[Mark '73 FJ40]

I started a debate with this know it all about how cranking up your torsion bars on your IFS is not a good idea.

I need some really good theory and explanations to shut him up. More theory then my limited experience can provide.

It all started when he said that adjusting your torsion bars wouldn't effect travel and I told him that wasn't true.

I had told him the more you crank the torsion bars, the higher the effective spring rate on your front end, thus taking more weight to get the same amount of compression.
Which results in
-harsher ride
-less travel especially in the downward direction (droop) of the suspension.

Here's his response.

Okay, spring theory 101, there is no way to change the spring rate of a spring once it has been made. The spring rate of a torsion bar or any other type of spring is fixed after it has been made and depends on the shape, cross section and material properties and no adjustment in the world can change it!!!! The spring rate of a torsion spring is in the form; radians/pound-foot. That means, if you twist a bar with 100 lb-feet of torque, then it will twist a specific number of radians, which can be expressed in degrees as well. Therefore, if you double the torque applied to the bar, you will also double the twist, linear relationship. There are a few real weird springs that don’t behave this way but a torsion bar surely does.

Now, if I preload a torsion bar spring with 25 lb-feet of torque, then to apply an additional 100 lb-feet or torque you would need to input a total of 125 lb-feet even though you only added 100lb-feet of torque to the system because of the previous 25lb-feet of preload. The net effect or internal stresses will be the same as if you applied 125 lb-feet or torque with no preload. In effect, by adjusting the torsion bars a couple of turns on that screw increase the preload a bit, but not a drastic amount. Now for the angle on the axles shafts, I calculated it before and after and it is

So, your statement is flat wrong about changing the spring rate of the torsion bars by adjusting them. Even the Pope couldn't change the spring rate man, there you go guessing again. What does happen though is you do change the pre-load if you adjust them. Pre-load is a far cry from changing the spring rate.

Thanks guys

[ 10-13-2001: Message edited by: Mark 73' FJ40 ]

 

[Pazuzu]

The problem with his arguement is that T-bars DO have variable spring rates, EVERY spring does. The thing is, you bring ANY spring near it's two limits (compressed or extended), and the value of "K" changes. Springs are only linear in the central part of their travel.

When you crank T-bars, you bring them towards the end of their travel, and so the value of "K" changes, the spring gets stiffer and the ride hardens.

Also, you DO lose total travel. I do not use the 8 inches of travel I have in front, even with the V6, because I'm cranked way up there. I probably only have 5 inches of travel during slow crawking, 6 or 7 if I get some air and come down hard.

 

[NoBrainR]

You will gain height, but lose travel, unless you also increase the weight of your vehicle, in which case you'll gain nothing. IOW, if you put a winch on and crank up your T-bars to recover ride height, your travel won't increase, you'll just wear your T-bars out faster. In order to change the travel, you need to change the geometry of the front suspension system, not just the spring.

 

[OffroadRunner]

OK OK Here is my opinion. The more you "crank" the t bats the more the adjuster arm moves, as that moves the lower a arm moves also. So how are you putting more load on them?
If the truck requires lets say 1000lbs of force to hold up that side of the truck if doesnt matter of it is 2 inches or 10 inches it still takes 1000lbs of force to hold up that side. ride harshness doesn't change. Unless you put in heavier bars or you are hitting the bump stops.
The only factor even to consider is if the bars are set "high" then on droop (if it does) then the bars are going to twist more then they normally would set at stock height. That may cause a problem. snap. I have personally never seen one broken, but if you jump bounce hard or "hill-hop" that would increase the chance. Carry a spare. You can find a set for 30-40 bucks. and it only takes about 15 minutes tops to change them out on the trail. 3 bolts thats it
Think about it. It makes sense. Alos take my word for it, if you think they don't flex with IFS then put on some 26mm jobs they DONT bundge one inch.
Just my 2 cents.

 

[racer0300]

When you crank up a torsion bar all you are doing is changing the ride height on that corner and transfering weight to a diagonal cornor, and if you crank up both front bars, you actually transfer weight to the rear and reduce the load on the front end. What you are doing to the the front end geometry is another story.

