snap oversteer

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SuperBuickGuy

SuperBuickGuy

10 Year
Joined
Aug 24, 2014
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Location
Sandpoint, Idaho
"I need to check the basics before I get into fine-art"

when driving, it seems to want to turn harder right than left. Left seems quite controllable but going right has a vague center to a good initiate the corner, to a feeling like it wants to snap oversteer. On a vehicle with bias ply, 38" tires - it does add a bit of drama that I'd rather not have. Absolutely everything under this is brand new

I know I could live with this, take some camber out and perhaps give it a bit of toe-in.

So the basics, what do I look for in any vehicle that goes from vague steering to oversteer?

Driving down the highway, driving along country lanes at full tilt, it drives and feels solid - nothing pops it off its line... it's just the right turns. A couple times I was in an oncoming lane because it didn't give me the steering I expected... mind you, when I'm not building 4x4s, I race cars - mostly old Corvettes, so it does take some doing to get me to get concerned...

and it may be much adieu about nothing - when I got back to my shop, the tire pressure between the driver's side and passenger side was 25 psi on the left, 20 on the right... I reinflated to 30 psi... and will do that before I take it out again.... brain fart on my part, but this issue did show up on another drive so I'm not convinced it was merely a tire pressure issue.
 
yes, but nothing under it is FJ40, even the wheelbase is longer.... I wonder if it has something to do with where the upper control arm is... I even cured the lean...
you know, I need to do something and see if it helps.... I've been lazy


I need to move the panhead bar link up one bolt hole so that it's exactly parallel with the steering cross arm... that could do this?
 
I wouldn't think your link setup would be giving you that kind of handling issue.

Both hubs unlocked? Not sure that would make a drastic difference but I know I can feel it sometimes when my hubs are locked.

I'd almost suspect box more than anything else. Your link setup looks good to me, nothing stands out to me anyway.
 
SuperBuickGuy said:
and it may be much adieu about nothing - .
Click to expand...

Much ado about nothing.

Have you had it aligned where they check ackerman angle and scrub angles?

Its a coil sprung vehicle on 38" bias ply. Probably the first thing to do if you want to go highway speeds and handle well is to put some good radials on it.
 
Gumby said:
Much ado about nothing.

Have you had it aligned where they check ackerman angle and scrub angles?

Its a coil sprung vehicle on 38" bias ply. Probably the first thing to do if you want to go highway speeds and handle well is to put some good radials on it.
Click to expand...
yes, it is aligned.

ackerman is what momma Ford set it to be - if it were this, then I'd have the same trouble in both directions....

scrub is what keeps you driving straight on the highway... why do you think that would matter for turning?

alignment, maybe... at this point it's toe-out, if I set it a bit toe in, that would slow that initial hit - but still begs the question why one way not the other?

on the highway, it drives very well.... it's just the whole turning thing that is the issue.

for the record, my first car was a 1962 Buick Skylark with bias ply tires on it, the FJ40 I owned in Reno (number 2) never had a radial tire on it.... point is, I've more than just a little experience with the quirks of bias ply tires.... this isn't a bias ply tire problem.
 
You're steering linkage and your panhard geometry is... well pretty bad in that picture. I'm not sure how far that is from actual driving, but if it's anything close to the angles in your pic, it's going to have all sorts of drivaeabilty issues with that front geometry. As the body rolls you have a negative feedback loop in one direction and a positive feedback in the other.

You need to get your panhard bar and your steering crossover link sitting nearly level at static ride height. It should look a whole lot more like this: (I think the first place to start is some histeer arms and a drop pitman on the steering box to level it out. That should help if you ever decide to go offroad - the location of your tie rod is prone to a very short lifespan being that low and exposed.)
DSC00433.jpg
 
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Jetboy said:
You're steering linkage and your panhard geometry is... well pretty bad in that picture. I'm not sure how far that is from actual driving, but if it's anything close to the angles in your pic, it's going to have all sorts of drivaeabilty issues with that front geometry. As the body rolls you have a negative feedback loop in one direction and a positive feedback in the other.

You need to get your panhard bar and your steering crossover link sitting nearly level at static ride height. It should look a whole lot more like this: (I think the first place to start is some histeer arms and a drop pitman on the steering box to level it out. That should help if you ever decide to go offroad - the location of your tie rod is prone to a very short lifespan being that low and exposed.)
Click to expand...

here it is at ride height


I have a high steer, but trying to get it to fit since I kept the ride height so low created a lot of problems.
 
