I'm pretty aware of how sway bars do things on the track and that part makes sense to me.
I'm thinking about the Express van. It will never handle well, and it's not like I'm having an oversteer issue in turn 3, it just has a lot of body roll. In the process of putting the new tires/wheels on, I'm getting an alignment. Current tires show a very mild camber or toe adjustment may be needed. Before doing that I might give a turn or three on the torsion keys to get the front up an inch or so and level things out.
So that will add a tiny bit of effective spring rate (LCA lower in its arc), but raise the CoG and also put the UCA at a slightly less-than-favorable downward angle.
Am I nuts to think I could combat some of the body roll and higher CG with stiffer sways?
That's just preload and won't increase the spring rate. Unless you're talking about something geometric between wheel travel and spring travel that I'm not following?
To your closing question,I would think "yes" in any case.
When not tuning handling balance, they're still totally suitable for reducing body roll without raising overall spring rate. So the van won't get any stiffer over heaves and speed bumps, and only somewhat stiffer over single-wheel bumps.
I always have a hard time making sense of talking about the upper and lower arms in isolation, but I doubt your ride height tweak is hugely moving your roll center.
In reply to Jesse Ransom :
The spring's effective rate changes as you drop the LCA from 90 degrees. It doesn't affect the physical torsion rate of the bar itself, but it places the moment of force on a different angle relative to the torsion bar. As the LCA further departs from 90 degrees (parallel to ground), the greater travel in its arc for any given vertical movement of the suspension (perpendicular to ground). This isn't something you normally think of from a traditional coil-over or coil spring setup since the movement in those is more linear as opposed to referenced to a central torsion point
It's a minimal effect, but a known entity. As you crank up torsion springs, the ride gets stiffer. I've never done the actual math, but think of it like this picture.
So I got curious and I measured.
Notice below that each angled line represents one inch of vertical motion. Notice the segments of the circle represented by A through D. The first inch of vertical motion occupies 36.5 degrees of rotation (A), and B, C, and D each result in less and less torsional rotation for each additional inch of vertical travel.
So, in this picture, if I were to raise the van 2 inches, I might go from a spot where 1 inch of travel equates to 12 degrees... to a spot where 1 inch of travel equates to 16 degrees... thereby effectively increasing the spring rate marginally.
... in case my picture above didn't clarify much.
Curtis73 (Forum Supporter) said:
I'm thinking about the Express van. It will never handle well, and it's not like I'm having an oversteer issue in turn 3, it just has a lot of body roll.
You say that, but the Hellwig suspension that Tom installed on the GRM van is awesome. I find myself comfortably taking cloverleafs at ~55mph.
I imagine the helper springs on the rear cause it to ride rougher than stock, but it's no worse than 1-ton E-series box trucks I've driven.
In reply to Curtis73 (Forum Supporter) :
Is there a heavier duty version? 3/4 T 1T? In junk yards? There is your swaybar
lacking that bend up your own swaybar and bring it in to be heat treated.
Pete Gossett (Forum Supporter) said:
Curtis73 (Forum Supporter) said:
I'm thinking about the Express van. It will never handle well, and it's not like I'm having an oversteer issue in turn 3, it just has a lot of body roll.
You say that, but the Hellwig suspension that Tom installed on the GRM van is awesome. I find myself comfortably taking cloverleafs at ~55mph.
I imagine the helper springs on the rear cause it to ride rougher than stock, but it's no worse than 1-ton E-series box trucks I've driven.
That's good to know. I can stand a wee bit stiffer ride but honestly I think GM got the oscillation frequency just about right. I think they just whiffed on weight transfer.
In the long run, I might put helper airbags in the back for towing, but I think I'm more limited by the axle capacity than I am springs.
In reply to frenchyd :
I will have to check for that. It's possible they will bolt up, but this is an AWD with torsion bars and the 3/4 and 1-tons were all RWD with coils. Potentially a whole different critter, but equal possibility that GM did some parts-bin engineering.
If you raise the ride height, you will reduce body roll.
Pete. (l33t FS) said:
If you raise the ride height, you will reduce body roll.
This is a learning experience and an honest question... how does raising CG reduce body roll?
Curtis73 (Forum Supporter) said:
Pete. (l33t FS) said:
If you raise the ride height, you will reduce body roll.
This is a learning experience and an honest question... how does raising CG reduce body roll?
CG height affects weight transfer, but body roll is only loosely related to CG height. The roll center height goes up faster than the CG does when you raise the suspension, so the effect is that you need more side load to get the same amount of chassis roll.
I mean, you CAN go too far with this, but in the range we're looking at, you'll be okay.
In reply to Pete. (l33t FS) :
Ok, I can dig that. I assumed the opposite since the UCA was shorter length, but maybe I logic'd it backwards in my head.
Update. I played with the torsion keys today. Disappointing results. Started by measuring stuff. Both tires at 50psi, level concrete surface, measured from the floor to the fender opening. Left was 33", right was 33.5". I got under it and realized that the left side key was already only about 4 turns from bottomed, so I gave it 4 turns. I could probably get one more, but meh. I drove it around a bit to make sure it settled and I got the left side up to 33.75. So I gave the right side two turns and brought it up to 33.75". So I only really gained about 1/2" on the average but at least I got it perfectly level left/right. Doesn't drive any different but I did measure another half-degree or so of negative camber. I'll get it aligned tomorrow.
Also, in completely non-scientific testing news, at full droop, I only have 36.5" to the fender, so cranking the keys for more than a little lift might not be the wisest choice on this Express, at least not without longer shocks since that seems to be the only thing preventing more droop.
Just dropping in to acknowledge getting apparently everything wrong. Oops. Apologies.
Where's that Billy Madison meme?
In reply to Jesse Ransom :
On the contrary... I found your input helpful. My keyway escapades didn't really change much anyway, so off to find a bigger sway bar
In reply to Curtis73 (Forum Supporter) :
Want me to measure my Suburban's?
Sorry, but what are torsion keys? I've never heard of them, what kind of suspension do you find them on?
In reply to CyberEric :
Many IFS vehicles with AWD or 4wd
Instead of a coil which would be in the way of the CV axle, there is a big hex bar that sticks in a socket on the lower control arm. At the rear of the torsion bar where it installs in the frame, there are keys which are adjusted by a bolt. Tighten the bolt and it turns the torsion bar to raise/lower.
In reply to Stampie :
I don't think it will be apples/apples. I was only able to get a little bit of height so I'll call it good for now.
Curtis73 (Forum Supporter) said:
In reply to frenchyd :
I will have to check for that. It's possible they will bolt up, but this is an AWD with torsion bars and the 3/4 and 1-tons were all RWD with coils. Potentially a whole different critter, but equal possibility that GM did some parts-bin engineering.
Parts bins will help find suitable stuff in junkyards but I go bend up tubing and make my own sway bars. Once they fit I pull them and take them to my local spring shop to be heat treated.
Instead of a solid 3/4 inch shaft I use 1 inch tubing with a schedule 40 wall thickness. You may want 1.25 tubing with schedule 80 wall thickness. ( use DOM not ERW).
There is a way in the service manual to measure the "z" height. On my S-Jimmy it onvoled a level and measuring to the floor from a certain point ... It confusing and difficult when lying on the floor. Your van probably has a similar thing. The idea is to take the body out or the equation. I gave up and measured from the frame to the floor.
