Trying to wrap my head around Dual Axis Dynamic Caster/Camber Gauge

[Mineral_'01]

So I've been obsessed lately with ideas on how to improve on DIY alignments other than an expensive Longacre caster camber gauge (or similar) and the string and tape method for toe.

The Longacre CC gauge is nothing other than a cheap digital inclinometer and wheel adapter that they charge a lot of money for. You could build one yourself for a lot cheaper, but I am looking for ways to improve upon a single axis CC gauge like these.

This led me to think about using some kind of dual axis gyroscope inclinometer to make setup even easier and more accurate. So I did some digging and found this: http://store.drpperformance.com/dual-axis-dynamic-caster-camber-gauge/

This is exactly what I was referring to for a dual axis gyroscope inclinometer. Again this company wants a lot of money for this rig when you could duplicate it yourself for under $100 using this: http://www.amazon.com/Function-DXL360S-Digital-Protractor-Inclinometer/dp/B00C3XKZ98

Look familiar? And only $75

Some video of this thing in action:
https://www.youtube.com/watch?v=v9P0QnlMkvI

So I was thinking using this inclinometer and a wheel alignment adapter fixture I could have a pretty accurate caster camber gauge for pretty cheap that would have many other uses for suspension setup as well.

So some questions; would there be any complicated math formulas to read caster and camber? Or just zero the meter at ground level and then take the readings once mounted to the wheel adapter? I wonder exactly how to measure caster like the DRP performance unit does using the same inclinometer? Anyone have ideas?

I even found another product that uses the same type of meter to measure caster/camber all in one kit. See here:
http://www.ebay.com/itm/FIT-TOOLS-W...1113897734&pt=Motors_Automotive_Tools&vxp=mtr
It incorporates my exact purposed setup with some kind of additional stand/fixture for caster measurement, but I can't really figure out how it works. Edit: after watching a video on this product, caster is measured by taking readings using the 20° sweep method. The extra stand is just a electric protractor notifying with a beep sound once you have turned the wheel 20° one way.

Finally, would it not be possible to use this meter to measure toe using the gyroscope function? (rotation of X-axis) Just zero it to your rear wheels, (these would already be at zero toe) make sure your front wheels are straight, and then compare measurements from the rear to front wheels?

 

[ArizonaGT]

Keep plumping

 

[Mineral_'01]

^Yeah not sure what they meant by that. Probably Chinese for keep spinning haha.

 

[Whiskey11]

Your rear axle definitely does NOT have zero toe, nor does it have zero camber. My car actually has a significant amount of rear toe out to the tune of about -0.16º total toe IIRC.

 

[Mineral_'01]

Your rear axle definitely does NOT have zero toe, nor does it have zero camber. My car actually has a significant amount of rear toe out to the tune of about -0.16º total toe IIRC.

Interesting, so you are saying that when people are using the string method, (squaring the string to the rear wheels) they are actually inducing toe out to the front wheels if adjusted to the string? The fact that the rear wheels have some camber should not matter in the case of adjusting toe off the rear wheels.

So where is a good reference mark on the S197 that runs perfectly parallel with the vehicle centerline when viewed from the side? Pinch weld below the rockers maybe? If you knew this reference mark, you could zero the gyro to it and then adjust front wheels to be the same.

 

[Whiskey11]

Interesting, so you are saying that when people are using the string method, (squaring the string to the rear wheels) they are actually inducing toe out to the front wheels if adjusted to the string? The fact that the rear wheels have some camber should not matter in the case of adjusting toe off the rear wheels.

So where is a good reference mark on the S197 that runs perfectly parallel with the vehicle centerline when viewed from the side? Pinch weld below the rockers maybe? If you knew this reference mark, you could zero the gyro to it and then adjust front wheels to be the same.

If you use the center of the axle and go out 90º as close as you can you are going to be "within the ball park" but ultimately, yes you'll induce some error. That is why toe plates, designed properly, are a better method for measuring toe. IMO anyway.

