Building a tire/wheel balancer

[stryped]

I am probably not as smart as most of you. However, I like to think what I lack in skill I make up for in will...
I would like to be able to balance my own wheels at home. My family has 4 cars plus 1 additional "project car". I also live in the middle of nowhere near an amish community.

I would like to dynamicly balance the tire. I can either make a stand, and spin the tire with an electric motor or perhaps build a power roller that would actually spin the tire on the car/truck.

I have read of shafts being balanced with two acelerometers and a strobe light. I am a little in the dark of accelerometers, but i assume they would somehow read the high point of the tire while it is spinning. This i assume would trigger a strone light to fire, which would"freeze" the tire and indicate the high point. I guess then a weight would be added to 180 degrees from this location?

If a vibration causes a "high" spot on the side of the tire, could this not be done mechanically by using a dial indicator on the tire while it is spinning? Setting up the indicator to ground a strobe light to come on when it read the high spot while the tire is spinning?

Again, i am sorry if the question is dumb. I am just trying to understand. I appreciate the help!

 

[JBA]

For a bit of general information google "wheel balancing", "how to statically balance a wheel", etc

 

[stryped]

I have a static bubble balancer. I want to build a dynamic balancer...

 

[Mech_Engineer]

I recommend you purchase a used tire balancer from a tire shop going out of business or an online used equipment reseller. It seems like new balancers are available for around $900-$1000 (without many bells or whistles), so you might be able to buy a used one for 50-75% of that. I doubt you'll be able to build one from scratch for less than that, especially when you take into account the time invested.

Good luck.

 

[Mech_Engineer]

Another option is to consider trying "tire balancing beads." The product description says:

"[Dynabeads are] a high-density ceramic bead that, when easily installed, continuously balances your tires as you drive. The amount of material will distribute itself in weight and position dependent on the balance requirements of the individual tire."
http://www.innovativebalancing.com/

 

[berkeman]

http://www.innovativebalancing.com/

Do you know how that works? I don't get it yet...

 

[Mech_Engineer]

Do you know how that works? I don't get it yet...

I've heard good things about them from off-roader buddies. Haven't used them myself yet, but this thread inspired me to buy some for install this weekend on my 4Runner. My understanding is the beads tend to re-position as a wheel vibrates, and so after a couple rotations they settle in such a way that they can reduce or eliminate vibration (when spinning at sufficient speed).

Here's a video in case you're interested:


I also hear they make a mess when you un-mount the tire, so you won't be making many friends at the local tire shop if these are in there FYI ;-)

 

[Mech_Engineer]

This is another cool video on a similar application (ball bearings in a circular tube mounted externally on the wheel). He uses stop-motion strobe photography to show you where the ball bearings situate as well.

 

[Dr.D]

Dynamic balance of a wheel entails two parts:
(1) the center of mass has to be moved to the axis of rotation, and
(2) the mass distribution must be adjusted such that the axis of rotation becomes a principal axis for the mass moment of inertia tensor.
The first part of this is what most people think about when they speak of balancing, but the second part is much more tricky. This is why I would never try to balance my own tires. Its just too easy to go to Discount Tires and get them dynamically balanced on their machine.

 

[berkeman]

Extremely cool, @Mech_Engineer -- I did not know that. And I need to think more about how that works. Clearly it does work, but the mechanism isn't obvious to me. Seems like a very good effect to understand.

 

[Dr.D]

I question the demonstration in #8; I don't think it shows what it purports to show.

The structure supporting the axle is far more compliant vertically than it is horizontally. Thus, when the magnet is used to unbalance the wheel, we see lots of motion, but it is almost entirely in the vertical direction. There is very little motion in the horizontal direction. When the tube of small spheres is added, they adjust the center of mass to be on the axis of rotation (item #1 in mys short list above).

The whole test rig is designed to suppress the conical motion that is the natural result of having non-principal axis rotation. It looks good for the demo, and probably helps to see the product. I seriously doubt that it would work nearly that well on your car or truck that does not have the special characteristics of the test rig.

 

[berkeman]

The structure supporting the axle is far more compliant vertically than it is horizontally.

Um, the wheels on my vehicles are constrained in their horizontal motion much more than they are in their vertical motion. What vehicles do not do this?

