Over the couple years that I've been on the boards I've repeatedly run into some common misconceptions regarding coil spacers, tbar cranking, and preloading. For instance, a lot of people incorrectly think that adding spacers or cranking tbars add preload.

To dispell these myths I've put together an article that discusses basic suspension component functions and how simple modifications effect the system. Keep in mind that this is a basic look at suspension systems and there are many more things going on than I have explained. Also, this article focuses on coilover suspension but the theory transfers over to any coil sprung suspension and to torsion bars.

I welcome any comments, questions or suggestions you may have. Enjoy.

http://www.robinhood4x4.com/suspension1.htm

i see EXACTLY where you are comming from on the t-bar thing(in my head it makes sence to me as well), BUT when you crank the t-bars the ride is firmer. i can say that without any doubt. i know this is true on my 90 4runner. when i crank them up the ride is rough as hell with the 25mm t-bars, when i let them down, the ride is softer with the same 25mm t-bars.
i can also give an un-biased opinion. my dad has an 87 4runner. he put 32's on it and said the tires rubed a little up front, i told him i would take care of it. well i cranked the t-bars one weekend and sure enough "what did you do? its stiffer now".

cranking the t-bars does make the ride stiffer, im almost positive i cant be convinced otherwise. cranking them may not change the spring rate, but it makes the ride stiffer and the angle on the a-arms could have nothing to do with that.

I think the fact that you are moving the suspension very close to the droop bumpstops and therefore hitting them all the time is the primary reason for the perceived stiffer/firmer/rougher ride.

Yes, the angles of the A-arms play a role, but I don't think they play as significant a role as you seem to think or imply. IOW, the difference between the "X" and "Y" lengths in your picture don't change significantly enough to matter or be noticable. Say our A-arms are 12" long ("X") and are horizontal at stock ride height. Now add 2" of lift from cranking or spacers. Your "Y" length is now 11.83", which is only a 1.5% change in length. 3" would be 11.62" or 3.2%. Not significant, IMO.

But yes, I do agree that adding spacers or cranking the bars does not increase or change the spring rate.

keep in mind that when you crank the tbars up, you are changing the percentage of the vehicle's weight on the front vs. on the rear, which would effect the 'feel' of the vehicle substantially...

Yes but the A-arms aren't horizontal at stock ride height, they're angled already. Since the change in the length of the lever arm is not a linear function of vertical height (it's a circular function), the "Y" length will change much more as the vehicle is lifted.



This, may very well be true, but don't a lot of people who crank the tbars also use low profile bumpstops?

Cranking the bars makes the ride feel stiffer because of the interaction he described with the a-arms. Remember, the upper a-arm is shorter by about 4" or so than the bottom so it swings through its arc much faster. I can go and measure mine but just from my memory I'm pretty sure its around 10-15 degrees(about a 6% reduction in leverage) downward stock, cranked approaching 30 degrees. (15% reductoin in leverage) Over about 20 degrees there is a much more rapid change in actual leverage per degree rotated.

I think the main purpose is to dispel the myth that stiffer t-bars are necessary for lift, not that cranking the torsion bars doesn't effect ride characteristics.

Frank.

About cranking t-bars part not affecting ride I say bullsh*t! It is simply not true that cranking them does'nt have any effect on spring movement/stiffness. If you have a coil spring and you force the coils closer together with a spacer (or in the case of motorcycle or high end racing shocks/springs, an adjuster) you make a significant difference in the length and stiffness of the spring. That is called a preload adjustment in the racing and motorcycle world. You use an adjustment like that to reduce the amount of possible motion in the spring, it will help compensate for more weight and provide just the right amount of travel in the spring. When you crank the torsion bars you are doing exactly the same thing, if they had 90* of total motion available in the up direction (oversimplification I know) and you crank them 5* they now have 85* available and as with any progressive spring and even most "linear" ones the force required to deflect the spring a given angle/distance will increase towards the limits of the spring's travel. You are using up the initial travel "soft" zone when you crank them and they get very frikking stiff. I have cranked t-bars, with ultra low pro bumpstops, and some 33" tires with very low pressure to soak up road bumps, and it rides like a hay wagon. I have some brand new bilsteins on it too, no improvement. My A-arms are NOT smacking against my bumpstops, as evidenced by the dirt buildup on the stops unless I am wheeling it. The whole concept that you don't change the behavior of the spring by using up some of it's travel is ludicrous. Like some of the other guys said try some real world comparisons, go crank some an inch and tool down a familiar stretch of asphalt, you'll find a bunch of seams you didn't know existed I promise.

I'm getting a headache thinking about this.... <img src="/forums/images/graemlins/lol.gif" alt="" />
I think the T-bar spring rate is not linear...The difference in force needed to compress the suspension increase as you compress the suspension. When you crank the t-bar, you basically increase the force needed to compress the syspension. That's what people refer to as "preload".
Another way to look at is the resistant of the t-bar from the rest state increases as the bar is twisted is not even. As the t-bar gets cranked, more down force is needed to move the suspension downward. This translates in to stiffness.

In the real world experience, I cranked the t-bar temporary to compensate for the 35" MT/R. I notice imediately that the ride is stiffer. When I go through speed bump, the wheels wants to drop down a lot quicker than the truck. Gas shock increase this effect further ( I have Edelbrock ) This also make a rough ride. When I'm on the frwy, the same thing happen also but at a much higher speed.
Overall, cranking the t-bar is probably ok to a certain extend. I don't recommend people do it to fit 35's tires with 2" body lift.

Go back and read it agian carefully, when a spacer is installed the coils DO NOT get compressed any more than normal. At ride height you are NOT forcing the spring coils closer, it only seems that way. The shock gets extended, but the spring does not compress anymore. The only way to compress the spring more is by compressing the travel all the way to the normal control arm travel limits. Then, the spring will be compressed to the amount of the spacer.

Another analogy is that adding a lift block to a leaf spring does not add preload, nor does it compress the leaf anymore.

Again, like frank said, I do realize the ride gets stiffer when the tbars are cranked...but the REASON is not because of preload.

Not true with the rear coil springs. On the motorcycle, you have a coil over type suspension which do exactly what you discribe. You are squeezing the spring further as you add spacer in the coil-over suspension.
The rear coil suspension of the 4 runner is a bit difference. The truck actually "floats" on the coil springs. When you add the spacer, all you're doing is increase the distance between the frame and coil springs. The springs do not compressed any more than before.