Roll Centres

[whrdnsx]

Has Anyone with track dedicated NSX's messed around with changing Roll Centres?

After lowering the NSX the roll centres must be close to ground or lower? (Haven't done any actual calculations) just observing the control arm angles.

How did you change them? I have some thoughts but will need some work!

Any feedback with handling differences? is it worth pursuing?

Thanks in anticipation.

 

[Mac Attack]

[MENTION=10956]whrdnsx[/MENTION]
The negative handling when drastically lowering mine has made me look into this too. I think the only thing that can be done cost-effectively is to fix the bump steer with a taller ball joint on the tie rods (or go to a heim joint that would be even weaker), but this will increase the loads and shorten the ball joint life. You can't really change the suspension arm pivot points, and it looks like Honda came to that same conclusion for their factory-sponsored race programs.

It looks like the HPD NSX and the old GT2 NSX used the same suspension pickup points but resorted to using shorter custom hubs to get the roll centers back up. Obviously the arms are different, but they're just stronger/lighter than ours:

HPD:
https://engineswapdepot.com/wp-cont...SX-with-a-Twin-Turbo-Stroked-HR28TT-V6-09.jpg

Link to a lot of GT2 pics:
https://www.wirewheel.com/inventory/available/1997-acura-nsxr-gt2-/

I think the best thing is to just increase aero drastically. That's what I'm doing now. I'm curious what your thoughts are!

 

[Ponyboy]

I like the idea of a longer ball joint even if it doesn't have an extensive life. I've got a quite bit of grip but I think it'd be much better if the roll center were closer to the center of gravity.

I've attempted to band-aid the issue with super high spring rates and sways.

 

[whrdnsx]

Yes, it seems not too many options that are not expensive.

I've been looking at all the suspension subframes and I've worked out that I can machine approx. 10mm off the front suspension & 12mm off the Rear mount bosses to effectively move the whole suspension up.
Not much I know & the knock on effect of other parts. Ie Rear Engine mount. But I'm going to do the work.
I can also use the extended balljoints too.

 

[Ponyboy]

I can also use the extended balljoints too.

As far as I've seen, most aftermarket companies use the extended balljoint method. Interested to see what you develop.

Kudos to you.

 

[Old Guy]

As far as I've seen, most aftermarket companies use the extended balljoint method. Interested to see what you develop.Kudos to you.

Are you are talking about those modified (lengthened) lower ball joints that effectively increase the angle of the lower control arm there by raising the roll center? If so, I have seen those on other applications and I find them conceptually scary. A bit like those bump steer correctors. There is a lot of horizontal force going on at the ball joint interface and the vertical offset created by those ball joints adds a moment arm which just increases the forces at the ball joint mounting point at the lower A arm. Aside from elevated wear on the lower ball joint, I would be obsessed with distortion and damage where the ball joint attaches to the lower A arm. I haven't done the diagrams; but, isn't the modified lower ball joint option going to alter the static camber and the camber change as the suspension goes through compression?

As to the question posted by the OP, I am assuming that the objective is to raise the roll center reducing the moment between the roll center and the C of G? If so, the kinematic diagrams would suggest that increasing the track width will raise the roll center. Depending on where the instantaneous center of motion created by the converging lines associated with the upper and lower control arms is located, track change may have significant or trivial effect. If the upper and lower control arms are close to parallel (the angle formed by the lines through the upper and lower control arms is closer to 0 deg) the instant center may be so far horizontally from the center of the car that track change has an imperceptible effect on roll center. If the angle formed by the lines through the upper and lower control arms is less acute the horizontal displacement of the instant center will be closer to the center line of the car and changes to the track width might have a material effect on roll center location.

Edit - further to the OP's original question, when you lower a car with shorter springs you typically move the roll center down; but, the C of G also moves down so you may not have altered the moment between the C of G and the roll center that much by lowering the car. Only checking the geometry will confirm that. Another thing to consider is that the C of G at the front of the car has to be a lot lower than the C of G at the rear of the car. There is not much body above those upper suspension points. You might want to be careful trying to alter the front roll center because you might get some interesting steering effects.

@Mac Attack's comments on the use of shorter hubs on the GT2 and HPD cars to raise the roll center is interesting. If shorter hub means an effective reduction in track width (assuming everything else is unchanged), that would seem to conflict with my understanding of the effect of the location of the center point of contact of the tires on the location of the instant center of motion that is used to determine the instant roll center. Perhaps the objective wasn't to raise the roll center? Some sources suggest that a drop in roll center resulting in additional weight transfer may be desirable if the objective is to improve transient steering response as opposed to increasing total grip.

