Building Bicycle Wheels

Disclaimer: We try to tell you facts, but will make some mistakes. Your interpretation and use of information given here is your responsibility.

The views expressed here do not reflect ...

Introduction

Administrivia

• Books — hand out at end of class, stick around
• Those building wheels:
  • We provide tools and supplies
  • You bring wheel parts, heavy gloves, eye protection
• Lab: two students build one wheel
  • if you are not building a wheel → partner with somebody who does
  • we have 2x "demo" wheels you can build for us

Why build your own wheels?

• fun & interesting
• cheaper than hiring somebody else
  • change a rim without replacing spokes (shops won't)
• may get a better-built wheel than hiring somebody else
• learn how to cope with failures out in the boonies

Building wheels is scary!

• wheels are legendary and mysterious
• I worked on everything except wheels
• then met a guy who _only_ worked on his wheels
• with the mystery gone ... you can do it!

Scope of this class

• "ordinary" wheels with mainstream parts and many spokes
• common: 36-spoke road wheels, 32-spoke MTB wheels
• common: rim section about same width and depth
• some things said here do not apply to all wheels
• ... low spoke count, deep-section rims, carbon rims, etc.,
• you can still build those, but may need more care or information
• ... e.g., 8-spoke wheels w/ 12" rims

Structure of class

• two lectures + workshop
• by end of 1st lecture you should have enough info to choose parts
• ask questions!
  • often forget stuff
  • sometimes unclear
  • if you want to know, many others do, too
  • ask once — everybody benefits

Lectures

• theory
• practice
• within each will try to proceed in linear fashion
• ... but will hop around as things come up

Keep in mind

• whatever we say: don't believe it
• or at least don't believe it just because we said it.
• you can demonstrate a lot of this stuff yourself
  • somebody had to figure it out, after all
• goal is understanding, not just repetition/recitation
• understanding: you will build better wheels and avoid our mistakes if you prove or disprove to yourself the things we say.
• fortunately, you can demonstrate a lot yourself
  • don't need a laboratory with a million dollars equipment

Theory

Theory overview

• introduction
• parts — general description
• spoke length
• all together — how a wheel supports load
• parts — specifics
• requirements — deciding what you need
• choosing parts

A wheel is composed of

• rim
• nipples
• spokes
• hub
  • can be disassembled but we will describe them as a unit
  • here, we care only about where the spokes attach
  • least-important part of wheel structure
  • you care about bearing life, axle breakage, etc.
  • moving parts tend to be the high-service parts of a hub

Tools for wheel building

• most important: spoke wrench — all other tools are optional
  • come in sizes, get the right size
  • if get one size big, seems to fit but then destroys nipples
• truing stand
• dishing tool
• spoke "tensiometer" — tension meter

Tools

• if you don't have a truing stand you can use your bike as one
  • a little awkward, which makes it slower, but is adequate
• if you don't have a dishing tool you can use the truing stand
• if you don't have a tensiometer you can approximate it

Supplies

• oil — any kind will do
  • boiled linseed oil or spoke prep
  • tho' if you need these your wheels may be near collapse
• rags — where there's oil, there's rags
• gloves
• eye protection

"Tools" for wheel building

• knowledge
• "The Bicycle Wheel" by Jobst Brandt
  • "everything is in there" but I'm still re-reading it
  • (and hence this class)
• "Building Bicycle Wheels" by Robert Wright
  • simplified
  • good: gentle introduction
  • bad: more chance of mistakes
• beware myth and lore
  • "do X" — X is wrong
  • "don't do Y" — Y is correct
  • "do Z" — Z is correct but they tell you the wrong way
  • this is engineering — there is a right answer
  • we don't always know the right answer
• I don't want a book on the "art" of wheelbuilding
• ... I can figure out colors myself, I want engineering!

A word in advance

• actually two words: strength and durability
• in common use, these words are used interchangeably
• in technical use they mean different things
• strength is "how much weight it holds"
• durability is "for how long a distance"
• how many kilograms vs. how many kilometres
• they are related: a stronger wheel is often more durable
• but:
  • some tradeoffs increase strength but reduce durability
  • or increase durability but reduce strength
• strength and durability — how much and how long
• Example: thinner spokes
  • often increase wheel durability
  • often decrease wheel lateral strength

Parts

Parts

• rim
• nipples
• spokes
• hub

Rim features (more later)

• what does a rim do, what is a "good" rim, how does one fail?

