Balance Stuff

[type26owner]

Gee, I was hoping to start a brisk thread on DIY balancing. Roger, Tom,
Rod, Peter, why the silence? Okay, can anyone tell me what's wrong with
the descriptions on this website? The diagram that's labeled with the
result which says 'Dynamic Unbalance' shows the situation I'm trying to
measure.
http://www.unbalance.com/dynamic_unbalance.htm

Now envision reorienting the rotation axis by 90 degrees about the
vertical but still centered with the drum and you can see my how my
solution works. This is the main difference from a dual plane balancer.

I spent two hours convincing my son the physicist that this theory
works. I succeeded but he commented why the hell would I give an idea
like this away on the list. It's only viable because it should cost
under one hundred dollars to build it. Of course my time is free.

Of course this theory might not to be practical at all. The system has
this quirky behavior when the static and dynamic balance is achieved. It
will not move once placed in any attitude because there is no 'restoring
force'. So the indication that the balance is perfect is it becomes
totally unresponsive. This might drive the person doing this procedure
nuts if they don't understand it. It's also where any friction or errors
will skew the results. The real question is the balance good enough at
this point?
--
Keith Franck

Martinez, California

Hint; The folks at the website omitted an important piece of
information. Your first assumption is wrong!

[gobw2]

Keith - over the years there have been many inexpensive balancers on the
market - using bubbles like a spirit level, knife edges. They did not do
the job, and hence are no longer sold. One of the problems that they do
not adress - especially for bias ply - is that an elastomer restrained
with cords does not act like a steel drum in dynamic conditions. It
grows, and since everything is not precisely uniform, it grows unevenly.
A wheel can be balanced perfectly on one of the modern very low speed
computerized balancers, and when up to speed, be unsatisfactory. The
same wheel, when balanced on a 1950's on the car balancer, which spun it
to high speed, is a joy to ride on. This may be worse as wheel diameter
decreases because the wheel has to spin faster for the vehicle to reach a
given speed.
Those of us with KO wheels have another problem - the centering point
is not the hub hole, it is the pins, which on my wheels, are not
concentric with the hub hole! I would like to buy a functioning old on
the car balancer. Now that they are 50 years old, and considered
obsolete, perhaps they sell for under $100. George

[type26owner]

George,
I could be totally wrong but it's my understanding that the stroboscopic
on-the-car balancer has a fundamental problem, it's a dynamic balancer
but only for a single plane. The steering wheel will probably be
dithering at some level and the rack tooth in the straight ahead
position will still wear out prematurely as a result.

My solution kicks ass because I've solved the dual plane problem with a
cheap static setup. All the other balancers you've mentioned just have a
static or single plane capability and I agree that's not good enough for
an Elan.

I'm betting your argument about the effects of centrifugal force
distorting the symmetrical structure of a tire enough to cause every
tire to be total junk at speed is not the case. If that were so a tire
shaver would have had to spin the tire up to the maximum speed of the
vehicle while shaving it. This is not done, nor is it necessary.
--
Keith Franck

Martinez, California

PS: If you happen to find two old crummy balancers, let me know please.

[TimMullen]

Actually there is a new spin balancer out now that applies a load to the tire
(to simulate the load of the car) as it "balances" it. It's supposed to be
REALLY good, and cures a shimmy problem that Miatas suffer...

Tim Mullen

Chantilly, VA
72 Elan Sprint

[type26owner]

Tim,
That's not quite right I believe. It actually stresses or exercises the
tire like it's under a regular load before balancing so it can take it's
'shape'. This process is run for a short period and then stopped so it
can be balanced. These machines cost between $5k and $8k and are only as
good as the operator's attitude or ability. Can you tell I'm not
satisfied by lots of tire installers in my area? Some of these people
are total idiots and can't answer a technical question without trying to
resort to pure bullshit. Gee, sounds like at work.
--
Keith Franck

Martinez, California

[gobw2]

