jimrockford

According to dictionary.com, a torsion bar is a part of an automotive suspension consisting of a bar that twists to maintain stability.

Can someone explain how this works on a 2nd generation 4Runner? I know that one end connects to the frame, and the other connects to the upper control arm. As I (mis)understand it, torsion bars are installed with the suspension "unloaded", or hanging freely. When the vehicle is lowered, the control arms flex, causing the torsion bars to twist. This twist causes downward pressure, preventing the suspension from bottoming out.

If this is correct, does "cranking" the torsion bar increase the amount of twist, resulting in more downward pressure? It would seem logical that if the torsion bar pushed downward harder then the front would ride higher. But, does this change the spring rate? Does cranking the torsion bars result in a stiffer suspension?

I'll be installing my new Downey 1 1/2" HD coils tomorrow and would like to know exactly what I'll be doing if I need to adjust the torsion bars.

Shane

A torsion bar is basically an uncoiled coil spring. "Cranking" the bars changes the ride height and amount of travel available up and down. It does not "preload" or increase the pressure on the spring until you crank it so far that you're pushing the a-arm into the bumpstop with it. With the bars "cranked" the suspension has less downtravel which means it tops out earlier and results in a rougher bouncier ride.

jimrockford

When you crank the bar, you twist it, correct? Twist might be the wrong word, since it would indicate a load. I guess what I mean is it rotates the bar causing the unsprung suspension to move downward. Is that close?

If so, continuing to rotate the bar would move the suspension closer to its maximum extension, causing the rougher ride since it would top out sooner, right?

Robinhood150

Yeah, a common misconception is that by cranking the tbars or adding spacers to a coil will preload the spring/tbar. The spring rate does not change either. However, the suspension might feel stiffer for two reasons that I can think of.

1. The geometry of the suspension changes, such that there is less of a lever arm on the spring at ride height.

2. The amount of travel is the same, but the tbar is forced to twist further than stock when the suspension is cycled.

There might be more reasons, but I can't think of any.

Also, just an FYI, as shane said, a coil spring is a torsion bar too. It's just coiled up.

Steve

Robinhood150

That sound reasonable.

Shane

Yes, and yes. Rotate, not twist. That is until it hits the limit, then it's twist cause it can't go any farther. Before you lift it, measure from the lip of the fender opening to the top of your rim and then again after adjusting. Don't twist them any more than 1-1.5" up, any more than that and it'll hurt the ride. Also don't adjust them with the weight on the wheels, put it up on stands. You'll also need to get an alignment afterwards as your toe-in will have increased.

To squeeze out a little more downtravel you can cut down the extension bumpstops or get low profile poly replacements.

Shane

This here is pretty much the max travel you'll ever get out of the stock IFS without some sort of lift kit.

Victor

Max space from a 15" rim to the fender is 15" before the ride quality is degraded. I have mine at 14.75" and it rides very nice. You have to disconnect your sway bar if you want to have more travel up front.

jimrockford

Cool. Thanks for the information. I feel smarter.

I plan to go with low profile bump stops, but I stopped by Central 4WD and they were out of them. I'll tackle that project when they get them in.

I measured 13.75" from rim to fender in front, and a hair under 12" in the rear. I haven't installed manual hubs yet, so I intend to keep the front as low as possible, but I'm not real fond of the a$$-high look. Of course I dislike butt sag even more.

I'm hoping to eliminate the sag and increase my departure angle with the new coils. I'm not looking for a huge amount of lift. I'm just tired of knocking the crap out of my stock rear bumper.

Victor

With the Downey HD springs I'm at 13.75 in the rear. I was about where you are before my rear lift.

jimrockford

I installed my coils and measured 14" at the rear. I remeasured the front and it came out 14" as well. I think it might need to settle a little bit - especially the front which has magically raised 1/4" without having done anything except put it on a lift. I'm looking into getting manual hubs and will probably crank the torsion bars a little.

Victor

I'm at 13.75 rear and 14.75 front. The back on mine is still slightly taller than the front with those settings. The fender lips front to back are not the same. Try 14.5 in the front and see how much it levels it out.

GV27

Don't forget to move the truck after you drop it off the lift before measuring the front - the negative camber from the wheels drooping in the front then not straightening out do to the grip of the tires will keep the truck higher off the ground.

C

Victor

I wouldn't go above 14.5" in the front until you have manual hubs.