soft vs stiff springs for offroad

[crowt]

Hey guys here's something I read and was curious about. First off, this came from a range rover site so they are obvously going to talk highly of their rigs - but I thought this was interesting:

The Range Rover Secret: Suspension Design
Range Rovers have always been distinguished by innovation in suspension design. The Classic Range Rover was able to use exceptionally soft springs, while retaining a 1600 lb payload capacity, by virtue of the Boge self-levelling strut fitted to the central A-frame link on the rear axle. This is, in effect, a variable rate self-adjusting air spring which provides a restoring force on the center of the axle to compensate for load, allowing very low spring rates to be used at the road wheels. This results in maximum possible traction on uneven terrain.
Why does a soft suspension give better traction? This is a secret that other 4x4 manufacturers and aftermarket suspension builders have apparently never learned. When a wheel droops even an inch or two on uneven terrain, that wheel is "unloaded" -- ie its ground contact force is reduced -- in direct proportion to the stiffness of the spring and anti-roll bar (if fitted). Any loss in ground contact force reduces available traction at the wheel in question. With an open differential on the axle, traction is lost at both wheels simultaneously.

Conventional and "lifted" 4x4s overwhelmingly use leaf springs or stiff coils with anti-sway bars tuned for flat high speed cornering on pavement or supposed "heavy duty" use off-road. Aftermarket "upgrades" invariably include even stiffer springs, shocks, bushings and/or anti-sway bars. The net effect is a very stiff suspension that not only provides less maximum wheel travel (resulting in wheels lifting off the ground in very uneven terrain) but much reduced traction even in mild off-road situations requiring only modest vertical wheel movements.
This is why the conventional dogma dictates that serious off-road vehicles must use "lockers" on the differentials to maintain traction. Lockers force both wheels to rotate at equal speed, transferring all the torque to whichever side has the grip. They therefore greatly increase stress on the drivetrain components, and have adverse side effects on steering control.

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I guess my question is - do you guys think this is BS, and they are trying to make up science to support not having lockers from the factory? It is true that most offroad suspension mods stiffen the springs instead of softening them (OME medium, stiff etc). I have read on MUD many times that SFA LR's have great axle articulation. - and that the real plus of having a SFA is to keep both front tires on the ground as much as possible - so do they have a point that springs should be softer as opposed to stiffer?

Of note as well is that the RR classic has more payload than an 80 series (according to the above text anyway).

Also - my goal here is a suspension design discussion not a LR vs LC discussion.

Also keep in mind that I'm not really talking about rock-crawling here - more expedition-style off-roading as both of these vehicles were designed for.

Thoughts?

 

['74 UA FJ]

Softer suspension will give you more traction off road in low range but does not discredit the fact that for serious four wheeling, you need lockers.

Most lift springs are stiffer than stock springs.

 

[LX_TREME]

Talking about stiffer springs..

I have 5 inch lowering, stiffening spring, the 80s holds the road and handles like a go-kart.

 

[Tools R Us]

To properly support a lifted truck (raised center of gravity) lift springs need to be somewhat stiffer than stock. Overall it's a compromise, heavier springs will handle better at highway speeds, softer springs will allow easier suspension movement, more even tire to ground pressure, making for a better ride and traction off road.

Defining "off road" also plays a big part. Touring forest service roads, especially with a heavy truck, loaded roof rack, etc stiff springs work better. Lighter trucks that see more uneven terrain (rocks, washouts, etc) will benefit from a softer spring, allowing the suspension to move easier for better traction and ride.

 

[FJBen]

I think a lot of the more crawling/off-road rovers change that in the rear to a 4 link for better travel.

I would want lockers before a super flexxy suspension. And toolsrus is right. You want stiffer rates as you lift. Your COG is higher and those rovers are pretty top heavy.

 

[Tools R Us]

Talking about stiffer springs..

I have 5 inch lowering, stiffening spring,

Is your frame and oil pan notched? The stock front axle is only ~1.5" from the stops and not much further to the frame/oil pan. If you took the front springs out of a stock truck it would only lower it ~2".

the 80s holds the road and handles like a go-kart.

