suspension design details

[RaceMag]

I am interested in getting some detailed information about performance suspension so I can compare some aspects to other vehicles. This will form the basis of an article in Race Magazine. Since the NSX was such a milestone I thought I would ask here first, but I am after information from the latest series of NSX's.
Does anyone have information about front/rear: roll centres, suspension arm lengths, scrub radii, camber gain in bump/droop, kpi, static camber, bush compliance, mass centroid, damper settings and spring rates and roll bar rates, component weights (unsprung weights) etc etc.

 

[Jin1976]

 

[RaceMag]

thank you but not quite what I had in mind.

 

[710]

Sorry Racemag, I haven’t had time to get exact measurements, but its something I will do. I would like some detailed info too but not had time to measure it yet.

Just some thoughts (and questions) about the suspension, no answers I’m afraid.

With my new bigger (but not wider) wheels I would like to move the centre line (offset) outwards to fill the wheel arches.

But that will alter the scrub radius a little and the feedback from the existing scrub radius is already perfect, in the dry and in the rain. It’s even “feel-able” on snow and ice. I must to measure it some day.
It appears Honda gave the NSX a large castor, as partly evidenced in the quite heavy steering when parking (only when parking!) and then they tried to correct this fault with a very high (easy) steering ratio.
So this castor angle, coupled with increasing the scrub radius by moving the centre line of the wheels outward would make it a little heavier when parking.
But the main difference would be in the feel during driving, I hope it’s not going to be bad and it’s my main concern.
I am producing a steering rack that is a little quicker than stock, much needed in my opinion, but this will result in a little heavier steering when parking. Tests show no heavy steering when moving.
Why Honda settled with such a high castor angle would have to do with their tests to get good handling of course. They ended up sacrificing the parking ease. Good.

Someone would have to make suspension that is adjustable (like on a racing car) to determine what would make it better. Has anyone done this? Please let me know.

I would like to find measurements of the suspension details too. I considered shorting my new quick steering rack slightly to introduce a less calculated bump steer on corner entry when the car is lowered, but I don’t have enough suspension measurements to calculate this so I left it identical to stock. Anyway the “turn-in" is already very good.

The car also has toe–out (out) on the front, so any slight alteration of the bump steer would be critical. Do many other mid engine cars have toe out on the front? Ferraris etc? I would like to know.

Many NSX owners have lowered their cars; this would change the suspension characteristics a lot (including the bump steer).
It would be interesting to test these cars, I suspect they don’t handle as nicely as the stock car because the neutral point has been lost and the suspension is effectively in bump all the time. Does anyone know if Honda lowered the car when they went to the 17” wheels? By how much? Does the later NSX with the 17” wheels handle as well as the older model?
How much if any difference is due to the power steering on the newer models? And why doesn't anybody like the power steering in comparison to the manual steering? Even the Zanardi version, normally with power steering, had the older manual specially installed. Why? I understand the electric power steering essentially shuts off when the car is moving above 30kph or so. Any feedback on this would be appreciated.

The front steering seems to compensate perfectly for bump steer IMO. Obviously this is due to all round suspension compromises, but the compromises are not even noticeable except in the large castor angle, difficult parking. Still feels nice and sharp when driving tho.

I’m going to put 17” on the front (instead of the stock 15”) with higher profile tyres, maybe 40 or 45 series instead of the normal 35 series, so I will have to lower the car to compensate for this. I’m afraid it will change the handling, but I have no choice, as the stock brakes are just not up to the job. In the days of the NSX, early 1990’s, 15 inch wheels where big. Now they are too small for good brakes.

The rear suspension seems interesting too, the arrangement of the upper and lower A-arms and their connection points give very stable and usable handling even though there are weird changes in toe, castor and camber.
The NSX has the classic very slight understeer on corner entry, settling in and slow (but not sluggishly) going to slight oversteer in the corner, very very easily controlled by the accelerator. Stay on the gas, oversteer continues, very slightly ease off, comes back to neutral. Or sharply let off and there is a little comfortable oversteer quite controllable with a little opposite lock then going calmly into understeer. It feels like the driver can do anything he wants with the car, in a corner on the limit. This results in a big smile.
The setup is what we try to aim for in our race cars but rarely find.

I am still fooling around with the suspension; I will start with adjustable coil-overs to see the difference in handling in bump. Then I will install the larger offset wheels, to see the difference in scrub radius.
A new balance will have to be found, but I hope it is close to original, because it’s great now.

I am making a 3D digitiser, a really simple one, to design the chassis and suspension of another car I’m building. In SolidWorks. I will use this to measure the pickup points, steering and other dimensions on the NSX too. But it will be in a couple of months. No time just now.

Anyway I would love to find detailed measurements of the suspension. If anyone has any technical drawings with dimensions and angles, I too would appreciate seeing them.

Sorry for the rambling, I’m still learning about the handling of my NSX, and may change some of my opinions as I go on. Feel free to comment or correct, I can only learn more.

RaceMag, pity I don’t have specifics yet.
Peter

 

[john@johnhudakracing]

I am interested in getting some detailed information about performance suspension so I can compare some aspects to other vehicles. This will form the basis of an article in Race Magazine. Since the NSX was such a milestone I thought I would ask here first, but I am after information from the latest series of NSX's.
Does anyone have information about front/rear: roll centres, suspension arm lengths, scrub radii, camber gain in bump/droop, kpi, static camber, bush compliance, mass centroid, damper settings and spring rates and roll bar rates, component weights (unsprung weights) etc etc.

