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There's been a thread running for several months now "New NX Suspension", started by Bucko, where various members have shared their recent suspension upgrades. It was getting quite long, so I will raise these observations and questions here on a new thread in the hope of getting wider feedback.
(Can I also point out at this stage that while I have had some history with motorcycle suspension, my interest or knowledge of four wheeled suspension up until a few months ago was nil. While I've given it some deep thought since, my knowledge of it could still be written on the back of a stamp.)
The general consensus on that thread has been that the Kings progressive rate rear coils are a more suitable option for IRS Pajeros, i.e. Gen 3's and 4's, as their progressive properties better handle the varying rear loads. The assumption has also been that the progressive rate Kings are linear, that is, their spring rate increases at a constant rate as more load is applied.
There are two ways to achieve a variable rate spring, (sorry for stating the obvious here.) The first is to have uniform diameter wire from end to end, and vary the pitch (the space between each wrap) of the coils. The closer the spacing, the lower the spring rate.
The second, and preferred way, is to vary the diameter of the wire progressively over the length of the coil, and maintain the same pitch throughout. (There is possibly specialised springs which combine both methods, but I'll stick to these two.)
I've recently fitted Kings KCRR-35 rear springs. Kings give a spring rate range of 11.78kg/mm to 17.86kg/mm, of which we have been assuming is linear, or a constant progression from soft to hard. Prior to fitment, the free spring appeared to have a constant pitch, that is the gaps between each wrap were the same. I measured the wire diameter at the top coil at 18.45mm, and the bottom coil at 21.4mm. I got similar dimensions on both the right and left springs. Hence, this is where the variance in spring rate comes from. I gave it little more thought at that stage, and fitted the springs.
On reflection, a few weeks later, I've noted that when compressed with a normal rear vehicle load, (full fuel, towbar, 3rd row seats in, no passengers or luggage), that the top three coils are very closely compressed, then the bottom four coils are all evenly spaced at a much larger amount. It's difficult to confirm if the top coils are either starting to become trapped (close up completely), or if they are compressed at a variable or constant amount, as I refitted the factory split sheath rubber insulator which wraps over the upper coil.
When I now measure the wire diameter of the intermediate coils, the lower four coils are all pretty uniform at 21.4mm, similar to the lowest coil. They are also compressed at a uniform spacing. Again, since the coils are now fitted, I do not have access to measure the upper 2 or 3 coils wire diameter. All of these measurements are similar between left and right.
(Observing the new front coils, which are a constant rate, when loaded they have a constant pitch between each coil wrap, and had a measured uniform wire diameter between top and bottom coil.)
What this indicates to me is that the progressive spring rate of these rear coils is not linear, and almost appears to be "twin rate"- or at least a constant rate in the lower four coils.
This also brings to mind a conversation I had with one of Kings Springs tech advisors when I phoned for some guidance. When we touched on the topic of their progressive rear springs for the Pajero, he did mention that the progressive design was more to allow the spring to remain captured within it's seats at full extended travel, or droop. It wasn't something which I gave a lot more thought to at that stage.
This could well be the design parameter of the spring regardless, where the last quite substantial part of travel is at the highest rate. As I've previously stated, my questions far outweigh my knowledge.
But it does raise a question that if this theory is correct, then a lighter rear comfort coil KCRR-35C, with a variable rate of 9.64 to 15.30 kg/mm, could be more suitable coil than previously thought. If the spring gets into its working range at a nearly constant 15.3kg/mm earlier in its loading than what you would think, its still quite a bit heavier than the factory rear rate of 11.6kg/mm. It also may explain to me why the springs I fitted feel firmer than I would have thought, reaching their higher 17.86 rate much earlier in their travel/ loading than I bargained for. This same theory could be applied across all of the Kings progressive rears in their range if they all are made in a similiar fashion. It also may give some more reasoning into why people with Lovells or Dobinsons constant rate springs don't seem to have comfort concerns, as the progressive property of the Kings spring is not across much of it's working range.
On the subject of the factory rear coils, which have also been assumed to be a constant rate of 11.6kg/mm. My old removed rear coils, from a 2016 NX, both measured with a slight change in wire diameter from top to bottom. The upper coil was 18.1, then 18.4, 19.0, 19.3, then 19.3 at the lowest. So on these there was a more linear progression in the change of diameter, but it would indicate that they are not a constant rate spring. (There would be some more inaccuracy in those exact measurements, as the factory coils have a very uneven coverage of paint in comparison to the new Kings coils, which have what appears a very uniform powder coated finish. But there was definitely a progression.)
