# Bicycles & Parts

A bicycle is a frame, wheels and a drivetrain sized to one rider; discipline (road, trail, commuting) sets wheel size, suspension and gearing, and electric assist adds a regulated motor and battery layer. The costliest mistakes are the wrong frame size, the wrong wheel or bracket standard, or ranking bikes by a gear count that overstates how many gears differ.

## How it works

A bicycle turns leg power into motion through a chain line: pedals turn a crankset, the chain pulls a cog on the rear wheel, and the ratio between chainring and cog teeth sets how hard or fast each stroke feels. Frame geometry and wheel size decide how it handles rough ground versus pavement; mountain bikes add a suspension fork, and sometimes a rear shock, so the wheel moves with the terrain instead of the whole bike jolting. Brakes turn motion into heat through friction, either a pad on the rim or a caliper squeezing a rotor near the hub; the rotor route keeps working when the rim is wet. An electric-assist bike adds a motor and battery that boost pedaling, or on some models replace it, up to a wattage and speed cutoff set by law. [9] [11] [4]

| Family | What it is | Suits |
|---|---|---|
| Drivetrain | Pedals, crank, chain and cassette turn leg power into wheel rotation; chainring and cog size set how each stroke feels. | every pedal bike; e-bikes add a motor on top of this |
| Frame and geometry | The frame's angles and tube lengths, plus wheel size, set how the bike handles and how it fits the rider. | choosing between road, mountain, hybrid and kids bikes |
| Braking | Friction stops the bike, either a pad on the wheel rim or a caliper on a rotor near the hub. | every bike; rotor brakes dominate off-road and modern road bikes |
| Electric assist | A hub or mid-drive motor, powered by a battery, adds power under a legal wattage and speed ceiling. | e-bikes only |

## How an expert narrows the choice

```mermaid
timeline
  section 1 · Riding type
    mountain : ask Suspension, Fork travel, Wheel and tire size
    road / hybrid_commuter / kids : skip Suspension, Fork travel
    road : ask Wheel and tire size, Chainring count, Groupset tier, Brake type
    hybrid_commuter : ask Brake type, Wheel and tire size
    kids : ask Wheel and tire size, Brake type : skip Groupset tier, Chainring count, E-bike class, Motor power, Battery capacity, Tubeless ready, Bottom bracket standard
  section 2 · Electric assist
    yes : ask E-bike class, Motor power, Battery capacity
    no : skip E-bike class, Motor power, Battery capacity
  section 3 · Buying a whole bike or a part
    whole_bike : ask Frame size, Frame material
    replacement_part : ask Wheel and tire size, Axle standard, Brake type, Bottom bracket standard : skip Frame size
  section 4 · Frame size
    What frame size: XS, S, M, L, XL, or XXL?
```

1. **Riding type.** Mostly pavement, trail, commuting, or a kid's bike?
   Discipline sets wheel size, suspension, tire width and gearing before anything else; a trail bike and a road bike share almost no parts.
   If mountain: ask Suspension, Fork travel, Wheel and tire size.
   If road or hybrid_commuter or kids: skip Suspension, Fork travel.
   If road: ask Wheel and tire size, Chainring count, Groupset tier, Brake type.
   If hybrid_commuter: ask Brake type, Wheel and tire size.
   If kids: ask Wheel and tire size, Brake type; skip Groupset tier, Chainring count, E-bike class, Motor power, Battery capacity, Tubeless ready, Bottom bracket standard.

2. **Electric assist.** Pedal power only, or electric assist?
   A motor and battery bring a legal wattage and speed ceiling, extra weight, and a different spec sheet than a pure pedal bike.
   If yes: ask E-bike class, Motor power, Battery capacity.
   If no: skip E-bike class, Motor power, Battery capacity.

3. **Buying a whole bike or a part.** A whole bike, or just one part?
   A whole-bike buyer needs frame fit; a parts buyer needs the wheel, axle and bracket standard already fixed by the bike they own.
   If whole_bike: ask Frame size, Frame material.
   If replacement_part: ask Wheel and tire size, Axle standard, Brake type, Bottom bracket standard; skip Frame size.

4. **Frame size.** What frame size: XS, S, M, L, XL, or XXL?
   The letter label is what the listing itself states; height plus the brand's own chart is the fallback when the label is missing, since the cm behind the same label can vary between brands.