Snap oversteer is.... when you're cornering, let off throttle, and the weight/dynamics of the vehicle take it into oversteer (and usually uncontrollable). I'm pretty aware of this having MR2's (lots of them, modified, and heavy into auto-x), and they have a rear-ward bias weight (about 40/60). Watched a new 2nd gen MR2 owner experience it as he flipped into the woods. I almost sent a friends 2nd gen (very highly modified, and I was pushing it at an auto-x) off a cliff when I barely regained control (I doubt most would have regained control, though I doubt most would have pushed that car that hard... I did beat the owners time in it) after snap oversteer in his because we were playing with suspension firmness on the track.

So are the issues you experience during throttle, constant throttle, changing throttle, or anytime just when steering right, regardless of throttle/brakes?

I understand the vehicle is heavy, and front heavy.... but that doesn't change the dynamics of braking/throttle during corners and it's impacts on the vehicle.

Have you verified none of your brakes are dragging badly? (though, to be honest that would probably impact other aspects of driving you covered).
 
actually, (this is an eduguess), I think the vehicle has more weight over the rear than the front

letting off the throttle tends towards understeer. but this is such nuance that I think mentioning it may mislead - it tends to understeer.

Of course, I didn't mention and it would affect this issue - the rear has a loc-rite locker. Power into the corner with a loc-rite tends to understeer then oversteer if you let off (thus letting the inside tire go faster than the outside tire). With that said, if it were a loc-rite issue, it'd do the same thing in either direction (and let me tell you that loc-rite in the back of a 70 Buick Skylark with a 4 speed and 455 is a lot of fun after you learn to drive it - it's utterly dead-nuts predictable... of course, it's not intuitive which gives the white knuckles a chance to come out).

I'm going to change the panhard bar point - it's easy to do and it would seem to me to be the most likely culprit followed by the tire pressure...
 
high steer isn't an option. If I had my way, I'd be a billionaire and make others do the dirty work for me, then I'd swoop in at the end and claim credit for it. Alas, I've got a fatal case of the morals so that won't be happening.... anymore than high steer will be happening on this one ;)

toe in would help turning radius too... so that could happen, it'll certainly be tested.
 
good idea, but this one has all U-joints - no rag joints. More basically, I did check to make sure nothing was hanging - and heaven knows it is tight in there - but there is clearance....
 
Jetboy said:
You're steering linkage and your panhard geometry is... well pretty bad in that picture. I'm not sure how far that is from actual driving, but if it's anything close to the angles in your pic, it's going to have all sorts of drivaeabilty issues with that front geometry. As the body rolls you have a negative feedback loop in one direction and a positive feedback in the other.

You need to get your panhard bar and your steering crossover link sitting nearly level at static ride height. It should look a whole lot more like this: (I think the first place to start is some histeer arms and a drop pitman on the steering box to level it out. That should help if you ever decide to go offroad - the location of your tie rod is prone to a very short lifespan being that low and exposed.)
Click to expand...


Full droop.
 
Ackerman is wheelbase specific, so you probably have not enough for the short 40 series wheelbase. What is your roll center angle in the 4 link in the back? Maybe all these added up with your toe out is making it oversteer. That being said, I have no idea how to check that, nor fix it.
 
toe doesn't change on a solid front axle - I suspect you mean wheelbase changes when cornering (as you're pulling the bottom of the triangle that is made up of the front pivot and rear axle pivot). I'll look at it, but since both lower arms are parallel with the ground at rest, I can't imagine they'd move far enough to affect the wheelbase enough to induce steering.

ackerman ... I've not wrapped my brain around how it could be different in one direction as opposed to another. In short, if it does this oversteer to both left and right, then I'd agree that I need to spend some time on ackerman... however, to get a solid axle to have different ackerman angles left and right would be at trick I'm not sure is possible without something else being readily apparent. I need to add to this that there is a sway bar on the rear that would keep the lean down on turns. without the sway bar, then all sorts of other discussions would happen since the front is a 3 link set up and would react differently enough to right and left to be an issue at speeds about 30mph (which is where this happens).

after spending a day or two on this, I'm starting to lean to it being the panhard bar that's caused the most issue followed closely by the tire pressure in the rear tires coupled with the loc-rite ....

thanks for the input
 
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