How does body flex affect handling?

[kenjiMR]

I was reading a newsgroup recently and people were comparing various sports cars... the discussion was arguing that the 911 and the NSX was on a league of their own when compared to the Supra or 300ZX (like we already didn't know that) Well, someone mentioned that they've experienced their windshields cracking while driving their Supra and the 300ZX on the track! As far as anyone knows, has that ever happened to a NSX before? I know that the NSX is a stiff car, but its hard to believe that the Supra and the 300ZXs are that soft! What kind of issues arise due to a soft car? I've heard that the Miata aren't very stiff, yet it handles good right?

 

[lemansnsx]

Originally posted by kenjiMR:
I was reading a newsgroup recently and people were comparing various sports cars... the discussion was arguing that the 911 and the NSX was on a league of their own when compared to the Supra or 300ZX (like we already didn't know that) Well, someone mentioned that they've experienced their windshields cracking while driving their Supra and the 300ZX on the track! As far as anyone knows, has that ever happened to a NSX before? I know that the NSX is a stiff car, but its hard to believe that the Supra and the 300ZXs are that soft! What kind of issues arise due to a soft car? I've heard that the Miata aren't very stiff, yet it handles good right?

Can't comment on Supras and the others that you mention but C4 Corvettes were so flexible that if you had the rood off and then parked the car on a slant you could not attach the roof - the attachment points wouldn't line up!

------------------
Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates

 

[nsxtasy]

As far as anyone knows, has that ever happened to a NSX before?

No.

I know that the NSX is a stiff car, but its hard to believe that the Supra and the 300ZXs are that soft!

The NSX is considerably stiffer than other sports cars.

There are many different kinds of rigidity - torsional rigidity (ability to twist), longitudinal rigidity (ability to flex lengthwise), etc. One way of determining how stiff an open-top car is, is to jack the car up on both sides at the center jacking point, and see how much the distance increases from the top of the windshield to the top of the rear of the cockpit. In the NSX-T, this is reported to be about 1/16". This is an incredibly small number. This distance on some other cars will increase several inches, even up to a foot.

What kind of issues arise due to a soft car?

There are issues of feel (if the car just feels like it's not holding the road as well) as well as sound (squeaks and rattles). Virtually all cars lose some rigidity when the top is opened, but some are better than others. The NSX is perhaps the best of all cars in this regard.

 

[maomaonsx]

There is more than that, but simply stated:
chassis flex changes suspension setting, makes handling less predictable, thus harder to drive faster.

------------------
G Dummy~

Faster than stock.

 

[Lud]

The S2000 is stiffer than the NSX, which is not surprising since it's the same company 10 years later, the car was designed from the start without a fixed roof, and the car is smaller. I'm not sure about some of the other newest cars designed with an open top in mind (360 Modena, etc.) Manufacturers rarely publish this data anywhere particularly easy to find.

 

[DanO]

Originally posted by kenjiMR:
What kind of issues arise due to a soft car?

I think the major issue with a soft chassis is that it is like having a soft suspension, that is, weight transfer is delayed at turn in and therefore less grip at turn in (less crisp) and then there is weight transfer rebound somewhere and sometime in the corner which can have a weight overloading effect on the tires and suspension geometry thus making the car less predictable, controllable and grippy in the corners.

DanO

 

[Edo]

Another issue with Chassis flex is the inability to tune a suspension to the car's characteristics. If the Chassis is flexing through the corner, the suspension points are moving in relation to each other, which makes it a bit imprecise, not to mention thje fact that the Chassis is absorbing some of the suspension's work by moving around.
When you put a very stiff (race track oriented) suspension in a car with a soft chassis this exacerbates the problem as the suspension sometimes ends up being even stiffer than the chassis, thus causing the chassis to flex more than than the suspension moves.
Bad idea. Go drive a V-8 Convertible Mustang, preferably a new one. I rented one last week and it made me almost nauseas(sp?) driving around in it because of the excessive cowl shake. BAD BAD BAD. The NSX has a VERY rigid chassis to it, although I have not driven a T, so I cannot speak for those cars. Suffice to say, stiffer=better..in more things than just cars...

 

[DeHaldaswerth]

I have long wondered what the numbers are as to rigidity on the NSX, especially when the T and Coupe are compared.

When the C5 Corvette was introduced, GM made a big deal about the stiffness of the hydroformed main frame rails. In the book "All Corvettes Are Red", the author gives a pretty thorough explaination of how chassis flex is measured. It seems like its in hertz -- or some derivitive of the word. As I recall, the C5 coupe was many times more rigid than the car it replaced; having owned a '94 and a '99, I can certainly confirm that there was a huge improvement.

It's been so long since I've driven a C5 that I can't comment on how it compares to my NSX coupe. All I can say is that the NSX feels like it was machined out of a solid block when I'm driving over rough surfaces. WE HAVE GREAT CARS!

 

[Edo]

As far as I know there is no standardized unit for Chassis rigidity.
You might hear 50% stiffer than last year's model about once every 2 years. Heck that would mean my Ford Ranger is something like 900% stiffer than it was 10 or so years ago. And it still waffles over bumps like a cattle barge.

As Nsxtasy said there are many ways you can benchmark chassis rigidity. Consequently most manufacturer's claims can be pretty much useless or at least must be taken with a grain of salt.

All I know is that the NSX still has one of the stiffest chassis' in the world. Heck C&D in one of their articles said even the F-355 didn't feel quite as solid as the NSX.
GO NSX!!

 

[JoeSchmoe]

Another common measure for torsional rigidity is (ft/lbs) per degree.

This is a measurement of the amount of force required to twist the chassis 1 degree.

I ran across a book some years back and I recall that F1 cars were in the 30K range and stock cars (nascar) were in the 10k-15k range. Most of the other cars came in under 5K, with a lot of stuff from the 60s and 70s hovering around 1-2K.

I also recall the EV1 brochure listing it (EV1) as well over 10K.

I am still looking for the equivalent number for the NSX.

On a different note, I recall the EV1 quoting a 0-60 of ~7sec and GM had videos of the EV1 toasting a stock miata at the strip. It does have a 85 mph limiter, so 1/4 mile was a different story.

 

[1BADNSX]

As Joe pointed out there are standard measures of stiffness. First, there are two types of stiffness (torsional and bending). Torsional is a measure of how much the chassis will twist (in degrees) due to a moment (in ft pounds). Therefore it has units of lb ft/deg. Bending stiffness is a measure of chassis deflection (inches) with a given load (lb). Bending stiffness isn't as critical as torsional stiffness only because a chassis with good torsional stiffness will also have good bending stiffness.

Typical unibody vehicles have torsional stiffness of 4000-10,000 lb ft/deg. I do not know the NSX value, but the OEM's generally just claim percentage improvements because the public doesn't care or understand the number and they probably don't want to list the figure for other companies to know. But stiffness is very easy to measure if the other companies want to rent or buy a car to make the measurement.

A final note. How stiff is stiff enough? The chassis must resist the difference between the front and rear roll rates (lb ft/deg) or the chassis will twist causing the camber, toe, and load to change for every corner which is not good for handling (obviously).

Bob