## What to surface

### Riding type

What terrain and purpose the bike is built for: road, mountain trail, hybrid or commuting, or a kid's bike. Discipline is the biggest fork in the catalog: it sets wheel size and tire width, whether there's suspension, how wide the gear range needs to be, and how upright the rider sits. A road bike built for pavement speed and a mountain bike built for traction over roots share almost no parts, so asking this first removes the most catalog of any question. [14] [9]

Values: road, mountain, hybrid_commuter, kids.
Question to ask: Mostly pavement, trail, commuting, or a kid's bike?

Used as: top-level split, filter. Data: on the listing, backfill cost low. Look for it as: Usually in the product title or category breadcrumb (road bike, mountain bike, hybrid, kids bike).
Almost always inferable from the title or category; rarely needs research.

### Electric assist

Whether a motor and battery add power to pedaling, as opposed to a pedal-only bike. An e-bike brings a whole extra layer of specs (motor watts, battery Wh, legal class) plus extra weight and cost, and it is regulated separately from a pedal bike by a wattage and speed ceiling. Getting this wrong early means asking several irrelevant questions either way. [1] [4]

Question to ask: Pedal power only, or electric assist?

Used as: top-level split, filter. Data: on the listing, backfill cost none. Look for it as: In the title ('e-bike', 'electric') or a dedicated spec line; almost never ambiguous.

### Buying a whole bike or a part

Whether the shopper wants a complete bicycle or a specific replacement or upgrade part. A whole-bike buyer needs fit facets like frame size; a parts buyer needs the compatibility facts already fixed by the bike they own, such as wheel size, axle and bottom-bracket standard, and brake type. Asking this first stops the assistant asking a parts buyer their height.

Values: whole_bike, replacement_part.
Question to ask: A whole bike, or just one part?

Used as: top-level split. Data: on the listing, backfill cost none. Look for it as: Category breadcrumb or title distinguishes 'bicycles' from 'bicycle parts'.

### Frame size

The maker's own size label (XS to XXL, or a seat-tube cm) for which rider height the frame fits. Wrong frame size is the beginner mistake experts flag most: too big and the bike is hard to control, too small and the rider runs out of room to stretch out. Brands size proportionally by height, but the cm figure on two brands' same-labelled frame can still differ by a couple of centimetres, so a rider's height plus that brand's own chart beats comparing raw cm across listings. [8] [9]

Values: XS, S, M, L, XL, XXL.
Question to ask: What frame size: XS, S, M, L, XL, or XXL?

Used as: top-level split, filter, shown on the card. Data: on the listing, backfill cost none. Look for it as: Size selector or spec table; almost always present as a letter size or a cm number.
If the rider doesn't know the letter, use their height against the brand's own size chart rather than comparing raw cm across brands.

### Suspension

Whether the bike has no suspension (rigid), a front fork only (hardtail), or front and rear (full suspension). Suspension lets the wheel move with the terrain instead of the rider; a hardtail climbs more efficiently and costs less to maintain, full suspension is more controlled on rough descents but heavier and pricier to service. Road, hybrid and kids bikes are rigid by convention; this mostly matters once the riding type is mountain. [14] [15]

Values: rigid, hardtail, full_suspension.
Question to ask: No suspension, front only, or front and back?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Title or spec table ('hardtail', 'full suspension', 'dual suspension').

### Brake type

How the bike stops: a pad on the wheel rim, a cable-pulled (mechanical) disc caliper, a fluid-pulled (hydraulic) disc caliper, a coaster brake built into the rear hub that engages by pedaling backward, or a drum brake enclosed inside the hub. Disc brakes grip a dedicated rotor instead of the wheel's own rim, so they keep working when the rim is wet or muddy; hydraulic discs need less hand force and self-adjust as pads wear, but need occasional fluid bleeding most home mechanics skip. Every bicycle sold as such must still pass the same stopping-distance test regardless of type. [1]

Values: rim, disc_mechanical, disc_hydraulic, coaster, drum.
Question to ask: Rim, mechanical disc, hydraulic disc, coaster, or drum?

Used as: filter, shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Spec table or title ('hydraulic disc brakes'); mechanical versus hydraulic is sometimes only in the full spec sheet.
Mechanical and hydraulic disc calipers look identical in photos; check the brand's spec sheet when the listing just says 'disc brakes'.

