Thread: Chassis flex - how much is required?

landrover chassis are not designed to flex because landrover can build decent offroad suspension.

fozzys got a long split in a weld on the chassis and the handling is very very odd when you have chassis flex.

Chassis flex is usually reserved for vehicles that have a c section chassis.

heres a test

grab a piece of thin steel shim or cut a section out of a coke can fold it and then repeatedly bend and unbend the shim. What happens?

think thats a good idea for a chassis?

no, me either.

G'day Dave,

What you indicate makes perfect sense and I have made the tray-back ridgid for a reason to avoid movement. This has turned out the right thing to do then based on what you indicate regarding the 'c' sections and box sections differences.

Flexing like a coke can would not be good for handling - no. The noise would drive me nuts!

Cheers,

Phil

In the early days of motoring and on the appalling roads of the time, it was chassis flex thet made the reputations of the American cars in the bush. The alloy steel frames of the Ford "T", Dodge 4's, Buick, Hudson, and others withstood the hammering from the "roads" and the flex gave extra suspension movement. The rigid steel frames of the Brit and Euro sourced vehicles cracked and broke up badly in outback service.

Any surviving members of the outback mail and passenger carrying fraternity will confirm that they would have gone broke using English or European cars.

But..

Get a Defender fully crossed up, & you can eyeball the twist across the roof panel. There is some flex there, whether good or bad.

Regards
Max P

Originally Posted by Blknight.aus

grab a piece of thin steel shim or cut a section out of a coke can fold it and then repeatedly bend and unbend the shim. What happens?

think thats a good idea for a chassis?

no, me either.

I think this analogy is wrong. You are talking about flexing the coke can beyond it's point of elasticity, if you don't go beyond the point of elasticity, it will survive thousands of flexes. Your saying a Landy chassis should be stiff for longevity, this would reduce the Chassises elasticity causing welds to tear. The stiffer a metal object is, the easier it will crack if as it's window of elasticity is smaller, If not pushed past it's elasticity point, it would be fine. But still offer less damping to vibrations etc.
I'm not saying Landys shouldn't have stiff chassis(to a point), I'd just imagine if it's too stiff it will probably shake to bits or crack.

In landys its the driver that shakes to bits, sometimes its the suzi engine there is some flex but not much

I know the old HJ45 Land Cruisers would flex upto 6 inches from one corner to another I dont know how many times I ended up with them so badly flexed that I couldnt get out of the doors lol.
Land Rovers dont Flex much at all even with the leaf sprung ones.
The Land Cruisers in used hard use to break in halves after about 12 years of hard work but many 40 year old Land Rover have no issue.
In Africa they use to plate both Land Cruisers and Series 3 Land Rover chassis the Series 2 and 2A never broke up even under the most extreme abuse provided they were not rusty.

Windsock,

What you have done by rigidly connecting the tray to the chassis is create two load paths. One the original chassis, the second the tray back - the load that the tray bay carries is directly proportional to the relative flexural stiffness of the chassis and tray back.That is that tray back is now part of the vehicle.

The original chassis will be fine, it now carrying less load then before and for what is was designed. Will flex less, so a little less wheel articulation, doors wont bind as easy, etc.

But the tray back is now acting as an integral part of chassis and needs to built as so it is part of the chassis. Have good quality ductile welds would be my main concern - metal fatigue over rough roads may be an issue. But if all the work high grade and considered as part of the vehicle can not see a problem.

Clive