BC Coilover spring rates

[madras]

Hi Guys,

i have a 93 NSX Looking to order some of these BC coilovers but just wondering what spring rates to order. It says they come with 7 front 8 rear or 8 front 10kg rear.

Looking on prime the early type R had 6kg rear and 8kg front so I was thinking of going fort the same.

What do people think? or what have others ordered?

Thanks,
Chris

[madras]

http://www.nsxprime.com/FAQ/Performance/suspension.htm

all of the stock NSXs are softer on the front, and all of the special NSXs type S,R etc are softer on the rear, are there other suspension changes that the non standard ones have to work better with stiffer on the rear, and for this reason should I go with softer on the front, eg 8 front, 10kg rear?

thanks

[Sudesh]

I think this will purely depend on how your NSX is used, normal driving, track, etc etc.

I have BC installed in my car for a few years now, I just used the standard springs that BC recommended and have the 30 way adjust set to soft. It drives just fine for me and comfort level is great, my car is not driven fast or ever tracked though, so this suits me just fine; but I guess if I did want to stiffen it up, then I can just adjust the knob up some clicks.

[m666 edd]

The most important thing is you have dampers which have enough dampening for the springs installed. The worst thing you can do is put really stiff springs on dampers which aren't rated that high, the car will just bounce about and give bad handling as well as ride.

I currently have the comptech pro setup which is 1000 lb front / 600 lb rear. The main reason for such a setup (strong front bias) is to keep the car from diving too much under braking (on track). Because the koni dampers that are used are well matched and have enough dampening the ride isn't too bad at all as many here can attest to.

If you go for a stiffer front than rear setup (from the oem bias) you'll have to go with a stiffer rear anti roll bar setup otherwise you will just understeer a lot.

I've got some 800 lb springs which I'm going to experiment with on the front and either set the front anti roll bar a notch tighter or loosen the rear 1 notch. The current setup is no doubt stiffer than my driving ability can make the most of so a bit softer at the front I feel should help.

[madras]

Hi Sudesh, do you know what your standard spring rates are? or were then? they currently offer 8kg front paired with either 10kg at the rear or 7kg at the rear. It is tracked so i'd err to the softer 7kg rear to keep the car flatter under braking. (thanks m666)

[Kaz-kzukNA1]

Hi, Chris.
I posted the asnwer to your comment in my Blog so here is the copy and bit extra for you......


The short answer is, you need to try it by yourself.

Quite surprised so many forums focuses on spring rate.

I’m afraid it’s like asking the question 'in what colour should I paint my room' to someone who you have never met.

Discussion on spring rate alone means almost nothing.
For example, applying 100kg input to a 10kg rate spring on damper A doesn’t mean it will be the same response on damper B.

Without knowing the lever ratio, rest of the chassis setup such as weight distribution, rideheight, etc, damping/compression spec, pre-load, brake setup, antiroll bar spec, etc, not much to say.


100kg input at the contact on 10kg/mm spring doesn’t mean 10mm movement especially at the front on our NSX.


Not sure what kind of chassis package you have and also how many days you are likely to track your NSX each month but there are several options for you.

I went for F: 10Kg, R: 8Kg with Swift spring because that’s what I drove using the same Swift spring at the same spring rate at F/R, on similar damper spec, pre-load 4mm to start with, coupe package, OEM tyres, removed Type-R front/lower bars, standard front antiroll bar, Type-S rear antiroll bar, later spec calipers with upgraded ABS, spare wheel removed, etc.
For me, I didn’t like Type-R thick front antiroll bar or the Type-R front/lower bars.
Just couldn’t shift enough weight towards the front with my skill.


If going for BC kit with 15inch wheel at the front, you need to review your required ride height because even with the max adjustment, you are still lower than the OEM setup.


NSX Prime member Honcho has great write up on Prime so worth reading.
I posted the link in my blog.


If you track your NSX regularly, you may want to invest a lot more as the response speed on this damper may not be sufficient for your demand.
KW seemed to be the most cost effective one for NSX but unless you have the skill to make enough suspension movement or have the ability to setup the car, bit of overkill.
You are better off spending the extra money on tyres and also pillow bushing at the rear and practice more.


If your NSX is track day only car and lap time means everything, then you can ask Penske or likes to valve their adjustable damper to your needs.
Mega-expensive but worth it.


