Planet-9 Porsche Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
23 Posts
Discussion Starter · #1 ·
I have heard that the Cayman has 100% stiffer chassis than the Boxster and as a result it delivers more sports car feeling than the Boxster.

I have been wondering that what is the difference in 911 coupes and cabrios? Has anyone heard any percentage figure? I do find the 911 cabrio rigid enough, even with 19" and PASM in sport there is no problem even on bad road surfaces, just wondering about the figures.

In addition, does anyone know the difference between the Boxster and 911 cabrio? There definitely is one, but it would be nice to hear a percentage figure on this, too.

Thanks for any inputs!
 

·
Premium Member
Joined
·
2,219 Posts
From what I have read the 911 coupe chassis is the stiffest of the group, with the Cayman being right behind it. Then I would say the Cab and then the Boxster. I don't think any one of them is anywhere near 100% stiffer than another. All of them are close if not the best in class for either coupe or convertible chassis stiffness.
 

·
Registered
Joined
·
23 Posts
Discussion Starter · #3 · (Edited)
From what I have read the 911 coupe chassis is the stiffest of the group, with the Cayman being right behind it. Then I would say the Cab and then the Boxster. I don't think any one of them is anywhere near 100% stiffer than another. All of them are close if not the best in class for either coupe or convertible chassis stiffness.
If I am not mistaken the 100% between the Boxster and the Cayman has also been mentioned on this site, originally I read it in some magazine, don't remember any more which and when...

Absolutely, all of them are best in class (or so close that it makes no difference)!


EDIT: I found the 100% mentioned, in French, so my translation follows.

Grâce à son toit, le Cayman est 100% plus rigide que le Boxster et cela se ressent très bien -- Thanks to its roof, the Cayman is 100% more rigid than the Boxster and you can really feel that.

http://fr.cars.yahoo.com/essai/porsche-cayman_s_s-237-1137172001.html
 

·
Registered
Joined
·
1,830 Posts
I have heard that the Cayman has 100% stiffer chassis than the Boxster and as a result it delivers more sports car feeling than the Boxster.
What does this mean? Instead of flexing .1mm (Boxster), the Cayman chassis flexes only .05 mm? How does one measure chassis stiffness?
 

·
Registered
Joined
·
159 Posts
Logic tells us that a coupe should be stiffer than a open car because of the roof structure, all things being equal. I remember reading in Christophorus that Porsche used heavier body panels in the cabs than in the closed 911's and went to great effort to make sure the drag was the same on both cars. Specifically this was on the Turbo but I would assume the engineers would be just as attentive on other models. Unless you are racing it I think the point would be moot for most of us. if I was racing it I would prefer the CS but as someone who only puts the top up in the rain or very very cold I'll sick with the Boxster S
 

·
Registered
Joined
·
620 Posts
What does this mean? Instead of flexing .1mm (Boxster), the Cayman chassis flexes only .05 mm? How does one measure chassis stiffness?
Basically - yes. I have read the 100% greater stiffness figure attributed to Torsional stiffness. I'm pretty sure I read it in Porsche literature. They also quoted a similarly impressive increase in bending stiffness.

Stiffness can be measured by physically applying a load and measuring chassis deflection. It can also be approximated by vibratory methods and FEA (finite element analysis - a computer-based calculation).

Stiff chassis will be appreciated even on the street when encountering heavy bumps. It has less obvious benefits on the track - less-stiff chassis allow greater un-damped chassis motions - stiff chassis allow greater damping and tuning at the suspension.

There is a point of diminishing returns - and there is debate about this point.
 

·
Premium Member
Joined
·
1,844 Posts
How does one measure chassis stiffness?
There are two ways I'm aware of. One is to measure the torque required to bend the chassis a given distance, like newton-meters per millimeter. I've seen BMW discuss this sort of measurement. The other method I've seen is to measure the resonant frequency of the chassis. The higher the frequency in Hertz, the stiffer the chassis.
 

·
Registered
Joined
·
23 Posts
Discussion Starter · #8 ·
There are two ways I'm aware of. One is to measure the torque required to bend the chassis a given distance, like newton-meters per millimeter. I've seen BMW discuss this sort of measurement. The other method I've seen is to measure the resonant frequency of the chassis. The higher the frequency in Hertz, the stiffer the chassis.
The story in French that I found says that Porsche engineers have calculated that it takes the torque equivalent of 92 CaymanS engines to twist to the body one degree. My knowledge stops here...;)


Pour la petite anecdote, les ingénieurs de Porsche ont calculé que pour que la carrosserie puisse se tordre d'un seul degré, il faudrait un couple maximal équivalent à celui de 92 moteurs de Cayman S !
 

·
Registered
Joined
·
620 Posts
The story in French that I found says that Porsche engineers have calculated that it takes the torque equivalent of 92 CaymanS engines to twist to the body one degree. My knowledge stops here...;)


Pour la petite anecdote, les ingénieurs de Porsche ont calculé que pour que la carrosserie puisse se tordre d'un seul degré, il faudrait un couple maximal équivalent à celui de 92 moteurs de Cayman S !
If we take the CS torque to be Gen1, it is 251 lb-ft. 251 x 92 = 23,092 ft-lb/deg.

Without divulging too much....that's pretty darned good - even by racing standards. The roof really helps.
 

·
Registered
2012 911 S
Joined
·
97 Posts
Basically - yes. I have read the 100% greater stiffness figure attributed to Torsional stiffness. I'm pretty sure I read it in Porsche literature. They also quoted a similarly impressive increase in bending stiffness.
Could you tell me where I can read about this? The Porsche literature that is.

Thanks
 

·
Premium Member
Joined
·
2,173 Posts
A 100% increase is doubled, so it follows then that the Cayman has twice the torsional rigidity of the Boxster? Turning it around, the Boxster has half of the Cayman's torsional rigidity? I think I need to see this stated clearly in print from an original Porsche source.
 
1 - 11 of 11 Posts
Top