### Frame material

What the main frame tubes are made of: aluminium, carbon fibre, steel, titanium, or chromoly, a stronger steel alloy. Carbon is lightest and can be shaped so it's stiff where power goes in and flexes where comfort needs it, but costs the most. Aluminium has a better strength-to-weight ratio than steel but is more vulnerable to fatigue, lacking the clear fatigue limit some steel and titanium alloys have; steel and its chromoly alloys are strong, easy to work and inexpensive but denser, so heavier for the same strength. [9]

Values: aluminum, carbon_fiber, steel, titanium, chromoly.
Question to ask: Lightest you can afford, or tough and forgiving?

Used as: filter, shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Spec table or title ('aluminum frame', 'carbon frame'); almost always stated above entry level.

### Wheel and tire size

The bead-seat diameter (BSD) the rim is built to, sold under names like 700C, 650B, 26-inch or 20-inch. A 700C (622 mm BSD) wheel, a 650B (584 mm) wheel and a 26-inch (559 mm) wheel are not interchangeable: tires and tubes are sized to the BSD, not the marketing name, and at least six different historical '26-inch' sizes exist under that one name. Mismatching this is the most common part-swap mistake. [6] [7]

Values: 700c_622mm, 650b_584mm, 26in_559mm, 20in_or_smaller_406mm.

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Often in the title (700c, 29", 27.5", 26") or spec table as tire size, e.g. '700x28c'.
If only the inch-based marketing name is given, map to BSD via the standard conversion table; flag ambiguous '26 inch' listings for a width check.
Chart: Wheel size scale.

### E-bike class

The US three-class system for low-speed electric bicycles: Class 1 (pedal-assist only, cuts off at 20 mph), Class 2 (adds a throttle, also cuts off at 20 mph), or Class 3 (pedal-assist only, cuts off at 28 mph). The class decides where the bike can legally go: most states restrict Class 3 from multi-use paths and require a minimum age and helmet, while Class 1 and 2 generally keep the same access as a regular bicycle. It only applies once electric assist is yes. [2] [3] [1]

Values: class_1, class_2, class_3.

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Often on a classification sticker required by law, and in the spec sheet; sometimes only inferable from motor watts and whether a throttle is listed.
41 US states use this three-class system as of August 2023; infer from motor power, throttle presence and stated top assisted speed when the class isn't named directly.

### Speed count

The number of sprockets on the rear cassette or hub, advertised as '7-speed', '11-speed' and so on. More speeds usually spreads a wider range between the easiest and hardest gear, but the number printed on the box can mislead: multiplying chainrings by cogs overstates how many genuinely different gear ratios the bike has, because several combinations land on nearly the same ratio. [11]


Used as: shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Title or spec table ('11-speed', '1x12'); some listings give only the total ('21-speed'), folding in chainring count.
Chart: position on a speed-count axis, paired with chainring_config so the nominal-versus-distinct gear point can be annotated.

### Chainring count

How many sprockets sit on the crank at the pedals: one (1x), two (2x), or three (3x). A 1x drivetrain is simpler and lighter and can't drop the chain between rings, but gives up some top-end range; 2x and 3x spread the same range across smaller jumps and need a front derailleur to maintain. Mountain and gravel bikes have mostly moved to 1x; touring and some road bikes keep 2x or 3x for a wider range. [11] [14]

Values: 1x, 2x, 3x.

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: Spec table or title ('1x11', '2x10'): the number before the 'x'.

### Motor power

The electric motor's continuous power rating, in watts. More watts climbs hills and carries cargo more easily but adds weight and drains the battery faster. US law caps a vehicle that still counts as a 'bicycle' at under 750 W, and the EU's pedelec category caps at 250 W, so motor power also decides which legal bucket the bike falls into. [1] [4] [5]

Range: 250 to 750 W. EU pedelecs sit at 250 W; US e-bikes run up to 750 W, with 350 to 500 W common.

Used as: shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Spec sheet lists continuous (sometimes 'nominal') watts; a separately given peak figure is higher.
Chart: position on a watts axis with the 250 W EU pedelec line and the 750 W US bicycle ceiling drawn.

### Battery capacity

The battery's energy capacity in watt-hours (Wh), the figure that roughly tracks range. Bigger batteries ride farther between charges but add weight and cost. Manufacturers quote wildly different ranges for the same battery depending on assist level and terrain, so Wh is a rough sort key for comparing bikes, not a promise of miles. [4]


Used as: shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Spec sheet states Wh directly, or gives volts and amp-hours separately (Wh = V x Ah).
If only V and Ah are given, multiply to get Wh.
Chart: position on a Wh axis; pair with motor_power_w since real-world range depends on both.