You have obviously have never driven a performance go cart, or maybe you meant a 2.5 ton go cart with a really high center of gravity!

 

[mainemike]

Why does a soft suspension give better traction?[/FONT][/COLOR][/B] This is a secret that other 4x4 manufacturers and aftermarket suspension builders have apparently never learned.

This is a poorly written piece of propaganda. There are no secrets among manufacturers concerning mass produced vehicles.

Any loss in ground contact force reduces available traction at the wheel in question.[/FONT][/COLOR]

they got this right.. if the wheel isn't touching the ground it can't pull you along... musta been written by a pee-H-dee.


But the overall message remains kinda correct - soft suspensions do work great for off-road, look at crawling buggies and downhill mountain bikes. But to carry gear and people, and to be driveable at 75 mph...you need to stiffen it up. But stiffer suspension does not directly equate to less suspension travel - the basic design of the vehicle suspension is what ultimately determines the articulation (up and down travel measurements). By basic design I mean leaf springs, coil springs, solid axles, IFS, etc.

Toyota does a pretty exceptional job at designing suspensions, especially on the Land Cruisers.

 

[little_joe]

There is plenty of merit to that writeup, and it is universally applicable.

I find it absurd the high spring rates of all aftermarket springs. For the heavily laden vehicle they make sense, but that there are no springs available at or near stock rate is a disappointment.

As an example, aftermarket swaybars for the Minis have a 66% higher spring rate than stock. That is simply outrageous. Even the OME springs for our rigs have ridiculously high rates for many needs.

Soft/stock spring rates + quality shocks such as Bilsteins + stock sway bars = perfect setup.

 

[Atoyot1031]

Yeah...if you enjoy feeling like you're sailing a boat (IMHO of course).

A lot depends on lift, weight, and primary use.

 

[Nay]

I have gone to a relative extreme using the same links on the same vehicle - this was a highly modified XJ. My experience? It's a moot point if your suspension travel is properly designed.

For reference, I had a very low spring rate 6" spring for about a year (remember a longer spring with a softer rate has the same effective spring rate as a shorter spring with a higher rate). And then about a 33" increase in stiffness (155 lb/in to 210 lb/in) at the same basic lift height.

Because I was using the same shock designed for spring travel in the middle range of the spring, it was irrelevant offroad. Onroad the stiffer spring was better tuned to the suppleness of the Bilstein 5100 shock platform, but not a big deal.

People spend too much time looking at springs in isolation. Where the spring travel occurs through the range of available articulation is critical to designing the "best spring" - you can add plenty of spring rate in a quality spring without adding harshness as long as you haven't engineered in 8" of up travel hoping to get balanced offroad performance.

Bottom line is how you design links is critical to spring performance. Shorten your radius arms into a 15" length 4-link and see what it does to your spring performance and perception of stiffness. Whether the LR stuff is bunk or not doesn't matter. What matters is choosing or designing a suspension that maximizes spring performance for your range of intended usage, as that will have a greater effect on your perception than anything else. Longer links operating at an angle will feel softer on a stiffer spring that shorter angled links (lifted rig) on a soft spring. You might notice that both LR and Toyota have long link systems for this reason (coil sprung expedition designs virtually have to), unlike Jeep and their very short link suspensions.

The tradeoff that occurs is link and link mount clearance within the objectives of load bearing and comfort.

 

[cruiser-poor]

...Of note as well is that the RR classic has more payload than an 80 series (according to the above text anyway).

I suspect the Classic's greater payload capacity owes less to clever suspension design than to overall lighter construction of the rig. This is not to suggest it's flimsy -- but to say that the 80 series uses up some of its payload capacity on luxury features, i.e. power everything.

 

[dclee]

I think this is why systems like KDSS and Rover's own ACE are so revolutionary. You get the versatility of both soft and stiff suspensions.

 

[Cruiserdrew]

Just me, but I prefer stiffer springs. I've never had the overall stiffness of the spring being the limiting factor off road. I hated the J springs just because with a heavy load they had so much squat when climbing.

