R32 Gtr Spring Rates - Front To Rear Balance

[Phrase]

Hi all, am looking to change the springs in my R32 GTR. Currently has Koni Adjustables all round with circlips for height adjustment. King Springs Front @ 3.2kg/mm (apparently) and HKS springs rear(apparently).

Springs have sagged therefore car is riding low.

Will eventually track the car but it is foremost a daily driver.

Have looked in the factory manual and the R32GTR has a softer front spring rate than the rear.

Have been recomended Tein S.Tech Springs which also have a softer front than rear: 3.7 front, 4 rear.

Now, most of the coil over systems I have seen for the R32 GTR specify a firmer front than rear and I have seen on these forums that a 5kg/mm Front and 4kg/mm Rear seems to be a good option.

It makes sense to me to have a firmer front spring in the front because of the forward biased weight distribution.

What is the handling and comfort difference between having a: “firmer front than rear spring” vs “Softer front than rear spring”?

Thanks in advance,

Fraser.

[djr81]

That is a simple question to ask & a more difficult one to answer.

Basically, a softer spring helps generate grip at the end it is fitted. So you get a softer front spring stock than rear.

But there are a heap of other factors involved. When you bolt on sticky tyres (eg R comps) you need a stiffer front spring to hold the front end up. You don't increase the rear spring rate in parallel because to do so makes the back end skittish & gives you a car with poor traction. So you never see, for example a 6kg/mm front with a 7 kg/mm rear.

If you want a car for the road then the Tein rates will be fine. 5kg/mm & 4kg/mm works ok too.

What are the current rears rated at?

[Phrase]

I do not know what the rears are rated - I don't really want to have them removed and tested because of the cost and the time off the road.

Would I be somewhat correct in saying: softer front spring - more front grip - more understeer. softer rear spring - more rear grip - more oversteer?

or is it more about control under heavy braking?

Thanks,

Fraser.

[Mr. Keets]

I have 5/4 on my 32R..a reasonable balance for the road and the occasional trip to the track etc.

Bang for buck, suspension upgrades are excellent value...sway bars? For instance I spent $200 on some KTA117 adjustable rear uppr radius arm...it help get the power down earlier. You dont get much on a GT-R for 200 bucks that adds value

[djr81]

I do not know what the rears are rated - I don't really want to have them removed and tested because of the cost and the time off the road.

Would I be somewhat correct in saying: softer front spring - more front grip - more understeer. softer rear spring - more rear grip - more oversteer?

or is it more about control under heavy braking?

Thanks,

Fraser.

If you did say that you would have it upside down.

Softer front spring - more front grip - less understeer (Mostly).

But there are many other devices on the car to fix oversteer/understeer & to be honest I wouldn't be overly focussed on using spring rate alone in a GT-R. You should also look at sway bars & camber adjustment.

[Phrase]

At the moment I am primarilary concerned with the ride height (scrapes the muffler on some speedbumps) and ride comfort (brisbane roads arrghh). Once I get that sorted, I will look at swaybars.

I just want to make sure that a) i understand why there is a difference in the front to rear spring rate ratios and b) that the springs I do put in best allow for future 'enhancement' with swaybars etc.

At the moment I can get S.Techs or get a set of 5/4's custom made....then I need to look at hot rolled vs cold rolled....

What brand etc are your 5/4's?

Cheers.

Edited July 27, 2009 by Phrase

[bnr#@]

As a side note, the nismo r tune coilovers for the r32 were 9kg front 9.8kg rear

[djr81]

As a side note, the nismo r tune coilovers for the r32 were 9kg front 9.8kg rear

Wierd I had the S tune down as 5.5kg/mm front, 4.5kg/mm rear.

The other models are harder & yeah the rear is stiffer than the fronts. But htat is probably because their ATTESSA systems work better.

