asymmetry of the wheel alignment problems

[sierra4000]

Hello ,
How way the asymmetry of the toe alignment (thrust angle) affects tire wear and car stability?

Thank you
Radek

 

[BrianPetersen]

?? Not sure what you mean.

If you arbitrarily lengthen the left tie rod by (let's say) one turn and shorten the right one the same amount ... is that an example of what you are talking about?

If you were to do this with the steering wheel locked in place then the effect will be to put the car into a right turn (assuming rear steer). If you allow the driver to do what needs to be done to drive straight ahead then the steering wheel won't be centered when driving straight ahead. Depending on how the steering stops work, maybe the turning circle won't be the same left vs right. If the steering wheel angle is an input to stability-control, that system might be unhappy. The thing that clicks the turn signal off when re-centering the steering wheel might be unhappy, too.

Or did you mean something else?

 

[GregLocock]

On the front wheels you just get steering wheel off centre which is primarily an aesthetic issue, although if you have your hookes joints set up to give fast or slow on centre it'll affect the symmetry of that as well, but not to any noticeable extent. If you've got it on the rear wheels you'll induce vehicle crabbing which again is mainly an aesthetic issue.

Cheers

Greg Locock


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[cibachrome]

Me take stab at this:
In front view, tierods may have different lengths because steering wheel or steering shaft is not positioned to design intent.
so, count threads showing to verify. should be same count. if different, then slope of tierod is different, too. slope is ride/roll steer.

if different, then asymmetric ride steer and higher tire wear from scrub. can also cause steering lead: car moves to right or left on its own. no feel in steering wheel.

 

[BrianPetersen]

Ford "twin I beam" front suspensions had left-right steering geometry asymmetry by design. The tie-rod for the right spindle went from the steering box (which was somewhere near the "I-beam" chassis-end pivot for the right wheel on the left side of the truck, although not really in the right spot) all the way across the truck to the right steering arm, and the left tie-rod attached partway along the right tie-rod and doubled back to the left spindle. So, bump/roll steer for the left wheel varied depending on the instantaneous position of the right suspension within its travel, because the attachment point for the left tie-rod varied in height depending on what the right suspension was doing.

On Ford vans that I've driven, which have all been old crapboxes, what the driver did with the steering wheel was a vague suggestion. They're notorious for wearing out front tires, too.

 

[sierra4000]

Thank You,
I'm will trying to be more specific,
toe setting recommendation is +1mm per left wheel, +1mm per right wheel (+2mm total)
If is +2mm left and 0mm right wheel
I know about steering wheel position change, but exist difference in tire wear and car stability?

 

[BrianPetersen]

Nothing. The total toe is what matters for that.

 

[XR250]

I imagine electric PS could have an issue with this.

 

[lucky-guesser]

toe setting recommendation is +1mm per left wheel, +1mm per right wheel (+2mm total)
If is +2mm left and 0mm right wheel

This is what we were needing to know.

Nothing. The total toe is what matters for that.

I somewhat disagree. Asymmetric toe like this can be compensated for by turning the wheel slightly. The last time I had my sierra worked on the steering wheel was installed about 15deg off center and I haven't bothered to fix it, but beings as 15deg is a lot, I know that I need to hold the steering wheel considerably to the left to keep things straight. However, that small amount of asymmetric toe could be enough to make the vehicle pull to one side but with how small that amount is you may not know to compensate for it, so it will feel like something is out of whack. This is especially going to be the case since it is the left wheel that is toed in, it will be pushing to the right, compounding the already rightward slope of the road (this is totally assuming you are in a country where you drive on the right side of the road. If you drive on the left side of the road these forces may actually cancel out and it will track straight when on a sloped road, but still pull right when on a flat road.)

If I were doing the alignment myself (which I have done before) or paying someone else to do it, I would not want one side to be on one end of the tolerance range and the other side to be on the other end. There is a reason that total toe, left toe and right toe are all called out separately.

Sierra 4k -- This is not going to hurt anything, you can run it just fine, but I would hope that a quality alignment shop would get you to where everything will track true, not just get things more or less in spec and call it a day. This may be perceived as being nitpicky so take this how you wish.

 

[GregLocock]

The elephant in the room is the tolerance stack in height between the inner tie rod and the lower arm bushing, snd the same for the lateral location.


In the case of MacPherson you've also got the front view installed angle of the strut, since the spring tower's relationship to the lower suspension arm is by guess and by god, in production, as it involves a tolerance path of many stampings welds and bolted joints.

Your tie rod adjustment for toe and steering wheel on centre is being affected by all of this, as is your kinematic roll steer.

Cheers

Greg Locock


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