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At risk of appearing facetious (who, me?) it seems that for years each successive generation of cars from just about any manufacturer has been described as 20 or 30 or 40 percent stiffer in construction than its predecessor. Either they were bendy as rubber at one time or they must be inflexible as granite by now.
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>>Is the handling 10% better?
Well exactly! Like most engineering measures which leak out via marketing, the meaning gets lost or diluted. When designing a car body, or chassis, there are targets for both static and dynamic stiffness - usually, these are derived relative to the stiffness of the suspension. Once you have a body torsional stiffness that is N times the roll stiffness of the stiffer suspension (front or rear), then it is diminishing returns to go any further - i.e., bad engineering, wasteful use of materials and welding processes to try to go any stiffer.
N will vary from manufacturer to manufacturer, or in some cases, the minimum stiffness and maximum mobility as a function of frequency will simply be specified.
In most cases, convertibles are stiff enough to allow adequate handling - most of the difference is in our response to phenomena like scuttle shake, rather than a real diminution of the car's limit performance. Or, put another way, because the car body moves around a little bit, we erroneously lose confidence in its performance.
>>it seems that for years each successive generation of cars from just about any manufacturer has been described as 20 or 30 or 40 percent stiffer in construction than its predecessor.
I don't believe the numbers quoted by the marketing types either.
Either they were bendy as rubber at one time or they must be inflexible as granite by now.
Quite!
Number_Cruncher
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As an aside, what is "scuttle shake" ?
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As an aside, what is "scuttle shake" ?
A term for the flexing of the scuttle or sill usually noticable by the movement of the rear edge of the door relative to the body, door catches can rattle etc.
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And the scuttle is ?
Basically the structure comprising the bulk head behind the dash. It is an old term though that was perhaps more relevant when cars had a seperate body and chassis.
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Scuttle: A small opening or hatch with a movable lid in the deck or hull of a ship or in the roof, wall, or floor of a building.
Translate to cars. The area where there are openings in the body shell. Door openings or more obviously where the roof has been cut off. Scuttle shake is where the surrounds of these openings flex.
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TourVanMan TM < Ex RF >
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The area where there are openings in the body shell. Door openings or more obviously where the roof has been cut off.
Nope, cheddar was right - it's the area in front of the windscreen and the front bulkhead.
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Nope, cheddar was right - it's the area in front of the windscreen and the front bulkhead.
When I worked for a car manufacturer it meant what most people would call the front bulkhead, i.e. the body panel in front of the fascia.
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L\'escargot.
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Extract from The Volvo Owners CLub website:-
The Volvo P1800 has an integral body (monocoque) so that there is no inde-pendent chassis frame. The body is composed of a number of pressed steel plates, each of which forms part of the supporting construction. The main parts of the body consist of the floor, side sections, rear section, scuttle, roof section, front mudguards, doors, luggage compartment and bonnet. The floor section consists of the front and rear floor plates and inner cantrail Front and rear cross- members), tunnel and scuttle.
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L\'escargot.
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When I worked for a car manufacturer it meant what most people would call the front bulkhead, i.e. the body panel in front of the fascia.
Yep, historically the opening was the transmission tunnel.
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Either they were bendy as rubberat one time or they must be inflexible as granite by now.
That's about the size of it in fact. Vintage cars tended to have chassis made from longitudinal steel channels with cross-members, with stiff cart springs and rigid axles. The body only began to play a structural role in the late thirties with cars from Citroen and Lancia. The whole thing used to flex quite perceptibly.
Stiffness is thought important because it enables the much more complex suspension of modern cars to work as it is designed to work, without any random movement that might alter weight distribution or wheel angles.
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The first stiff car I met was a Mercedes. I stopped to help a lady one day in Zambia, where she had drawn off the road edge, because of a flat nearside rear tyre. The road edge was surfaced with laterite (like red sand, but not loose), cambered to a drain. The lady had neither jack nor tools, so I jacked it up with my vertical screw jack under the back axle. I was accustomed to flexible cars where you lifted the wheel just enough to make the change. But, when I took the weight off that wheel it took the weight off the other too, my jack fell over and the car slid into the ditch. Fortunately I was a little concerned at doing what I did, and was paying attention.
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Thanks folks - this has made very interesting reading.
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If you want to feel how stiff a car is, push your fingers into the gap between door and body from the inside while the car is traveling. Some flex so much they pinch your fingers.
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TourVanMan TM < Ex RF >
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one thing I was impressed with, was Rovers design on 2/400 series 95 and before.
it could take bends at ammazing speed without giving signs of slipping, it holds the road, even my one can take a bmw on a half decent roundabout without losing its hold on the road,so its strenght relies on its chassis/body construction suspension build and most of all tyres,any weak spots would show.
and some run down rovers ;)
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Steve
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But stiffness, steve?
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The stiffness of the chassis is but one of many aspects, i.e. if the design of the suspension is carp then it matters not how stiff the chassis is, an integrated package is what is required, all parts working in harmony.
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one thing I was impressed with, was Rovers design on 2/400 series 95 and before. it could take bends at ammazing speed without giving signs of slipping, it holds the road, even my one can take a bmw on a half decent roundabout without losing its hold on the road,so its strenght relies on its chassis/body construction suspension build and most of all tyres,any weak spots would show. and some run down rovers ;) --
If you study the dynamics of tyres you'll find that they slip at about 5mph and above, so your Rover was sliding around that roundabout! As for the "I can take a BMW on any roundabout", so could I with my MG Midget. As long as the BMW driver wasn't trying and I was....
Ultimate cornering speeds won't be that different for road cars on road tyres, it's just how close to the limit you're prepared to get.
Gareth
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Pre-95 2/400 wasn't, of course, a Rover (I think)...
Real Rovers like the P6 (2000 and 3500) were designed properly to go round corners while keeping their wheels upright on the road.
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If you want to feel how stiff a car is, push your fingers into the gap between door and body from the inside while the car is traveling. Some flex so much they pinch your fingers.
I'm so glad my kids don't read this, because they would try it...
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