Basic alignment question - Caster

[jstagl]

When using the standard caster/camber gage you turn the wheels 20 degrees or so in each direction for measuring caster.

With the front wheels turned LEFT, should the RIGHT front read positive or negative camber. Shoulde the LEFT read positive or negative?



John

[Bob Coury]

It has been a while, but if memory serves me correct, when your wheels are turned, the outside wheel should go negative. I am going to use that method in a few weeks, when I get home I will have to dig up my old notes.

[Daryl DeArman]

Inside goes positive, outside goes negative.

[Brian]

Lets say you just have a camber gauge. If you turn the wheels 20 degrees and you get a new camber reading, how do you translate that into castor?

Brian

[Jim Garry]

Here's how I do it. It's from the manual for the Smart Camber gauge (http://www.smartracingproducts.com/p...ber_manual.pdf)

Since the below text is copied from a pdf online, the formatting will be hard to read. I suggest you click on the link above and go to the chapter on Caster.

Jim


[FONT=Arial]

Measuring Caster

[/FONT][FONT=Times New Roman][SIZE=2]

Caster is calculated by measuring the camber angle in two different
positions, and then putting those measurements into a simple formula.
To measure caster, do the following, but be sure to take your time the first
few times you do it:
1. Start with the left front wheel.
2. Place the layout template sheet (included) on the floor and use chalk (or
paint for permanent marking) to scribe lines that are about a foot longer
than the template. Then remove the template and connect the lines as
on the template.
3. Roll the car until the front wheel is on the centerline (CL) axis and
parallel to the X axis.
4. Turn the steering wheel until the left front wheel is parallel to the Z
axis.
5. Use a stiff piece of cardboard approximately 7”x18” as a “plane”
reference template (flat sheet metal is better), carefully put the plane on
the Z axis line and carefully lean the template against the tire. If it
touches the tire evenly, then the wheel is turned 20[/SIZE][/FONT][FONT=Symbol][SIZE=2]°[/SIZE][/FONT][FONT=Times New Roman][SIZE=2].
6. Measure the camber angle in this position and note.
7. Steer the wheel back through the center-steer position and parallel to the Y axis. Repeat the plane template alignment method.
8. Measure the camber angle in this position and note.

[FONT=Times New Roman][SIZE=2]

9. 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.
1. If both measurements are negative then

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]

subtract the small number

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]-3 *

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]

from the larger number

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]-1
——
Equals 2
Multiply 2 by 1.5 = 3
The wheel has 3[/SIZE][/FONT][FONT=Symbol][SIZE=2]° [/SIZE][/FONT][FONT=Times New Roman][SIZE=2]of caster.
2. One negative and one positive, then

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]

Add the numbers together

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]-3 *
+1
——
Equals 4
Multiply 4 by 1.5 = 6
The wheel has 6[/SIZE][/FONT][FONT=Symbol][SIZE=2]° [/SIZE][/FONT][FONT=Times New Roman][SIZE=2]of caster.
3. If both are positive, then

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]

Subtract the smaller number

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]+3 *

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]

from the larger number

[/SIZE][/FONT][FONT=Times New Roman][SIZE=2]+1
——
Equals 2
Multiply 2 by 1.5 = 3
The wheel has 3[/SIZE][/FONT][FONT=Symbol][SIZE=2]° [/SIZE][/FONT][FONT=Times New Roman][SIZE=2]of caster.
10.Make whatever adjustments are required and remeasure until you have
the angle you want.
11. Repeat the same steps on the right front wheel.
12.Reset the toe (can be done with SmartRacing Products-SmartStrings).
Any changes to the caster or camber angles will have changed the toe
settings.

[/SIZE][/FONT][/SIZE][/FONT]

[Bob Coury]

John:

I had two methods from years ago; one from the now defunct Formula Magazine, one from the mfg of my camber gage. I never compared the results between the two:

From Formula Magazine:

1. Turn wheel 15 degree left of center and take a camber reading.

2. Turn the wheel 15 degrees right of center and take acamber reading.

(You can make a 30 degree chalk line on the floor)

3. Multiply the difference x 2 and that is your castor.

4. When turning from outside to inside a neg camber change equals positive castor. i.e. a change from zero to -1 x 2= a 2 deg pos. castor.


From Performance Marketing Camber Gage:

1. Turn 20 degrees left of center and take a camber reading.

2. Turn 20 degrees right of center and take a camber reading.

3. Take the difference and multiply by 1.5, that is your castor. i.e. left reading +1, right reading +4. Difference =3 x 1.5 = 4.5 deg positive castor.

[Brian]

It occurs to me that since I've raced for 20 years never knowing what my actual castor is, only that I had "some" castor, this method will certainly give me a real quick and easy way to know that I have "some" castor, that it's in the right ball-park, and that it's equal side to side (the last being what I actually want to know!).

Once I get faster than a dead chicken, I may need to know actual values to a tenth of a degree, but I will probably not actually pass the dead chicken any time soon (there's a quick Reynard pilot up here with a dead chicken as a mascot).

Thanks for opening my eyes to something I should have figured out on my own quite a few years ago...

Brian

[jdp526]

Any suggestions on preferred gauges? I would like to find one that would work on the FC and on my sedans with 13" and 15" rims. Thanks,

[rickb99]

We just purchased this one:
http://www.longacreracing.com/catalo...d=1299&catid=5

Will work on different sized wheels. Acculevel can be used for setting wings, checking suspension part angles, etc. As to it's ease of use and functionality the most I can tell you so far is, it's looks really nice in the Longacre supplied case that it came in. And my work bench is 0.2 degrees out of level

I guess with the info above, could have purchased a $ 0.28 pencil and borrowed a piece of paper. But what fun would that be? Ahh but then I'd need a $200 degree measurer.

After getting all them angles right, maybe we'll see that Dead Chicken off in the horizon going into the corner at the FAR end of the straight (on lap 2)! Oh wait, we need to get the car started 1st too.

[Dave]

According to this: http://www.smartracingproducts.com/alignment.htm

Smartcamber works from 5" to 22". I know for sure that it works for 13" and 15" wheels.

[rickb99]

Yes, here's the 'home' of that ART Smart one and other stuff from ART:
http://www.advancedracing.com/smart_camber_gauge.php

Looked at that one but they want $75 for the carry case