Edited July 27, 2009 by djr81

[Sydneykid]

I could easily write 20 or 30 pages on this subject, it’s not simple as you are getting deep into vehicle dynamics which is quite a complex subject. So I will keep it simple and brief;

Ride comfort is best when the balance of the effective spring rates is close to the weight balance of the car. So a 60/40 weight balance should have somewhere near a 60/40 effective spring rate balance. R32/33/34's have the same movement (1 to 1) and leverage ratios (1 to 1) front and rear, so you can directly compare the spring rates. This is not the case with many other cars, for example in a Silvia (1.2 front and 1 rear) the compariosn is not as straight forward.

The problem with the 4wd R32/33/34's is they understeer quite noticeably on corner entry and mid corner, plus when sufficient power is applied on corner exit the understeer generally decreases. One R32's the ATTESA is lower reacting so you can easily get corner exit oversteer until the torque split is more front biased. One way to mitigate the corner entry and mid corner understeer is to use a higher rear spring rate that the weight balance would indicate. The problem is you sacrifice ride comfort and make the corner exit oversteer worse, the more power it has the worse the problem.

This is where and understanding of the Japanese circumstances is necessary. Firstly they tend have superior road surfaces to us, so higher spring rates don’t cause the same ride discomfort, plus losing traction due to poor road surface is less of problem. Secondly Japanese workshop hourly rates are unbelievably high, $500 per hour is not unusual. So when you get things fitted to your car every attempt is made to minimise the labour cost. This means fitting alignment products and carrying out complex wheel alignment set ups only occurs in heavily supported race cars. Lastly swaybars, the Japanese don't have our history of engineering, manufacturing and fitting swaybars to a large range of cars. So not a lot of their cars have them and only a small/limited range are available.

Add all that together and we find that they try and do everything with one quick off the shelf, bolt on solution. Hence use higher spring rates than is ideal and have more of a rearward spring rate balance. Sure it's not technically correct, but a customer who pays $2K for a coil over kit, doesn't want to know about $3K to fit it and another $1K for a wheel alignment.

Whereas here we have a large range of swaybars available, even adjustable ones and our labour costs are not so out of proportion to the parts costs. So we can take the technically correct route, have ride comfort that suites our conditions and end up with a superior handling solution.

Cheers

Gary

[Phrase]

Thanks for the feedback and information guys. I think I will get the springs done to remedy the ride height and comfort, then look into swaybars in more detail.

Now to find me somewhere to make me some 5kg/mm and 4kg/mm springs to fit my konis.

Thanks again,

Fraser.

[Sydneykid]

Thanks for the feedback and information guys. I think I will get the springs done to remedy the ride height and comfort, then look into swaybars in more detail.

Now to find me somewhere to make me some 5kg/mm and 4kg/mm springs to fit my konis.

Thanks again,

Fraser.

Off the shelf Eibach's, $250 per pair, all you need to know are the simple spring dimensions of ID and free height then order the spring rate.

Cheers

Gary

[Mr GTR-32]

Tein monoflex coil overs are awesome for R32 7kg front and rear very comfortable and great handling would recommend them very highly, also base height adjustment. mY 2 CENTS

CHEERS,

Dave

[Phrase]

Well, in my copious surplus nanoseconds, I have done some further research and made a new decision. I want to share my thoughts to assist others going through similar situations.

Knowns:

Fulcrum Identified the front springs as sagging Kings originally with a spring rate of 3.2kg/mm (Kings KDFL-101 – free length 305mm) and rear springs as HKS of approx 6kg/mm !?

Actual ride height from centre of wheel to bottom lip of guard is: Front 320mm, Rear 335mm.

The other knowns are that the car rides quite rough, is too low and pulls to the left (despite having wheel alignments and adjustable camber and castor)

Research:

I have read that ride comfort and handling is ‘best’ when the spring rates mirror the weight distribution. In this case, I am working to 60/40 ish. – Makes sense to me.

I have read that some people use a linear rate spring on the front to maintain predictability of front geometry and use progressive rate on the rear for comfort – Makes sense to me. (The Kings set are linear front - progressive read btw)

I have read that the ‘optimum’ or ‘preferred by most’ ride height is 355Front, 345 Rear. (which is an increase of 35mm at the front and 10mm at the rear compared to my current measurements)

Did some ringing around to confirm spring rates of Lovells, Kings, Tein STech. The Kings Rear Springs (KDRL-102) are progressive 2.7kg/mm with free length of 305mm.