Old Jack in particular has done much research on spring rates, and I think he has also done some real world testing of various springs/ loads. So I look forward to some more feedback on this.
Thanks in a advance, Paul
(Can I also point out at this stage that while I have had some history with motorcycle suspension, my interest or knowledge of four wheeled suspension up until a few months ago was nil. While I've given it some deep thought since, my knowledge of it could still be written on the back of a stamp.)
The general consensus on that thread has been that the Kings progressive rate rear coils are a more suitable option for IRS Pajeros, i.e. Gen 3's and 4's, as their progressive properties better handle the varying rear loads. The assumption has also been that the progressive rate Kings are linear, that is, their spring rate increases at a constant rate as more load is applied.
There are two ways to achieve a variable rate spring, (sorry for stating the obvious here.) The first is to have uniform diameter wire from end to end, and vary the pitch (the space between each wrap) of the coils. The closer the spacing, the lower the spring rate.
The second, and preferred way, is to vary the diameter of the wire progressively over the length of the coil, and maintain the same pitch throughout. (There is possibly specialised springs which combine both methods, but I'll stick to these two.)
I've recently fitted Kings KCRR-35 rear springs. Kings give a spring rate range of 11.78kg/mm to 17.86kg/mm, of which we have been assuming is linear, or a constant progression from soft to hard. Prior to fitment, the free spring appeared to have a constant pitch, that is the gaps between each wrap were the same. I measured the wire diameter at the top coil at 18.45mm, and the bottom coil at 21.4mm. I got similar dimensions on both the right and left springs. Hence, this is where the variance in spring rate comes from. I gave it little more thought at that stage, and fitted the springs.
On reflection, a few weeks later, I've noted that when compressed with a normal rear vehicle load, (full fuel, towbar, 3rd row seats in, no passengers or luggage), that the top three coils are very closely compressed, then the bottom four coils are all evenly spaced at a much larger amount. It's difficult to confirm if the top coils are either starting to become trapped (close up completely), or if they are compressed at a variable or constant amount, as I refitted the factory split sheath rubber insulator which wraps over the upper coil.
When I now measure the wire diameter of the intermediate coils, the lower four coils are all pretty uniform at 21.4mm, similar to the lowest coil. They are also compressed at a uniform spacing. Again, since the coils are now fitted, I do not have access to measure the upper 2 or 3 coils wire diameter. All of these measurements are similar between left and right.
(Observing the new front coils, which are a constant rate, when loaded they have a constant pitch between each coil wrap, and had a measured uniform wire diameter between top and bottom coil.)
What this indicates to me is that the progressive spring rate of these rear coils is not linear, and almost appears to be "twin rate"- or at least a constant rate in the lower four coils.
This also brings to mind a conversation I had with one of Kings Springs tech advisors when I phoned for some guidance. When we touched on the topic of their progressive rear springs for the Pajero, he did mention that the progressive design was more to allow the spring to remain captured within it's seats at full extended travel, or droop. It wasn't something which I gave a lot more thought to at that stage.
This could well be the design parameter of the spring regardless, where the last quite substantial part of travel is at the highest rate. As I've previously stated, my questions far outweigh my knowledge.
But it does raise a question that if this theory is correct, then a lighter rear comfort coil KCRR-35C, with a variable rate of 9.64 to 15.30 kg/mm, could be more suitable coil than previously thought. If the spring gets into its working range at a nearly constant 15.3kg/mm earlier in its loading than what you would think, its still quite a bit heavier than the factory rear rate of 11.6kg/mm. It also may explain to me why the springs I fitted feel firmer than I would have thought, reaching their higher 17.86 rate much earlier in their travel/ loading than I bargained for. This same theory could be applied across all of the Kings progressive rears in their range if they all are made in a similiar fashion. It also may give some more reasoning into why people with Lovells or Dobinsons constant rate springs don't seem to have comfort concerns, as the progressive property of the Kings spring is not across much of it's working range.
On the subject of the factory rear coils, which have also been assumed to be a constant rate of 11.6kg/mm. My old removed rear coils, from a 2016 NX, both measured with a slight change in wire diameter from top to bottom. The upper coil was 18.1, then 18.4, 19.0, 19.3, then 19.3 at the lowest. So on these there was a more linear progression in the change of diameter, but it would indicate that they are not a constant rate spring. (There would be some more inaccuracy in those exact measurements, as the factory coils have a very uneven coverage of paint in comparison to the new Kings coils, which have what appears a very uniform powder coated finish. But there was definitely a progression.)
Old Jack in particular has done much research on spring rates, and I think he has also done some real world testing of various springs/ loads. So I look forward to some more feedback on this.
Thanks in a advance, Paul
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