Asymetrical steering effort vs corner balancing with KW V3 clubsport coilovers

[CB72]

I recently fitted some KW V3 clubsport coilovers to my NSX and discovered that while the car drives perfectly straight, the steering effort is greater in one direction than the other?
The camber is respectively L to R 2°28' and 2°10'
The trail is 7°38' and 7°48'
The Toe (out) is -0°08' and -0°07' (equivalent to 1 mm each on 17" wheels)

The wheels are CE28N's shod with Pirelli PZero Corsa's in 205/45*17

My only explanation is that the car needs corner balancing given that the springs are rated at 8kg/mm upfront.
A difference of 1 cm would mean a difference of 80 kgs in load on one wheel.
The 1 cm is off course exagerated but .5 cm on one front wheel and .5 cm on the opposite side rear wheel could be quite possible.
Given that it requires less effort to turn left I would tend to compress the FR and the RL springs a little more short of balancing the car on scales?
Any other idea?

 

[jwmelvin]

You didn’t list your caster?

 

[CB72]

You didn’t list your caster?

Sorry, by trail, I meant caster!

 

[Mac Attack]

I recently fitted some KW V3 clubsport coilovers to my NSX and discovered that while the car drives perfectly straight, the steering effort is greater in one direction than the other?
The camber is respectively L to R 2°28' and 2°10'
The trail is 7°38' and 7°48'
The Toe (out) is -0°08' and -0°07' (equivalent to 1 mm each on 17" wheels)

The wheels are CE28N's shod with Pirelli PZero Corsa's in 205/45*17

My only explanation is that the car needs corner balancing given that the springs are rated at 8kg/mm upfront.
A difference of 1 cm would mean a difference of 80 kgs in load on one wheel.
The 1 cm is off course exagerated but .5 cm on one front wheel and .5 cm on the opposite side rear wheel could be quite possible.
Given that it requires less effort to turn left I would tend to compress the FR and the RL springs a little more short of balancing the car on scales?
Any other idea?

I'm surprised you only run 8 kg/mm front springs with clubsports, and you use your car extensively for tracking.

When you calculate the difference in front spring preload and the effect on the wheel weight, you have to take into account the front motion rate (or wheel rate). For developing a suspension system on my NSX, I measured ~0.7:1 at my nominal ride height. Therefore, if you put 1 cm more of a preload on one of your front shocks than the other, the corner weight could be off by ~115 kg.

That's why it is important to corner balance (with your representative weight in the drivers seat) and not rely on estimating preload by feel or a crude length estimate. I used to disconnect toe links when doing a corner balance, but now I don't. If the car is rigid and straight, it is faster and simpler to leave them connected.

By the way, have you ever tried removing your rear sway bar?


I'm in the process of redoing my suspension, and measured motion ratios of ~0.7:1 front and 0.95:1 rear if that helps when you go to balance it.

 

[jwmelvin]

Sorry, by trail, I meant caster!

Oops, I’m the dummy skimming too fast while at a track day. The caster isn’t way off. I’ll be surprised if a bit of cross-weight imbalance throws off steering effort though.

 

[CB72]

I'm surprised you only run 8 kg/mm front springs with clubsports, and you use your car extensively for tracking.

When you calculate the difference in front spring preload and the effect on the wheel weight, you have to take into account the front motion rate (or wheel rate). For developing a suspension system on my NSX, I measured ~0.7:1 at my nominal ride height. Therefore, if you put 1 cm more of a preload on one of your front shocks than the other, the corner weight could be off by ~115 kg.

That's why it is important to corner balance (with your representative weight in the drivers seat) and not rely on estimating preload by feel or a crude length estimate. I used to disconnect toe links when doing a corner balance, but now I don't. If the car is rigid and straight, it is faster and simpler to leave them connected.

By the way, have you ever tried removing your rear sway bar?


I'm in the process of redoing my suspension, and measured motion ratios of ~0.7:1 front and 0.95:1 rear if that helps when you go to balance it.