 

[CB72]

[MENTION=10956]whrdnsx[/MENTION]
The negative handling when drastically lowering mine has made me look into this too. I think the only thing that can be done cost-effectively is to fix the bump steer with a taller ball joint on the tie rods (or go to a heim joint that would be even weaker), but this will increase the loads and shorten the ball joint life. You can't really change the suspension arm pivot points, and it looks like Honda came to that same conclusion for their factory-sponsored race programs.

It looks like the HPD NSX and the old GT2 NSX used the same suspension pickup points but resorted to using shorter custom hubs to get the roll centers back up. Obviously the arms are different, but they're just stronger/lighter than ours:

HPD:
https://engineswapdepot.com/wp-cont...SX-with-a-Twin-Turbo-Stroked-HR28TT-V6-09.jpg

Link to a lot of GT2 pics:
https://www.wirewheel.com/inventory/available/1997-acura-nsxr-gt2-/

I think the best thing is to just increase aero drastically. That's what I'm doing now. I'm curious what your thoughts are!

Amazing to see the size of the anti-roll bars on the GT2!
I wonder what was the asking price for the car...
As far as roll centers are concerned, I looked into one of my old books on the subject ( Design of Racing Sport Cars by Colin Campbell) where the author looked into the design of the Porsche 917.
In this case the rear RC is estimated to be 2.5" above ground while the front is .5" below ground level.
The roll axis is thus inclined upwards towards the rear of the car.
The purpose beeing to balance the roll moment front to rear by making the roll axis parallel to the mass centroid line of the car.
This alleviates transient effects when negociating corners.
It would be interesting to determine the roll centers (F and R) of the OEM NSX before going any further?
BTW if the roll moments F to R are very different it could explain why so many NSX's went out of control in straight lines when changing lanes on wet roads???

 

[Mac Attack]

That's a great point [MENTION=19738]CB72[/MENTION] . It seems like most NSX owners when they go to lower the car they remove the original height balance and lower the front substantially more for a more "raked" look. It's good for aero but I never liked the handling.

You can change the suspension geometry to modify the roll centers, or you can alleviate the effect by either increasing aero substantially or stiffening the suspension as [MENTION=4055]Ponyboy[/MENTION] mentioned. It's all a balancing act and you have to know how they all work together. It just takes knowledge, time, and money - Three things that seem to elude me!

 

[Mac Attack]

@Mac Attack's comments on the use of shorter hubs on the GT2 and HPD cars to raise the roll center is interesting. If shorter hub means an effective reduction in track width (assuming everything else is unchanged), that would seem to conflict with my understanding of the effect of the location of the center point of contact of the tires on the location of the instant center of motion that is used to determine the instant roll center. Perhaps the objective wasn't to raise the roll center? Some sources suggest that a drop in roll center resulting in additional weight transfer may be desirable if the objective is to improve transient steering response as opposed to increasing total grip.

Sorry for the confusion but by shorter hubs I meant vertically shorter so they don't impact the track width! Therefore, the width wouldn't change - only the angle between the upper and lower arms.

 

[stuntman]

I've already put an NSX on Morse Measurement's K&C rig and have all of the roll centers mapped at various ride heights, as well as a complete analysis of the camber gain and bumpsteer.

There is a pretty steep roll axis inclination in the NSX, the roll centers drop much faster than Cg as the car is lowered, and this all explains why it's popular to run an extremely stiff front spring and bar, and softer rear spring and often no rear bar in track cars.

The NSX needs the front roll centers changed a lot more than the rear, at least that would yield the biggest benefits. I really want to make a set of billet drop spindles, which would replace the entire outer knuckle and ball joints, and the OEM wheel bearing would bolt right up to it. But these would probably run at least $4K for the front set, so it's not a very cost effective solution for most NSX owners. However, this would improve the bumpsteer at lower ride heights, raise the front RC, and the NSX would require less front spring and bar to be balanced, thus improving the ride quality and handling of the car.

One of these days I will make a set for my car, but right now i'm more focused on a dry sump pan that retains AC.

 

[CB72]

I've already put an NSX on Morse Measurement's K&C rig and have all of the roll centers mapped at various ride heights, as well as a complete analysis of the camber gain and bumpsteer.

There is a pretty steep roll axis inclination in the NSX, the roll centers drop much faster than Cg as the car is lowered, and this all explains why it's popular to run an extremely stiff front spring and bar, and softer rear spring and often no rear bar in track cars.

The NSX needs the front roll centers changed a lot more than the rear, at least that would yield the biggest benefits. I really want to make a set of billet drop spindles, which would replace the entire outer knuckle and ball joints, and the OEM wheel bearing would bolt right up to it. But these would probably run at least $4K for the front set, so it's not a very cost effective solution for most NSX owners. However, this would improve the bumpsteer at lower ride heights, raise the front RC, and the NSX would require less front spring and bar to be balanced, thus improving the ride quality and handling of the car.