If you want to keep OEM spring but better dampening, then using Bilstein damper is good option.
I installed it on LHD NSX and ex-F3 driver test driven it with very good feedback.
It’s valved for the OEM spring and has two ride height setup.
It uses the OEM upper mount and not pillow one so quieter than the BC one.
Having said this, by the time you obtain all the short parts and new damper, you better compare the price with complete BC kit as it will allow you extra adjustment such as ride height, damping.


If you contact Andy at Vtecdirect, he may have another option (not BC kit) suitalbe for NSX.


If you want OEM, Type-S kit is good option but not sure whether it is still available or not.
The Type-S kit spec is [ figure in ( ) is of the standard model ];
Spring rate: F: 6.5kg (3.5kg), R: 5.0kg (4.0kg)
Damper spec at 0.3m/sec: F: damp195kg/comp150kg (115kg/109kg), R: damp230kg/comp170kg (183kg/125kg)
Antiroll bar spec F: 18.3mm (same), R: 19.1mm (17.5mm)
Damper mount bush F: 370kg/mm (83kg/mm), R: 370kg/mm (83kg/mm)
If using this kit on standard Coupe model, you must raise the rear a bit by adding spacer at the damper mount otherwise your weight distribution would be completely wrong.
The rear would be too low compared to the front.
I mentioned this on here in the past and I always ask this kind of question to the vendors by pretending to be an amateur to see whether the person I’m talking to knows NSX setup well enough or not.

Another good example of not much point in talking about only the spring rate.
On my NSX, I have Type-S kit.
As you can see from above, the spring rate is F: 6.5kg, R: 5.0kg.
The BC kit with Swift spring, I requested the spec as F: 10kg, R: 8kg.
Much higher than Type-S kit.
If you have ever driven Type-S kit on UK road, you would think that the spring rate that I requested for BC kit would be a disaster because on bumpy surface B-road, my NSX looses traction because the dampening is not suitable and the weight input to the tyre is lost.
Basically, the car is jumpping and damper mount bush is too hard.
With BC kit, the result is completely the opposite.
Better ride quality with good traction.
The damper is doing its job and suitable for the B-road.


From what I heard, as long as the spring rate is within +/-2kg, you can ask BC Racing to swap the spring rate to your spec without re-valving or any extra charge.
Also, if you order directly through BC Racing UK, they won’t be able to offer you the discount but if you search through their official distributor, there is always someone offering some discount so worth checking.

BC Racing UK used to send out the kit with F: 10kg, R: 10kg.
When I measured the kit, they were using the same spring diameter and length between the front and rear.
So, if you get 10kg and 8kg spring, you can swap them between the front and rear after you have played a bit.
One simple concept is that if you are getting close to the adjuster limit (30 clicks) then it’s time to move on to the next spring rate.

Kaz

[Sudesh]

Hi Sudesh, do you know what your standard spring rates are? or were then? they currently offer 8kg front paired with either 10kg at the rear or 7kg at the rear. It is tracked so i'd err to the softer 7kg rear to keep the car flatter under braking. (thanks m666)

I don't recall as I have my BC installed quite a while, I'll take a look at my old invoice to see if there is anything on there, but to be honest, I would say the spring rates, are still sold the same today, as what I purchased.

A friend if mine is now a retailer for BC and if your UK based and can supply a UK VAT number, then he can sell them with the VAT zero rated, so you'll get a good price.

[NSXGB]

If using this kit on standard Coupe model, you must raise the rear a bit by adding spacer at the damper mount otherwise your weight distribution would be completely wrong.
The rear would be too low compared to the front.


Kaz



Hi Kaz, I have the Type S kit on mine but knew nothing of this spacer, have you more details please?

[madras]

thanks Kaz, It's got Eibach Pro on it at the moment and it's way too low.

What is the minimum lowering on the BCs? - that's where i'd have it set. Standard car on 15/16" wheels

[Tokyo-Joe]

Thank you Sudesh and Kaz for your knowledge, it always makes a fine read.

[Kaz-kzukNA1]

Hi Kaz, I have the Type S kit on mine but knew nothing of this spacer, have you more details please?
Hi, NSXGB.

The Type-S kit is designed to lower the ride height by 10mm on Type-S chassis setup compared to standard Coupe model.
However, if you install it on the standard NSX, the rake between F and R won’t be correct.