You are a gold mine Mr Mac Attack!
You are right, I ought to take into account the spring rate at the front wheel.
So many times one reads that it's useless to corner balance a production car but when the springs are this strong it must be mandatory.
BTW with 8kg/mm upfront I'm only slightly off the NSX-R that I believe came with 10kg/mm?
I'm also concerned about the rear sway bar ( 22 mm OD currently) and I was planning to go back to the OEM 17 mm one ( like the NSX-R) but I should try without.
Many years ago I drove the racing NSX of Honda Switzerland and I was surprised to get so much understeer but I believe it's only because I wasn't driving it fast enough...
Here's a video taken from a 991 GT3 (485 hp) where one can see the rear wanting to step out in the medium fast downhill right hander (still with my Zanardi/Bilstein combo)
You have to watch until the end as I passed the Porsche a little later.
https://www.youtube.com/watch?v=wvS3UwvfzeQ

I must also mention that I'm running 33 mm offset on my front wheels to clear my Brembo/Porsche calipers.
This creates a larger circle for the front wheels to go through as I turn the steering wheel.
I had a second thought about the wheel rate.
Isn't it 8 kg x 0.7=5.6 kg ? This would match the rear wheel rate at 6 kg X 0.9= 5.6 kg

 

[Mac Attack]

Yeah, I was wrong above! My mistake! I've been working nights the past two weeks and swapped back to days yesterday. I'm all messed up. Used to be easier when I was younger....

So doing I correctly like you did would yield 56kg. Not really significant like Jason said before!

 

[CB72]

I purposely loaded the front left spring by two full turns so that on my drive tomorrow to the local monthly sunday car meeting I should get an answer?

 

[CB72]

I went for the ride today after checking the tire pressures ( one never knows...) and the steering effort seems well balanced left to right and right to left.
Of course it's not really scientific but I would not have noticed any unbalance if the steering had been like this in the first place!
I'll try to get the car on scales to confirm I did the right thing by loading the front left spring two turns (btw that's close to my own weight...)

 

[jwmelvin]

I had a second thought about the wheel rate.
Isn't it 8 kg x 0.7=5.6 kg ? This would match the rear wheel rate at 6 kg X 0.9= 5.6 kg

I’m pretty sure wheel rates should be the square of the motion ratio times the spring rate.

But it’s interesting to learn that altering your cross weights affected steering feel, thanks.

 

[Mac Attack]

I’m pretty sure wheel rates should be the square of the motion ratio times the spring rate.

But it’s interesting to learn that altering your cross weights affected steering feel, thanks.

Is that because it's like an inertial calculation (I=m*r^2)? I haven't ever taken the time to study this stuff unfortunately. I just took the measurements and sent them to the professionals!

The extent of my (mis)information above was just thinking about it from a statics perspective....

 

[jwmelvin]

I believe it’s because the force gets scaled and the displacement gets scaled. So the effective spring rate at the wheel includes both effects.

Fw=M*Fs
Xw=Xs/M

Kw=Fw/Xw=M^2*Fs/Xs=M^2*Ks

 

[CB72]

I believe it’s because the force gets scaled and the displacement gets scaled. So the effective spring rate at the wheel includes both effects.

Fw=M*Fs
Xw=Xs/M

Kw=Fw/Xw=M^2*Fs/Xs=M^2*Ks

I found this article that confirms it:
http://performancetrends.com/Definitions/Wheel-Rate.htm
This could also be of interest:
https://eibach.com/us/p-101-suspension-worksheet.html

 

[stuntman]

Make sure to set your spring perches the same right to left. Doing so usually gets close to a 50% cross weight in many NSXs I've seen.

You want to keep your spring perches within a turn or two from each other (a few mm difference max) and make small adjustments on the scales to get it perfect, working all 4 corners slowly rather than cranking on just 1 perch.

Without this time and discipline, just make sure the perch heights are even..

 

[CB72]

Make sure to set your spring perches the same right to left. Doing so usually gets close to a 50% cross weight in many NSXs I've seen.

You want to keep your spring perches within a turn or two from each other (a few mm difference max) and make small adjustments on the scales to get it perfect, working all 4 corners slowly rather than cranking on just 1 perch.

Without this time and discipline, just make sure the perch heights are even..

That's where I started : same height right and left.
By adding two turns on the front left, I just wanted to determine if the problem would increase or decrease.
It decreased which is what I expected given that the steering was easier to turn going left before the change.
To quote "Milliken": "The more the kingpin angle the more the car is lifted when it's steered. This is one source of steering returnability, the weight of the car returns the steering to center"

 

[stuntman]

Caster has a bigger influence on this feel than kingpin angle -which changes slightly on the NSX as you adjust camber.

