Thread: Landrover Design Philosophy

I hope not reads!

Who'd be driving, or have reigns replaced the steering wheel? Hi ho silver, away! LOL

GQ

BTW: note for John JDNSW:

if you don't mind, whats the difference between a parabolic leaf and one that isn't, genuine question as I don't know.

cheers, GQ

Originally Posted by Quiggers

BTW: note for John JDNSW:

if you don't mind, whats the difference between a parabolic leaf and one that isn't, genuine question as I don't know.

cheers, GQ

A conventional leaf spring consists of a stack of flat leaves with the length of the leaves varied to match the change in the bending load from the axle to the shackle. Invented around 800 years ago they are simple to build and have been used effectively on the vast majority of car and truck designs since the invention of cars, and before that on horse drawn vehicles and railway vehicles etc.

The so-called parabolic spring consists basically of a single leaf with the thickness of the leaf varying parabolically with distance from the axle to match the load. In practice they always have at least two leaves to make breakage of a leaf less of a disaster.

What makes the difference is interleaf friction. For a conventional leaf spring to bend when you hit a bump requires that the leaves slide against each other. As they are in contact for their full length and there are a lot of them pressing tightly against each other (usually roughened with rust) there is quite a bit of friction to overcome before it moves, so for small bumps, the spring does nothing. With a parabolic spring, for a start there are usually only two or three leaves, but also, because of the taper on the leaves, they only touch at the axle and at the tip, often with a nylon antifriction pad, so there is virtually no friction to stop movement, and they respond almost the same as a coil or torsion bar.

Up until about 1930 the friction was an advantage, as it enabled the manufacturers to get away without fitting dampers or shock absorbers, but since these became normal parts of a car, leaf springs have had their drawbacks. Replacing them with coils, however, has normally been more expensive (not because the coils are expensive - they aren't, typically less than half the price of a leaf spring) but because the leaf spring holds everything in place and handles driving and braking torque as well with no extra bits, plus it spreads the suspension load to two widely separated bits of the chassis. To change to coils you need to redesign the chassis and provide locating links to and torque reaction arms.

Parabolic springs can replace leaf springs with no changes to the vehicle, although the dampers will need to change as they have to do more work, and because usually the parabolic springs are set up to give more travel.

Hope that helps.

John

Thank you John:

YOUR QUOTE: Parabolic springs can replace leaf springs with no changes to the vehicle, although the dampers will need to change as they have to do more work, and because usually the parabolic springs are set up to give more travel.



I had a transit van LWB from the mid '70s which had single leafs at the front and it rode and handled surprisingly well, but the lower shock mount on the rhs broke clean off - and you've explained why - thank you.

It was a camper with a fair it of gear on board, (weight) which helped tie down all those (obviously not parabolic) leaves on the rear... despite being maybe three tons it was a lot of fun to punt around....

How long have you lived in Dubbo, John?

Cheers, GQ

Originally Posted by Quiggers

Thank you John:

......

How long have you lived in Dubbo, John?

Cheers, GQ

I don't actually live in Dubbo, but about 60km away, and have done so for about thirteen years.

John

Originally Posted by Quiggers

I hope not reads!

Who'd be driving, or have reigns replaced the steering wheel? Hi ho silver, away! LOL

GQ

Santana's problem is that it's still a "cottage industry" - it focuses on the local (Spanish & Portugese) markets and is slowly branching out toward the EU. Where Land Rover did really well was to make their product a global one. No matter how poor a market was, it still had Land Rovers.

As for Parabolic Springs, the new Mercedes Sprinters (Ambulances @ work) have them, I had some on the SIII and they rode and handled really well, but I broke a parabolic spring on outback corrugations, so how have standard leaves on the front. Coils allow the end user to better customise their suspension - height & rate -wise. This customisation is more in keeping with the philosophy that made Land Rovers so successful. LR should have released the SIII with parabolics, but in this day and age, coils are the go.