You need to measure the ride height with full tank of fuel and check the rake between F & R based on your existing package such as the wheel size, spare wheel, ABS type, toolbox, etc.
Based on the measurement, you will very likely need to place thin spacer on top of the rear damper top mount before installing the assy.
It’s just a round disc sitting on top of the damper top mount.
You must have enough stud bolt thread left with the tower bar bracket installed so you can only add about 5mm max.
The spacer thickness depends on individual package so you really need to measure your ride height.

The lever ratio at the rear is about 1.1 so 5mm change at the damper length will increase the ride height about 6mm.
Be aware that changes at the rear ride height will affect the front at the same time.
You can drive your NSX for street driving with the wrong rake. I’m in the same boat at the moment as I gave my spacer to my friend but not ideal for the track day.

You can feel that the rear is dropped although it could be just my imagination as I measured the ride height by myself so my brain keeps reminding me.

Kaz

[Kaz-kzukNA1]

thanks Kaz, It's got Eibach Pro on it at the moment and it's way too low.

What is the minimum lowering on the BCs? - that's where i'd have it set. Standard car on 15/16" wheels
For your reference, when BC kit left the factory in Taiwan, it had 10kg/10kg spring rate at F/R for the original design.
The spec on their Taiwan headquarter web site still shows the same spec so not sure whether UK spec is just for UK market or not but they can change the spec without advance notice.

I haven’t finalised the ride height adjustment for the other owner as we are planning to do it in a few months.
Also, I don’t have experience with standard 10kg/10kg spring combo on BC so I can only assume but with 15/16 wheel and 3mm pre-load, your front ride height could be about 30 - 35mm lower even at the max damper length on BC kit.
This is with leaving at least 25mm of thread inside the bottom mount for safety reason. You can lower the front as much as you want until the point you can’t drive the car and the rear has enough adjustment left for going up as well as down.

From what you wrote, I don't think BC kit will be suitable for you with 15/16 wheel if you are feeling that Eibach spring is too low. I think it lowerd your NSX about 30 - 40mm which will be similar to what you will get from BC kit at the front with that wheel size.

Again, please note that I don’t know the rest of your chassis package so your ride height could be quite different from the other owner and also the spring manufacture/spec is different.

Not sure about the purpose of your modification. For the performance or the looks??? If you only replaced the spring on OEM damper, then I’m not sure how it reacts each other. OEM damper is gas type with dampening spec designed for all sorts of drivers and depending on the mileage you have covered, it won't be the same characteristic from the time when it left the factory.

If you want to keep the original ride height or just lower it a bit, you can use Bilstein damper with OEM spring.
If you use lower perch, it will lower the car about 20 – 25mm. Upper perch will be almost the same as the OEM.

As mentioned above, if you contact Andy at Vtecdirect, he may have other suitable option for your needs.

Kaz

[Sudesh]

Thank you Sudesh and Kaz for your knowledge, it always makes a fine read.

Might have some good new for you Joe on that other project, Ill keep you posted nearer the time.

[madras]

thanks Kaz! It was to get a better damper really than stock, I did look at the Bilsteins as have put some B8s on a 996 turbo recently as I didn't want it any lower.

I guess the B8 Sprints are similar a similar price £738 for all 4 last time I checked but I saw the good reviews of the BCs on prime so went for those. I didn't realise it would lower it quite that much on minimum lowering! We'll see how it is, as the Eibach I think is conservative with it's stated lowering, it's more like 1.5" not 1.2".

Do ever use spacers with the coilovers, I noticed on the Eibach the wheel is more noticable in the arch when lowered. On my E36 M3 with Eibach pro street S I HAD to put a front spacer or the wheel touches the spring.

[Kaz-kzukNA1]

Just a note when you install the coil over kit.

Whenever you change the ride height or alignment (and not necessarily the same reason but using wider rim) especially at the rear, make sure to double check the stress on the drive shaft.
Because of the suspension geometry, the drive shaft is one of the weakest point on our NSX even using the pillowball roller design at both the inner and outer joints.

Lots of NSX with aftermarket wheels, coilover kits or aggressive setup could be running without knowing the above fact and overstressing the drive shaft components.
You won't notice it until you check the drive shaft at full droop and full compression or open the drive shaft or in fact, until when it fails.......

Kaz

[NSXGB]

Thanks for the info Kaz.