Tyres, Wheels and Drivetrain Engineering

Crr is a dimensionless ratio: the resisting force equals Crr times the normal load (mass x g).

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Good racing clinchers and tubeless tyres measure around 0.003-0.004 on smooth drums and roads.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

0.004 x 80 x 9.81 x 11.1 m/s is about 35 W.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

0.001 x 80 x 9.81 x 11.1 is about 8.7 W, which is why tyre choice matters so much.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Since force = Crr x load, a heavier rider and bike pay proportionally more rolling resistance.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Surface roughness makes the tyre and bike bounce, adding energy losses that smooth drum tests do not capture.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Rubber hysteresis generally falls as it warms, so the same tyre tests faster on a warm day.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

At 40 km/h aero power is typically several hundred watts against a few tens for rolling resistance.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Aero power falls with the cube of speed while rolling power falls only linearly, so rolling gains weight at low speed.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

A steel drum is smooth and curved, so absolute numbers differ from roads, though tyre rankings usually hold.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Vibration passed into the bike and rider is dissipated as heat in the body and components.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Below the breakpoint, more pressure lowers losses; above it, rising vibration losses make the tyre slower on real roads.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

The breakpoint falls as surfaces get rougher, so the fastest pressure drops.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Soft tissues damp vibrations, turning mechanical energy into heat instead of forward motion.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Frank Berto suggested pressures that let the tyre compress about 15% of its height under the rider's weight.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Deflection depends on load and pressure, so more load needs more pressure to keep the same shape.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Greater volume and contact width let a wider tyre carry the load with less pressure and less vibration.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Typically around 55-60% of the load sits on the rear wheel, so it needs a bit more pressure.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

On a very smooth surface the breakpoint is high, so casing losses keep falling as pressure rises.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

The harsh, buzzy feel of an over-inflated tyre is often mistaken for speed, while real losses rise.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Higher TPI usually means finer threads and a more supple casing.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Thinner, more flexible casings deform with lower hysteresis losses.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Protection layers stiffen the tyre and add rubber, so they typically raise rolling resistance.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

ETRTO codes give tyre width then bead seat diameter; 622 mm is the standard 700c road size.

Source: ETRTO Standards Manual (2023) · recall

The first figure is the nominal section width of the tyre.

Source: ETRTO Standards Manual (2023) · recall

Actual width depends on rim internal width; modern wide rims often make a 25 mm tyre measure 27-28 mm.

Source: ETRTO Standards Manual (2023) · recall

Hookless rims are limited to 5 bar because the tyre is held without a hook.

Source: ETRTO Standards Manual (2023) · recall

Only tyres designed for hookless beads hold safely; others can unseat and fail.

Source: ETRTO Standards Manual (2023) · recall

Softer, lower-hysteresis compounds can roll faster and grip better but wear sooner.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Road bike tyres are too narrow to aquaplane at cycling speeds, so tread adds little grip.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Wider internal widths spread the beads, giving a wider, less rounded tyre profile.

Source: ETRTO Standards Manual (2023) · recall

Wheel designers found drag rises when the tyre is wider than the rim, so rims are made slightly wider than tyres.

Source: Poertner, Zipp wheel design notes (2010s) · recall

A bulging tyre disrupts the smooth transition onto the rim, especially at yaw.

Source: Crouch et al., Sports Eng 2017 · recall

A wider tyre has a larger frontal area; matching rim width limits the penalty.

Source: Crouch et al., Sports Eng 2017 · recall

Evidence that wider tyres roll well led to wider rims to keep tyre and rim shapes aerodynamically matched.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A tyre much wider than its rim is poorly supported sideways and can roll or squirm.

Source: ETRTO Standards Manual (2023) · recall

Keeping the tyre within the rim's outer profile helps airflow stay attached across the rim.

Source: Crouch et al., Sports Eng 2017 · recall

ETRTO tables match internal rim widths with a range of compatible tyre widths.

Source: ETRTO Standards Manual (2023) · recall

A tyre wider than the rim spoils the rim's intended profile, costing some aerodynamic advantage.

Source: Crouch et al., Sports Eng 2017 · applied

The rear wheel is partly shielded by the frame and legs, so the front sees more of the undisturbed flow.

Source: Crouch et al., Sports Eng 2017 · recall

Relative to the air, the top of the wheel moves at roughly twice the bike speed while the contact point is stationary.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Because the upper spokes move quickly through the air, reducing their number and shaping them cuts drag.

Source: Crouch et al., Sports Eng 2017 · recall

Deeper rims smooth the flow around the wheel and can produce a forward sail force at yaw.

Source: Crouch et al., Sports Eng 2017 · recall

Side force on a front disc creates steering torque; at the rear it barely affects steering.

Source: Crouch et al., Sports Eng 2017 · recall

Laterally flexible wheels can rub pads or frames and feel vague when cornering or sprinting.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Prolonged braking heats the rim; carbon resin and tyres are sensitive to high temperatures.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

At constant speed on the flat, mass affects only rolling resistance slightly.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Uneven tension pulls the rim sideways or radially, causing wobble.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Rankings can reverse between low and high yaw, so a single number hides real-world behaviour.

Source: Crouch et al., Sports Eng 2017 · recall

In strong gusty crosswinds, a shallower front limits side-force steering effects while a deep rear stays manageable.