 

[SeaBass44]

Just tell him to "Shut his Fuckin PieHole!" or send him over here and we will put him in his place <IMG SRC="smilies/wink.gif" border="0">

 

[Mark '73 FJ40]

Just tell him to "Shut his Fuckin PieHole!" or send him over here and we will put him in his place

BAAAHHHHHAHAHAHHAHAHAHAHHAHAHAHAH

 

[NE-RokToy]

Originally posted by Pazuzu:
<STRONG>The problem with his arguement is that T-bars DO have variable spring rates, EVERY spring does. The thing is, you bring ANY spring near it's two limits (compressed or extended), and the value of "K" changes. Springs are only linear in the central part of their travel.

When you crank T-bars, you bring them towards the end of their travel, and so the value of "K" changes, the spring gets stiffer and the ride hardens.

Also, you DO lose total travel. I do not use the 8 inches of travel I have in front, even with the V6, because I'm cranked way up there. I probably only have 5 inches of travel during slow crawking, 6 or 7 if I get some air and come down hard.</STRONG>

This is 100% correct, and for you non Physics people k = spring constant for a given spring, 1/2kx^2 is the energy for hat spring. so the higher the k the more force necasary to compress that spring a given x distance.

You also have to take into consideration the lower bumpstops when talking about travel, the more you crank the T-bar the closert he lower arm gets to the bumpstop so you lose down travel.

 

[NoBrainR]

Originally posted by SeaBass44:
<STRONG>Just tell him to "Shut his Fuckin PieHole!" or send him over here and we will put him in his place <IMG SRC="smilies/wink.gif" border="0"></STRONG>

I read that, then look to the left, I swear I saw his lips moving. <IMG SRC="smilies/biggrin.gif" border="0">

 

[SeaBass44]

Originally posted by BrianR:
<STRONG>I read that, then look to the left, I swear I saw his lips moving. <IMG SRC="smilies/biggrin.gif" border="0"></STRONG>

BaaaaaaaaaHaaaaaaaaaaaaaaaaaaaaaaaaaa!!!!!!!!!!!

 

[GRABBER]

Whats a torsion bar?? <IMG SRC="smilies/laughing.gif" border="0"> <IMG SRC="smilies/laughing.gif" border="0"> <IMG SRC="smilies/laughing.gif" border="0"> <IMG SRC="smilies/laughing.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0">

Who cares?

[ 10-14-2001: Message edited by: GRABBER ]

 

[ErikB]

Cranking the bars doesn't change the "K" or spring rate because the bar still works in its normal range (until you get close to bottoming out, which is hard to do anyway except when jumping, etc.). All you have changed is the height.

If you have stock, cranked bars, the ride harshness only comes from having less droop because the UCA is constantly bottoming out on the upper bumpstop. Lo-pro stops can help this, but only to a certain extent.

Travel:
You know you only have a limited amount of IFS travel, say 8" w/ lo-pro bumpstops.
When you crank the bars, you are loosing droop and gaining compression. However, it will be MUCH harder to actually USE that compression, so for the most part all you've done is lost droop, which basically means you've lost travel. (Part of the reason its harder to "use" is that the "K" goes way up as you get that far into compression...)

In "theory," the travel is still there and you haven't "lost any travel."
The problem is that its just not all "useful" travel any more.


And the other reason NOT to crank the bars that hasn't been mentioned yet--
More angle on the CV's equals effectively weaker joints. When you crank the bars, the CV's will always be operating at steeper angles than they do w/o cranked bars...

 

[SoundmanCA]

Okay, I don't know all the technicall mumbo Jumbo everyone is saying, but I can tell you from experince that lifting your truck by the torsion bars is a bad idea. When I first bought my '88 truck I didn't really understand how the suspension worked, and I went wheeling in Gorman. I did fine until mt drivers side front wheel had to drop about six inches into a hole as I was going down a hill. Well my back end fliped up and I rolled end over end 3X down the hill. I thought it was just from driver error until I decided to put a 4" lift on my truck. I then realized that the previous owner of my truck had cranked the torsion bars so far that low profile bumpstops would not even fit. It turns out that I had about 1/4" of droop. And that why I rolled. (well the main reason anyway)