Joined: Tue Mar 13 2007, 12:47PM
Location: Oregon
Posts: 65
Presetting allows the torsion bar to carry a greater load before it snaps. That is the safety margin issue that I brought up. The best example is the use of the drag race bars on something like a big block A body car. Without the presetting those bars are close to snapping at full travel.
There is an old SAE paper that covers the design of torsion bars. I think it is still available on the SAE website if anyone is interested. It is a very good reference paper and it explains the whole preset issue as well as describing the formula for calculating the spring rate of a torsion bar.
Joined: Wed Dec 06 2006, 12:50PM
Location: North Carolina
Posts: 23
Andy is correct that presetting is critical. But one cannot confuse presetting a bar and having offset hexes. Presetting is pre-loading (pre-twisting) the bar in the direction of its load in order to enhance its strength and longevity. Ma Mopar preset the bar (pre-twisted it) AND offset the hexes in order to get a comfy ride and durability we all know. We've preset the bar for durability like mopar, but left out the hex offset so that you can run the car lower without losing the spring rates. I think you'll like the crisp and confident feel they create. It just means that our bars give you the ability to lower the car more than the Ma Mopar bars (or other bars with offset hexes) will allow you to.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
JustSuspension wrote ... Andy is correct that presetting is critical. But one cannot confuse presetting a bar and having offset hexes. Presetting is pre-loading (pre-twisting) the bar in the direction of its load in order to enhance its strength and longevity. Ma Mopar preset the bar (pre-twisted it) AND offset the hexes in order to get a comfy ride and durability we all know. We've preset the bar for durability like mopar, but left out the hex offset so that you can run the car lower without losing the spring rates. I think you'll like the crisp and confident feel they create. It just means that our bars give you the ability to lower the car more than the Ma Mopar bars (or other bars with offset hexes) will allow you to.
After re-reading I see where I was getting confused, I'd assumed that adding a preset would automatically introduce an offset, but this doesn't appear to be true. I guess the preset does introduce side dependency and that the bars should always be used in matched pairs.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
NFURY8 wrote ... The whole preset twist thing makes no sense to me. The only thing I see being different is the amount of threads in/out on the adjusting bolt and the angle of the adjusting arm in the lower arm. The amount of tension produced by the lower arm doesn't change. None of the distances change. The angle of the lower arm to the body or T bar doesn't change. How does this relate to safety?
I've been pondering this as well, I have a theory that Andyf will maybe confirm or shoot down in flames.
To make it easier to explain, assume one end of the bar is clamped such that it can't move and assume the free end of the bar can be twisted, say 45 deg before it fails. Now assume the normal load on a bar will tend to twist the bar clockwise, then it makes sense that you could extend its range by putting a permanent counter-clockwise twist into the bar before it's heat treated. If this twist was 15 deg, then the bar could handle 60 deg down load and 30 deg rebound load before failure. As a side benefit the bar would give a softer ride when operating around the zero twist point. I suspect the preset twist is actually changing the neutral alignment of the steel molecules before they are locked in position by hardening.
Sorta like lining up molecules when iron is magnetized, which if heat treated will lock the alignment to make a permanent magnet.
To my knowledge no one here has used either a full air rear suspension or the air over leaf system. The Air Over Leaf looked very promising to help out some old springs. But once you added on all the extras to make it convenient to use on a routine basis, it got costly - Quick!
I have settled in using the set of low mileage 6 leaf springs that I had made back in the early 90's. They ride great! I hind site, I think this was the best route. Luckily, it didn't cost me any extra. The nice part is that the rear compliments the front well, has plenty of capacity, rides well and puts the height where it really should be. It is still lower, but I can now load the trunk full and the passenger compartment and not worry about dragging tail!
Joined: Tue Oct 23 2007, 07:15PM
Location: Strathmore, Alberta
Posts: 73
A tip when you remove the old torsion bars, before you install the new ones just take the edge off the edge of the new torsion bars it will make them easier to install and you won't cut a ridges in the bore. You don't have to take off much just enough to make it slide in instead of hammering it in. In case you didn't already figure it out the floor pan is going to get in the way. take your time and work it in slowly, if you force it you will cut a ridge in the bore and it will bind the torsion bar.