Kieth - you may have solved it - I have not been able to follow your idea
completely. My concern is that it is static.
Tires - you have expanded beyond my statement - "every tire to be total
junk at speed " certainly is not the case. At speed - especially with
bias ply, there is some distortion from the static dimensions which
slightly change the balance. On a big heavy car, not really noticeable.
A light, precision car like Elan is sensitive to the small imbalance,
and we have the vibration and wheel sensitivity issue. For those who
are not aware, Radial tires offer many advantages - particularly response
and adhesion on corners. One disadvantage is greater tendency to tread
shift - caused by several factors, most notably belt shift. This cannot
be balanced out, and, along with wheels that are not rotating in the same
plane ( bent wheel, distorted hub, etc) and from my experience, is the
principal cause of dithering.
A while back, I went to a tire seminar, and was told it is best to have
your tires balanced after several hundred miles at highway speeds, and
preferably right after car has been driven to tire operating temperature
- when it is still warm - try and get that . New tires (they were
talking radials) take a set after initial run in. They said ideally,
balance when installed, and again several hundred miles later, or just
later. On my DD's, I buy Sears "lifetime balance" and come back 500- 1000
miles later. It is rare that the weights are not shifted or changed. The
on the car balancer in skilled hands can do 2 planes - The second will
cause axial movement instead of radial, and a skilled operator can read
this, after a try or two, balance it out. The best balances I have ever
had have been on the car. Rotating the tires or a panic stop usually
requires re balance. George

[gobw2]

Keith - this is very close to what I was saying - tire changes shape
slightly at speed /load causing that perfect static balance to be
something else on the highway. On the car - balances all rotating parts
as an assembly, as they are positioned at that time. Has to be better
than off car. George

[type26owner]

George,
I did take a bit of a liberty embellishing to make a point. If the tire
seriously distorts in an asymmetrical way then I'll never realize my
vision of getting it perfect. I don't believe this happens since all
tires are inspected for this by the manufacturer. They have a trick
inspection device which automatically mounts and inflates the tires and
applies a simulated road load at it's speed rating.

I installed a set of four new steel K/O wheels which I inspected for
trueness along with new Michelin 155-13 several months and had these
carefully balanced to the center hole. I also managed to repair my
steering rack and pinion to like new. With this effort I reasonably
expected to no longer have a vibration in the steering wheel. Damn if it
doesn't still vibrate I just reduced it a bunch.

I now believe one has to run the tires for few hundred miles then shave
them round and properly balance them to get it right.

Relish it if you can find a tire installer who's competent. In the Bay
Area those folks look as if they would be better suited flipping
hamburgers.

My idea is unique because I've changed the way to measure the dynamic
unbalance condition by reorienting the inspection axis. This effectively
allows a tilting about that axis which can be measured and corrected.
The heavy bits will rotate towards the bottom. This too obvious for me
think no one has ever thought of it before but I've never seen it put
into practice. This stuff is very similar to the problems I solve at the
lab. It just doesn't have X-rays illuminating it.

Should I wait some more before telling everyone what's wrong with the
professional balancer outfits website explaining static and dynamic
balancing? Here's another hint, it's so obvious that it's stupid.
--
Keith Franck

Martinez, California

[type26owner]

The off-the car dual plane balancer is the best solution because it not
corner or clocking specific.
--
Keith Franck

Martinez, California

["Peter Boegli"]

Hi Keith, George and Bill (forgot any one?)

I have been watching that thread for a while and before really all is said
I'd like to throw in my 2 cents, too

Whenever I had a balancing problem on my Elan it was traceable to one or
more of these reasons:

* The guy at the balancing machine did not understand what he was doing: He
did not set up for the correct rim diameter / width / offset or weight
planes (horn offset, center etc.) He did not center the wheel precisely
enough on the machine. He did not fasten the wheel well enough on the
machine so it slid circumferentially when the machine stopped. If he then
considers the job as done when the remaining imbalance is < 1/4 ounce then
it is _not_ done for an Elan.

* The good old Lotus steel wheels are of (too) lightweight construction and
can easily be bent when a Gorilla is mounting a tire. Most of my wheels were
out of true / round by about 1/10". Automobile industry considers 1mm
(1/25") as tolerable. For an Elan even this is too much, methinks.

* When the car suddenly develops an imbalance, the reason was in many cases
that a balancing weight had come off.

* All our Elans are by nature quite old. Things like steering rack, ball
joints, trunnions get some play which makes an already nimble car even more
responsive to slight balancing imperfections. Yesterday I was driving on the
highway. On several occasions I felt some imbalance which after a while
cured itself. I think it was not tire imbalance but some oscillation within
suspension play, triggered by road distortion. (Yes, my shock absorbers are
new.) My Elise in comparison, which is certainly not less nimble than the
Elan, is definitely less sensitive to wheel imbalance.