One of these days I will make a set for my car, but right now i'm more focused on a dry sump pan that retains AC.

At long last, we get an explanation of why the racing NSX's use such stiff anti-roll bars upfront.
It would be interesting to get some data to judge the effect of lowering the car on the lowering of the roll center(s).

 

[docjohn]

Thanks Billy! btw how does the new Mustang 500 handle extended track days? Is it as reliable as the 350R?

 

[stuntman]

At long last, we get an explanation of why the racing NSX's use such stiff anti-roll bars upfront.
It would be interesting to get some data to judge the effect of lowering the car on the lowering of the roll center(s).

Cars almost always need more front roll stiffness than rear (except most FWD & AWD cars), but yes this explains why the NSX needs SO much front.

Thanks Billy! btw how does the new Mustang 500 handle extended track days? Is it as reliable as the 350R?

Handles them just fine with zero brake fade or overheating. The 500 CFTP blows the doors off the 350R on track and is probably more reliable.

 

[docjohn]

Thanks again!

 

[whrdnsx]

I've already put an NSX on Morse Measurement's K&C rig and have all of the roll centers mapped at various ride heights, as well as a complete analysis of the camber gain and bumpsteer.

There is a pretty steep roll axis inclination in the NSX, the roll centers drop much faster than Cg as the car is lowered, and this all explains why it's popular to run an extremely stiff front spring and bar, and softer rear spring and often no rear bar in track cars.

The NSX needs the front roll centers changed a lot more than the rear, at least that would yield the biggest benefits. I really want to make a set of billet drop spindles, which would replace the entire outer knuckle and ball joints, and the OEM wheel bearing would bolt right up to it. But these would probably run at least $4K for the front set, so it's not a very cost effective solution for most NSX owners. However, this would improve the bumpsteer at lower ride heights, raise the front RC, and the NSX would require less front spring and bar to be balanced, thus improving the ride quality and handling of the car.

One of these days I will make a set for my car, but right now i'm more focused on a dry sump pan that retains AC.

So are you suggesting to leave the rear roll centres alone on a lowered nsx and just concentrate on raising the front RC for improvements in handling?

 

[stuntman]

So are you suggesting to leave the rear roll centres alone on a lowered nsx and just concentrate on raising the front RC for improvements in handling?

There's far more benefit from fixing the front RC. The rear can benefit more from improving the camber curve/camber gain than from changing the RC.

 

[latzke]

Since docjon's attempt to go offtopic didn't work, I doubt mine will, but...

One of these days I will make a set for my car, but right now i'm more focused on a dry sump pan that retains AC.

Is this just an idea, or something you are actively pursuing (and is it being pursued in a way that will result in product others could obtain)?

 

[stuntman]

Since docjon's attempt to go offtopic didn't work, I doubt mine will, but...

Is this just an idea, or something you are actively pursuing (and is it being pursued in a way that will result in product others could obtain)?

The front drop spindles? I have everything I need to get them designed and produced, but I don't think the demand is there to move forward and it's currently not a priority to dump a lot of money into having a set made.

The dry sump pan that retains AC? It's a pretty trick setup that does not require touching any of the main cap bolts and is a pretty easy bolt-on solution (when doing a timing belt). The pan design is almost complete, the harmonic balancer/drive gear is being designed, the oil cooling solution is pretty trick, the sump location has been determined, has adaptability for turbo & NA applications, and i'm pretty close to pressing "go" on the CNC machine.

This is the first time i'm publicly talking about it. If people are interested, I could become a vendor or work with one to provide these dry sumps to the community.

 

[docjohn]

Impressive!..you should gauge interest here with a poll...I'm sure FB as well will get more eyes..Thanks for staying involved in the old nsx...

 

[Anopheles]

The front drop spindles? I have everything I need to get them designed and produced, but I don't think the demand is there to move forward and it's currently not a priority to dump a lot of money into having a set made.

The dry sump pan that retains AC? It's a pretty trick setup that does not require touching any of the main cap bolts and is a pretty easy bolt-on solution (when doing a timing belt). The pan design is almost complete, the harmonic balancer/drive gear is being designed, the oil cooling solution is pretty trick, the sump location has been determined, has adaptability for turbo & NA applications, and i'm pretty close to pressing "go" on the CNC machine.

This is the first time i'm publicly talking about it. If people are interested, I could become a vendor or work with one to provide these dry sumps to the community.

Price point for such a system would be?

 

[stuntman]

Price point for such a system would be?

It's looking like it'll be in line with most other dry sump systems with billet oil pans. It will also include a new harmonic balancer with an integrated drive gear.

 

[latzke]

Price point for such a system would be?

It's looking like it'll be in line with most other dry sump systems with billet oil pans.

How does "in line with most other dry sump systems with billet oil pans" convert to USD?