Even my FJ40 is set up fairly stiff for a spring over truck, and all of the springs have an extra load leaf just to stiffen it up.

I think that wallow feeling of very soft springs blows, and leads to way too much body roll when off road.

Talking Discos here-the guy that goes on our trips all the time with a Disco I is mostly limited by the lack of TRAVEL, not the softness or stiffness of his springs. Generally, a Land Cruiser will way out flex it's competition, at least until recently.

 

[450 DUDE]

First off . I know nothing about suspension.
But what I do know is that I was running the J's (soft springs) and OME shocks , and it sucked! The on road handling was sub par.


Now with the same springs and Bilstein 7100 it handles like a regular SUV .

ken

 

[LX_TREME]

Is your frame and oil pan notched? The stock front axle is only ~1.5" from the stops and not much further to the frame/oil pan. If you took the front springs out of a stock truck it would only lower it ~2".

I dont have the bump stops anymore, I have 5 inch lowering spring and lowering shocks.If you want to see it more clear I'll be glad to take pic for you.

You have obviously have never driven a performance go cart, or maybe you meant a 2.5 ton go cart with a really high center of gravity!

Obviously What do you know about me? Now do you really know my weekend job I'm imported and selling go-karts?

 

[IdahoDoug]

I think the original post has some merit, with the basic point that a softer suspension more easily flexes with very uneven terrain and therefore does a superior job maintaining a balance of traction among the 4 contact patches. All true. But to say the RR engineers somehow use it to their advantage is laughable. Some clever stuff exists in most vehicles with pedigrees like the LandCruiser and their Land Rover brethren. In a global sense though, the RR crowd need to answer for appalling reliability issues, the ghastly ACE debacle, air ride blowouts on pricy air spring and a myriad of gremlins,

 

[dclee]

I think the original post has some merit, with the basic point that a softer suspension more easily flexes with very uneven terrain and therefore does a superior job maintaining a balance of traction among the 4 contact patches. All true. But to say the RR engineers somehow use it to their advantage is laughable. Some clever stuff exists in most vehicles with pedigrees like the LandCruiser and their Land Rover brethren. In a global sense though, the RR crowd need to answer for appalling reliability issues, the ghastly ACE debacle, air ride blowouts on pricy air spring and a myriad of gremlins,

Believe me, I've been down this road arguing with the Rover purists on the 100 and 200 forums. The one I like is the universal fix of whacking the air compressor with a hammer to get it working again.

No one ever said they were reliable (well, KDSS might be). But the theories have merit. Even the newest air system on the Range Rover with the spring cross-lnking (advantages of 4-wheel independent suspension on-road, but can force air into and remove from opposing springs to mimic the behavior of solid axles off-road) is an intriguing idea IMHO.

 

[Walking Eagle]

No one ever said they were reliable (well, KDSS might be). But the theories have merit. Even the newest air system on the Range Rover with the spring cross-lnking (advantages of 4-wheel independent suspension on-road, but can force air into and remove from opposing springs to mimic the behavior of solid axles off-road) is an intriguing idea IMHO.

I agree- just because a good idea or theory is applied with bad quality control does not mean that the theory behind the design is bad.

There are also ways of designing a suspension that works great on road that does not include flat cornering that we tend to associate with good handling. I don't think the classic Range Rover has very flat cornering, but that doesn't make it unstable or unsafe. A real good exception to the flat cornering rule the first gen VW GTI. Far from flat cornering, it would actually lift it's inside rear tire, but once you got used to it, it would out handle any FWD car of the time. My buddies '73 230 Mercedes also had really soft springs, and would body roll into corners, but it would hold a line perfectly through a corner. Felt odd as could be, but you couldn't argue with the results.

So as always, there is more than one way to skin a cat, but you still have to figure out what to do with a skinned cat when you're done.

On the cross linked air spring - that's actually what I started thinking about reading the first post. Keeps the pressure on each tire equal, and is on the list of things to include when I finally airbag my truck.