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Are tighter shut lines a sign of a stiffer chassis, or can you have tight shut lines and a not so stiff chassis ?
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Landrover always managed shut lines you could drive a 'bus through - but then they have bendy chassis too. I'm not a fan of their products.
659.
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I've always taken it (them) as a general sign of tighter tolerances, but I guess you couldn't do it without plenty of stiffness. It must mean better quality control, which can't be a bad thing.
Edited by J Bonington Jagworth on 20/10/2007 at 21:13
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Always remember my old Pug 106- if you jacked up one corner on it and then opened one of the doors it was difficult to shut it again as it seemed misaligned by about 1/2 an inch. It must have had diddly-squat rigidity.
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Does chassis stiffness really matter?
I can understand it being important in a modern racing car, but some of the best handling motors I've had used to visibly twist on uneven corners.
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Does chassis stiffness really matter?
In steady state cornering, it only matters if there's a large difference in the roll stiffness between the front and rear axles - effectively, the chassis twist softens the roll stiffness of the stiffer axle.
Dynamically, and in unsteady conditions, like bumps, the chassis experiences twist, and the torsional stiffness of the body becomes important.
Bending stiffness for cars other than soft-tops is usually not a big issue.
Number_Cruncher
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>>Bending stiffness for cars other than soft-tops is usually not a big issue.
Omigoodness !
Have you just added a whole new issue?
I can understand 'roll stiffness'.
Does 'bending stiffness' mean what I think? Folding in the middle?
Edited by Dynamic Dave on 10/03/2008 at 19:22
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>>Does 'bending stiffness' mean what I think? Folding in the middle?
Mmmm - think bananas!
Number_Cruncher
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And to answer the OP: body stiffness (whether torsional or bending) has no connection with the width of shut lines, as moveable panels like doors, bonnet and bootlid have no structural function in modern cars. Chassis and body can be treated as the same thing in nearly all contemporary cars.
If however the shut lines can be seen opening and closing when the car is in motion, that is an indication of poor stiffness somewhere.
:o{
Edited by Lud on 21/10/2007 at 06:00
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body stiffness (whether torsional or bending) has no connection with the width of shut lines as moveable panels like doors bonnet and bootlid have no structural function in modern cars.
I think the reason the OP suggested it, is that if you've got a flexible bodyshell there's no way you can have tiny panel gaps, because they'll close up and knock off the paint when you hit some bumps.
Perhaps it's also to do with manufacturing tolerances? However I know that some cars are pulled into shape after the body is welded so they've almost got a machining tolerance for the bodyshell!
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Torsional regidity is extremly important. Firstly the suspesion is designed, or should be, to keep the tyres in contact with the road and upright. It cannot do this if the suspension pick up points ar moveing around in space due to lack of torsional regidity. A secondary benefit of stiff chassis/shell is that there is less of a tendency to develop squaks and rattles.
If the chassis/shell has sufficient torsional regidity then it will have sufficient beam stiffness.
When the roof removed from a normal stressed skin car to create a convertible a lot of the stiffness is lost. Useually extra strengthening will be added to attempt to replace some of the lost stiffness at the cost of adding more weight.
The opening panels add nothing to teh stiffness of the shell. A two door car will usually be stiffer, lighter and cheaper than the corresonding four door model.
When BMC as it was enterd the Maxi in the world cup rally (1970 ?) they welded up the tailgate to stiffen up the shell. If I remember correctly that doubled the stiffness.
Torsional regidity is next to godliness should be the adage of the chassais designer, along with simplicate and add lightness of course.
(I think that 'simplicate and add lightness' came from Tommy Sopwith, famous WW1 aircraft designer)
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