Lord_Galva

What is up with the curb weight of the 968? I have checked 3 sorces and they all say different weights. What is the weight of the 968?

968 Racer

According to the 2007 POC rule book, the factory DIN weight specification with full factory installed fuel tank, spare tire and complete tool kit, is 3,086 lbs.

That's with an empty ash tray ...

968 Racer

Oh, and that's for a coupe with manual trans. Not sure about Cabs and Tips ...

Lord_Galva

Well, whats up with the sticker in the door that says 3,752lbs?

SpeedBump

with cargo and occupants

flash968

yes - that is the gross weight - this is the maximum permissable weight including all passengers and payload

i think that is why i see so many of these cars sagging in the rear - i think they have overloaded the torsion bars and twisted them - i think people figure "oh, i have 4 seats, so i can carry 4 people AND all my gear) - i think they fail to realize how much people weigh - according to the owner's manual, the maximum load capacity is 639 lbs - that doesn't leave any room for gear if you have 4 adults in there

it's even worse in a cab - we have a maximum load of 397 lbs

GeorgeNZ

I would have thought plastic deformation of a torsion bar by overloading would be unlikely on a road car - you'd run out of travel long before this.

flash968

it happens - all springs sag over time - like any spring, (and a torsion bar is just a spring in a straight line), a constant load will cause fatigue - that rate of fatigue goes up as the load goes up - it also is related to the number of cycles at that load - there is a limit rate to the bar too - go past it, and if there aren't bump stops to stop it first, it can actually break - hold it close to the limit long enough, or cycle it a bunch, bump stops or not, and it won't spring back fully

trailers are a really common example of what overloading can do - people overload these all the time - i've twisted a set of torsion bars on a trailer before - not fun - the bump stops had been removed before i bought it - i loaded it up, not knowing what the load capacity was - boink

GeorgeNZ

loss of spring rate over time (sagging) is due to fatigue is a different mode of failure to the overload situation you suggested where the yeild point has been exceeded and plastic defoemation has taken place

You would have insufficient travel to induce plastic defomation unless you had an in-ordinate amount of preload or some 'special mods' like your trailer.

Point being - saggy arsed 968's are unlikely to have got that way by overloading.

flash968

hmmm - i think we're circling around semantics

we know that a spring will retain it's rate unloaded - loaded it sags - how much it sags and how quickly is entirely dependent on the amount of the load and the cycles of that load

my point is that the car is already overloaded empty - the spring rate is not high enough for the amount of weight applied to it - the "preload" is already too high - this car has the lowest load capacity i have ever seen in a 4 seater

add a heavy load and you are stressing an already weak spring - the result is not unlike running it at normal load for a long time, just sooner

you can actually create the situation in a test if you'd like - throw 500 lbs in the back and drive around with it for a month and see what happens - i don't think you'll like the outcome

we did something like this in a car with a small block - we threw a big block in there, and just twisted the torsion bar adjusters up to reach ride height - mistake - after about 6 months the torsion bars twisted and we were dragging on the ground - we yanked them and installed the big block version and all was right with the world again and stayed that way

i had a similar thing happen on a customer's sandrail - he converted a 2 seater to a 4 seater without changing torsion bars - it was ok for a while, never great, but it did not take long for them to stay bottomed out

so, no plastic deformation is likely not instantaneous, and bump stops would prevent this in the short term, but as the metal's ability to recover from elastic deformation wanes from fatigue, reducing its elastic deformation range, it ultimately moves to plastic deformation - increased loads merely accelerate this process

GeorgeNZ

how do you figure its oveloaded already - a vehicles load rating is not determined by a springs capacity to support the applied load - just like your draw bar rating is not based on spring rates.

Anyway - none of this helps in providing clarity around the original question and I don't think anyone has plans to drop a big block in the back of a 968.

Lord_Galva

Yea, umm now i'm more confused.

GeorgeNZ

OK - 3572lb will be the max permissable weight; Curb weight is less and is the fully fuelled car with spare, tools etc without occupants or luggage

For a manual ROW coupe handbook gives the following;
Curb Weight 3086lb
Max Load Capacity 639lb
Total Permissible Weight 3726
Max front axle 1807lb
Max Rear Axle 2182lb
Permissible Rack Load 165lb

'the gross vehicle weight rating includes the weight of the basic vehicle plus full tank, oil and coolant plus max load which combines passenger (150lb/68kg per designated position) and luggage weight. Luggage weight is not increased by the use of roof racks unless the passenger capacity accordingly'

hope this helps

Damian in NJ

Back when I was a research scientist at Bell Labs we had a neat test bench set up to measure stress. We measured the amount of stress a dime put on a manhole cover-imaged it first without the dime, then placed a dime near the edge and reimaged it.

Yes a dime does put stress on a manhole cover. Is it going to bend it? I don't think so.

rpm's S2

The only way to get four adults in a 968 is to recruit those 'little people' from the Discovery Channel.