 

[Norm Peterson]

So some questions; would there be any complicated math formulas to read caster and camber? Or just zero the meter at ground level and then take the readings once mounted to the wheel adapter? I wonder exactly how to measure caster like the DRP performance unit does using the same inclinometer? Anyone have ideas?

In order to get camber, you'd first have to zero the meter against a known true vertical. And you need to either know that your setup area is level, or if it's not level how far out of level it is (so you can adjust the meter readings). Similarly, setting tire pressures to be the same left vs right is also important.

Caster can be determined by measuring camber with the wheels steered some angle to the left, and again steered the same angle to the right, and taking the algebraic difference between the readings. Most of the commercially available C-C gauges use 20° for these angles steered, but there is nothing keeping you from using different angles once you can determine the factor to apply to the difference in camber readings. Incidentally, you want to do each front wheel separately so that the Ackermann correction doesn't affect the results.

Finally, would it not be possible to use this meter to measure toe using the gyroscope function? (rotation of X-axis) Just zero it to your rear wheels, (these would already be at zero toe) make sure your front wheels are straight, and then compare measurements from the rear to front wheels?

Like Whiskey said, do not assume that either rear tire/wheel is at zero toe or that thrust angle is zero. The easiest way I've found is with parallel strings, done by setting nails equally far apart on two long and reasonably rigid sticks. Set them on jackstands or blocks such that the strings are about at axle height, equidistant from the rear wheel centers, and equidistant at the front wheel centers. Front and rear probably won't be the same, but you want the side to sides to be. Then measure from the strings to the front and rear of the wheels at the flanges and do a little trig.

Then drive the car and check for steering wheel centering in particular. You may have to make a final tweak or two.

Heh . . . if you trust your rear wheel centering in the chassis to be good (and your eyes to distinguish at least three distinct "edges"), you can even eyeball it close enough to where you'll only be making fraction of a turn adjustments when you set the strings up.

Interesting, so you are saying that when people are using the string method, (squaring the string to the rear wheels) they are actually inducing toe out to the front wheels if adjusted to the string? The fact that the rear wheels have some camber should not matter in the case of adjusting toe off the rear wheels.

You could be introducing either toe in or toe out depending on what the rear toe actually is. Separately, extrapolating parallelism from measurements made over one wheel diameter will tend to introduce more error than making measurements with a similar level of precision spaced somewhere over 15 feet apart.

So where is a good reference mark on the S197 that runs perfectly parallel with the vehicle centerline when viewed from the side? Pinch weld below the rockers maybe? If you knew this reference mark, you could zero the gyro to it and then adjust front wheels to be the same.

There are body control holes that are used by the body repair industry to determine "frame" damage. If you get hold of the diagrams showing these holes and the dimensions between them you may be able to work up measurements or chalk-line constructions to obtain the chassis centerline.

I think you could also jig up a pair of lasers that shoot a line rather than a dot to measure toe with, one axle at a time. For thrust angle, you'd need to check against known chassis references, comparing the left side against the right.


Norm

 

[Mineral_'01]

In order to get camber, you'd first have to zero the meter against a known true vertical. And you need to either know that your setup area is level, or if it's not level how far out of level it is (so you can adjust the meter readings). Similarly, setting tire pressures to be the same left vs right is also important.

Very good info. So from what you're saying, I could zero the meter first to a decent bubble level to have a "true vertical". Then, place the meter on the floor next to the tire you are measuring and subtract the angle read from true vertical.

Caster can be determined by measuring camber with the wheels steered some angle to the left, and again steered the same angle to the right, and taking the algebraic difference between the readings. Most of the commercially available C-C gauges use 20° for these angles steered, but there is nothing keeping you from using different angles once you can determine the factor to apply to the difference in camber readings. Incidentally, you want to do each front wheel separately so that the Ackermann correction doesn't affect the results.

