How accurate are computerized alignment systems?

[BigBlue]

Out of curiosity I took my car to a local alignment center. They dialed it in as a 2004 Corvette but got some strange readings on all parameters. The caster was expected, 2.7 but the camber and toe were out of spec by quite a bit, even listing one wheel as positive camber by .4 degrees. I bought the Sears digital level and re-checked the camber at home, all correct. -0.2. I checked toe front and rear by clamping straight-edges to the wheels and measuring across, also correct. So now I'm skeptical of the 10-minute computer alignment systems. How good are they and what part does the operator play?

[billybobracing]

Modern alignment systems are very accurate. There can be some operator error and they do go out of calibration from time to time, but any reputable shop will have the calibration checked occasionally. I'm also wondering how you make a toe measurement at the center of the wheel front and rear. My body and frame get in the way.
Cheers
Bill


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[MK4]

When i got mine done it took about 45min (but mind you i stuck around and was talking car with the operator thé whole Time) allignement is right on car goes straight and stays straight.

Cheers

Mk4

[mikespms]

Alignments are as good as the person doing it. Most alignment shops techs dont know how to set up a car like a gtm in fact in my area I called several places with the best equipment available and they did not know what bumpsteer is or how to set ride height. You need to find a race or chassis shop that has the know how and can set up your ride height, set it with scales,check your bump steer and then dial in your alignment. Not to mention there could be discrepancies the the frame and you may have to make some modifications to get it right. With some basic tools like a camber and caster guage and a set of tow plates you can get it very close,set your ride height before you do your alignment.

[BigBlue]

Originally Posted by billybobracing

Modern alignment systems are very accurate. There can be some operator error and they do go out of calibration from time to time, but any reputable shop will have the calibration checked occasionally. I'm also wondering how you make a toe measurement at the center of the wheel front and rear. My body and frame get in the way.
Cheers
Bill


Sent from my Autoguide iPhone app

My wheels are 25' F and 26" rear so I used straight edges longer than this clamped to the wheel below the frame and marked these 25" and 26" centered on the wheels. As the camber is almost nothing, this simulates measuring at the center of the wheel. The Corvette specs give toe in degrees, so this can be converted to any point on the tire using the sine factor if one wants to measure directly.

[vector1]

alignment machines are very accurate. the newer ones are very easy and almost foolproof to use. alignment will change between driver weight in the car and no driver, by how much depends on the car. if you do not have solid bushings just moving the car will change things. on my jbl just tightening the lock nut on one of the steering arms will change the toe a .010, that will give you an idea how sensitive alignments can be.

[GeeTM]

When done properly, good aligners will be within .03 degrees. I can only speak for the Hunter models because I was a mechanical engineer working on alignment machines a few years ago. Proper jouncing and slip plates are critical for an accurate alignment. Again, good techs with good equipment will get good results. I am the product manager for wheel balancers now, but still remember those days like it was yesterday...

[wadd]

Big Blue,

I think the other factor is that when you are measuring the car yourself, the floor not only has to be dead flat, but also dead level. No way could I measure them correctly in my garage!

[lbperry]

The operator shouldn't be setting is as if it were a 2004 Corvette or any other machine that it's not. If he knows how to use his machine, it should have the capability of inputting specific alignment parameters.
Good Luck

[VD2021]

Originally Posted by BigBlue

Out of curiosity I took my car to a local alignment center. They dialed it in as a 2004 Corvette but got some strange readings on all parameters. The caster was expected, 2.7 but the camber and toe were out of spec by quite a bit, even listing one wheel as positive camber by .4 degrees. I bought the Sears digital level and re-checked the camber at home, all correct. -0.2. I checked toe front and rear by clamping straight-edges to the wheels and measuring across, also correct. So now I'm skeptical of the 10-minute computer alignment systems. How good are they and what part does the operator play?

Originally Posted by lbperry

The operator shouldn't be setting is as if it were a 2004 Corvette or any other machine that it's not. If he knows how to use his machine, it should have the capability of inputting specific alignment parameters.
Good Luck

No doubt a properly functioning alignment machine will be very accurate. I agree with Ibperry here. You need only give the tech the alignment specs you're looking for so he/she can dial them in.

The manual's alignment spec:
Appendix C – Wheel Alignment Specifications
Toe In(inches)Camber(deg)Caster(deg)
Front 1/8 -0.25 2.5(You can get close to 7 on the Gen2)
Rear 3/16 -0.5 N/A

Most say you should dial in as much caster is possible. Here is a good alignment thread Alignment and Ride Height Gen 1 and great chassis set up thread Chassis Set - Up .
HTHs

[BigBlue]

Well, lots of info, thanks. Every alignment shop I have been to tells me they must input data for a car that is in the system, they cannot input individual values themselves. My GTM has the rear track 4" wider than the front and I don't know how the machine handles this. The Corvette specs from my shop manual are very close to what is in the FFR manual when translated from degrees to inches. The only interesting thing is the tolerances. e.g. front toe 0.08 +/- 0.20 degrees. I read this as a target of 0.08 but limits from 0.28 to -0.12. It would make more sense the other way around, e.g. a target of 0.20 with limits from 0.12 to 0.28. The big question is does the machine read actual true values regardless of input? i.e. does the input serve only to color the reading green or red or does it affect what the machine outputs in terms of numbers? I am doing my alignment on my lift which is completely level in both planes. I cannot see how the computer can read my rear camber as +0.4 when I measure it as -0.3.

[vector1]

on mine which is an older hunter d111, i can input values, i don't know about the newer stuff but i don't know why there wouldn't be a provision for this. the machine compensates for wheel offset, runout, etc., so that is no problem.

you should be able to eye ball the tires and tell the difference between positive and negative camber.

[BigBlue]

No question about the camber by eyeball, digital level and bubble level, it is negative.