Gt-r Spring/sway Bar Rates

[djr81]

I have an old R32 GT-R to which I have fitted some Whiteline HD adjustable sway bars & approx 25% harder springs than standard, albeit on stock ride height. Next step (after the HICAS is gone & the cradle mounts fixed up) is some springs/shockers.

The current spring rates are about:

Front 2.4 + 25% = 3kg/mm (2.4 is stock rate from the manual)

Rear. 2.7 + 25% = 3.38kg/mm (2.7 is stock rate from the manual)

I have access to some Tein comfort spec coilovers which are supposed to be:

Front: 5 kg/mm

Rear: 4 kg/mm

Presently with the sway bars in and both on their softest settings - the car feels a little taily on turn in - something I put down to the HICAS. However, the predominant handling characteristic is still understeer - which will hopefully be reduced with new castor rods next Wednesday.

From what I understand going to a higher rate front spring (relative to the rears) will make the thing understeer even more. However all the aftermarket springs on offer ex Japan (not sure about the Whiteline offerings) use a harder front spring than rear.

Other than fiddling with roll centre differentials front/rear and/or tyre pressures is there a straight forward means to reduce this understeer?

[hrd-hr30]

yes, more castor will help reduce the understeer. while they're doing the alignment, ask them to check your toe settings too. front and rear toe settings can also be used to tune the cars balance, if they know what they are doing. Don't go making too wild adjustment to rear toe, or you may end up with a very 'nervous' car on high speed corners.

stiffening the rear sway bar settings will reduce the understeer tendancy. I recommend even settings on both sides, but others say it doesn't matter and gives extra settings (5 instead of 3) with more fine increments between them. I stand by that giving different handling characteristics on on left and right turns. (not wanting to continue that here, just presenting both sides of the story). Try it for yourself and see. Stiffening the rear bar will probably accentuate the twitchy turn in though too, unless its being caused by changes in rear toe geometry as the suspension moves, in which case it may reduce the effect slightly.

if you are getting Tiens, the shock valving will help determine the car's characteristics in transient behaviours - eg turn-in and change of direction, intitial braking and accelleration. Spring rates come into play when the car is 'settled' into the turn. It does seem strange that factory has higher rates in the rear and Tien use softer rears...

My R32 GTR has only adjustable castor rods and Buddy club coil overs, everything else is standard at the moment, and there is no hint of understeer. Well, except on off-camber surfaces. My HICAS is still connected and it's not nervous at all on turn in. Wether the system is doing anything is another matter I guess. Predominant characteristic on the limit is slightly biased towards oversteer, which suits me fine. Point is, that my car hasn't got many suspension mods, and seems to have got rid of the understeer that people say affects the GTRs, so it shouldn't be too hard or expensive to do.

Edited November 10, 2005 by hrd-hr30

[djr81]

I suppose if I had to try & characterise the handling it would be as follows:

Stable state: Understeer

Turn in: feels slightly taily (HICAS?).

Power on: Wheel spin + understeer

For example there is a largish (3rd gear) chicane on the main straight at Collie. Steering input in the first half is less than in the second. I cannot get mid corner oversteer for love nor money, but get wheel spin on corner exit.

I am a bit reluctant to introduce more rear roll stiffness as this will degrade the rear grip & make it even more twitchy on turn in. Most of the loses/half loses I have is on turn in with the car wanting to swap ends. Braking & turning in at the same time is a complete other world.

As for toe in I run very little on the front, but approx 1mm total on the rear I have had more rear toe in, but then it tram lines like a bitch on the road.

My gut feel is to fix the HICAS & then worry about the springs. I just can't reconcile the spring rates with the needed (ie more neutral) handling characteristics.

[Sydneykid]

My 20 cents;

1. Standard shocks are not so good at controlling standard springs. So 25% higher rate springs will cause the tyres to jump from small bump to small bump. The shocks need to control the springs to maximise the tyre contact.

2. Stiffer stabiliser bars just accentuate the lack of damping/control from the shocks.

Add the 2 together and you have a recipe for poor traction at both ends, which is what you are experiencing. Personally I wouldn't be looking for other reasons until the obvious shock problem is sorted

The spring rates are not ideal either, I never run higher spring rates in the rear than in the front with upgraded stabiliser bars. If you are running the BNF28Z front and BNR26Z rear you have increased the rear antiroll by about 3 times what you have increased the front. This obviates the need for stronger rear (than front) spring rates. If you want to test this, try puting the standard rear springs in.

If you are looking at doing a reasonable amount of track time I would be looking for something a bit better than Tein shocks.

Hope that helps

cheers

[djr81]

Not sure if I mentioned what dampers the thing is presently running...

To be honest the sway bars are a new addition. I have found that the traction difficiency (such as it is) has, if anything, been lessened by the stiffer sway bars. I can dig up the data logger info to support this, but it will have to wait until another run at Wanneroo for a definitive answer. The last time at Collie the track was filthy, so it was hard to be 100% sure - but it did feel better & looked better on the traces. For the record the sway bar combination is BNF27Z front & BNR26XZ rear and has reduced the steady state understeer. Yes it feels taily on turn in - but I can live with this until the HICAS is cancelled. I believe the better traction is because of less body roll which in turn compensates for the otherwise unhelpful lateral spring load transfer of the sway bars.

