-----Original Message-----
From: Wally Plumley [mailto:wplumley@bellsouth.net]
Sent: Friday, March 08, 2002 9:11 PM
To: 928
Subject: [928] Tire Balancing


At 05:13 PM 3/8/02, Walt Konecny wrote:
>While the Hershey-bar (stick-on) weights can be hidden on the inboard
>portion of the wheel, the clip-on type on the rim edges, inside and out,
>actually give a better balance. Static vs dynamic as I believe shops call
>the balance.


Ummmm ... No.

"Static", or non-rotating, balance is radial balance only - no effort to 
balance from side to side. Normally, static balance was done on a bubble 
balancer, and all weights were on the outer rim (and were almost invariably 
clip-on type. A statically balanced tire would run pretty smoothly when the 
tires were 6.00 - 16, and were tall and skinny.

When tires got shorter and wider, static balancing was no longer adequate. 
Several methods of "dynamic", or rotating, balance had been in use, such as 
the Bear units used at Indy during the 'thirties, but they now became 
almost universal. A dynamically-balanced wheel is balanced both radially 
and laterally, so weights are commonly applied to both the inside and 
outside periphery of the wheel as required.

A statically-balanced wheel won't hop up and down, but may well jerk the 
steering wheel back and forth, while a dynamically balanced wheel should do 
neither - if it is round.

An out-of round wheel can be perfectly balanced, so that it will not create 
any movement while it is spinning in midair - but it will bounce the car 
around going down the road. An out-of-plane belt will do the same thing.

Larry mentioned shaving a tire. The mounted tire is placed on a machine 
that is in effect a large lathe and spun by a motor. A sharp rotating knife 
is slid across the tread, cutting off the high spots and making the tread 
round. Works great if the tire carcass is round and the tread isn't - 
unfortunately, any out-of-round is usually in the carcass.

Latest hot trick is to balance the tire with a roller that actually presses 
against the mounted wheel, so that any out-of-round condition is 
theoretically taken care of. Not too many of these machines around yet, and 
it costs more.

Either clip-on or stick-on weights can be used to balance a tire both 
statically and dynamically. The computer-aided machine that I use can tell 
you where to put clip-on weights, and precisely how much (what size) 
weight. If I use stick-ons, and hide them behind the spokes, it takes more 
weight, and I have to estimate how much more weight to use. Takes about 
three times as long to zero a tire with hidden stick-ons as with clip-ons.

Since my '86 has chrome wheels (Hi, Ed!), clip-ons won't work - the wheels 
are too hard and slick, and the weights won't stay on. I don't like the 
clip-ons on the Cups on the '90 GT, so I use stick-ons on both cars. My 
wife found that I could balance wheels with hidden stick-ons, so guess what 
I have to use on her Trooper w/aluminum wheels, her STS w/aluminum wheels, 
and her Suburban w/aluminum wheels. I still get to use clip-ons on the old 
Ford pickup and the Bugeye, though.

Wally