Chassis Stiffness

king_julian · 8th December 2008, 15:04

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.

Tejas@perioimpl · 8th December 2008, 16:09

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.

nitrous · 8th December 2008, 16:43

Quote:

Originally Posted by king_julian

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.

Shashank.A · 9th December 2008, 10:31

Quote:

Originally Posted by king_julian

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 ?

aaggoswami · 9th December 2008, 10:43

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.

getsurya · 9th December 2008, 11:10

aag, thats a very educative note. Thank you.

king_julian · 9th December 2008, 11:50

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.

nitrous · 9th December 2008, 17:18

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.

vikram_d · 9th December 2008, 17:22

Quote:

Originally Posted by nitrous

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.

Shan2nu · 9th December 2008, 17:26

Nice vid of a spoon tuned honda fit vs a street tuned honda fit aria (NHC).

YouTube - Vtec Club BM vol. 13 Honda Fit Chassis

Shan2nu

tush · 9th December 2008, 18:22

Quote:

Originally Posted by aaggoswami

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.

vikram_d · 9th December 2008, 18:49

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.

aaggoswami · 9th December 2008, 21:44

Quote:

Originally Posted by nitrous

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.

tush · 10th December 2008, 13:50

@vikram_d

Thank you for the precise explanation.

mallumowgli · 17th May 2010, 12:25

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?

8th December 2008, 15:04	#1
king_julian BHPian Join Date: Feb 2006 Location: Pune Posts: 99 Thanked: 3 Times View My Garage	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.
	() Thanks

8th December 2008, 16:09	#2
Tejas@perioimpl Distinguished - BHPian Join Date: Sep 2008 Location: Bombay Posts: 4,423 Thanked: 9,582 Times View My Garage	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.
	() Thanks

9th December 2008, 10:43	#5
aaggoswami Senior - BHPian Join Date: May 2007 Location: Vadodara Posts: 4,982 Thanked: 2,931 Times	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.
	() Thanks

9th December 2008, 11:10	#6
getsurya Senior - BHPian Join Date: Aug 2008 Location: Hyderabad Posts: 1,641 Thanked: 1,929 Times View My Garage	aag, thats a very educative note. Thank you.
	() Thanks

9th December 2008, 11:50	#7
king_julian BHPian Join Date: Feb 2006 Location: Pune Posts: 99 Thanked: 3 Times View My Garage	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.
	() Thanks

9th December 2008, 18:49	#12
vikram_d Senior - BHPian Join Date: Jul 2006 Location: Bangalore Posts: 2,427 Thanked: 1,185 Times	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.
	() Thanks

10th December 2008, 13:50	#14
tush BHPian Join Date: Feb 2008 Location: Pune Posts: 331 Thanked: 12 Times	@vikram_d Thank you for the precise explanation.
	() Thanks

17th May 2010, 12:25	#15
mallumowgli Senior - BHPian Join Date: Apr 2010 Location: Palakkad/Coimbatore Posts: 1,226 Thanked: 1,079 Times	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?
	() Thanks