my GTR ones measured 517mm top to bottom.

[THENIG]

Appreciate the advice regarding washer that comes with ISC strut tops, placed order yesterday, 10 day lead time on fronts though, will give me time to get springs sorted.

Thanks again for all your advice guys.

[djr81]

The last thing that hasnt been mentioned is the bump stops.

You need to work out how long they need to be and obviously they can be different from stock.

The way to do it is to get the car at the ride height you need. Work out how much spring & shock travel you have left. Point being that lowering the car reduces your shock travel but not your spring travel - hence the bump stop length can/should change.

You need the shock to hit the bump stop before the spring runs out of travel, but not too far before otherwise your car turns in to a pogo stick. Unfortunately it requires fitting, measuring then cutting and refitting. There is a blog/blurb (Not on SAU - out there on the inerweb) somewhere on a bloke going through the process for some teins. Be worth finding.

Anyway if you can post up how you get on, did you end up needing helper springs, how much spare length etc you had on the coils & shocks, shock dyno sheets, or anything general to help people it would be good.

Attached photo of chromed bushes and plates.

[KiwiRS4T]

Your spring rates at 500lb seem off the planet.

My Stagea, which would be at least 200kg heavier than your car has Bilsteins with Tein S Tech springs Front 3.1 (172lb) Rear 3.8 (213lb)

I would guess your car will hardly touch the ground with springs as hard as you are proposing.

[djr81]

Installed some new springs on the weekend.

See photos for sleeve info on the rear shocks. Pretty self explanatory really - the stock Bilstein with the two grooves is next to the sleeved version. Obviously the sleeve sits alot further down the shock than the two grooves would normally allow.

Spring rate is 5kg/mm and they are just trapped. The underside of the spring collars is 35mm from the bottom of the thread. So if you want to run a higher rate spring or a lower ride height the it wouldnt hurt to run a lower threaded section. The extra clearance makes it easier to install the shocker as it takes a bit of fiddling/levering to get it in place.

For what it was worth there is 50mm of clearance at the front between the underside of the spring seats and the bottom of the thread - and that is with the thread mounted on the top of the two grooves. Bottom line is you will need a groove for a rear 10" spring but not at the front for a 8".

Edited February 13, 2012 by djr81

[THENIG]

Installed some new springs on the weekend.

See photos for sleeve info on the rear shocks. Pretty self explanatory really - the stock Bilstein with the two grooves is next to the sleeved version. Obviously the sleeve sits alot further down the shock than the two grooves would normally allow.

Spring rate is 5kg/mm and they are just trapped. The underside of the spring collars is 35mm from the bottom of the thread. So if you want to run a higher rate spring or a lower ride height the it wouldnt hurt to run a lower threaded section. The extra clearance makes it easier to install the shocker as it takes a bit of fiddling/levering to get it in place.

For what it was worth there is 50mm of clearance at the front between the underside of the spring seats and the bottom of the thread - and that is with the thread mounted on the top of the two grooves. Bottom line is you will need a groove for a rear 10" spring but not at the front for a 8".

I would recomend getting the aftermarket tops as drj81 mentioned, mine atm is sitting in the garage with the nissan tops, theres stuff all travel, put it this way i didnt even bother testing it, i have had some bushes made up to suit the 10mm bilstein shafts and the ISC tops (15mm) I think dj mentioned this in another thread.

cheers

OK, so the shocks have been in the car for about 5 weeks, completely transformed the car on the road, I wish I got around to doing it two years ago.

I haven't had time since they have been fitted to round up this thread incase anyone was wondering what had happened.

I've attached some quick drawings I did months ago and just got around to refreshing them with the final configuration. They aren't perfect, just something I whipped up in an afternoon to take to the guy who was rebuilding them for me. Without seeing the car with them dummy fitted he needed to know exactly where to machine groove for the rears & how much length the strut needed to be sticking out etc. It was too easy to guess wrong so I put it down on 'paper'.

Looking at them again after a few months I've noticed a few things that probably aren't right but they're on the car now and too late to check.

R32 GTR BILSTEIN INTO GTST.pdf

FRONT SHOCK ASSEMBLY (AFTER).pdf

REAR SHOCK ASSEMBLY(AFTER).pdf

I ended up assembling the spacers, washers & sleeves in a different order to what has been suggested previously hence why the sleeves I machined ended up being a different length. I'm not sure whether it is correct or not but it seems to be working fine on the car.

Below is the dyno chart of the shocks. I have no Idea what it all means but its there to look at if it means anything to anyone else.

bilstein shock dyno.pdf