Fordnatics List Archive

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Mail From: "Paul R Keidel" <(email redacted)>


Fellow Fordnatics,

I have some questions relating to balancing wheel/tire assemblies.

1. Is it possible to balance a wheel/tire assembly with _one_ single
lead weight?

2. Is the mass of the required weight directly related to the tire
rotational velocity?

3. Do the different stiffnesses of the wheel and tire, aluminum vs.
rubber, make it difficult to accurately balance a wheel/tire
assembly at high rotational velocities?

My guestimates are 1.) maybe, 2.) yes, and 3.) maybe.

My reasons for asking are these. The other day, I had to have a nail removed
from a Michelin on my '91 LX 5.0. I also asked the shop to re-balance the
tires while they had the car up. I occasionally run my car in open track
events on the Michelins. When I asked the shop manager to have the tires
balanced for high speeds, say 100 mph, I was told that it was illegal for them
to balance the tires at any speed above 55 mph.

The mechanic performing the actual work allowed me to watch him balance
the wheel/tire assemblies. When I told him what the manager said about the 55
limit, the mechanic said that his machine did not even go over 35 mph.

When the car was done, I noticed that there was only one lead weight on
the inside of each wheel. When I asked what the reason was for not having
weights on both the inside and outside, I was told that most people did not
like the _look_ of the weight on the outside.

So, am I being given lines of BS here, or what? It was hard for me to
believe any of their comments.


Paul K.
Tucson, AZ

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Mail From: DARIUS RUDIS <(email redacted)>

No bs from these guys.
Usually you pay more (or have to say *pretty please*) to get the weights
put on the inside of the wheel. The weights that I normally use are the
glue-on ones. This way you dont see the weights on the outside of the
rim, and when you reballance the tires, you can have the weight easily
removed. This leaves a little glue that needs to be cleaned off, but no
scratches on the edge of the rim.
Ballancing speed is usually what the machines are rated for... about 35mph.

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Scott Griffith, Sun Microsystems Lumpyware)

On Feb 22, Paul Keidel wrote:

> 1. Is it possible to balance a wheel/tire assembly with _one_ single
> lead weight?

Often, yes. But it depends upon the trueness of the tire, the skill of
the operator, and most importantly the tolerance you specify. To
achieve +- 1/8oz (Autobahn!) balance at speed will almost certainly
require more than one weight, but getting to +- 1oz (a pretty standard
close-enough, shove-em-outta-here tire shop spec), can usually be done
with little enough effort, and only a single weight or two.

> 2. Is the mass of the required weight directly related to the tire
> rotational velocity?

Yes, as a second-order effect, as the tire grows asymmetrically due to
centrifugal forces at speed. But barring pathological conditions in
the tire carcass (such as 10oz more rubber on one side of the tread
than the other), if it's in balance to a decent tolerance at 35mph,
it'll still be in semi-decent balance at 100.

> 3. Do the different stiffnesses of the wheel and tire, aluminum vs.
> rubber, make it difficult to accurately balance a wheel/tire
> assembly at high rotational velocities?

Ahh- there's the rub. The answer is a huge "it depends". The tire may
move around quite a lot at speed, especially if it is _way_ out.
Modern radial tires are a great deal better behaved that bias-ply
tires were, but you can still get the odd weird one that dynamically
just doesn't want to behave. If the excess rubber mass is concentrated
out-of-plane, the tire is going to _move_ out of plane at speed. The
more, the merrier.

Many race tires are balanced at nice low speeds, like 35, on regular
street tire balancers. They depend on the QC in the carcass to hold
that balance at speed. The only place I'm aware of that routinely
balances tires at higher speeds is the Goodyear truck that drags tires
to the various Indycar venues. But then again, they have a _very_
picky clientele.

I get my street tires balanced to +- 1/4oz, and my race tires I
scarcely bother with. That +- 1oz coarse tolerance is _fine_ for
those, because they pick up so much rubber from the track that their
balance condition continually varies all over the place anyway. So why
spend the money going for ultrafine balancing, when they'll be _out_
by the time you get to the end of the pit lane?

> When the car was done, I noticed that there was only one lead weight on
> the inside of each wheel. When I asked what the reason was for not having
> weights on both the inside and outside, I was told that most people did not
> like the _look_ of the weight on the outside.

If it needs it out there, they should freakin' _put_ it out there.
Looks don't matter, if it is needed to meet your tolerance.

Tape-on weights, located inside the wheel's lip in such a way that the
centrifugal forces affix them more firmly at speed, are the only way
to go. I'm always amused at the first track event of every year, as
all the new folks go out to play in their street cars with their
brand-new factory clip-on weights. The first few sessions are like a
*lead hailstorm*, as all those weights get thrown off the wheels due
to track-speed centrifugal forces and sidewall flex.

And you know what? _Nobody_ has ever complained to me about their
tires having "gone out of balance" over the course of the event
(except for flat spots from brake lockup, which are a different
story). This despite the fact they'll finish up the day short 20oz or
so of lead that used to be there, distributed among their 4 wheels.
Nobody ever notices until the drive home. Hmm...

-skod

- --
Scott Griffith, Sun Microsystems Lumpyware
Nor Cal SAAC/Green Flag Driving Association driving instructor
(and driver, of anything that turns both right and left,
and can pass tech...) Return Path : (email redacted)