NSX Roll Center Adjuster (RCA)?

[stuntman]

Has anyone made a front or rear Roll Center Adjuster (RCA) for the NSX?

A&J Racing has made a kit for the S2000 rear, does anyone know if the S2K's balljoints have the same ID (Inner Diameter) as the NSX's balljoints = so we can use A&J's roll center adjusters on the NSX?

A&J Racing RCA:
http://www.maxrev.net/index.php?location=RCAreview.htm

http://www.aj-racing.com/catalog/product.php?productid=639&cat=81&page=2
http://www.speedstar.ca/main_jsracing_suspension.htm

 

[john@johnhudakracing]

Has anyone made a front or rear Roll Center Adjuster (RCA) for the NSX?http://www.speedstar.ca/main_jsracing_suspension.htm

Not that I am aware of. Maybe a project we could get going so as to mitigate R&D costs? With my slightly lower engine position and other John CG mods I was wondering about that effect myself- as again my stock geometry still remains unchanged, likely causing my roll couple to increase leading me to wonder what I have locked up there.

I can easily measure the ball joints tommorow evening if you would like on both.

 

[stuntman]

Not that I am aware of. Maybe a project we could get going so as to mitigate R&D costs? With my slightly lower engine position and other John CG mods I was wondering about that effect myself- as again my stock geometry still remains unchanged, likely causing my roll couple to increase leading me to wonder what I have locked up there.

I can easily measure the ball joints tommorow evening if you would like on both.

Measure the inner diameter of both the front and rear ball joints. It would be too convenient if the ID is the same as the A&J Racing S2000's balljoints - perfect drop in.

If not, I would hope that the ID of the NSX is smaller, so the A&J balljoints would just have to be machined down -that would be the cheapest.

Worst case, we would be SOL if the NSX's balljoints were larger than the S2K, therefore cannot do anything with the A&J balljoints.


John, look at your rear lower control arms. Are they parallel with the ground, slanted down (from subframe to wheel upright) or are they angled up (from subframe to wheel upright)? -as you lower the car, the angle of the arm should start to be angled up more and more...

 

[john@johnhudakracing]

Measure the inner diameter of both the front and rear ball joints. It would be too convenient if the ID is the same as the A&J Racing S2000's balljoints - perfect drop in.

If not, I would hope that the ID of the NSX is smaller, so the A&J balljoints would just have to be machined down -that would be the cheapest.

Worst case, we would be SOL if the NSX's balljoints were larger than the S2K, therefore cannot do anything with the A&J balljoints.

Sounds like a plan, I'll measure one of the AP1's up.

John, look at your rear lower control arms. Are they parallel with the ground, slanted down (from subframe to wheel upright) or are they angled up (from subframe to wheel upright)? -as you lower the car, the angle of the arm should start to be angled up more and more...

I'll have to look. Let me get it back off jack stands tommorow and I'll reply back.

 

[stuntman]

Sounds like a plan, I'll measure one of the AP1's up.




I'll have to look. Let me get it back off jack stands tommorow and I'll reply back.

Make sure to measure the front and rear LOWER control arm balljoint (that attaches to the hub).

 

[L8apex32]

On one hand, I have to assume that the NSX has pretty low roll centers already.

On the other hand, if a decent improvement could be made to the NSX's roll centers, it would allow for softer springs, sways and shocks and could make a big improvement to the car's track handling.

If we are going to talk about roll centers, can we also talk CG (height) also?

This thread sounds really interesting.

 

[stuntman]

On one hand, I have to assume that the NSX has pretty low roll centers already.

On the other hand, if a decent improvement could be made to the NSX's roll centers, it would allow for softer springs, sways and shocks and could make a big improvement to the car's track handling.

If we are going to talk about roll centers, can we also talk CG (height) also?

This thread sounds really interesting.

Just so you're on the same page, read this:

http://www.maxrev.net/index.php?location=RCAreview.htm

 

[docjohn]

This may explain why Honda's own R and S suspensions don't lower the car much from stock.