Rim

• holds tire — right shape/dimension for the tires you use
• space to change a tire
• structural
  • strong — supports a load
  • durable — keeps supporting that load year after year
  • pothole dent resistance
• brakes
  • brake force
  • cooling
    • too hot: brake failure
    • too hot: tire blowoff — brake and steering failure
  • brakes wear out the rim
    • wear indicators
• weight
• aerodynamics

Rim style

• two basic styles of tires: tubular and clincher
• each takes a different rim
• here: clinchers, most issues the same for tubulars

Rim material

• usual: aluminum (aluminium)
• aluminum assumed here
• steel
  • mostly lower-quality rims
  • so you are less likely to see those
  • heavy and poor wet braking → you are less likely to want them
• stainless steel (Dutch bikes)
• carbon fiber
  • most "carbon-fiber" clincher rims are carbon-aluminum composite
  • do not treat as an aluminum rim
• magnesium, titanium, wood ("the original carbon fiber"), plastic
• not all the rules we give here apply to "exotics"
  • especially estimating spoke tension on non-metal rims

Rim dimensions

• tire size — "bead seat diameter" aka ETRO
• section width
• section height or section depth
• center drop for changing tires
• nipple circle diameter — "spoke bed" aka ERD
• nipple offset — aka "asymmetrical rim" or "off-center"
• brake track height — how precise does pad position need to be?
• brake track thickness — how long will the rim wear?
  • Jobst: new to worn out in 3 weeks of wet riding
  • A new MTBr wore out rims approx 3 mo. intervals
  • Rim wear is a common reason to replace rims
  • But: rim wear rate depends on your riding habits
  • If it has not been a problem for you so far...

Nipples (more later)

• hold together rim and spoke
• adjust spoke tension
• use brass nipples
  • except special circumstances

Spokes (more later)

• connect rim/nipples to hub
• support wheel loads
• appears to be axially rigid
• actually a long spring
  • just stiff

Spoke attributes

• here: tension-only spokes
• materials: steel, titanium, aluminum, carbon fiber, other plastics, ...
  • usually stainless steel
  • here: only stainless steel
• length: determined by hub, rim, and lacing pattern
  • how is length measured?
  • from "root" of elbow to far end of threads
• diameter: you choose
  • thinner: lighter, more aerodynamic
  • thinner: more axially springy (more soon)
  • thinner: winds up during wheel tensioning/truing
  • thinner: may build a radially stronger/more durable wheel
  • thinner: may build a laterally weaker wheel
• swaged — aka "butted"
• section: round or not round
  • "aero", might not be aerodynamic
  • here: round

Hubs (more later)

• axle, bearings, hub shell
• shell: flanges and center spool
• here: assume conventional flanges
  • also straight-pull, threaded holes, ...
• flanges
  • goal: support the spoke
  • radius from axle to spoke hole
  • distance between flanges
  • lateral position ("offset") of flanges (dishing)
• subtle
  • flange thickness
  • diameter of holes

Lacing patterns

• radial, 1x, 2x, ...
• what are "cross"?
  • trace spoke from hub to rim
  • cross over/under other spokes
• how much do you want?
  • typically 3x or 4x
  • depending on total # of spokes
• how many cross maximum?
  • rule of thumb: "divide by 9"
  • #spokes/9 == maximum cross

Lacing: why you care

• radial: hard on the hub
• radial: no torque capacity for drive wheels or hub brakes
• crossed supports spoke detensioning
• might want same front and rear — only one length of spoke
  • depends on hub and rim details
  • nice not necessary

Lacing tradeoffs

• max wheel torque capacity if spoke is tangent
• lower cross on drive wheel → higher spoke/flange loads
• more crossings — better spoke support
  • detensioning
  • broken spoke
• more tangent → longer spoke → heavier
• 4x and more crossing → harder to replace "in-place"

Spoke Length

Spokecalc

• spokes
  • nearest 1mm or 2mm is close enough
  • some shops have spoke threading machines
• spokes too short — strip out nipple threads, wheel collapse
• spokes too long
  • bind, wind up and damage spoke
  • damage nipple threads and pull out, wheel collapse
  • poke hole in inner tube
• tension balance
  • all else equal: better balance build stronger & more durable wheel