Again excellent info. I learned more from Whiskey's and your replies then hours of internet research on the subject. I found the following for different formulas in relation to different steer angles/°

Calculate the caster angle using one of the following examples:
Note: 1. Example No. 2 is the most common.
2. What you are trying to achieve is camber difference from
turning left and right.
* Ignore Negative and Positive
symbols when adding and
subtracting


1. If both measurements are negative then
Subtract the small number
from the larger number -3° - (-1°) = 2°
Multiply 2° by 1.5 = 3°
The wheel has 3° of caster.

2. One negative and one positive, then
Add the numbers together -3° + 1°= 4°
Multiply 4° by 1.5 = 6°
The wheel has 6° of caster.

3. If both are positive, then
Subtract the smaller number +3°
from the larger number +3° - (+1°) = 2°
Multiply 2° by 1.5 = 3°
The wheel has 3° of caster.

Make whatever adjustments are required and remeasure until you have
the angle you want.

Repeat the same steps on the right front wheel.

Note:
If you cannot turn
your wheels 20°
determine the
angle you can turn
both wheels. Note
that number and
use the
multiplication
factor below. The
procedure does not
change, however.
Multiplication
Factors
20° = 1.5
15° = 2.0
10° = 3.0

Like Whiskey said, do not assume that either rear tire/wheel is at zero toe or that thrust angle is zero. The easiest way I've found is with parallel strings, done by setting nails equally far apart on two long and reasonably rigid sticks. Set them on jackstands or blocks such that the strings are about at axle height, equidistant from the rear wheel centers, and equidistant at the front wheel centers. Front and rear probably won't be the same, but you want the side to sides to be. Then measure from the strings to the front and rear of the wheels at the flanges and do a little trig.


Then drive the car and check for steering wheel centering in particular. You may have to make a final tweak or two.

Heh . . . if you trust your rear wheel centering in the chassis to be good (and your eyes to distinguish at least three distinct "edges"), you can even eyeball it close enough to where you'll only be making fraction of a turn adjustments when you set the strings up.


You could be introducing either toe in or toe out depending on what the rear toe actually is. Separately, extrapolating parallelism from measurements made over one wheel diameter will tend to introduce more error than making measurements with a similar level of precision spaced somewhere over 15 feet apart.

I comprehend that concept, but what are the "trig" equations you are talking about?

Edit: Wait after rereading this multiple times, I am confused by this statement, "Front and rear probably won't be the same, but you want the side to sides to be."
So take a stick, pipe or similar with bolts or nails placed perpendicular on either end, run a string from nail to nail, then make that string parallel to the front and rear axle centerlines via tape measure, and repeat on the other side. After than I am kind of lost. Are you saying the front and rear measurements between each parallel string (measure perpendicular in front and behind the rear bumpers) will not be the same because of the trust angle or the arch of the panhard bar effecting the rear axle side to side?

There are body control holes that are used by the body repair industry to determine "frame" damage. If you get hold of the diagrams showing these holes and the dimensions between them you may be able to work up measurements or chalk-line constructions to obtain the chassis centerline.

I think you could also jig up a pair of lasers that shoot a line rather than a dot to measure toe with, one axle at a time. For thrust angle, you'd need to check against known chassis references, comparing the left side against the right.


Norm

This is interesting and do you sudjest setting up a jig to measure toe? Are you saying to square and make parallel a laser line to the front and rear hub centerlines to measure? Exactly like you were talking about with strings, but replacing it with the laser for faster setup. Something like a self-leveling construction cross laser?

 

[Norm Peterson]

Very good info. So from what you're saying, I could zero the meter first to a decent bubble level to have a "true vertical". Then, place the meter on the floor next to the tire you are measuring and subtract the angle read from true vertical.

Zero the meter to the vertically oriented level. Then set the meter to or against the wheel by whatever means you're using. Basically you want the edge of the meter that you zeroed to the level now in the plane of the wheel. The outer flanges are good as long as they aren't scarred from curb rash or dents. What you read is camber. If you have to put the gauge upside down or get a funny reading, chances are that the camber is actually positive.

