0.15 degrees is 1.4mm across a 19" rim. That's pretty much what I'd expect to get with the "strings" method, upgraded to a cheap laser line.
I always assumed the digital racks (which use cameras now, not lasers) were more about speed than accuracy.
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How does an independent shop reset steering angle after alignment?
- Thread starter G26okie
- Start date
I always assumed the digital racks (which use cameras now, not lasers) were more about speed than accuracy.
TacoSteve
Closed
I am saying the specs from manufacturers have a tolerance of .15-.25 degrees typically, the machine is accurate to .005 degrees. And Yes it is a Camera based machine, not laser.
Accuracy of 0.005 degrees seemed amazing to me, so I had to go check more.
A Bendpak/Ranger lists the specs as +/- 2' - which is 2 minutes. That's +/- 1/30th of a degree, or 0.03 degrees.
I'd put that right in the neighborhood of what you can do with a string.
https://www.bendpak.com/Target-3DPRO-OPERATION-5900963-09-16-21-Web.pdf (Page 9)
TacoSteve
Closed
That's not a Hunter Machine, and I'm not saying string isn't accurate enough. When they calibrate our machine it is calibrated to .005 degrees.
TacoSteve
Closed
Gauss Guzzler
Safety Score = 42
An alignment rack cannot be accurate to .005 degrees. At best it's maybe accurate to .2 degrees if it's perfectly calibrated and expertly used.
And at best it's maybe repeatable to .1 degree, this is not the same as accuracy.
It can be precise to whatever number of decimal places the marketing department wants. This has nothing to do with accuracy or repeatability, it's just marketing. But note that precision must always be higher than accuracy so it would have to read angles of .0005 degrees in order to be usefully accurate to .005 degrees.
FYI, a layer of conventional automotive wax on the rim of an 18" wheel would change the measurement by 0.005 degrees if modern Hunters still used static rim references. Driving a 1/4 turn with the swinging targets compensates for wheel surface imperfections but the car's suspension can easily wiggle more than .1 degree just from rolling a little on the rack.
Note that Hunter's "acceptable range" for the rack's calibration accuracy is +/-0.1 deg:
And on top of that, each wheel target has its own errors and calibration:
And if you did all the math to see what the maximum cumulative error could be between a barely in-spec frame and 4 barely in-spec targets you'd see what I mean. Then add in the fact that these calibrations aren't accurate either - there's all the unknown inaccuracies of the targets and sensors that aren't even being considered here because you're using those very same targets/sensors to perform the calibration.
And at best it's maybe repeatable to .1 degree, this is not the same as accuracy.
It can be precise to whatever number of decimal places the marketing department wants. This has nothing to do with accuracy or repeatability, it's just marketing. But note that precision must always be higher than accuracy so it would have to read angles of .0005 degrees in order to be usefully accurate to .005 degrees.
FYI, a layer of conventional automotive wax on the rim of an 18" wheel would change the measurement by 0.005 degrees if modern Hunters still used static rim references. Driving a 1/4 turn with the swinging targets compensates for wheel surface imperfections but the car's suspension can easily wiggle more than .1 degree just from rolling a little on the rack.
Note that Hunter's "acceptable range" for the rack's calibration accuracy is +/-0.1 deg:
And on top of that, each wheel target has its own errors and calibration:
And if you did all the math to see what the maximum cumulative error could be between a barely in-spec frame and 4 barely in-spec targets you'd see what I mean. Then add in the fact that these calibrations aren't accurate either - there's all the unknown inaccuracies of the targets and sensors that aren't even being considered here because you're using those very same targets/sensors to perform the calibration.
P3D-R
Closed
I don't even know if all this accuracy down to 3 decimal places matters because our shop alignments have been working well for some time now. All I know is it's still a good idea to get your alignment. I doubt everyone will do string or ballasted alignments so do what's convenient and always inspect your tire wear. Learn a little bit about alignment angles and ask to review your baseline values when you go to a shop so you can connect the dots between your tire issues and the #'s you see. It seems to me that the level of accuracy on the machines I have used works for whatever real life parameters it needs to work within. In simple terms, an alignment on whatever machine, if done properly, has saved me a bunch of money in tires as well as made my car drive way better.