Looked up the factory manual to get the stock spring rates (and free length) : Front 2.4kg/mm @ 405mm free length, Rear 2.7kg/mm @ 345mm free length.

My koni Adjustables have circlip rings for the lower spring mount. Both front and rear are set on the highest position.

I couldn’t find any front and rear sets with the 60/40 proportions I wanted. Didn’t want to go softer than stock, so: Stock Rear Spring rate is 2.7kg/mm. Kings do a progressive rate 2.7kg/mm spring (KDRL-102)

So if that is the 40%, the front should be 2.7 / 4 * 6 = 4.05kg/mm which doesn’t sound outrageous until you compare it to the stock front spring rate of 2.4kg/mm…. Yes, that’s right the new one will be 69%(tee hee) stiffer(double tee hee) than stock!

Anyhoo, I am going to go with:

Front - 4 or 4.1kg/mm linear springs from Kings with free length of ???. And try to set the ride height close to 345-355 by moving the circlip as required.

Rear – 2.7kg/mm progressive (King Springs KDRL-102 free length of 305) and try to set the ride height at 345. I have a feeling that this free length will result in a lower ride height than what I have now so:

I am going to Fulcrum tomorrow so they can take some measurements of the springs loaded up so that we can better determine what free length the new springs should be.

I am leaning towards getting slightly longer springs because I can adjust the ride height down using the circlips. I would prefer to not have extra circlip rings machined in to raise the ride height due to cost.

It will take 2 weeks to make the custom springs, then I will get them fitted and get the valving of the shocks checked at the same time. Hopefully they wont need revalving (I have no idea of their valving at the moment).

Would anyone like to advise if they think there any issues I should be aware of getting slightly longer springs then adjusting the ride height with the lower spring mount circlip?

Similarly, would anyone like to point out if there is a major flaw in my plan?

Thank you!

Fraser.

[bradsm87]

Those S.Tech rates look about right. Slightly stiffer on the rear to help reduce understeer which GTR's have a tendency to do.

[Phrase]

Those S.Tech rates look about right. Slightly stiffer on the rear to help reduce understeer which GTR's have a tendency to do.

Brad, I know that Tein would have done far more R&D than myself, but I just can't deal with the fact that the rears are stiffer than the fronts in a car with a forward weight bias.....maybe I just don't know enough about it all....

[_Ryan_]

Those S.Tech rates look about right. Slightly stiffer on the rear to help reduce understeer which GTR's have a tendency to do.

Rear toe out and thicker swaybars can be used to tune out the understeer without going to a stiffer bar, without sacrificing comfort and traction(going off of Gary's post in this thread and others similar)

[Phrase]

Rear toe out and thicker swaybars can be used to tune out the understeer without going to a stiffer bar, without sacrificing comfort and traction(going off of Gary's post in this thread and others similar)

ryan, rear toe out or front toe out? I though front toe out would help combat Corner - Entry understeer and rear toe out helps combat Consistent understeer ?

Have been reading This.

of course, it might not apply to GT-R's

hey, why don't I try both!

cheers,

Fraser.

Edited October 15, 2009 by Phrase

[_Ryan_]

ryan, rear toe out or front toe out? I though front toe out would help combat Corner - Entry understeer and rear toe out helps combat Consistent understeer ?

Have been reading This.

of course, it might not apply to GT-R's

hey, why don't I try both!

cheers,

Fraser.

Rear toe out was recommended for GTR's and Stageas IIRC and is used for drift to promote oversteer, I didn't run any on my stag as it turns in fine, but temped to try it to see how much better it could be.

Toe out on the front is also wanted.

[Phrase]

cheers, will post tomorrow about developments after going to Fulcrum.

[bradsm87]

Brad, I know that Tein would have done far more R&D than myself, but I just can't deal with the fact that the rears are stiffer than the fronts in a car with a forward weight bias.....maybe I just don't know enough about it all....

Nismo suspension is the same. Heavier on the rear. I'm pretty sure stock is the same too. Also Nissan, Nismo and Cusco ALL run stiffer rear swaybars too.