abecedarian

Everything I've ever heard about springs, torsion or otherwise, says that you should only use a spring stiff enough to support your vehicles weight at the desired height. Using anything stronger or higher-rate is generally only recommended when there is limited travel and shocks/struts don't have the proper valving on the jounce and rebound strokes to sufficiently slow down the wheel's upward / chassis downward travel to prevent bottoming out, or to compensate for your vehicle's gained weight.

I could understand a slightly stronger torsion spring on our trucks when a long-travel suspension kit is installed due to the fact that the control arm is longer than stock and increases the leverage of the suspension against the torsion springs (although not that much, relatively speaking: would another 3" on that big-a**-breaking bar give you all that much more advantage?) or when necessary, as mentioned, to counter any additional weight being carried such as heavy tube bumpers, winches, etc. However, for most stock, or semi-stock situations like 'differential drop' IFS lift kits where the control arms sit at the stock angles, the stock torsion bars are actually more than adequate.

The whole concept of 'preload' on these springs means little-to-nothing since it is not a valid argument with regards to the operation of the torsion spring. The only 'preload' the spring has is whatever tension is on the spring when the suspension is at full droop. When the vehicle is placed on the ground the springs become 'loaded', not 'preloaded'. Adjusting the torsion bars does not add any additional tension to the spring once the vehicle is on the ground- it is carrying the same load if the suspension is 1/8" from the droop-stop or 1/8" from the compression-stop.

Does the truck magically gain weight if you crank in that extra 1" or so lift with the bars or add ball-joint spacers? NOPE. The difference is once lifted, the torsion bar has an extra 1" or so of compression travel to cope with, not any extra weight. That extra travel equates to a few extra degrees of rotation which puts additional stress on the bar that it didn't have to cope with to begin with. This extra stress may be enough to fatigue the bar and eventually cause its failure since the extra stress is something the bar wasn't designed for in the first place. Your real options here are install a 1" taller compression bump stop, a bar capable of handling the extra twist- which counter-intuitively means a softer bar, or a stiffer bar that won't break when over-leveraged. Ask any SAS equipped truck what stiffer springs would do to their ride and they'll probably say it would limit travel and flex. Well, no wonder IFS trucks don't have much articulation. Imagine if that torsion bar was strong enough to support the truck at the proper height on flat ground but soft enough to let that wheel climb all the way up the wheel well without upsetting the chassis. What we're dealing with here is called 'spring rate' or how quickly does adding tension to the spring cause it to get more firm.

On a related note, it is the shock/strut's job to respond to the bumps in the road and help slow down the lifting wheel and falling chassis, not the springs. The springs are there to keep the wheels on the ground and the chassis off of it. If you find yourself bottoming out too often, get more appropriately tuned shocks for your driving style. If you can't get the shocks to meet your needs, then a progressive rate spring is in order, but good luck finding a progressive rate torsion spring.

There are a few notable exceptions to what I've written above which I won't go into now except to say that a purpose-built vehicle has different requirements for operation than many of our trucks which operate on the highways as well as off-road. Everything is a balance and choosing only what you need and not what some marketing spin says you have to have is the better way to go. Stiff springs, in my opinion, are only useful as mentioned above- for carrying extra weight, or when it is not possible for the shocks to sufficiently dampen the suspension movement.

/me steps off of the soapbox

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