Dual Rate / Progressive Springs

[bishbosh]

I can't recall how many times I have read on here and other 4x4 sites the question as to which way up to fit dual rate / progressive springs.

Invariably the responses are evenly split - close coils at the top / close coils at the bottom.

Now, what I would like someone to do, preferably a grown up who can put forward a reasoned argument, is explain to me how on earth it makes a blind bit of difference, other than the somewhat tenuous argument of having the close colis at the bottom will trap more mud ( I think the technical response to that one is "b0ll0x!")

Surely a spring confined between two points will react to load applied through those two points in exactly the same way regardless of its orientation? (neglecting its own self weight for the pedants).

Or am I missing something?

Then, when we have a definitive answer perhaps we can put it in the tech archive?

[Bowie69]

Not saying I am a grown up at all, but here goes

From a spring POV, it makes no odds, however having more coils at the bottom increases the unsprung weight(the axle and associated steelwork) marginally, so in theory you get slightly worse handling.

But this is on a 2+ton truck, so who cares

[Guest]

Sort of an adult response....

With progressively wound springs, the coil pitch gets tighter the closer to the top of the spring you get. This has the effect of giving the spring increasing resistance, the more it is compressed.

The spring constant (stiffness) of a coil spring equals: k = compression / force = D^4 * G / (64*N*R^3)

where D is the wire diameter, G an elastic material property, N the number of coils in the spring, and R the radius of the spring.

So increasing the number of coils decreases the stiffness of the spring. Thus, a progressive spring is progressive because the two parts are compressed equally until the tightly wound part locks up, effectively shortening the spring and reducing its compliance.

So for normal driving, you'll be using mostly the upper 3 or 4 'tight' winds to soak up the average bumps and potholes. When you get into harder driving, like cornering at speed for example, because the springs are being compressed more, they resist more. The effect is to reduce the suspension travel at the top end resulting in less body roll, and better road-holding. Invariably, the fact that the springs are progressively wound is what accounts for the lowering factor. The springs aren't made shorter - they're just wound differently.

​Of course I stole the above text but it was a more eloquent way of putting what I understood.

Jason.

[bishbosh]

Pete - that unsprung weight argument is in the same category as the less mud answer!

Jason, all very interesting but you didn't answer the question - which way up??

Back of the class, both of you!

[Off Road Toad]

If you have Gwyn Lewis's coil catchers on the rear then you have no choice but to fit the tight coils at the bottom (that was an embarrassing learning moment!) However, between having them the 'correct' way with tight coils at the top and then having to flip them I found no difference in handling/ load carrying whatsoever, things have somewhat improved now I've got rid of the darn things and just fitted plain HD springs!

[Bowie69]

Pete - that unsprung weight argument is in the same category as the less mud answer!

Maybe, but it actually has some science attached, and when talking about a track car which its suspension/brake components weight components may weight only ~10Kg, a 100g shift of weight from sprung to unsprung may make more difference.

As above, you won't notice any difference on a truck

[Hybrid_From_Hell]

I have had this discussion with some peeps

There is a formula that answers this,

X is unknown,

0 being the differences between the LH and RH springs weights

B is progessive spring type

L being Length of springs (LH) and L (RH)

and 0 being the orientation as to which way up you fit them.

Once calculated the answer is complete

So, the argument goes that Complete B+0+L-L+0*x = Actual Importance up or down

Nige

[mickeyw]

Good one Nige

[Daan]

I would fit the closely wound coils at the top, because with the weight on it, they are probably closed and therefore fill up with mud and stones, as you mentioned in your post. I dont think that argument is BL at all, as trying to clean this out is a complete PITA. Other than that, no difference.

But I dont use dual rate springs, because the result is more droop than bump and I dont think that is a good idea full stop.

Daan

[Roverdrive]

For what it is worth, my Disco 1 had progressive springs as standard ( 7 seat) and the tighter coils were fitted at the top.

I don't think there was space between the coils for the retaining strap if they were fitted the other way round.

[Guest]

I have had this discussion with some peeps

There is a formula that answers this,

X is unknown,

0 being the differences between the LH and RH springs weights

B is progessive spring type

L being Length of springs (LH) and L (RH)

and 0 being the orientation as to which way up you fit them.

Once calculated the answer is complete

So, the argument goes that Complete B+0+L-L+0*x = Actual Importance up or down

Nige

Very droll Nigel, however the formula is important despite your flippant comments.

Jason, all very interesting but you didn't answer the question - which way up??

Sorry I thought I had explained that the tighter coils should go at the top but not for the reasons people think of on a Land Rover.

The assumption is correct that if the force is applied a a vertical motion then it make absolute no difference which way up the spring is, and this is how we tend to think of the force in a Land Rover especially when off road.

However the above formula describes the force on a spring as the vehicle goes around a corner, the car needs to lean into the corner to make it easier to corner so the bottom coils are further apart allowing the lateral force in the car to let the car lean into the corner. However as the lateral force becomes greater the upper stiffer part of the spring has more force applied on it together with the now compressed and stiffer lower part of the spring allowing for faster cornering tighter handling.

But as a Land Rover is hardly know for it's cornering ability, the benefits of progressive springs is probably a bit of a moot point.

Jason.

[bishbosh]

Not sure I understand this lateral force agument - sure if your bushes are all in good order then the springs cannot experience any lateral forces, only an axial force created by (steps into the deep end, well out of his depth) rotation of the sprung mass about the roll centre?

[defender dinky]

one ,one way, and one thee other, sorted