Heh . . . that next stuff you wrote with the note sounds like something I might have typed somewhere a long time ago . . .

I comprehend that concept, but what are the "trig" equations you are talking about?

Say you measure a 5.15" gap between the front edge of the wheel rim flange and the inside of your string and 5.12" between the rear edge of the wheel flange and the inside of the string. Let's say that it's for a 15" wheel, which measures pretty close to 16" between the flanges across a diameter. The arctan (or arcsin, doesn't make any difference which you use at such a small angle) of 0.03"/16" is 0.1°, which would be the toe for that wheel. Do the same for the other side for total, keeping in mind that you may not be steered perfectly straight. Won't be if the toes are not both in or both oout by equal amounts. Incidentally, those numbers aren't just off the top of my head - yesterday afternoon I was checking front toe on the car we used to own that is now our granddaughter's car.

This is interesting and do you sudjest setting up a jig to measure toe? Are you saying to square and make parallel a laser line to the front and rear hub centerlines to measure? Exactly like you were talking about with strings, but replacing it with the laser for faster setup. Something like a self-leveling construction cross laser.

I never got around to making anything up, but all you need is a single line. What you're trying to do is project the laser lines in a vertical plane and measure on the floor the distance between them at two distances and compute the toe that way. It would solve the matter of the strings being a little tricky to work around as you adjust the tierods without knocking them out of kilter. You'd just have to ensure that the laser line was being set at zero camber.


Norm

 

[Mineral_'01]

First of all, I wish to express my gratitude to you Norm. You have been a great help and I really appreciate your thorough and detailed responses.

Zero the meter to the vertically oriented level. Then set the meter to or against the wheel by whatever means you're using. Basically you want the edge of the meter that you zeroed to the level now in the plane of the wheel. The outer flanges are good as long as they aren't scarred from curb rash or dents. What you read is camber. If you have to put the gauge upside down or get a funny reading, chances are that the camber is actually positive.

Heh . . . that next stuff you wrote with the note sounds like something I might have typed somewhere a long time ago . . .

Roger that, that makes perfect sense. Also, the information I listed earlier was sourced from the Smart Racing Products website.

Say you measure a 5.15" gap between the front edge of the wheel rim flange and the inside of your string and 5.12" between the rear edge of the wheel flange and the inside of the string. Let's say that it's for a 15" wheel, which measures pretty close to 16" between the flanges across a diameter. The arctan (or arcsin, doesn't make any difference which you use at such a small angle) of 0.03"/16" is 0.1°, which would be the toe for that wheel. Do the same for the other side for total, keeping in mind that you may not be steered perfectly straight. Won't be if the toes are not both in or both oout by equal amounts. Incidentally, those numbers aren't just off the top of my head - yesterday afternoon I was checking front toe on the car we used to own that is now our granddaughter's car.

So I will assume that the rest of what I said earlier about setting up the string before toe is measured would be correct? Quoting below for clarification:

Edit that: I now fully understand how you were saying to set up strings or lasers. Just like in the picture below right?

Now back to the above paragraph from you. I think I understand this fully now. So for example, in my case with a 19" wheel, let's say I measured a difference between the flanges across a diameter of 0.02". So I would take 0.02"/20" (apply trigonometry using ATAN or ASIN) = .06° for one wheel. Used this for trig btw: http://www.1728.org/trigcalc.htm Math look good to you?

I never got around to making anything up, but all you need is a single line. What you're trying to do is project the laser lines in a vertical plane and measure on the floor the distance between them at two distances and compute the toe that way. It would solve the matter of the strings being a little tricky to work around as you adjust the tierods without knocking them out of kilter. You'd just have to ensure that the laser line was being set at zero camber.


Norm

Yep, got it now. This would make for a pretty nice setup. I wonder how taking two lasers clamped to either ends of a stick/pipe
and placed on jack stands would work out. I am envisioning a setup just like the photo above, but with two lasers on either ends of the piece of conduit to act as strings.



