On 4/5/19 1:05 am, Arlen G. Holder wrote:
On Fri, 3 May 2019 20:02:29 +1000, Xeno wrote:

On a modern car it's a waste of time.

Hi Xeno,

Most people who posted to this thread, IMHO, have proven that they own
completely imaginary belief systems, where the logical proof is that their
ludicrous excuses instantly failed the simplest of the simple tests of any
belief system, which is the three words when someone declares an opion
o Name just one FACT from which that belief system is based upon.

Given these vehicles I'm working on are all about two decades old (give or
take), can you name just one FACT that supports your belief system stated
above?

I'm not saying your belief system is correct, nor am I saying it's not
correct, since you stated your belief system clearly, but you didn't state
even a single fact that backs up that strongly held belief system.

What FACT is your strongly held belief system actually based upon?

A number of *facts* prime among them being my training and involvement
in the automotive industry as a mechanic since the 60s. First and
foremost, it's clear from what you have written that you do not
understand the concept of *dynamic unbalance* and the ramifications it
has for anyone doing a *static* balance. You make too many assumptions
based on your *limited* experience and minimal training.

First, assume a tyre with a heavy spot central to the centreline of the
tread. this tyre is only in static unbalance. This will cause only wheel
tramp, ie. the bouncing of the wheel and tyre assembly up and down and
should not have any effect on the steering (shimmy). This type of
imbalance can be statically balanced but it requires a little common
sense when applying balance weights. If you apply balance weights
incorrectly you can remove static unbalance but create dynamic unbalance.

Second, assume the same tyre but with the heavy spot over to one side of
the tread and away from the centreline. This tyre is not only in static
unbalance but it is also in *dynamic unbalance*. It will cause wheel
tramp but also steering shimmy. The issue here is that a static balancer
will not tell you which side of the tread area the heavy spot is, only
that it is on that side of the wheel/tyre assembly. That means that when
you add balance weights to the opposite side of the rim, you need to add
weights to both sides. You look at the counterweight needed, then halve
it and add half to each side of the rim opposite the heavy spot. Might
add, when carrying out a static balance you need to always use balance
weights on both sides of the rim at the light spot, even in cases that
are clearly only statically unbalanced, else you will potentially end up
with a dynamically unbalanced wheel. This type of dynamic unbalance can
only be reduced, on average, by 50% even if the static balance is
corrected 100%. The point here is that your steering joints will be
affected by the unbalance

Third, now assume a wheel that has two heavy spots, one each at opposite
points on the wheel diameter. To a static balancer, this wheel assy.
will be balanced producing no wheel tramp. However, assume one heavy
spot is located at the *outside* of the tread centreline and the other
on the opposite side located on the *inside* of the tread centreline.
The wheel is, if both heavy spots are of the same mass, will evince no
tramp but will show up as steering shimmy, the severity of which will
depend on the amount of imbalance and the distance it is located from
the tread centreline. It is caused by the two masses attempting to
alternately get to the centreline. Note too that the type of suspension
system and the steering geometry can play a significant role in the
sensitivity to unbalanced wheels.

So, of the 3 imbalance situations, a static balancer can fully address
the first and only partially address the second depending on the mass
location. In the case of the third imbalance situation, the static
balancer is totally useless. So, to ensure correct balancing over all
situations, a dynamic balancer is the only choice to be made.

As to the situation where, in the past, static balancers covered most
bases, what has changed today? It's simple really, older cars had narrow
tyres fitted to large diameter rims so less prone to dynamic unbalance
effects. Today's cars have much wider tyres so accentuating the
possibility of dynamic imbalance. Road speed with respect to wheel assy.
diameter plays a role in this. That brings me to truck wheel balancing.
Given the large diameter and relatively narrow section width of truck
wheels, static balancing is Ok for most cases. In these cases, on
vehicle balancing, usually of front wheels only, is carried out using
equipment like this;
https://www.bigwheels.net.au/on-vehicle-wheel-balancer
I have done this task many times since the late 60s when I first entered
the trade and I can attest to the efficiacy of this type of balancing
for truck wheels. That, however, was in the past and trucks now travel
at relatively high speeds so dynamic unbalance with consequent steering
shimmy has become an issue with truck wheel balancing. In this case you
*need* an off vehicle dynamic balancer like this;
https://www.bigwheels.net.au/off-vehicle-wheel-balancer

I must add too, just because you feel no vibration or shimmy from the
wheels doesn't mean no imbalance exists. What it means is that the
effect is not being transmitted through to you, the driver. The steering
and suspension may well be feeling the effects and this could cause
aggravated wear in suspension and steering joints. Power steering, for
instance, has an effect on nullifying road feedback. After all,
manufacturers adopted power steering on FWD vehicles in order to reduce
or nullify the effects of unwanted feedback, in this case torque steer.

What would you do if you had a vehicle that had a vibration in the front
through the suspension akin to wheel tramp? Let's assume you static
balanced the wheels with no luck. You checked the tyre for runout, the
rim for runout and the tyre to rim concentricity - all perfect. A spin
up on the dynamic balancer shows the wheels are perfectly balanced both
statically and dynamically yet that vibration in harmony with road speed
persists. Where do you go now? Balance is perfect, runout is perfect,
concentricity is perfect, what is left?




--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)