I do not believe in the noticeability of dynamic deformations of a modern
tire, at least not in the speed range that is of importance to me (up to the
first resonance frequency at about 75 MPH and beyond to some 110 MPH).

So I do a number of things:

I carefully (and often) balance all my wheels myself using my neighbor's
dynamic balancing machine (small, hand-driven = low speed) to < 2 gm. (1/14
ounce) residual imbalance. So Keith, I do not have a need for a home-made
wheel balancer depending on high precision bearings, and brain-shaking
algorithms making something tedious that should be an easy routine job.
(sorry)

I had all my wheels "massaged" to true and round to < 1 mm. (I still am not
quite satisfied and think about switching to alloys.) BTW: my knock-ons are
really centered by the cone of the center nut and not by the 5 pegs these
only serving as torque transmitters. Keith and George: are yours different
from mine?

I try to keep my suspension parts as play-free as possible.

I hope I did not step on anybody's feet. After all this is my very personal
opinion and need not be true for everyone.

Peter
(Elan Sprint 1971 & Elise 2000)

[Rob_LaMoreaux]

My wheels were static balanced and they don't vibrate up to 80 unless the road is corrugated. Of course all my bushings and dampers are new, so thereis no play in th suspension.

Speaking of wheels and tires. Has anyone bought the 14x6 Minilite clones Spyder is advertising? The stock wheels and stock size tires are fine for normal roads, but the limited slip diff gives low speed understeer which would not be good for autocross,so I'd like wider tires too. The 14" rims wouldgive me more options for tires (size and brand), and since I plan on goingto adjustable spring perches this winter I'd have lots of choices.

Rob LaMoreaux

["Peter Boegli"]

Rob,

I have indeed bought the 14x6 "Minilites" from Spyder some time ago, just to
find out that I would have to flare the fenders on my Sprint by about 1/2".
I did not want to do this, so I sold the wheels to a friend who did the
conversion on his S4. In addition to the fender mod you do need the 2 1/4"
springs for inside clearance. The wheels look good and are nicely
manufactured. So if you not mind the business attitude of Spyders, go for
it. (IMHO)

Cheers
Peter

[type26owner]

Peter,
I'm envious that you've got access to a hand spun (dual plane?)
balancer. They start at $2K. There's lots of references on the web for
this stuff.

Try this for me please. At freeway speed remove your hands from the
steering wheel and tell me how much it oscillates. Mine's under an 1/8"
now on the circumference. But it shouldn't be moving at all.

Personally I like the feel of a well designed steel wheel. I've made a
comparison with steel versus alloy wheels on some of my other
performance vehicles. I'd take a grippy bias ply tire any time too. The
amount of give at the slip angle of a radial tire sucks. Because I'm a
big guy I'm forced to run 35 psi in the rear tires or die.
--
Keith Franck

Martinez, California

["Peter Boegli"]

Keith,

Freeway speed = 55 MPH? "Oscillation" = regular movements, i.e. _not_ taking
movements due to road imperfections into account? If twice "yes", then I'd
agree with < 1/8", i.e. not discernible.

At our highway speed (120 km/h = 75 MPH), my steering wheel may "oscillate"
by 1/2" for 10 seconds and then get quiet(er) again. As I wrote I assume
this is a combination of suspension play, wheel imperfection and time
elapsed since last balancing. The tires are road-legal race tires = carcass
of a racing slick (radial!) & rubber compund of a racing slick & "some
profile" & (most important) DOT-sign and TWIs. It sticks to the road like
shit... The downsides are price (USD 175 a piece), life time (about 5000
Miles at brisk road speed), noise (not so important) and width (185/50x13
requires really a 6" rim. I drive it on a 5.5" Elan +2 steel wheels which
fit nicely into my standard fenders.) making them "tramline" a bit. Bump
steering correction has helped quite a bit in this respect.

Peter Boegli

[type26owner]

Peter,
Sounds like maybe you've got multiple frequencies of vibrations going
there. One or two coupling together just happens to be detuned somewhat
from the natural frequency of the vehicle (stiffness). This explains the
extended periods of no vibrations and then it comes back again. Does it
sometimes start up after hitting a bump? Do this please. Do the same
test at 10 mph.

My vehicle does not do that. I would consider your condition to be a
more serious problem.

I'll bet everyone has some sort of a vibration problem. The issue is
just by how much.
--
Keith Franck

LBNL Engineering