 

[1BADNSX]

Just so you're on the same page, read this:

http://www.maxrev.net/index.php?location=RCAreview.htm

I agree it can be a problem, but this link uses poor choices to illustrate the point. They only show changes of the RC with changes in ride height. You really need to also show the RC movement with actual body roll.

In general, you want:
- Front roll center at or slightly above ground level
- Rear roll center slightly higher than the front RC
-- Higher roll center in the rear allows for the response of the rear end
to be quicker and catch up with the front (which is first to react)
- Want the roll center to move up and down the same amount as the CG
-- This is important to keep the roll couple constant with bump or rebound
- Would like the roll center to stay near the longitudinal axis
- Most important – design the front and rear roll centers to have similar
movement during roll, bump, and rebound

Bob

 

[titaniumdave]

Has anyone made a front or rear Roll Center Adjuster (RCA) for the NSX?

A&J Racing has made a kit for the S2000 rear, does anyone know if the S2K's balljoints have the same ID (Inner Diameter) as the NSX's balljoints = so we can use A&J's roll center adjusters on the NSX?

A&J Racing RCA:
http://www.maxrev.net/index.php?location=RCAreview.htm

http://www.aj-racing.com/catalog/product.php?productid=639&cat=81&page=2
http://www.speedstar.ca/main_jsracing_suspension.htm

Has there been a documented problem?

 

[stuntman]

Has there been a documented problem?

Some of us are building track cars that far exceed simply adding 'off the shelf' coilovers, and have so many things changed, and are low enough to have this problem :wink:

 

[titaniumdave]

Pics of the NSX knuckles.
Front does not lend it's self to the S2000 fix. Could do a longer stud ball joint for the rear...

I think moving the inner front suspension pivots has been the choice of some teams in the past. I have not heard of any one addressing this issue in the rear suspension.

 

[stuntman]

Pics of the NSX knuckles.
Front does not lend it's self to the S2000 fix. Could do a longer stud ball joint for the rear...

I think moving the inner front suspension pivots has been the choice of some teams in the past. I have not heard of any one addressing this issue in the rear suspension.

The fronts do look like a problem...

When lowering the NSX REALLY low, the rear definatley could benefit from the S2000 fix, and it wouldn't be too hard to replicate that for the NSX....

 

[titaniumdave]

The fronts do look like a problem...

When lowering the NSX REALLY low, the rear definatley could benefit from the S2000 fix, and it wouldn't be too hard to replicate that for the NSX....

With my 18" wheels, you could drop the ball joint about 2 CM and not hit the rim. Do you think that would be enough to matter? Have you run a computer simulator? I always look at the 'suspension programs' @ HRP World, seems like they are about $100 and it could answer all these questions...does some one have a copy and would run the numbers?

 

[titaniumdave]

Some of us are building track cars that far exceed simply adding 'off the shelf' coilovers, and have so many things changed, and are low enough to have this problem :wink:

How low are you going? Height to jack points for comparison?

 

[stuntman]

With my 18" wheels, you could drop the ball joint about 2 CM and not hit the rim. Do you think that would be enough to matter? Have you run a computer simulator? I always look at the 'suspension programs' @ HRP World, seems like they are about $100 and it could answer all these questions...does some one have a copy and would run the numbers?

18" front and rear. 2CM would be help out a lot in the front (and rear -but preferably more in the rear if possible).

It would be enough to matter... so can you make these up for me?

I have not run a comp simulator, but I really need them and they will help. I dont want to argue if they'll work or not, but I know they will and I need them

How low are you going? Height to jack points for comparison?

REALLY low. less than 4", hopefully lower than 3.

 

[L8apex32]

Just so you're on the same page, read this:

http://www.maxrev.net/index.php?location=RCAreview.htm

You are right; I said that wrong. Its been a long time since I read my suspension books.

I think using a simulator would be the key. There are so many interrelated issues to consider.

Now, to get us all on the same page, 1BADNSX said the ideal roll center was slightly above ground. And, the stock roll center is well above ground. Should we not, then, be trying to lower our roll centers? The RCA page discusses raising the roll center.

