Joe Weinstein

Hi all,
I heard someone say that even the fanciest new Hunter alignment machines are no more accurate than string-methods, just a whole lot more convenient... I was taking that with a grain of salt, but I got two alignments to the same car, at the same shop (Porsche dealer service department), same operator, same machine, with only 15 miles of street driving between, and the 'before' numbers from today aren't the same as the 'after' numbers from yesterday!

Yesterday's 'after' numbers: -----------------------------------------

LF
camber -2.47
caster 10.76
_toe__ -0.62 deg (This was the problem I needed fixing. The tech had misplaced the decimal point converting my specs from inches to degrees. I wanted 0.06 degrees.)

RF
camber -2.70
caster 10.78
_toe__ -0.65

LR
camber -1.96
_toe__ -0.13 deg

RR
camber -1.96
_toe__ 0.13 deg

Today's 'before' numbers: --------------------------------------------

LF
camber -2.33
caster 10.70
_toe__ -0.58 deg.

RF
camber -2.74
caster 10.78
_toe__ -0.59 deg.

LR
camber -1.88
_toe__ 0.08 deg.

RR
camber -2.01
_toe__ 0.21 deg.

Odd and disconcerting to me...

mdrums

Rubber in the suspension, fuel level...and so forth will cause change.... as an experiment have the tech roll the car off the rack and roll it back on...readings will even change then.

okie981

I think those numbers are not that far off considering you are comparing two digits to the right of the decimal. Lots of variables besides the machine itself and when all of them add up, I don't think the variation you see is that surprising.. The LF camber has the most variation, and it's 0.14 degrees.. My track alignment tech using a Hunter system says 0.1 degree repeatability is typical. What does Hunter expect for the back-to-back repeatability?

altonj

What others have said. No 2 times is a car on the rack in the exact same state. Unless the same day, when you should get repeatable results.

The tool of measure is irrelevant. Pick your favorite brand of aligner (we are partial to RAV) and they all read accurately. On most you can choose the resolution you wish to see as well. But, string alignment can be just as accurate with the correct tools. That is what is used at the track.... But string introduces the human element into measuring, where a quality machine looks after that. The resolution with string will not be as finite measuring toe as compared to a machine, but should yield similar accuracy on angles with the proper tool.

Cheers

mark kibort

usually it is the process of how the test is conducted. most common as variables is how they zero out the runout of the wheels. if they lift the car vs roll the car back and forth, this will introduce a setting difference that will alter ride height and ultimately alignment settings.
as was said, rubber bushings will provide some variability to the settings as well.

KevinGross

Agree with others, and will add that the differences are small even if "correct." You're unlikely to notice them, even if they weren't phantoms.

altonj

And the best new machines don't require rollback!

altonj

Exactly, although we are borderline OCD about getting the car perfectly set up, the only time it is in that state is while it is on our alignment lift. Change the fuel load, changes result. As soon as the car is on a surface other than the lift, changes occur. When you are driving or racing the car is never (or very rarely) at the exact position we aligned it at.

mark kibort

that has caused havoc for most alignments for years... there should be an ignor function on the "older" hunter machines... after all, how much run-out can a wheel have on a race car..... if a lot, you are going to have bigger issues. how do the "newer" machines deal with the runout check... just curious.

altonj

Mark,

To be honest, I am not sure of the technology. We looked at every major player prior to our purchase or our second machine. All had no or little roll back. Hunter had very minimal (a few degrees) and the RAV we use has zero. Even at SEMA I could not get a straight answer from the reps. I can tell you, that our RAV is incredibly repeatable and gives us great results. I expect the Hunter would have done the same. As all of the major competitors produce high quality products at similar prices, for shops it comes down to small features and service in your area. Can't have the machine down waiting for service. Like all of our specialty equipment we keep extra parts on hand to minimize risk. Batteries, clamps etc for alignment machine and mount heads and rollers for tire machine. But, I do like handing a tablet to a "waiter" in my office area so they can watch the alignment specs change in real time and also like the fact we can read out a car in less than 10 mins (drive on, set up machine, caster sweep) to present data to a client they can see on the tablet.

Cheers

ace37

Have you tried literally pushing on the wheels with the machine hooked up? The thought is a minor force applied laterally to the wheel by hand might be a reasonable way to estimate an acceptable alignment tolerance.

My Alfa 4C has intentionally soft rear bushings to give a rear steer effect. I hated the slop and had them replaced with metal bushings. I suspect with the big rubber bushings, static alignment specs would be evasive. It would vary depending on how the bushings were loaded when you took the measurements. I think it’s reasonable to assume some amount of this is true for the vast majority of street cars.

dgmark

In our shop we have the latest John Bean (Snap On) Alignment system. I still string all race cars the resolution is not good enough on production machines.

Matt Romanowski

That gets towards a k&c machine or even a pull down rig. You would be surprised at how much some things change with force.

altonj

We have compared strings vs our machine and found the machine very accurate. When stringing, we use smart string set up with hub stands.

How much resolution can your eye detect while using strings? .5mm? less?

Cheers