 

[Dr.D]

Um, the wheels on my vehicles are constrained in their horizontal motion much more than they are in their vertical motion. What vehicles do not do this?

In most cars and trucks, you have a spring assembly that allows compliance for the vertical motion. You also have a tie rod that is far from infinitely stiff, along with fittings, etc. with clearances, as the ultimate constraint against horizontal motion.

The more important point, however, is that you respond more to the vibration that you feel than to a small vibration you cannot see (such as the horizontal motion in the video).

 

[JBA]

The principle for the ball weight balance is a very old system utilized for decades in just about every top loading washing machine for spin balancing. Inside of that rectangular tube ring at the top of the washing machine tub is partially filled with sand that shifts around that ring to offset the clothing weight imbalance for the spin cycles.
I first became aware of this concept in the early 1960's when some people started writing about using ball bearings in tubes on automobile wheel rims for dynamic wheel balancing. One added element in those at that time was to also fill the tube with oil to act as a damping fluid to reduce oscillation of the balls as they adjust to orientation to correct the imbalance.

 

[Ranger Mike]

Ifin you are out in the boon cocks, it will be cheaper to buy a used dynamic balancer. I grew up on static bubble balancer and it can be very acceptable if you do it right. You need to add 2 weights on underside of the wheel/tire and final balance with two weights on top side of the wheel.The factory spec on wheel runout is 0.030” on a wheel dial indicator. ( the dial indicator has a small wheel on the indicator stem). This is the same spec with a tire mounted on the wheel. This still will not find a heavy spot on that tire/wheel assembly as the tire may develop heavy spots in the tread during manufacture. Your idea of spinning the tire while mounted on the wheel has merit but now you have to make sure you always mount the wheel exactly in same position, if you ever remove it from the wheel to check brakes, etc…

 

[Mech_Engineer]

So for what it's worth (anecdotal, so not much ) I installed some of these tire balancing beads in my poorly-balanced 33" off-road tires this past weekend. I bought this particular brand mainly because they were available with free same-day shipping through Amazon.

http://www.eztirebeads.com/

According to the manufacturer they are "high density ceramic beads," and came with an installation kit and filtered valve stems so the beads don't plug it up and cause a leak. The beads flow very easily and are very small, no more than 1.0 mm in diameter I would guess; I found installation to be straightforward but tedious. I installed 8 oz of beads in each tire (which is a bit more than recommended but oh well) and it took quite a while, because the valve stem with the core removed only allows a very slow flow of the beads without getting plugged up. It took me about 30 minutes per tire which was annoying but partly because I was putting in so many.

The result is better than I expected actually! I think probably not better than a well-balanced tire from a dynamic balancing machine, but the ride is miles smoother than previously so if the option is no balancing or these I would definitely use the tire beads! I tested them out by driving around both in-town (~30-45 mph) and on the highway (~70 mph). With these tires previously you wouldn't notice obvious vibration until about 25 mph, and now I'd say I only notice a little vibration initially around 25 mph but then things smooth out; I'm guessing it's the beads re-positioning in the tire after each stop. I find the ride to be even smoother at higher speeds, and since that's where the balancing matters most I'm very happy.

So, the tire balancing beads do appear to work in my tires. Your results may vary.

 

[Baluncore]

@stryped.
The first problem with designing a dynamic wheel balancer is mounting the tyre and spinning it at a safe speed. An old wheel balancing machine would give you a good start and provide the cones needed to centre the wheel.

You need to check first that the tyre is seated correctly on the rim and is round. You then need to monitor the forces on each of the two axle bearing mounts as the wheel rotates. Those sinewaves have different amplitudes and phases relative to an index on the rotating wheel shaft. From that force information, knowing the bead diameter and wheel width, it is possible to compute where on the wheel rims you need to attach balance weights of particular sizes. Tire balancing beads work most of the time. The best way to get them into the tyre quickly is to separate the bead on a tubeless tyre and pour them in through the gap before reseating the bead and inflating the tyre. Inner tubes make it more difficult.

 

[HowlerMonkey]

Bubble balancer works fine but don't expect it to "balance" a tire that has radial or lateral runout properly.

Just get a better tire and be done with it.