Also, from following other R32's around the track they commonly buzz the inside rear out of slow corners.

The reason I asked the question is that the Nissan manual has the rear spring rates higher than the front. This goes against what I understood would be the case (Particularly given the horrible weight distribution in the R32 GT-R). My springs (Both front and rear) are 25% higher than the stock Nissan units - the windings appear the same - just the wire diameter has increased.

All of the aftermarket springs on offer from Japan seem to have the front springs stiffer than the rears - which makes sense to me. I do understand the function of the dampers in maintaining surface contact for the tyres - but it was the springs I was asking after.

What I was trying to do is to get some understanding of the apparent discrepency between the rates quoted in the good book & those chosen by aftermarket suppliers.

By the way the Tein coilovers have 30% larger diameter dampers & are adjustable - not Bilsteins to be sure, but then again they won't cost me Bilstein money.

SK - can you tell us what the rates are for the Whiteline GT-R springs on offer?

Some of the frustration I have is that the whole world believes that GT-R's oversteer. Mine used to on road tyres, but won't on R compounds. Perhaps it is insufficient power - but in any case understeer + wheelspin isn't the quickest way around the track. I am trying to work towards a more stable turn in & a lower propensity to heavy understeer in the tight stuff & to be honest I am having trouble getting my head around the springs. Maybe I will have to wait until after the HICAS is gone & the castor rodes are installed.

[MerlinTheHapyPig]

Get rid of the hicas first. Then you can start to narrow down where your problem lies. But a fair bet, stock shocks & springs won't be helping...

If you have access to tiens, maybe just try them out and see how you go. Though in japan they tend to be known as poor mans adjustable coilover -- but they can take a beating...

[hrd-hr30]

I agree, it does sound like the standard shocks are too soft in both bump and rebound. Too much initial weight transfer will cause alot of the characteristics you are describing - nervous turn-in, power-on understeer

[Sydneykid]

The reason I asked the question is that the Nissan manual has the rear spring rates higher than the front.  This goes against what I understood would be the case (Particularly given the horrible weight distribution in the R32 GT-R).  My springs (Both front and rear) are 25% higher than the stock Nissan units - the windings appear the same - just the wire diameter has increased. 

I can't get into the minds of the Nissan engineers, so I don't know for sure why they did it. So all I can do is apply the usual suspension rules and hypothesise.

What I do know is the standard rear stabiliser bar is way too small (hence the need for such a large aftermarket upgrade). The usual reason for using such a small rear bar is to eliminate power off oversteer, which the early ATTESA doesn't handle very well.

So my hypothsesis would be that the engineers used a slightly higher rear spring rate to compensate for the lighter rear bar. This has the effect of holding down the inside front under cornering (no front LSD standard remember) similar to what a stabiliser bar would do. But without the power off oversteer.

Also the early ATTESA is a bit slow to react to rear wheelspin and kick some drive to the front. When it does send some drive to the front it is a large lump of torque fairly quickly. So any extra traction that the front can get, by limiting the rearwards weight transfer, is good. So heavier rear springs would be an answer to that problem.

All of the aftermarket springs on offer from Japan seem to have the front springs stiffer than the rears - which makes sense to me.

Unless you upgrade the rear stabiliser bar and/or the bump valving in the rear shocks, then you will suffer from the same problems as I think the Nissan engineers recognised. Some adjustment of the ATTESA would also help of course.

What I was trying to do is to get some understanding of the apparent discrepency between the rates quoted in the good book & those chosen by aftermarket suppliers. 

Simpistically thowing higher rate front springs at it, makes an R32GTR a pig understeerer. As many people have found out.

By the way the Tein coilovers have 30% larger diameter dampers & are adjustable - not Bilsteins to be sure, but then again they won't cost me Bilstein money.

Unfortunately you get what you pay for in shocks, simplistic valving (even if it is adjustable) is still simplistic valving. That's where the cost (not necessarily the selling price) differences are in shocks, everything else costs much the same. But more valves = more cost.

can you tell us what the rates are for the Whiteline GT-R springs on offer?

From memory the fronts are a bit over 200 lbs per inch and the rears a little under 200 lbs per inch.

Some of the frustration I have is that the whole world believes that GT-R's oversteer.

Not me, you have to be very carefull in the suspension set up to avoid understeer. We spend most of our time dialing out the understeer, very rarely do we have an oversteer problem. And if we do, it can be fixed with a small twist of the torque split controller.

I am trying to work towards a more stable turn in & a lower propensity to heavy understeer in the tight stuff & to be honest I am having trouble getting my head around the springs.

Realistically R32GTR's have crap weight distribution, they are % heavier at the front than many front wheel drive cars. If you barge up to a corner and yank on the wheel they will always understeer. It took quite a while for the drivers to optimise the slow in, power on early and fast out technique that it takes to make a GTR do fast lap times, lap after lap.

  Maybe I will have to wait until after the HICAS is gone & the castor rodes are installed.

The HICAS is biased towards understeer, at all costs, as it is safe for the Wally's. It really has to go, honestly it is the first thing I remove on any Skyline.

Hope the above was of some help

cheers

[T04GTR]

cool. that has shed some light on my current post. please give me a list?

of cource i noticed this post after i had started mine