Coils or Leaf?

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Alex Roux
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Re: GQ needed by research couple in Kgalagadi

Post by Alex Roux » 06 Dec 2013 12:52

This is off topic, but I am intrigued.

This had always been my summary:
Leaf springs:
Strronger, and simpler, can take heavier load, easier to lift but less flex.
Bette for heavier vehicles and vehicles with heavier load. E.g. overlanding.

Coils:
More flex, better technical off road performence,
Not as strong under heavy load as leaf srpings, hence possibly less suited for overlanding.

So in the Kalahari, I would expect them to cover lots of distance, with some load of equipemrnt etc.
Not doing much techinical terrain, albeit some corrugated dirt road and dunes etc.

So how come this terrain "eats" leaf springs?
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Re: GQ needed by research couple in Kgalagadi

Post by Peter Connan » 09 Dec 2013 06:55

My GQ gaan oor 'n week daar wees. Beter die sleutels mooi oppas!

Alex, leaves rub together. Not cool in dusty conditions.

My own feeling is that coils are best for virtually any application, but they are very difficult to package if they have to carry very heavy loads, and of course they need additional axle-locating devices, and these are the main reasons they are not used in heavy vehicles.
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Re: GQ needed by research couple in Kgalagadi

Post by Peter Vee » 09 Dec 2013 12:11

Alex Roux wrote:This is off topic, but I am intrigued.

This had always been my summary:
Leaf springs:
Strronger, and simpler, can take heavier load, easier to lift but less flex.
Bette for heavier vehicles and vehicles with heavier load. E.g. overlanding.

Coils:
More flex, better technical off road performence,
Not as strong under heavy load as leaf srpings, hence possibly less suited for overlanding.

So in the Kalahari, I would expect them to cover lots of distance, with some load of equipemrnt etc.
Not doing much techinical terrain, albeit some corrugated dirt road and dunes etc.

So how come this terrain "eats" leaf springs?

On viewing all of the Voetspore series once thing stands out - leaf springs can and will break - most obvious in their trip with 70 Land Cruisers - also happended with Patrol Pick up..

Cheers,

Peter
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Re: GQ needed by research couple in Kgalagadi

Post by Tinus lotz » 09 Dec 2013 12:40

Peter Vee wrote:
Alex Roux wrote:This is off topic, but I am intrigued.

This had always been my summary:
Leaf springs:
Strronger, and simpler, can take heavier load, easier to lift but less flex.
Bette for heavier vehicles and vehicles with heavier load. E.g. overlanding.

Coils:
More flex, better technical off road performence,
Not as strong under heavy load as leaf srpings, hence possibly less suited for overlanding.

So in the Kalahari, I would expect them to cover lots of distance, with some load of equipemrnt etc.
Not doing much techinical terrain, albeit some corrugated dirt road and dunes etc.

So how come this terrain "eats" leaf springs?

On viewing all of the Voetspore series once thing stands out - leaf springs can and will break - most obvious in their trip with 70 Land Cruisers - also happended with Patrol Pick up..

Cheers,

Peter
if I drive the same road with my hilux with OME and 2.5 bar wheels and then the same road again with a patrol with coils ......you can not compare the two .....like night and day
the leafs start to bounce all over long before the coils and the road holding is much better on coils
in the long run coils will work longer at the same job than coils but that is just my opinion :salute: :salute:

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Coils or Leaf?

Post by Stefan » 09 Dec 2013 12:58

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Re: GQ needed by research couple in Kgalagadi

Post by Gerrit Loubser » 09 Dec 2013 14:08

As is so often the case, it is difficult to be able to make absolute statements in favour of the one or the other for all applications.

Leaf springs allow simpler designs, because in addition to providing vertical suspension, they can do the job of locating the axle both longitudinally and laterally. They can also react the drive torque, whereas a coil spring setup requires separate linkages to do this. If one uses the leaf spring to do all of those jobs, however, it ends up having to be quite stiff to be able to locate the axle properly and this then means that ride comfort might also be compromised. If the vehicle needs to carry a lot of weight in any case this is obviously not such a great issue.

Having separate linkage to locate the axle makes it possible to do that job much more precisely and to react torque without nasty side effects such as axle wrap. This benefit is realised automatically in the case of coil sprung suspensions, but of course this can also be the case with a leaf sprung suspension, if one provides locating links and the leaves therefore do not have to do the locating job. This is often seen on powerful leaf sprung vehicles such as dragsters.

