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WheelsAndBearings

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Wheels and Bearings is mostly about how wheels work, how the fail and/or wear out, and how to care for them. Wheels are expensive ($50 ea. for the cheapest aluminum ones, $3,500/pr. for racing wheels). The emphasis in the bearings section is on hub bearings, but the other bearings are mentioned.

This class covers hands-on truing, as this is an important emergency repair skill.

Safety, reliablility, economy, efficiency!

Outline

  • [T] Parts of a wheel
  • [T] Wheel theory
  • [T] Modes of failure
  • [T] Bearing theory
  • [T] Where bearings are found
  • [A] Evaluating hub bearing adjustment
  • [D] Adjusting hub bearings
  • [T] Truing stand use
  • [T] Wheel care - cleaning and lube
  • [A] Wheel truing

added 2013 03 12:
Class demo parts:
Wheels: Taco'ed, dented (with tire not seated), worn brake surface (we should have a section in each kit by April class), radial, Aerospoke

Box with hubs, failed rim sidewall, bb caged bearing set, cartridge bearings

Student boxes with 6 rim types, worn and good cone, good and bad hub adjust examples, 4 spoke types,



Parts of a wheel

Take a demo wheel that is in good shape and point out all of the parts: hub, hub flanges, skewer or nuts, spokes, nipples, rim, rim tape, tube, tire. Not all of these parts will be familiar to all students, so it is good to establish the vocabulary.

Wheel theory

Explain the basics of how wheels work. Bearings in the hub allow rotation. The spokes are under tension and make the wheel into a rigid structure by distributing stress as the bicycle rolls. Wheel roundness and trueness (define the terms) are controlled by changing spoke tension - mostly by equalizing it - which is done by rotating the threaded nipples. Tightening spokes on one side moves the rim to one side, and tightening spokes in one part of the wheel tends to pull the rim in toward the hub at that point. Leave the more practical details for later. Wheel life, conditions, weight, aerodynamics, etc (finish this edit)

Modes of failure

This covers both the ways that wheels fail and how to prolong the life of wheels. Modes of wheel failure: rim, spokes, hub. Keep in mind SREE when buying wheels (safety reliability economy efficiency — efficiency moves up in priority as needed or desired or "sold")
  • Rim Failure: Most fatal wheel failure occurs and the rim, and this is most often due to impact damage. A hard impact on a rim can either bend the rim wall or cause a flat spot. There are demo parts for these. A bent rim wall usually cannot be fixed because aluminum does not respond well to being bent severely in different directions. A flat spot can sometimes be trued out, but the wheel is weakened due to the spoke tension being lower in that section. If a rim manages to avoid impact damage for tens of thousands of miles, it can fail due to the walls being worn thin by braking. Rims can also fail due to overtensioning of spokes. Impact failure can be prevented by careful riding and higher volume tires. Failure due to braking can be delayed by keeping dirt and chunks of aluminum off of the brake pads, which is part of the brakes and cables class. Avoiding failure due to overtensioning is a more advanced wheelbuilding concept, but is discussed a bit in the truing section of this class. Rims can be replaced, but this is a labor intensive process.
  • Spoke/Nipple Failure:
Show demo spokes: s/s, galvanized, chromed, 2.0, 1.8, swagged, with brass, steel, aluminum, and rounded nipples. Broken spokes are a common mode of wheel failure, but are much more easily repaired than rim damage. After putting a new spoke in place, you only need to get the wheel back into true. Nipples can get rounded in the process of wheel truing, but can be removed and replaced without a great deal of trouble. Nipples can also fail by getting corroded to the spoke enough that they won't turn, which will usually require replacement of both the spoke and nipple. There is nothing in particular to be done to avoid breaking spokes, but if the problem is chronic, you should probably be riding stronger wheels. (eventually spokes fail due to fatigue at the elbow)

  • Hub Failure: Most hub problems are not fatal to the wheel. If parts become worn, they can often be replaced, and even a broken axle will not doom a wheel if a replacement part is available. Wear of the bearing system of the hub in general is covered later in the class. In the rare event that a hub fails on the flange where the spokes connect, the wheel will need to be completely rebuilt with a new hub or replaced.

Bearing theory

Every rotational part on a bicycle contains a bearing of some sort. Some are ball bearings, and there are a few very good demo parts for these. A ball bearing assembly consists of a cup and a cone, with balls in between them. When the cup and cone are adjusted so that they are the proper distance apart, the bearing will turn freely but will be fit together tightly. Bearings that are too loose will not sacrifice much efficiency, but will wear faster than if they were properly adjusted. Bearings that are too tight will decrease efficiency and wear much faster. The process of adjusting any traditional ball bearing assembly is a process of making the distance between the cup and cone correct. Cartridge bearings are sometimes used on bicycles now, and generally do not need to be adjusted. Practical aspects of bearing adjustment are discussed under the heading of "Adjusting Hub Bearings".