### Fork travel

How far the front suspension fork compresses, in millimetres, which sets how rough a trail it can absorb. More travel soaks up bigger hits and suits steeper, rougher trails, but adds weight and a slacker, less efficient pedalling position. Cross-country forks run toward 80 to 100 mm; downhill forks run 200 mm or more, with trail and enduro bikes in between. [15] [14]

Range: 80 to 200 mm. cross-country sits toward 80 to 100 mm; downhill sits at 200 mm or more.

Used as: filter, shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Spec table under 'fork' or 'suspension travel'; common on mountain and gravel-suspension bikes.
Brand spec sheets carry this for any suspension fork; absent on rigid forks by definition.
Chart: Suspension travel band.

### Groupset tier

Where the drivetrain and brake components sit in the maker's own lineup, from entry-level to professional racing. Within one brand's lineup (Shimano's Claris through Dura-Ace, SRAM's Apex through Red, Campagnolo's Veloce through Super Record) a higher tier shifts more precisely and weighs less for a cost; tiers are not comparable one-to-one across brands. Consumable parts like the chain and cassette wear out long before the frame, so tier mostly decides how often those get replaced. [12] [13]

Values: entry, mid, performance, race_pro.

Used as: shown on the card, sortable. Data: on the listing, backfill cost low. Look for it as: Spec table or title names the groupset directly (e.g. 'Shimano 105', 'SRAM Apex'); map the name to a tier.
Brand pages publish the full hierarchy; mapping a named groupset to a tier is a lookup, not research.
Chart: Groupset tier ladder.

### Tubeless ready

Whether the rim and tire are built to seal air without an inner tube, using sealant instead. Tubeless setups resist pinch flats, since there's no tube to pinch, and let the rider run lower pressure for grip; the trade is sealant top-ups every few months and a messier, sometimes frustrating first setup at home. [16]

Question to ask: Tubeless tires, or inner tubes are fine?

Used as: filter, shown on the card. Data: on the listing, backfill cost low. Look for it as: 'Tubeless ready' or 'TLR' in the tire or wheel spec; absent usually means tubed.

### Axle standard

How the wheel attaches: a thin quick-release skewer through a hollow axle, or a thicker thru-axle that threads into the frame. A replacement wheel or fork has to match the frame's axle standard and diameter or it won't bolt on; thru-axles are stiffer and hold a disc rotor more securely under braking, which is why they have displaced quick-release on most newer disc-brake bikes. [17]

Values: quick_release, thru_axle.

Used as: filter. Data: needs research, backfill cost medium. Look for it as: Rarely in the title; sometimes in the full spec sheet as axle diameter and type (e.g. '12x142mm thru-axle').
Brand spec sheets for complete bikes usually carry it; aftermarket wheel and fork listings often omit it, so record as unknown rather than assuming quick-release.

### Bottom bracket standard

How the crank's bearing assembly fits the frame: threaded into the shell, or pressed directly into it, in one of several incompatible widths. A new bottom bracket or crankset has to match the frame's shell width and whether it's threaded or press-fit; the standards are not interchangeable, and getting this wrong is the compatibility mistake parts buyers make most often. It almost never matters to a whole-bike buyer. [10]

Values: threaded, press_fit, other.

Used as: filter. Data: needs research, backfill cost high. Look for it as: Only in the full frame spec sheet, rarely in a parts listing title.
Single-sourced on the exact mm widths (see notes.md); treat named standards (BSA, Italian, BB30, PF30...) as a lookup table rather than asking a buyer to identify it themselves.

