Dual exhausts? everywhere, but not on the right cars

argatoga

Can't Start His Wank
Joined
Oct 4, 2005
Messages
17,963
Location
Seattle
Car(s)
'13 Moto Guzzi V7, '08 Pontiac Solstice GXP
They don't have doors with deep cutouts that are the real culprits behind wobbly convertibles. Structurally speaking, the openings in those cars do little to compromise stiffness. And the S2000 weighs more than it could thanks to the bracing needed to keep it stiff, and if it'd been made as a coupe to the same stiffness parameters, it would easily have been much lighter.
I stand corrected. Still open top = fun. :p
 

Lastsoul

Well-Known Member
Joined
Jul 9, 2005
Messages
2,176
Location
Finland
Car(s)
MX5, 406 Coup?, 106 Rallye, Porsche 924, X300 Six
Yeah, best in theory doesn't always make it more fun. :)

But the stock NA could be just a bit more rigid... :D
 

prizrak

Forum Addict
Joined
Apr 2, 2007
Messages
19,981
Location
No, sleep, till, BROOKLYN
Car(s)
11 Xterra Pro-4x, 12 'stang GT
They don't have doors with deep cutouts that are the real culprits behind wobbly convertibles. Structurally speaking, the openings in those cars do little to compromise stiffness. And the S2000 weighs more than it could thanks to the bracing needed to keep it stiff, and if it'd been made as a coupe to the same stiffness parameters, it would easily have been much lighter.
Actually most of its stiffness comes from the monocoque construction more so than extra bracing. Yes it would have been more rigid if it were made as a coupe no doubt about that. Also it would have been more rigid and lighter if it were made out of composites. Point is, it's not exactly wobbly :p
 

Merc63

Active Member
Joined
Jan 6, 2010
Messages
380
Location
Pikesville, MD
Car(s)
'01 BMW 740i M Sport, '05 BMW 330ci ZHP
Yeah, a car (yeah, road car, with doors) with open roof can never be as light and rigid as a car with fixed roof. My mechanics of materials professor demonstrated this really well. Take a hard plastic tube and try to bend and twist it. It should be pretty unflexible. Now take a knife and make a transverse cut about 80% deep of the radius. Try to twist and bend it now. It's wobbly as hell, and you barely removed any material. You've just created open-top plastic tube. If you've ever opened both doors in a cabriolet, you've probably noticed there's only the floor keeping it together. Floor is also pretty flat part of sheet metal, which is not very rigid. Floor plus roof on the other hand is.

But S2000 demonstrates, a open top car can be rigid, but at the cost of additional weight. It can be minimized by clever design, just like Honda has done, but it's still heavier and less rigid than S2000 coupe could be. Do we care if it's well made? Of course not.
Caterham would like a word with you:



Got any coupes that light on the street? Oh, and BTW, the Caterham is a true roadster, as well (side curtains instead of roll up windows).
 
Last edited:

prizrak

Forum Addict
Joined
Apr 2, 2007
Messages
19,981
Location
No, sleep, till, BROOKLYN
Car(s)
11 Xterra Pro-4x, 12 'stang GT
Caterham would like a word with you:



Got any coupes that light on the street? Oh, and BTW, the Caterham is a true roadster, as well (side curtains instead of roll up windows).
In all fairness those doors arent all that deep so there is still quite a bit of metal, also I kinda have to wonder how its rigidity stacked up against other similar cars of the era with a fixed roof (lets face it a Caterham is really just a 7 with some minor tweaks).
 

bone

"bangle for president"
DONOR
Joined
Jan 14, 2004
Messages
16,298
Location
belgium!!
Car(s)
Volvo V40 & Yamaha Banshee
(lets face it a Caterham is really just a 7 with some minor tweaks).
it is on the outside...
i think the chassis, suspension and drive train has evolved quite a bit since the original 7 came out...
 

Lastsoul

Well-Known Member
Joined
Jul 9, 2005
Messages
2,176
Location
Finland
Car(s)
MX5, 406 Coup?, 106 Rallye, Porsche 924, X300 Six
Caterham would like a word with you:



Got any coupes that light on the street? Oh, and BTW, the Caterham is a true roadster, as well (side curtains instead of roll up windows).
Yes, The Caterham is light and probably pretty rigid chassis as well. The thing is, it's a compromise made basically for racing and things which work with this doorles wonder can not be generalized to normal cars. And really light aluminium roof from tubes and sheet metal would make it much stronger and only couple of kilos heavier. Or if they would completely forget those cutouts used as doors, it would also be quite a lot more rigid. But if you would weld the doors of an MX-5 to the body, you would also get extremely rigid chassis. But when we are talking about normal cars, these exceptions don't matter.