Where bearings are found

The important bearings on the bicycle in terms of maintenance are, in descending order, the hubs, bottom bracket, headset, and pedals. Explain where each of these are. There are also bearings in rear derailleurs, although they are usually bushings rather than ball bearing assemblies. Brakes have a bearing of some sort, but they are usually not ball bearings either. This class focuses on hub bearings, because they are easy to understand and are almost always poorly adjusted on new parts. Bottom brackets on decent modern bicycles are no longer adjustable, but instead are sealed cartridge units. Headsets and pedals do not frequently need adjustment.

Show cartridge bearing demo parts
cartridge bearings: press fit vs sliding fit, durability vs servicability.


Adjusting hub bearings

Show the parts of a hub in the "exploded" hub (old high flange track hub) that are relevant to adjusting the bearings: the cones, locknuts, and that the cone on the drive side of the rear wheel is hidden. Emphasize that hub bearing adjustment isn't something you do to each side - you are trying to get the correct distance between the cones. This leads to the idea of locking down one side and adjusting from the other. This requires a brief explanation of locknuts - that tightening the locknut against the cone creates friction on the threads that makes the assembly stay in the same place, which keeps the hub from coming out of adjustment as you ride.

Mention bearing retainer "cages" (demo b/b parts) and "fingers in the cup"

Evaluating hub bearing adjustment

There are four demo hubs: adjusted too tight, too loose, and perfect (but slightly worn), and new, expensive, cartridge Hugi hub ($250) to feel what REALLY perfect feels like), there are demo cones corresponding to each. ensure that the students can feel the difference: they should know what play feels like, what tightness feels like, and what the absence of the two feels like. Explain that a hub which cannot be adjusted to perfection is usually worn, although it may just be cheap.

Using a demo wheel, show the process of tightening one side. Explain that on a rear hub, the drive side should be tight, and you should assume that it is. If it isn't, it will cause problems. Then show loosening the other side, and make sure you communicate that the locknut needs to be loosened from the cone before you adjust.

Show the adjustment process, which should be done with fingers on the opposite side of the hub, holding the locknut, and a cone wrench on the cone. NOT a wrench on the opposite side: there should never be a cone wrench on one side and a locknut wrench on the other. This is important because it can lead to loosening the drive side locknut from the cone on a rear wheel. The students are familiar with what a hub feels like when is adjusted right, so the only thing to mention about actual adjusting is that the amount of rotation needed is usually far less than they think. Mention that hubs should usually be adjusted to be a little too tight because the process of retightening the locknut usually loosens them a little bit (you can demonstrate this to the technically-minded by tightening a locknut and asking them to watch the axle turn - since it turns and the cone stays in the same place, the bearing is being loosened).

Advanced hub adjustment

If students seem to be very comfortable with hub adjustment, you might mention the double cone wrench and double locknut wrench techniques, since they make it so much easier. But it is not a must, and avoid it if you think it will confuse. It is also a good idea to mention, if not fully explain, that quick release hubs should generally be adjusted a bit loose to compensate for compression of the axle by the skewer. You can introduce the sawed off dropout tool for this as well.

Break, put away demo parts, get demo wheels.

Truing stand use

Most people have trouble with the truing stand the first time they use it. Show the way all of the knobs work, but there are two points which are very important. The first is how to get the wheel in properly. Put a wheel in, and direct their attention to how you make sure the axle is down into the slots on both sides, and that the stand bears correctly against the locknuts so that the wheel is in straight. The second is to not overtighten the knob that holds the wheel in. It is not supposed to be tightened until you can't anymore, just enough to hold the wheel in.

Wheel care - cleaning and lube

The non-braking-surface part of the rim can be cleaned with a normal cleaner, the braking surface can be cleaned with alcohol, and the nipples should be lubed. Demonstrate nipple lubing technique and emphasize ONE DROP of oil. Students place their front wheels into truing stands and lubricate their nipples.

Wheel truing

Recall what makes wheels round - spoke tension pulling on the rim, and that the spokes pulling from the two sides make it true - that is to say centered. Get a wheel that is not totally true into the stand, and have the students observe the rim touching one of the gauge arms. Explain that if the wheel is too far to one side and touching one arm, it can be made truer by increasing the tension coming from the other side or decreasing the tension coming from that side. Explain approaching a trueness problem conservatively - loosening one spoke and tightening its mate (or several pair, if the problem is large) a quarter turn each at a time. Show what a quarter turn looks like, and explain how to be sure you're turning the wrench in the right direction by bringing it up to eye level and looking at it from behind the wheel - from that position, it should "feel right" to turn it the correct way, whereas turning the wrench when it is at the bottom of the wheel can be counterintuitive.

Pass out demo wheels and tire levers, students remove tire and tube (necessarry for using the cheap demo ture stands) Students should take 5 minutes truing on their demo wheel while you watch and help. Students replace tires on wheels, wash up.


Created by: pgarver. Last Modification: Wednesday 13 of March, 2013 05:35:10 UTC by JSheehan.