I see that if you can only change one thing, raising the roll center to be closer to the CG would reduce roll. I wonder how and why this is better than using stiffer sway bars or similar. I suppose that you'd be able to use softer springs which is better (so I've read).

I have further read in a suspension book that it is very hard to lower a car's CG - maybe that is why raising roll center, which sounds counter intuitive to start with, actually does help.

Any thoughts on this?

 

[stuntman]

You are right; I said that wrong. Its been a long time since I read my suspension books.

I think using a simulator would be the key. There are so many interrelated issues to consider.

Now, to get us all on the same page, 1BADNSX said the ideal roll center was slightly above ground. And, the stock roll center is well above ground. Should we not, then, be trying to lower our roll centers? The RCA page discusses raising the roll center.

I see that if you can only change one thing, raising the roll center to be closer to the CG would reduce roll. I wonder how and why this is better than using stiffer sway bars or similar. I suppose that you'd be able to use softer springs which is better (so I've read).

I have further read in a suspension book that it is very hard to lower a car's CG - maybe that is why raising roll center, which sounds counter intuitive to start with, actually does help.

Any thoughts on this?

Messing with roll centers, suspension geometry, and pick-up points is much more involved engineering wise than simply putting a stiffer swaybar/springs on your car.

When you lower your car, your CG lowers but your roll center lowers much more. If you lower your car too much, the Roll center becomes way too low -below the ground = attributes to poor handling, you need to run stiffer springs, and your suspension dosn't work properly.

Adjusting hte pickup points or using Roll Center Adjusters as discussed sofar raises the roll center to an appropriate geometry, thus utilizing a lower CG (from a lower car) and keeping the proper roll centers of your suspension geometry.


In regards to this thread, I really need these RCAs made for one of my projects. I have not used a computer to CAD the part or to test the geometry as I have not made those measurements. I do however have the knowledge and am working with people who have the knowledge that utilizing these RCAs will help our project and thus my need for them.

Can't wait to show you guys what car this is...

 

[titaniumdave]

It would be enough to matter... so can you make these up for me?

I can see about doing some rears, seems like a good idea. I won't have time to start till about the first of the year though, too many project already lined up.

Can you get drawings or samples of the RAC parts? Would help the planning stage, if I could just hog out the NSX knuckle and press a new ball joint in would be pretty cool. A buddy of mine made adjustable front lower ball joints for his Integra last year, might be able to steal some of his design too.

 

[stuntman]

I can see about doing some rears, seems like a good idea. I won't have time to start till about the first of the year though, too many project already lined up.

Can you get drawings or samples of the RAC parts? Would help the planning stage, if I could just hog out the NSX knuckle and press a new ball joint in would be pretty cool. A buddy of mine made adjustable front lower ball joints for his Integra last year, might be able to steal some of his design too.

Look at the 3 links that were on my OP. Check out those links for ideas...

Again, I need them soon so i'm hoping that the S2K balljoints are the same size if not a little larger ID (to be machined down) to the NSX size.

 

[titaniumdave]

Look at the 3 links that were on my OP. Check out those links for ideas...

Again, I need them soon so i'm hoping that the S2K balljoints are the same size if not a little larger ID (to be machined down) to the NSX size.

I get the idea, can you get drawings or samples??

I have NSX parts to get dimensions off, I need the RAC part dimensions to compare.

I am off to Monterey for the weekend, not sure if I will be checking prime...

 

[stuntman]

I get the idea, can you get drawings or samples??

I have NSX parts to get dimensions off, I need the RAC part dimensions to compare.

I am off to Monterey for the weekend, not sure if I will be checking prime...

RCA* :wink:

No drawings, samples cost $500 from their website.

I'm off to monterey in 7 hours, see you there!

 

[john@johnhudakracing]

Measure the inner diameter of both the front and rear ball joints. It would be too convenient if the ID is the same as the A&J Racing S2000's balljoints - perfect drop in.

