Posted to Technical Tips Forum on 6/6/2014
Understanding alignment angle changes
Recently I was asked a question by a younger Tech that made
me think. The thought was a realization, that there are
probably many young Tech's out there, that don't understand
how Caster angle affects Camber angle, when you steer a tire
away from the Toe angle's specification position.
If Caster is 0 Deg, then Camber does not change when you
steer the tires from right to left. But, Camber changes when
the tires move to the left or right, anytime Caster has a
value greater than 0. The higher the value, either + or -,
the more Camber will change as you steer the tires away from
Toe in Spec. Position. So it needs to be understood, that
you are not ever to set Camber on a wheel, unless you first
check Camber on that wheel while it is in Toe Spec. position
when the Camber is checked.
The Caster changing Camber relationship is not much of a
problem on most vehicles. But, it is very important on
vehicles that are set with very high Caster. You better
understand this concept should you decide to align any
vehicle with over + 5.0 Deg. of Caster.
So if you start on a alignment, on a vehicle with high
Caster, and the Toe is way out of specification, it is
better to adjust toe into the ballpark, before you consider
if this vehicle actually does need to have Camber set. The
most common reason a vehicle ends up on the rack, is having
had parts changed. Some Techs don't have the skills to get
them installed "in the ballpark". The new tie rods adjust
quickly, so just move them and get it close.
What I have seen happen, is a Tech will adjust Camber first,
on a wheel that is not pointing straight. The Inaccurate
Camber angle they see on the screen actually could be, "in
spec", IF they checked it, with the wheel straight ahead.
They adjust the Camber first, then they adjust the Toe angle
second, and then find the Camber went out of Spec. as they
moved the tire to straight ahead. Then they end up doing the
whole routine over again until finally it is right. I
actually watched a guy years ago, align a car in circles,
for almost two hours because he did not understand this
concept. The vehicle was a Euro with a Caster Spec near +10
Deg, and Camber tolerances that were very tight.
You don't have to do, Toe adjustment first on all of them.
You can steer the wheels individually to Toe in Spec., and
see what the Camber is on each wheel, one at a time. But, be
warned that on some vehicles, if toe is way out, the vehicle
will not be sitting correctly level because the excess Toe
will affect the way the vehicle is loaded, when one tire is
straight, and the other tire is turned a few degrees to the
Vehicle stance affects the Camber angle you see on a wheel,
not just from having one tire only turned, but it also is
changed from reality, when the Camber is drastically out on
the opposite wheel of the same axle. That is why you will
see Camber change, on a wheel opposite of the one you just
adjusted. After moving a L.F. wheel 1 full Deg., after Mac
Struts were installed for example, you will notice the R.F.
will often drop a couple of tenths lower. This is because of
load change. It is always better to adjust alignment angles
first, on the side that is most incorrect. Sometimes, the
other side will fall into Spec., and save you some time.
Understanding the angle to angle relationship, and how Toe
being drastically out of Spec. affects the reality of where
Camber really is at, is helpful to getting the alignment to
correct faster, when you get one on the rack that is in
"outer space" as a starting point.
David from Michigan