 

[CB72]

By the way, have you ever tried removing your rear sway bar?


I'm in the process of redoing my suspension, and measured motion ratios of ~0.7:1 front and 0.95:1 rear if that helps when you go to balance it.

I've now replaced the rear 22 mm sway bar with the OEM part( 17 mm I believe ?).
There is definitely a big difference both in terms of comfort and in terms of handling!
With the KW V3 clubsport coilovers the rear felt very very firm whereas now it's only firm and one doesn't dread every bump in the road.
As for the handling one can now apply the power much earlier when exiting a turn with less concern about the himalayan increase in torque from the turbo...
Last but not least it should ease the work of the NSX-R LSD as there is less weight transfer to the outer wheel.
My set-up is now quite close to the NA2 NSX-R specification and it's a pleasure to drive fast.
Track testing still to be done.

 

[goldNSX]

Now you know why Honda didn't went with the thicker rear Type-S swaybar on the NSX-R.

 

[CB72]

Now you know why Honda didn't went with the thicker rear Type-S swaybar on the NSX-R.

Yes, and on top I was surprised by the weight saving!

 

[goldNSX]

...the weight saving!

Unless you've completly thrown the rear swaybar out of the car, it can't be much, no? I won't dismount the brakes for example to save weight because I need them from time to time.

 

[Mac Attack]

I've now replaced the rear 22 mm sway bar with the OEM part( 17 mm I believe ?).
There is definitely a big difference both in terms of comfort and in terms of handling!
With the KW V3 clubsport coilovers the rear felt very very firm whereas now it's only firm and one doesn't dread every bump in the road.
As for the handling one can now apply the power much earlier when exiting a turn with less concern about the himalayan increase in torque from the turbo...
Last but not least it should ease the work of the NSX-R LSD as there is less weight transfer to the outer wheel.
My set-up is now quite close to the NA2 NSX-R specification and it's a pleasure to drive fast.
Track testing still to be done.

Some of the professional NSX racers on here a long time ago completely removed their rear sway bar (DAL Motorsports, Andrie Hartanto, etc).

I removed my rear sway bar about 11 years ago when I started doing my custom exhaust and needed the space as my first priority. Then, it felt better on the street as well as enthusiastic driving.

I had to cut the rear sway bar end links off, but that wasn't a big deal. It opens up a lot of space under there, saves weight, and drives better in my opinion.

View attachment 153493

 

[stuntman]

There's more than one way to set a car up. However due to the geometry of the NSX suspension, there's not much of a benefit/hard to make a large aftermarket rear swaybar work well.

 

[Mac Attack]

There's more than one way to set a car up. However due to the geometry of the NSX suspension, there's not much of a benefit/hard to make a large aftermarket rear swaybar work well.

What are your thoughts on the newer four-wheel steer systems Billy? I haven't driven any, but am really interested in the technology. Apparently, just up to 5 degrees steering angle in the rear changes the handling for the better according to most test reviewers on these new Porsches and Audi's. It doesn't seem hard to retrofit a setup like that on the NSX rear and I'm running out of things to modify....

 

[CB72]

Some of the professional NSX racers on here a long time ago completely removed their rear sway bar (DAL Motorsports, Andrie Hartanto, etc).

I removed my rear sway bar about 11 years ago when I started doing my custom exhaust and needed the space as my first priority. Then, it felt better on the street as well as enthusiastic driving.

I had to cut the rear sway bar end links off, but that wasn't a big deal. It opens up a lot of space under there, saves weight, and drives better in my opinion.

View attachment 153493

I'll try that next !

 

[CB72]

What are your thoughts on the newer four-wheel steer systems Billy? I haven't driven any, but am really interested in the technology. Apparently, just up to 5 degrees steering angle in the rear changes the handling for the better according to most test reviewers on these new Porsches and Audi's. It doesn't seem hard to retrofit a setup like that on the NSX rear and I'm running out of things to modify....

The GT3 I was racing against in the video has the four wheel steer system.
He took me for a ride and while I was very impressed by the PDK shifting at 9K rpm, the sheer braking power and the stability, I found it a little strange that exiting a rather slow corner the driver was not willing to give it full power?
Does it have to do with the 4 wheel steer, I don't know but it seemed very strange because I could feed in more power at the same point in the NSX?