Ok, measuring these on-car is a PITA. I can't get a micrometer, metric slide rule, etc.. or anything else with enough accuracy to be effective in between the arm and the hub.... and I do realize that precision does kind of count for this type of thing. The easy part is that So far as I can tell, on the lower A arms the ID's are 34mm front and 30mm rear for the NSX, with a 40mm or so cap and clip. But, reading the joint at the bottom of the hub, I just can't get anything in there.

I think the better way to do this is to have Dave measure the NSX hubs that I know that he has at his pad off-car so we get it right. I'll inspect the 2K tommorow after playing office space and see if I can't manage better results on that one.

John, look at your rear lower control arms. Are they parallel with the ground, slanted down (from subframe to wheel upright) or are they angled up (from subframe to wheel upright)? -as you lower the car, the angle of the arm should start to be angled up more and more...

Ok, I got this done at least. Tonight I set things in "John street trim" (defined as can be driven an exit and back without tearing the front splitter off) and did a quick loopy-loop up and back to settle things down. From what I see about shy of 4" to the jack tab or so, maybe a 1.3-1.5" drop.

From what I can tell, already my rear A lower arms at the hub ball joint are noticably angled up relative to the horizontal ground plane. I'd say by several degrees. I noted the vertical distance.

So I've been experiementing around with chassis setup lately having an idea of what I'm after; my thought here is that today I'll swap wheels/tires so I can gain a little better fender clearance (a problem for me at the moment), re-set the collars for 3" "John track trim" (defined as the stock jack no longer clears), and inspect again to see the difference.

 

[1BADNSX]

I see that if you can only change one thing, raising the roll center to be closer to the CG would reduce roll.
Any thoughts on this?

Raising the roll center all the way up to the CG would eliminate body roll, but it would also “jack” the CG up during a turn. This is due to the forces through the control arms are upward (toward the CG), the vertical part of this force raises the CG. Of course, this is bad.

This is why you want the rear roll centers slightly above ground level, assuming the front roll center is at ground level. You need the rear roll center to be slightly above the front roll center due to the front end reacting first to steering input.

Bob

 

[john@johnhudakracing]

Ok, since I have an upcoming chassis setup appointment, I decided to spend some time on chassis setup playing in the garage (up and down and up down on jack stands to calculate CG, etc... and experiment around. There is a Audi Club event I registered to help out with in two weeks.. I'm hoping to use as a test and tune day (since it will probably pour down rain being one of the last days of the year it should be fun).

First, as can be seen a relatively aggressive ride height that should make getting it onto a trailer interesting to say the least. I could probably go a little lower, but definitely not under 3" without trimming the fenders and liners, and swapping a few things around as under track load I'd probably rub.

Below is a close up to the jack tab. As long as you are bringing your own gas... I think 3.5-3.75 would probably get the job done. Maybe not the 50mm of JGTC or DTM, but you know for the club red line time attack stuff; from what I've seen of other race touring prepared style cars.. compared to Crawford, Matrix, GST, etc... if you aren't otherwise limited by rules this would probably be a pretty freakin' aggressive start.

With the new seating position (as low and far back as I could get it) my butt is essentially under the center line of the hub. All I know is that the highest point on the car is the rear wing at like 45-46" off the ground which means the BMW sedan in front of me looks like some kind of monster truck. :biggrin:

Now, you can see the effect on the rear lower A Arm. Relative to "street height" you can see how drastic an effect lowering has on the geometry. It's not linear, going from an 1.25" under stock to 1.85" under stock on the jack tab has a significant effect as the arm pivots. From a couple of degrees to what you see here which is probably closer to 25-30 degrees. I probably would need a little over an inch to set that rear arm level again. The front is harder to ascertain but appears similar to me... so the front roll couple to rear ratio roll couple is likely similar; which suggests that all four hubs could benefit from an adjustable RCA.

I have some free chassis setup software and am going to throw a few hours at this today and see where I arrive when I start plugging numbers in, as I've changed too many things to depend on anything I have written down.