Leaf springs work by allowing the individual leaves to slide over one another. This generates a lot of friction, which has a damping effect, but this damping effect is difficult to predict due to the effect that the actual leaf surface condition (think corrosion, contaminants, etc.) has as well as the effect of stiction. Leaf springs are pure spring elements with almost no damping effect, so the damping job can be left to dedicated damping elements (the shock absorbers) that can react in a predictable fashion.

I am not sure that leaf springs would necessarily be stronger. Both leaves and coils can be durable, if properly designed, but one has to bear in mind all of the loads that bear upon the spring (and in the case of a leaf spring that also locates the axle and reacts torque there are more of these to consider than in the case of a coil spring).

I am also not sure that leaf springs necessarily lead to less axle travel or flex. For instance, if one uses parabolic leaf springs and one locates the axle using four links in a parallelogram arrangement plus a Panhard rod, very good travel can be achieved. On the other hand, if a suspension is designed to carry a lot of weight, then it will be stiff, whether the springs are coils or leaves and a stiff suspension would be more likely to lift wheels than to flex when unladen. Load carrying vehicles are more likely to be bouncy when unladen, whether coil or leaf equipped.

Incidentally, there are some notable load carrying vehicles that have been built with coil sprung suspensions (e.g. Unimogs, Steyr-Puch Hafflinger, Defender 110 Pick-up).
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Re: GQ needed by research couple in Kgalagadi

Post by Clem » 09 Dec 2013 16:06

Peter Vee wrote:
Alex Roux wrote:This is off topic, but I am intrigued.

This had always been my summary:
Leaf springs:
Strronger, and simpler, can take heavier load, easier to lift but less flex.
Bette for heavier vehicles and vehicles with heavier load. E.g. overlanding.

Coils:
More flex, better technical off road performence,
Not as strong under heavy load as leaf srpings, hence possibly less suited for overlanding.

So in the Kalahari, I would expect them to cover lots of distance, with some load of equipemrnt etc.
Not doing much techinical terrain, albeit some corrugated dirt road and dunes etc.

So how come this terrain "eats" leaf springs?

On viewing all of the Voetspore series once thing stands out - leaf springs can and will break - most obvious in their trip with 70 Land Cruisers - also happended with Patrol Pick up..

Cheers,

Peter
Coil springs can also break - I've seen it happen. But it does seem quite rare by comparison.

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Re: GQ needed by research couple in Kgalagadi

Post by Clem » 09 Dec 2013 16:08

Gerrit Loubser wrote:Incidentally, there are some notable load carrying vehicles that have been built with coil sprung suspensions (e.g. Unimogs, Steyr-Puch Hafflinger, Defender 110 Pick-up).
Defender 130. Second coil spring pack ("helper" spring) inside the primary pack comes into play under very heavy loads. That way you get the best of both worlds - reasonable ride comfort and very good load carrying ability.

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Re: Coils or Leaf?

Post by Gerrit Loubser » 10 Dec 2013 08:57

Yes, dual springs with one only coming into play when laden can be a good solution to achieve reasonable ride comfort in both laden and unladen states. This is also often seen on leaf sprung light trucks. Although it is a good solution from the point of view of ride comfort, the system obviously still limits flex. One of the great things about air suspensions or hydro-pneumatic suspensions is that they can be designed to adapt to the load seamlessly and automatically and can therefore achieve great ride comfort as well as great suspension suppleness (at the cost of complexity and possible vulnerability as well as durability concerns).
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Re: Coils or Leaf?

Post by Clem » 10 Dec 2013 12:04

Gerrit Loubser wrote:Yes, dual springs with one only coming into play when laden can be a good solution to achieve reasonable ride comfort in both laden and unladen states. This is also often seen on leaf sprung light trucks. Although it is a good solution from the point of view of ride comfort, the system obviously still limits flex. One of the great things about air suspensions or hydro-pneumatic suspensions is that they can be designed to adapt to the load seamlessly and automatically and can therefore achieve great ride comfort as well as great suspension suppleness (at the cost of complexity and possible vulnerability as well as durability concerns).
I don't think air suspension is suitable for severe off-road work. Maybe its just a Land Rover thing but I've known too many guys to have problems with it, usually at the worst time and in the worst possible place. A coil springs gets tired but it rarely lets you down altogether.

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