Source: Crouch et al., Sports Eng 2017 · applied

Laboratory tests measured chain drive efficiencies up to about 98.6%.

Source: Spicer et al., J Mech Des 2001 · recall

Efficiency rose with larger sprockets and higher chain tension; lubrication made little difference in clean lab conditions.

Source: Spicer et al., J Mech Des 2001 · recall

In controlled clean conditions, lubrication had little measured effect; real-world dirt changes that picture.

Source: Spicer et al., J Mech Des 2001 · recall

Contamination creates abrasive paste in the rollers and pins, increasing friction and wear.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Paraffin-based wax attracts little dirt and tests with low friction, though it needs reapplying.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Chains do not stretch; wear lengthens the pitch, and around 0.5% signals replacement on many drivetrains.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

An elongated chain rides up the teeth, accelerating wear of expensive sprockets.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Independent test rigs drive a chain at set power and speed and measure losses.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A lube that is fast when clean may perform poorly once contaminated, so dirty-condition tests are more realistic.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A clean, fresh chain with good lubrication recovers watts lost to dirt and wear at low cost.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Extreme combinations angle the chain sharply, raising friction and wear.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Chain angle increases rubbing between plates and sprocket teeth.

Source: Spicer et al., J Mech Des 2001 · recall

Less articulation of the links around larger pulleys reduces friction, typically by a watt or two.

Source: Spicer et al., J Mech Des 2001 · recall

53/11 x about 2.1 m circumference is about 10.1 m per crank turn; 90 turns a minute is about 55 km/h.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Development = ratio x wheel circumference, used to compare gears across wheel sizes.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A larger ring lets the rider use larger rear sprockets with a straighter chain for the same gear.

Source: Spicer et al., J Mech Des 2001 · recall

1x systems simplify shifting but spread the range with wider steps between ratios.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Lower gears let riders climb seated at sustainable cadence and power.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Smaller sprockets bend each link more per tooth engagement, raising losses.

Source: Spicer et al., J Mech Des 2001 · recall

Moving to the big ring straightens the chain and uses larger sprockets, reducing friction.

Source: Spicer et al., J Mech Des 2001 · applied

Across 120-220 mm, maximal power varied only a few percent, with optimal cadence adjusting to crank length.

Source: Martin & Spirduso, Eur J Appl Physiol 2001 · recall

Shorter cranks reduce hip closure in a low aero position, which can help comfort and power.

Source: Martin & Spirduso, Eur J Appl Physiol 2001 · applied

Leg extension at the bottom of the stroke stays similar only if saddle height increases by the crank change.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

The foot's speed around the circle depends on both rpm and crank radius.

Source: Martin & Spirduso, Eur J Appl Physiol 2001 · recall

Reviews find inconsistent effects on power and efficiency; some riders prefer them.

Source: Leong, Elmer & Martin, J Appl Biomech 2017 · recall

Q-factor is the lateral spacing of the pedals, which affects knee tracking and comfort.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A taller stack effectively lowers the saddle relative to the foot, so it must be accounted for.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Maximal power occurs at a similar pedal speed, so a shorter crank shifts the best rpm higher.

Source: Martin & Spirduso, Eur J Appl Physiol 2001 · recall

Strain gauges measure torque; multiplied by rotational speed, that gives power.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Single-sided meters assume both legs contribute equally, which is not true for everyone.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

With a high centre of mass, weight transfer means the front wheel does most braking until the rear lifts.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Geometry limits bicycles to roughly half a g before pitch-over, far less than cars.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Deceleration transfers load to the front, raising its grip while the rear unloads.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Rotors stay cleaner and braking heat does not reach the rim and tyre.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Friction converts kinetic energy into heat, which is why long descents heat brakes.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Kinetic energy and hence stopping distance at a fixed deceleration rise with v squared.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A tyre has finite grip; using it for braking leaves less for cornering, the "friction circle".

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Overheated pads, rotors or fluid lose friction or pressure, reducing braking power.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Firm braking in bursts lets components cool between applications and keeps grip for the corner.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Reaching the base-bar levers takes time, which is why riders move to the base bar in technical sections.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied

Composite layups place fibres where loads run, giving high stiffness-to-weight and design freedom.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Carbon may crack internally after an impact with little visible sign.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Carbon is strong in its designed directions but vulnerable to clamping stress; a torque wrench prevents damage.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Hiding cables reduces the exposed, turbulent clutter around the bars and head tube.

Source: Crouch et al., Sports Eng 2017 · recall

Designing storage into the frame shape avoids the drag of add-ons placed in the airflow.

Source: Crouch et al., Sports Eng 2017 · recall

Placements in the rider's wake or between the arms often test with little or even negative drag change.

Source: Crouch et al., Sports Eng 2017 · recall

Aluminium alloys are affordable and more forgiving of knocks, though heavier than carbon for equal stiffness.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

A frame that is the wrong size limits how the contact points can be arranged.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Titanium offers durability and corrosion resistance with a compliant ride, at higher cost and weight than carbon.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · recall

Hidden damage can fail suddenly, so inspection or imaging by a specialist is advisable.

Source: Wilson & Schmidt, Bicycling Science (4th ed., 2020) · applied