I'm uncertain how you are consuming/conveying the data in your article, You mentioned you were interested in the above specs for late models- which model/year? Coupe/Targa, Zanardi, Type R, etc.. ? Given that you could likely obtain rough generic specs. Although to be frank precision is really important when doing calculations, and it is ideal to obtain the data points as accurately as possible on the specific vehicle whereas this data will be later applied as opposed to using generics for input as per above.

The most basic generic specs you inquired about above are already published for the various models- such as the OE f/r spring rates in kg, the stabilizer bar roll stiffness differences in percent, and the RC changes.

However, given your audience you would do better to derive these yourself; although it would be easier with specifics. For example, for the stabilizer bar roll stiffness- I'm unclear if you're just after the approximate torsional rate or wished to include bushing deflection, due to bending and torsional load taking into account conical and torsional bushing rates as well?

OE Suspension component weights and arm lengths are static and I might still have them recorded from awhile back- I'll have to see if I can dig that up it was awhile ago. Others might have that to offer to you as well.

Some of the remaining line items you mentioned (camber gain, shock dampening, etc..) aren't published and are best measured either with the proper tools or otherwise calculated as applicable.

 

[RaceMag]

710, thanks for your thoughts.
John, I am not yet sure how I will convey the information as the article series is in development. However Race Magazine is a technically focused magazine so the article would have as much space as required.
I imagine that I will list the relevant information from a range of cars of similar layout, thus the NSX information will be alongside the Lotuse Elise/Exige, Noble M400, Porsche Cayman etc.
I am interested to see what similarities/differences there are accross the board in things such as lateral/vertical control of RC's etc. Perhaps there are none, but this will be informative in itself.
I would appreciate any information you might be willing to pass on.
Attached it the cover of the latest issue, just to show that Race Mag really exists!

 

[710]

RaceMag, I’m really interested in that article about drivers' reflexes.

 

[RaceMag]

you can email me at [email protected]
Regards Neil

 

[710]

Hi Neil, I though I’d post this instead of sending a PM, because others may have comments about it that I would like to hear.

I really want to finish building my digitiser and measure several cars’ suspensions, including my NSX. It’s interesting that you are looking into the comparative roll centres etc of cars. I have never seen any technical drawings of any cars suspensions, I think they are secret or just plain unknown.

I am designing (then will build) a special chassis and suspension for a very special Lotus Elan 26R S2 (it’s the old elan). The suspension will be totally different and more modern.

This is specifically why I am making this digitiser, I have the body (which will remain exactly as original) and need to have several parts of the body in 3D CAD to design the new chassis and suspension to fit. I am an engineer and already proficient with 3D CAD. The digitiser will be able to do an area of about 1 metre by 1.5 metres and about 0.5 metre deep. I haven’t ordered the parts yet, because I can make it do 1m x 2.5m but the parts are more expensive. So I don’t know yet. The software will be first 2D into AutoCAD then into 3D Solidworks.

Do you think if I wanted to make some money with my digitiser, that I could measure several cars and sell/publish/use the results? I can’t see how, but something may come up. Any ideas? Suspension consultancy for example? If I had a data base of several suspensions of the Noble, Enzo, NSX, Lotus etc I could provide people with a suspension similar (or identical to) those cars. The industry is picking up lately; many people are building their own cars.

Most 3D digitisers are very expensive and then after all the digitising, the computer crashes because of the resultant “point cloud”! There is a lot of work required to make the information usable.
My digitiser will change that for me, it is more primitive but will give usable simple data easily imported to a 3D programme (SolidWorks). It is fiddly and labour intensive, not the kind of product that I would expect to sell. But I could use the information it gives for myself.

The trade-off is less accuracy, +/-0.5mm to +/-1mm. Most 3D digitisers have +/-.001mm or something ridiculous like that.
1mm is ok for me though, and to do something as big as a suspension and its mounting points the only alternative is a big 3D digitiser of €20,000 or more. Mine will cost €500 because I already have the electronics/CAD.

If I digitise several other cars’ suspensions, Ferrari, Elise, maybe an Enzo and a couple of Formula or LeMans cars, it will be very interesting to see the results in a 3D motion programme of the roll centres, camber, castor, kingpin incl., scrub radius, bump-steer, anti-dive, everything on real existing cars! Not just theory like I did before.
What do you think?

Peter
PS: About that article on drivers’ reflexes, my father was doing some work on reflex measurement, that is, how quick a person was able to react. That’s why I’m interested to read it. I’ll email you about that.
I have temporarily stopped taking new subscriptions to new magazines, so even though I would like to subscribe, I can’t at the moment. But in the future for sure.

 

[RaceMag]

you're welcome to subscribe anytime at your leisure. The reflexes article was done by a Neuropsychologist and looks at ways of maintaining reflex with ageing and strategies on the day to improve.
You would not be able to sell the information where I am and you would have to be very careful in most countries. The law will vary, but you get sued where the law is.
The digitiser sounds interesting, here I used the skilled services of a suspension engineer.