If you've any clue about structural mechanics, you know what I mean. If you don't, then don't take part in this discussion.
 

Merc63

Active Member
Joined
Jan 6, 2010
Messages
380
Location
Pikesville, MD
Car(s)
'01 BMW 740i M Sport, '05 BMW 330ci ZHP
I'm also bringing it up as an example of a roadster currently in production. AND it's a prototypical sports car, to show why open cars were part of that definition. Two birds with one stone, as it were. PLUS its a light, rigid, open car. Proving that a road car does NOT have to have a top to BE rigid and light. It simply has to be designed to be rigid and light.

And there are other modern examples of cars like this that are open top, rigid, sports cars AND roadsters.

But, it doesn't have dual exhausts so it doesn't really fit in this thread. lol!
 

Lastsoul

Well-Known Member
Joined
Jul 9, 2005
Messages
2,176
Location
Finland
Car(s)
MX5, 406 Coup?, 106 Rallye, Porsche 924, X300 Six
I'm also bringing it up as an example of a roadster currently in production. AND it's a prototypical sports car, to show why open cars were part of that definition. Two birds with one stone, as it were. PLUS its a light, rigid, open car. Proving that a road car does NOT have to have a top to BE rigid and light. It simply has to be designed to be rigid and light.

And there are other modern examples of cars like this that are open top, rigid, sports cars AND roadsters.

But, it doesn't have dual exhausts so it doesn't really fit in this thread. lol!
Tell me one open rigid sportscar/roadster. And by rigid I mean more rigid and as light as the coupe. There isn't one, unless doorless prototype racing cars count. The simple fact is, that rigidity comes from the material and form. The former is normally steel and maybe carbon fiber in ?berexpensive solutions like Zonda Roadster. The latter depends on design. The larger area that is "covered" by structural parts, the more rigid the part is. In hard top car, you can basically think the whole car as one closed shape (like a tube) when you look the passanger cell directly from the front or rear. Open car with doors isn't a "closed structure", and only the floor holding the thing together (like a tube which is cut 80% through). If you add even small strong bars that connect windshielf frame to the rear end, you'll get "closed shape" that will increase the structural area enormously and you'll improve rigidity by a factor of pretty big number. You can notice a difference in rigidity in NA Miata even by adding a plastic/glassfiber composite hard top, because it creates this effect. Sorry that the explanation is really bad, I don't know proper words for structural terms in English.

And MXM commented on IRC that 7 is not actually that rigid at all. Rigid enough of course, because light weight means relatively soft springs and dampers to control the mass so it works really well, but if we start to talk about numbers...

And good point Topgearfanatic about the dual exhaust on S2000 :D It's probably the only thing I don't like in that car, and easily fixed.
 

LeVeL

Forum Addict
Joined
Jun 16, 2007
Messages
12,495
idk about stock cars, but I bet my Miata with the rollbar is stiffer than the NB coupe.

The S2000 is pretty stiff. Sure, it would have been even stiffer if they made it into a coupe but had they done that, they would not have bothered reinforcing the underside, doors, etc as much as they had to for the coupe.
 

Lastsoul

Well-Known Member
Joined
Jul 9, 2005
Messages
2,176
Location
Finland
Car(s)
MX5, 406 Coup?, 106 Rallye, Porsche 924, X300 Six
idk about stock cars, but I bet my Miata with the rollbar is stiffer than the NB coupe.

The S2000 is pretty stiff. Sure, it would have been even stiffer if they made it into a coupe but had they done that, they would not have bothered reinforcing the underside, doors, etc as much as they had to for the coupe.
Rollbar helps a lot, but the critical point is the door area. There is nothing but the floor holding the thing together, and this is fixed in the coupe. Open both doors of your car and look the side profile and try to think about it without the doors. Only thing that's a bit higher is the transmission tunnel, other than that it's almost flat floor. If you'd weld metal bars between rollbar and windshield fame, it would get probably over triple as stiff as it's now. And from structural point of view, you'd get the same rigidity as in the couple :)
 
Top