I've heard a lot of talk that a coupe is lighter than a convertible from my friends. But doing the math, the 10lb top motor and around 8lb in piping and material. This easily beats a 40lb roof on a standard car. Am I missing anything here?

 

all convertible need to strengthen the chassis in order to acheive good handling.

that s why convertible are always heavier than coupe.

 

That's true when taking an existing design and producing a convertible, for example with BMW 3 series, but when you start with a blank sheet of paper there's no reason for the chassis to be overweight. The S uses a very lightweight, but strong box section chassis to achieve incredible rigidity (you'll find NO scuttle shake on an S) without compromising its light weight.

 

[QUOTE]Originally posted by SlicksAgain
[B]


That's true when taking an existing design and producing a convertible, for example with BMW 3 series, but when you start with a blank sheet of paper there's no reason for the chassis to be overweight.

 

Well I'd have to say that an S2000 coupe, based on the same chassis would be heavier. It's not that common for a drop top to later get a fixed top cousin - normally the other way around. One that does spring to mind is the BMW M3 Coupe, based on the Z3 - I believe.
Maybe someone can shed some light on just how mush of the coupe was borrowed from the Z3, and whether it is heavier?

 

[QUOTE]Originally posted by SlicksAgain
[B]


That's true when taking an existing design and producing a convertible, for example with BMW 3 series, but when you start with a blank sheet of paper there's no reason for the chassis to be overweight.

 

[QUOTE]Originally posted by SlicksAgain
[B]


That's true when taking an existing design and producing a convertible, for example with BMW 3 series, but when you start with a blank sheet of paper there's no reason for the chassis to be overweight.

 

If you can believe Edmunds' numbers, the Z3 3.0 hatch is 33 lbs lighter than the similar 3.0 coupe. Which on the surface lends credence to the arguments of at least one here that a from-ground-up convertible can be lighter. However, I'd still side with the opposition. At least on an apples-apples comparison (ie, of similar rigidity). By virtue of the lack of a roof, convertibles are a lot less stiff in torsion (probably in other modes too?). You have to add a lot of thick metal to make up for that. Simple structural mechanics (what little I remember of a class taken more years ago than I want to admit) clearly shows so. In the case of the Z3, the convertible is pretty darned floppy. Which probably explains why it can be lighter than the much stiffer coupe. You see a lot of convertibles (S2000, Viper, Vette) that have large central tunnels or side sills. This is in part to add rigidity. The downside is the weight.

If I recall, coupes were dominating Lemans. They had to handicap them to make the open-cockpit prototypes competitive.

 

[QUOTE]Originally posted by FCGuy
[B]By virtue of the lack of a roof, convertibles are a lot less stiff in torsion (probably in other modes too?). You have to add a lot of thick metal to make up for that.

 

The power top motor is only 10lb?
How did you guys know that?

Thanks,