Progressive vs Linear

[ron2503]

Hi guys,
Have trolled through the posts but I don't think this has been asked. Could someone tell me whether there is a great advantage getting progressive springs over the linear alternative. I'm looking at a suspension upgrade but the company I'm looking at only use linear rated springs in their kits. I've asked them if they can source Kings progressive springs instead and they have said yes but at a higher cost because they have to split up a set kit. Any thoughts would be appreciated.

TIA

[Ian H]

Progressive are a better ride in town but if you are towing anything like a caravan, they sag too much. Linear are better all round in my opinion, just get the firmness you prefer depending on your intended use.

[old Jack]

Progressive are a better ride in town but if you are towing anything like a caravan, they sag too much. Linear are better all round in my opinion, just get the firmness you prefer depending on your intended use.

If a progressive rate spring is sagging under load then it is the wrong coil for the load being carried.

A linear rate coil has the same spring rate through out its complete compression, for example a coil with a spring rate of 150lbs per inch the coil requires 150lbs to compress 1 inch then another 150lbs for another inch and a further 150lbs for the next inch of compression. So if this spring has 5 inches af compression travel it will compress 1 inch for 150lbs, 2 inches for 300lbs, 3 inches for 450lbs, 4 inches 600lbs and 5 inches of travel for 750lbs then it will be bottomed out and become solid.

A progressive rate coil has a spring rate range so if the first inch of compression for example is 130lbs per inch and the last inch of compression is for example 230lbs per inch and the spring has 5 inches of compression travel then the first inch of compression is 130lbs, the 2nd inch 150lbs so it will be 280lbs in total, 170lbs for the 3rd inch which is 450lbs in total, 200lbs for the 4th inch which is 650lbs total and 230lbs for the 5th inch of compression. Therefore at max load this spring will require 880 lbs to reach final compression. This spring will be more compliant and comfortable when lightly loaded but it can carry more weight in the last 40% of compression.

Therefore a progressive rate coil that is correctly designed can be more comfortable with light loads but have the ability to carry more weight, and this is why they are a better choice for rear springs where the total weight can vary by 400kg to 500kg.

I have had 5 different sets of rear coils in my Challenger, the first 2 where progressive rate that where undersized for the max weight I carry, the next was a linear rate coil that was also undersized, then a linear rate that was too high and too hard with lighter loads but ok at max weights then finally a custom progressive rate coil that is comfortable and maintains aceptable ride heights over a 600kg rear weight range.

OJ.

[ddeane]

OJ noticed that you have some Dobinsons gear on your PS. I have a Outback Armour 40mm lift kit on my PS. This includes the adjustable coilovers on the front. I purchased both the progressive rate springs (I believe that these are Dobinsons as when you scape off the poorly applied paint on the srings they a Dobinsons orange underneath) and the Linear springs (Dobinsons C43-203) for the back and had the progressive rate ones fitted. Have not yet towed the van with them yet, (it has about 200k on the towball), so have not yet really checked out the system but am chasing specifications (spring rates) for both sets. I have had a look at the Dobinsons catalogue but cant seem to find any specification for the springs. Can you Help.
Craig

[old Jack]

OJ noticed that you have some Dobinsons gear on your PS. I have a Outback Armour 40mm lift kit on my PS. This includes the adjustable coilovers on the front. I purchased both the progressive rate springs (I believe that these are Dobinsons as when you scape off the poorly applied paint on the srings they a Dobinsons orange underneath) and the Linear springs (Dobinsons C43-203) for the back and had the progressive rate ones fitted. Have not yet towed the van with them yet, (it has about 200k on the towball), so have not yet really checked out the system but am chasing specifications (spring rates) for both sets. I have had a look at the Dobinsons catalogue but cant seem to find any specification for the springs. Can you Help.
Craig

Hi Craig,

Your problem does not surprise me, linear rate coils are not suitable for rear axle applications unless the load is constant!

Dobinson Rear coils for the Challenger and Pajero Sport, lightest to heaviest duty, in order.

C43-099 Linear Rate 2.7094 kg/mm spring rate , free length 385mm.
C43-203 Linear rate 2.702 kg/mm spring rate, free length 405mm.
C43-097 Linear Rate 2.9674 kg/mm spring rate, free length 405mm.
C43-043V Variable Rate 3.0594 to 5.812 kg/mm spring rate, free length 400mm.
C43-045V Variable Rate 4.078 to 6.6281 kg/mm spring rate, free length 400mm.

The above specifications are converted direct from information from Dobinson Technical Department.

OJ.

[ddeane]

OJ are you suggesting that I am better off with the variable rate springs?

[old Jack]

OJ are you suggesting that I am better off with the variable rate springs?

Unless you have a constant rear axle load then progressive rate coils will give you the best ride comfort when lightly loaded and the best load capacity when loaded.

If you can measure your ride heights from centre of wheel hub to Unser the wheel arch in a vertical line on all 4 wheels and either weight your front and rear axle loads on a weigh bridge or list what accessories and their weights, then post this info. Then I can give you a few rear coils options for you to consider.

OJ.

[ddeane]

thanks