Wheel Balancing

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Static vs. Dynamic Balancing


Tire Markings

Most tire manufacturers supply some sort of marking on the tire to show where the lightest part of the tire is. This is usually a red, yellow or white mark. How accurate these marks are is a big question.

"Some METZELER tires have a red dot in the tire sidewall to indicate the lightest point which should be positioned next to the valve." [Metzler]

"Dunlop street tires have yellow balance dots in the bead or sidewall area to indicate the lightest point of the tire. All Dunlop street tires should be installed with these balance dots at the valve." [Dunlop]

Finding the Heavy spot on a tire

I am still thinking of a really nice way to find the heavy spot of a tire on my own. It shouldn't be too hard, I'm just distracted by other projects.


What tools are needed?

Esentially, all that is needed to statically balance a wheel is a section of shaft through the wheel bearings, some weights, and some tape to keep the weights secure.

Special stands are sold to make the job easier, but the are not required. All that is required is that the wheel be allowed to move freely to it's balanced position. A shaft held between two kitchen chairs will work just fine.
Wheel-balance-shaft4.jpg

The shaft should be slightly smaller than the bore of the bearing. The goal is not to fit the bearing. The bearing must be allowed to be as free as possible.

The shaft should be as straight as possible so that it does not influence the bearing angles.

I choose an 18" section of 0.7500" precision stainless steel shaft from McMaster-Carr. P/N# 6493K11. Rockwell hardness is 20C. OD tolerance is -0.0005" to -0.001" (Class L). Straightness tolerance is 0.001" per foot. $35.20.

Most balance kits use very small diameter shafts with adapters to hold the bearing. This is not the best way to do this. By using the largest, stiffest shaft and the wheel hung loosly on the bearings you will get the best results.

The saw cut end is ok to keep for general use, but for best results the end should be squared.


Wheel-balance-shaft1.jpg
The a nice collet lathe is used for this.
Wheel-balance-shaft2.jpg
A quality end.
Wheel-balance-shaft3.jpg

The Proper Technique

DO NOT FOLLOW TIRE MANUFACTURES ADVICE!!

I spent some time and balanced my rear wheel without a tire in place. I found that the heaviest point on the wheel was actually 90 degrees away from the tire valve. That would be the correct point to place the lightest point on the tire. I checked the wheel with the sprocket carrier in place as well, but it made no difference in the balance of the wheel. The red dot on the new metzler shown was very accurate as to the location of the lightest point on the tire.

Take some time and find the heaviest part of your wheel and mark it. I used some blue paint pen (my red paint pen was at work). you could also scripe the point with some sort of obvious mark.

This will make the wheel easier to balance and use fewer weights, sometimes, none at all.

This is how they would like you to mount the tire.

Redtiredot.jpg


This is actually the heaviest part of the rim, 90 degrees away from the valve. The red dot should have been placed with the blue dot.

Redtiredot2.jpg


Mathmatical Proof

Here is the math that proves that the way I suggest (method 2) is better than either other way. Method 1 is what the tire manufacturer recomends. Method 3 is interesting. When I first brought this topic up on a message board, a very experienced mechanic that works for Dunlop at AMA and AFM events chimed in. It was his contention that for truely fast riders, like Matt Mladden riding a 200hp bike to it's limits, the rear tire will spin on the rim causing a serious misbalance of the wheel at the speeds that they go. To reduce the magnitude of this misbalance, he said that they will balance the wheel first without the tire, then they mount the tire according to manufactures recomendations, then they balance the wheel again. This made no sence, so I did the math. With regard to tire spin, it makes no difference how the initial balance is done. In light of this, method 2 is superior since the least amount of weight is added to the wheel.

Wheelbalancing.gif

Tirespinmath.gif

Wheelbalancegraph.gif

A Better Way

After some time and after giving this subject some considerable attention, I have come up with an improved approch on wheel/tire balancing. What you do is dynamically lateral balance just the wheel, leaving it radially out of balance and mark the heavy spot. The weights used to laterally balace the wheel are marked so that they do not get removed later. Then the tire is mounted in a manner that mates the lightest point on the tire with the heaviest point on the wheel and radially balanced statically in the feild or track. This technique will give the wheel a reasonably good dynamic balance while allowing for static balances in the feild or on the track. Cool!