 

[latzke]

The front drop spindles? I have everything I need to get them designed and produced, but I don't think the demand is there to move forward and it's currently not a priority to dump a lot of money into having a set made.

The dry sump pan that retains AC? It's a pretty trick setup that does not require touching any of the main cap bolts and is a pretty easy bolt-on solution (when doing a timing belt). The pan design is almost complete, the harmonic balancer/drive gear is being designed, the oil cooling solution is pretty trick, the sump location has been determined, has adaptability for turbo & NA applications, and i'm pretty close to pressing "go" on the CNC machine.

This is the first time i'm publicly talking about it. If people are interested, I could become a vendor or work with one to provide these dry sumps to the community.

Yah, not interested in the front drop spindles. Dry sump idea seems interesting. Am I correct to assume the point is to eliminate the potential for oil starvation from sustained cornering as well as eliminate the weak link (oil pump gear) in a money-shift? So this would compete with one or more of baffled oil pan, accusump, and aftermarket billet oil pump gear. Or is there some other consideration/motivation?

 

[stuntman]

How does "in line with most other dry sump systems with billet oil pans" convert to USD?

Google searching "Dry Sump Kit" for other 6-cyl engine applications like BMW M3s and Supras, and looking for the kits with billet oil pans will give you a ballpark idea of the cost, in USD.

I'd suggest learning a bit about them, the components that make up a complete system, and determine if this is something you need or want to give you piece of mind.

Yah, not interested in the front drop spindles. Dry sump idea seems interesting. Am I correct to assume the point is to eliminate the potential for oil starvation from sustained cornering as well as eliminate the weak link (oil pump gear) in a money-shift? So this would compete with one or more of baffled oil pan, accusump, and aftermarket billet oil pump gear. Or is there some other consideration/motivation?

Yes; the NSX is known to have oil starvation problems, especially in right-hand sweeping corners. This is why a baffled oil pan is a MUST for tracked cars. Once you start putting modern R-compound tires, slicks, and or some aero on them, the stock oiling system struggles to keep oil in the pan without exposing the oil pickup tube, sucking air, and leading to a very expensive engine repair.

Accusumps are a cheap $700 fix, and provide a small layer of protection with a lot of headaches and complications. They are slow to react to a drop in oil pressure, a bit maintenance-intensive, have been known to leak, electric valves don't always function properly, manual valves are a pain to constantly open and close, checking oil level is a pain, only provides a few seconds of protection from oil starvation and will not help in long, sweeping, sustained corners, etc... As tires get stickier and people start using more and more effective aero, the benefit of the Accusump is limited and in some cases, are not enough. It took a few blown motors (due to oil starvation) for FXMD to install a dry sump in their race car. From then on, we never had an oiling issue or motor failure.

The goal for this dry sump was to:

- Retain A/C
- Be worry-free and ensure the engine would never starve of oil- regardless of how good of a driver you are, how sticky your tires are, or how much aero you have on your car.
- Increase oil volume to ensure both the bearings and oil-hungry VTEC solenoids have enough oil at all times.
- Eliminate the need for ugly and messy catch cans (you plug the valve cover vents and the scavenge pumps pull a vacuum on the crank case)
- Eliminate the need for an electric turbo scavenge pump (another stage can be added to the dry sump pump to scavenge the turbo)
- Avoid the hassles of an Accusump
- Bolt on to a stock block without touching the main caps or requiring the motor to be disassembled and machined.

 

[latzke]

Google searching "Dry Sump Kit" for other 6-cyl engine applications like BMW M3s and Supras, and looking for the kits with billet oil pans will give you a ballpark idea of the cost, in USD.

https://www.achillesmotorsports.com/Achilles-Motorsports-Dry-Sump-Kit-BMW-S54-p/11-am-dsks54.htm

So, not cheap...but not super crazy either.

The goal for this dry sump was to:

- Retain A/C
- Be worry-free and ensure the engine would never starve of oil- regardless of how good of a driver you are, how sticky your tires are, or how much aero you have on your car.
- Increase oil volume to ensure both the bearings and oil-hungry VTEC solenoids have enough oil at all times.
- Eliminate the need for ugly and messy catch cans (you plug the valve cover vents and the scavenge pumps pull a vacuum on the crank case)
- Eliminate the need for an electric turbo scavenge pump (another stage can be added to the dry sump pump to scavenge the turbo)
- Avoid the hassles of an Accusump
- Bolt on to a stock block without touching the main caps or requiring the motor to be disassembled and machined.

Sounds pretty good.

Will it have some kind of pressure relief valve (to let air into the engine) to ensure the vacuum pressure stays relatively mild and doesn't do funny stuff (pull gaskets in, etc) on an engine that wasn't designed for dry sump?