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Old 8th December 2008, 15:04   #1
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Default Chassis Stiffness

Hi,

A question that keeps popping into my mind - Does the chassis itself become less stiff as a car puts on more kilometers?

A car that has a lakh of kilometers under it's belt just doesn't seem as stiff as it used to be, even with regular suspension work, regular tightening of chassis nuts, etc. It could also be due to the tolerance of the fasteners becoming looser after so many bumps.

Thanks,
Amit.
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Old 8th December 2008, 16:09   #2
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Nope i don't think so if you regularly keep doing the maintenance checks that you have mentioned.
I may be wrong. Others please correct and clarify.

Could you elaborate "suspension work"?
The shock absorbers do get dampened and soft over a period of time.
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Old 8th December 2008, 16:43   #3
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Quote:
Originally Posted by king_julian View Post
Hi,

A question that keeps popping into my mind - Does the chassis itself become less stiff as a car puts on more kilometers?

A car that has a lakh of kilometers under it's belt just doesn't seem as stiff as it used to be, even with regular suspension work, regular tightening of chassis nuts, etc. It could also be due to the tolerance of the fasteners becoming looser after so many bumps.

Thanks,
Amit.
Correct. Chassis starts flexing over usage. Rust is also a reason.
This is an aspect that is easily missed out while getting a used car.
With respect to monocoques,there are techniques like Seam welding used to strengthen chassis rigidity.
Adding strut tower braces, uprated sway bars,etc help quite a bit.
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Old 9th December 2008, 10:31   #4
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Quote:
Originally Posted by king_julian View Post
regular tightening of chassis nuts, etc.
Can someone please tell me more about it ? I have never heard about this before ? where are the nuts ? how much does it take to tighten them ? what effect do they have ?
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Old 9th December 2008, 10:43   #5
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Yes its true that after wear and tear of many kilometers, the chassis will lose its original strength. But this depends upon manufacturer to manufacturer. But no doubt about the flex increasing.
In case of body on chassis configurations, the chassis is more rigid. Here the chassis holds on its stiffness for longer and wont flex much. This is why it is preferred for real off roaders.

In case of monocoque construction, each and every structural members supports the members adjacent to it, and hence it is safer as far as crash safety is considered as the energy is distributed in a better way as compared to body on chassis. And this is also the reason why the chassis lose their stiffness a bit faster than the body-on-chassis setup.
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Old 9th December 2008, 11:10   #6
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aag, thats a very educative note. Thank you.
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Old 9th December 2008, 11:50   #7
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Thanks for all the replies - strut braces seem like a cost effective method to improve stiffness.

@Shashank - I was referring to an item titled something like "Tighten all nuts and bolts" that the service station guy does during servicing. I figured that this refers to the nuts that hold the sheet metal, engine, etc., to the chassis, though I could be wrong. I believe this is a good thing to do after a long drive.

Amit.
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Old 9th December 2008, 17:18   #8
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Quote:
Originally Posted by aagoswami
Here the chassis holds on its stiffness for longer and wont flex much. This is why it is preferred for real off roaders.
An incorrect belief.
Off-roaders NEED flex.
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Old 9th December 2008, 17:22   #9
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Quote:
Originally Posted by nitrous View Post
An incorrect belief.
Off-roaders NEED flex.
In an typical off-roader the chassis is separate from the body. So the flex needs to come from the chassis. In a monocoque design there is no chassis per se. It is all a part of the body.
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Old 9th December 2008, 17:26   #10
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Nice vid of a spoon tuned honda fit vs a street tuned honda fit aria (NHC).

Shan2nu
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Old 9th December 2008, 18:22   #11
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Quote:
Originally Posted by aaggoswami View Post
Yes its true that after wear and tear of many kilometers, the chassis will lose its original strength. But this depends upon manufacturer to manufacturer. But no doubt about the flex increasing.
In case of body on chassis configurations, the chassis is more rigid. Here the chassis holds on its stiffness for longer and wont flex much. This is why it is preferred for real off roaders.

In case of monocoque construction, each and every structural members supports the members adjacent to it, and hence it is safer as far as crash safety is considered as the energy is distributed in a better way as compared to body on chassis. And this is also the reason why the chassis lose their stiffness a bit faster than the body-on-chassis setup.

Can anyone explain me what do we mean by "flex" in a chassis?

Is Swift, a body on chassis configuration. As far as i know swift is known for its chassis, i dont know why but.
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Old 9th December 2008, 18:49   #12
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Flex basically means the body twisting in different direction. It is something like wringing a wet cloth although on a much much smaller scale.

The swift is not a body on chassis but a monocoque construction. In this type of construction the chassis and the body are the same part. The engine, transmission, wheels etc are all bolted on to the body either directly or indirectly. The swift is known for chassis as the flex in the body is pretty less. This coupled with a decent stock suspension setup give it good handling characteristics.

In the body on chassis configuration you typically have a ladder frame chassis which holds your engine, transmission, wheels etc. The body is also bolted on to this chassis.
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Old 9th December 2008, 21:44   #13
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Quote:
Originally Posted by nitrous View Post
An incorrect belief.
Off-roaders NEED flex.

Yes, yes correct. I am messed up right now with many things.
The chassis of real off-roader needs to have flex, and that is also the reason they are not known for good on road performance.

The Swift is monocoque construction body. This technology was pioneered by Citroen. Citroen is the innovator in a way. Directional headlights, hydro pneumatic suspension were all available in DS. DS is said to be the first mass produced car to have these features.
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Old 10th December 2008, 13:50   #14
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@vikram_d

Thank you for the precise explanation.
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Old 17th May 2010, 12:25   #15
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Sorry to revive this old thread - I have one doubt on chassis stiffness

In the recent review of the new 5 series by Autocar, they said that the stiffness of the chassis has been increased by 50% and this has resulted in an amazing increase in ride quality. I was under the impression that stiffness improves handling and not ride quality. Stiffer chassis means better handling. Better ride is brought about by softer suspension and chassis set up. Or, rather, this was my intuitive reasoning

Can anyone reading this clarify?
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