What method do you use to measure the caster ?

[2004mountaineers]

What method do you use to measure the caster ? If you just use an angle sensor on a surface, what surface do you put the angle-sensor on ?
2004 Mercury Mountaineer, v6, 4liter, 'awd', previous owner removed front drive shaft for unknown reasons

 

[allmyEXes]

I think there is just one method.
A short course in wheel alignment
DIY alignment guide
inexpensive alignment gauge

 

[2004mountaineers]

I think there is just one method.
A short course in wheel alignment
DIY alignment guide
inexpensive alignment gauge

%From 6:02 of this video:
%

% So:
% 1. measure camber angle at +15deg steering angle
% 2. calculate caster = -2 * camber + 4
% 3. measure camber angle at -15deg steering angle
% 4. calculate 2nd caster angle = -2 * camber + 4
% 5. Difference the two numbers from steps 2 and 4. Divide
% that difference by 2. That's your caster angle.
% 6. Repeat all the above steps to for the other wheel.
Finally, since the 4 term cancels out, all of the
above is equivalent to just subtracting the camber angle from steps #1 and #3 and multiplying
that difference by 2.0 and that is your caster angle.

Unless the above video is wrong, the above simple calculation is right, in just differencing
two camber angles, one at 15deg steering angle and one at -15deg steering angle and finally multiply that difference by 2.
Btw, you don't need a $200 tool he uses to do that.... You only need a cheapo tilt sensor.
Amazon product ASIN B07R12DZQ9

 

[2004mountaineers]

%From 6:02 of this video:
%

% So:
% 1. measure camber angle at +15deg steering angle
% 2. calculate caster = -2 * camber + 4
% 3. measure camber angle at -15deg steering angle
% 4. calculate 2nd caster angle = -2 * camber + 4
% 5. Difference the two numbers from steps 2 and 4. Divide
% that difference by 2. That's your caster angle.
% 6. Repeat all the above steps to for the other wheel.
Finally, since the 4 term cancels out, all of the
above is equivalent to just subtracting the camber angle from steps #1 and #3 and multiplying
that difference by 2.0 and that is your caster angle.

Unless the above video is wrong, the above simple calculation is right, in just differencing
two camber angles, one at 15deg steering angle and one at -15deg steering angle.
Btw, you don't need a $200 tool he uses to do that.... You only need a cheapo tilt sensor.
Amazon product ASIN B07R12DZQ9

I just tried the above method on my jeep's left front wheel which I know has a caster angle of 6.5degrees .
The above caster-sweep method gave a caster angle of:
5.96degrees
which is only off by about 10%.

 

[2004mountaineers]

I just tried the above method on my jeep's left front wheel which I know has a caster angle of 6.5degrees .
The above caster-sweep method gave a caster angle of:
5.96degrees
which is only off by about 10%.

I just tried the above method on my jeep's left front wheel which I know has a caster angle of 6.5degrees .
The above caster-sweep method gave a caster angle of:
5.96degrees
which is only off by about 8%.

 

[AntonyU21]

Use a locator and positioning guide

 

[2004mountaineers]

Just tried the same method on the Mercury. Results here:

Mercury measurements on 3/6/2023:
note: right front tire was sitting on a piece of carpet in the garage, so not perfectly flat.
left wheel:
straight: camber = 0.4deg inward ---> -0.4deg camber, which is within specs [-1.3deg, 0.3deg] for Mercury.
15deg left: camber = 0.97deg outward == th1
15deg right: camber = 1.17deg inward == th2


right wheel:
straight: camber = 1.31deg inward ---> -1.31deg camber, which is almost within specs [-1.3deg, 0.3deg] for Mercury.
15deg left: camber = 2.23deg inward == th1
15deg right: camber = 0.65deg outward == th2

left-caster = 2 * (1.17 + .97) = 4.28deg, which is almost within specs of [4.3deg, 5.3deg].
right-caster = 2* ( 2.23 + .65) = 5.76deg, which is 0.46deg out of specs of [4.3deg, 5.3deg], 9% out of range.
diff-caster = right-caster - left-caster = 5.76deg - 4.28deg = 1.48deg
I wonder if that difference in caster is why it pulls to the right ?