1st Gen Understeer, SCARY

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Little Bro's 91 1/2, 250, 2whl/dr, caused me to break out into a quick cold sweat while leading a Z71 to Elk camp in the Rockies last fall. Dennis had reciently installed a set of 1 ton front springs, 235/85/16's, and 5" blocks in the rear to level things up. Looks great, but it all adds up to understeer. Especially on a long fast downhill with a loaded trailer.

Bro wants to install sway bars front and rear, I thinking the caster and camber can be set to non stock spec's to correct or help the understeer. Any suggestions?

Thanks, Ronnie

 

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Taking it back to the top with the hope someone will have a suggestion or two.

 

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Let me verify this... you have UNDERSTEER? The symptoms being you gotta keep cranking more and more on the wheel as you get deeper in the corner, and the front tires start squalling long before you're cornering very hard.

You can't correct understeer by adding a swaybar to the front. Normally, understeer is caused by looseness in the front end, or excessive anti-roll built into the suspension. For instance, you have soft springs in the back, stiff springs in front, AND an anti-sway (roll) bar too. This will lead to the outside front tire being extremely loaded and the inside being almost unloaded, and between those conditions, the pair of tires is unable generate side loading, and they slip to the side.

Now, if you have oversteer (feels like the back end wants to get ahead of you, or wants to go the outside of every curve, steering you to the inside), that's a whole different ball of wax. I'll discuss that too, if that's the case.

 

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Power Wagon, I'm struggling to accurately describe how this thing drives. It goes straight when it should, however you've got to be very attentive and not make a quick correction or it tends to overreact, (oversteer?) requiring a followup correction to keep things on a even tract.

While going around the Rocky Mountain curves that promped this post, if you didn't pick the perfect line going in, corrections almost seem to be exaggerated and while the tires didn't loose traction, the front end felt like it wanted to dig in and take you quickly and aggressively in the direction you hinted you wanted to go in. You have to really pay attention to avoid a whiplash type situation where any overcorrection requires a greater degree of correction. It requires very careful attention to avoid the need for violent corrections.

I strongly suspect the combination of the tall sidwall tires and suspension changes causing the truck to set about 6" above stock is the culprit.

I may need to dig out and old auto-cross book and enhance my vocabulary in order to accurately describe what's going on. After reading the definition of oversteer, I feel that better describes things than understeer.

 

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Alright... here's where I'd start... Tire inflation: You need SOLID tires in the back. Make sure they're up to snuff.

Next: Does the truck sit at the wrong attitude? Is it tail in the air? If so, that might be the problem.

Next: What kind of tires do you have? Are they the same front/back? Or are the back a tall aspect ratio (lots of load capacity, but kinda skinny) and the front low and wide?

Also, since you mentioned something about changing springs... Did you seriously increase the stiffness in the back, but not alter the front? If so, that will have the same effect. You can help that by installing a nice, heavy anti-sway bar in the front.

Wheels: Do you have REALLY narrow rims? Like 5 1/2 inchers? Those things let the tire wander all over. With a big load, it'll drive aweful.

Lastly... Have it aligned! It might not be right. Especially, you could have the caster off, causing the truck to actually attempt to steer itself into the corners.

Those are the things I can think of off the top of my head. I'm sure there's wiser heads than mine on this subject around... but what I suggested makes sense to me.

 

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Ronnie,
Have you checked the steering system? My truck has had a lot of stuff replaced such as the steering shaft from the steering column to the box, the box, tie rods. Also, the ball joints should be checked for wear.

Matt

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90 W250, 5-speed, 3. 54 gears, 16 cm2 housing, tach, pyro, and boost gauges, K&N air filter.