blue bmw wrote in
news


So, that makes FOUR separate spots, two on the wheel and two on the
ti 1. Wheel valve stem
2. Wheel white nick (presumably that's the low spot
3. Tire red dot (presumably that's the high spot)
4. Tire yellow dot (presumably that's the light point)

OK. Now what should I tell the installer to line up?

Q1: What two spots (of those four) should line up?
Q2: Should they remove all these weights first?
http://i39.tinypic.com/2q0o9xl.jpg



Those dots are a /starting point only/. The theory is that by, for
instance, matching the low spot on the rim with the high spot on the tire
it will be easier to mount the tire so as to spin smoothly. This is
necessary before starting the balancing procedure.

In practice, an aftermarket tire installer will often not have the rim's
dots available, and will mount the tire as his personal preference
dictates. He will spin the bare wheel, making sure it's actually in-spec
for that automaker. He will find the low spot(s) on the rim by eye. He may
try matching the high spot on the tire with the low spot he found on the
rim. He may try the light spot on the tire opposite the valve stem.

Either way, the idea is to get the tire to spin smoothly before balancing.
"Smoothly" means that, as the tire is spun, the tread does not hop up and
down or squirm from side to side. As a proxy for that, many tire installers
will observe the rubber ridges on the tire that sit immediately outboard of
the rims. If this ridge is perfectly even all the way around relative to
the rim, he will consider the tire to be mounted properly. To me, having
that ridge sit evenly should be backed up by actually studying the tread as
the tire spins. This means lifting the machine's guard and spinning the
tire slowly while watching the tread. If the tread hops or squirms, then
there will be vibration or harshness on the road even if the balance
appears to be perfect.

If the tire won't spin smoothly no matter what, then the installer will
turn the tire 180 degrees and try again. And then move it again.

THIS IS ASSUMING THE TIRE INSTALLER KNOWS TO DO THIS! A lot of cheapo shops
will simply throw the tire on the rim, balance, and be done with it. Little
or no checking or matching of any kind.

Proper mounting requires proper tire lubricant. Some aftermarket shops will
use inferior substitutes, such as soap-and-water. These will impart an
unacceptable level of friction between tire and rim, and prevent the tire
from popping in place all the way. This will result in a tread that hops
and squirms.

Sometimes drive-tires will rotate on the rim before all the tire lubricant
has a chance to squeeze out. To detect this, a chalk or grease-pencil mark
should be placed on the tire and rim. If the client comes back complaining
of vibration, the installer can check those marks and see if they have come
out of alignment. If they have, then the client has ignored the admonition
to accelerate and brake gently for a few days.

Many tires returned to tire makers as "defective" are actually fine; they
were damaged by poor mounting techique. Tire makers can tell this by the
marks the rim leaves on the bead.

A Hunter road-force machine cannot compensate for poor mounting, all it can
do is alert the installer that somesthing's wrong. The Hunter machine first
requires proper mounting in order to work as intended.

Costco goes through a large vvolume of tires. Their employees receive
training directly from the tire makers in the proper mounting procedure.
You are more likely to receive correctly-mounted and -balanced tires from
Costco than from them than from most tire shops.

And yes, all dirt and old weights should be cleaned off the wheel before
new tires are added.

--
Tegger