Lastly, going back to the meter I posted in the first post, I have an idea on how to use it to quickly measure caster, but want to make sure I am correct.

First, zero the meter to true vertical zero. Place the meter against the wheel using an adapter where it will not move. (thinking about using an old wheel alignment clamp) Make sure the wheel is straight. Turn the wheel 20° or whatever ° you want one way using the reading from the X-axis on the meter. Record the Y-axis reading at the number of °'s (X-axis) you used in the previous step. (this would be your camber reading) Then, repeat the measurement in the opposite direction by turning the wheel to the desired ° you used before. Finally, use the formula noted in the earlier post to compute caster. Sound right?

 

[Norm Peterson]

Just like in the picture right?

Yup.

Now back to the above paragraph from you. I think I understand this fully now. So for example, in my case with a 19" wheel, let's say I measured a difference between the flanges across a diameter of 0.02". So I would take 0.02"/20" (apply trigonometry using ATAN or ASIN) = .06° for one wheel. Used this for trig btw: http://www.1728.org/trigcalc.htm Math look good to you?

Yes. Just remember that you've only measured "individual toe".

Yep, got it now. This would make for a pretty nice setup. I wonder how taking two lasers clamped to either ends of a stick/pipe
and placed on jack stands would work out. I am envisioning a setup just like the photo above, but with two lasers on either ends of the piece of conduit to act as strings.

Sounds entirely workable (and maybe less sensitive to small errors than not getting the strings' sticks perfectly parallel to one another might introduce).

Lastly, going back to the meter I posted in the first post, I have an idea on how to use it to quickly measure caster, but want to make sure I am correct.

First, zero the meter to true vertical zero. Place the meter against the wheel using an adapter where it will not move. (thinking about using an old wheel alignment clamp) Make sure the wheel is straight. Turn the wheel 20° or whatever ° you want one way using the reading from the X-axis on the meter. Record the Y-axis reading at the number of °'s (X-axis) you used in the previous step. (this would be your camber reading) Then, repeat the measurement in the opposite direction by turning the wheel to the desired ° you used before. Finally, use the formula noted in the earlier post to compute caster. Sound right?

Yes. The procedure remains the same regardless of the specific method used to make the camber measurements.

The commercially available caster-camber gauges use essentially the same approach (although in detail they zero the camber with the wheels already steered in the first direction and directly obtain the total camber change when steered all the way to the other direction, before applying the factor via the caster vial's scale calibration). Even the $$$$$ alignment racks use something very similar, except that it's all done internally/electronically where you don't see what's going on). There used to be a SAE paper available here and there on the 'net that goes pretty deep into the detail geometry involved. Hunter (the alignment and wheel equipment people) took their site's copy down, probably for reasons involving protecting the copyright of the paper that was written by one of their own employees.


Norm

 

[Mineral_'01]

Yup.



Yes. Just remember that you've only measured "individual toe".

Got it. Just add both individual toe readings together for total toe.

Sounds entirely workable (and maybe less sensitive to small errors than not getting the strings' sticks perfectly parallel to one another might introduce).

Excellent, I will see what I can come up with searching cheap accurate lasers on ebay or something.

Yes. The procedure remains the same regardless of the specific method used to make the camber measurements.

The commercially available caster-camber gauges use essentially the same approach (although in detail they zero the camber with the wheels already steered in the first direction and directly obtain the total camber change when steered all the way to the other direction, before applying the factor via the caster vial's scale calibration). Even the $$$$$ alignment racks use something very similar, except that it's all done internally/electronically where you don't see what's going on). There used to be a SAE paper available here and there on the 'net that goes pretty deep into the detail geometry involved. Hunter (the alignment and wheel equipment people) took their site's copy down, probably for reasons involving protecting the copyright of the paper that was written by one of their own employees.


Norm

Good deal, I think with your help, I have everything sorted out on DIY style alignments. Thank you very much for everything. If I ever see you trackside or something, I owe you a beer or two.