## Numbers worth computing

| Metric | Formula | Why |
|---|---|---|
| Nominal gear combinations (combinations) | `chainring_config_count * drivetrain_speed_count` | The number manufacturers print on the box (e.g. '2x10 = 20-speed'). Experts' point is it overstates how many distinct ratios exist, since several combinations land on nearly the same gear. chainring_config_count parses chainring_config's leading digit: 1x/2x/3x become 1/2/3. [11] |

## What you give up

- Carbon is lightest and can be tuned stiff where power goes in and soft where comfort needs it, but it costs the most and a damaged frame usually needs a specialist, not a home fix. [9]
- More suspension travel soaks up bigger hits for rougher descents, but adds weight and a slacker position that costs pedalling efficiency on the way up. [15]
- A higher groupset tier shifts more precisely and holds up longer, but often narrows tolerances and, on electronic groups, adds batteries and software that most riders can't service themselves. Board branch: "See more low-maintenance drivetrains".
- One chainring is simpler, lighter and can't drop the chain between rings, but it spreads the same range across fewer, bigger jumps and may run out of gear on flats or fast descents. [11]
- Hydraulic discs need less hand force and self-adjust as pads wear, but need occasional fluid bleeding; rim brakes are simpler to service at home but lose stopping power on a wet rim. [1]
- Tubeless resists pinch flats and allows lower pressure for grip, at the cost of sealant top-ups and a messier first setup than popping in a tube. [16]
- A stronger motor and a Class 3 rating climb and carry more, but many states keep Class 3 bikes off multi-use paths, and the extra motor and battery weight becomes dead weight once the battery is flat. [2] Board branch: "See more trail-legal e-bikes".
- A thru-axle holds the wheel stiffer and keeps a disc rotor aligned under hard braking, but needs a tool to remove, unlike a quick-release lever. [17]

## How to draw it

**Groupset tier ladder** (scale, shows Groupset tier). A horizontal ladder from entry to race/pro lets a buyer see at a glance where a named groupset (105, Apex, Veloce) sits, without memorising three brands' separate hierarchies. Used today by Shimano, SRAM and Campagnolo each publish this ladder for their own lineup.. [12] [13]

**Wheel size scale** (scale, shows Wheel and tire size). A single bead-seat-diameter axis in millimetres, with 700C, 650B, 26-inch and 20-inch labelled on it, shows at a glance which marketing names actually share a rim and which only sound alike. Used today by The bike trade's own ISO 5775 conversion charts.. [6] [7]

**Suspension travel band** (range, shows Fork travel, Suspension). A travel-in-millimetres axis banded by cross-country, trail, enduro and downhill shows where a given fork sits without the buyer needing to know those discipline names in advance. Used today by Mountain bike makers group forks by travel this way in their own spec sheets.. [15] [14]

## Words you will meet

- **Groupset**. The matched set of shifters, derailleurs, brakes, crankset, cassette and chain that make the drivetrain work together.
- **Cassette (or cogset)**. The cluster of sprockets on the rear wheel that the chain shifts between.
- **Derailleur**. The mechanism that pushes the chain sideways from one sprocket to the next when you shift.
- **Crankset**. The pedals' arms and the chainring or chainrings attached to them.
- **Bottom bracket**. The bearing assembly inside the frame that lets the crankset spin freely.
- **Chainring**. A sprocket on the crankset, at the pedals, as opposed to a cog on the rear wheel.
- **1x drivetrain**. A drivetrain with a single chainring at the pedals and no front derailleur to maintain.
- **Thru-axle**. A thick axle that threads directly into the frame or fork, replacing a quick-release skewer.
- **Quick-release skewer**. A lever-operated rod through a hollow axle that lets a wheel come off without tools.
- **Bead-seat diameter (BSD)**. The exact diameter, in millimetres, where the tire's bead locks onto the rim; the real size behind names like 700C or 26-inch.
- **Pedelec**. The European term for a Class-1-style e-bike: motor assistance only while pedalling, capped at 250 W and cutting off at 25 km/h.
- **Class 1, 2 and 3 e-bike**. The US system for low-speed electric bicycles, split by whether there's a throttle and how fast the motor keeps assisting.
- **Tubeless**. A tire and rim combination that seals air with sealant instead of an inner tube.
- **Hardtail**. A mountain bike with front suspension but a rigid, unsprung rear end.
- **Standover height**. The clearance between the top tube and the rider standing over the frame; the old, now unreliable way people judged frame size.
- **Coaster brake**. A rear-hub brake that engages when the rider pedals backward; no brake lever at all.
- **Drum brake**. A brake sealed inside the wheel hub, pressing pads outward against a drum; shielded from rain and mud.

## Where we made a call

- A speed count printed on the box overstates how many genuinely different gears a bike has. (confidence high). A 3-chainring, 8-cog bike advertises 24 combinations but has only 16 to 18 distinct ratios; several combinations duplicate each other. [11]
- A labelled frame size in centimetres is not standardised across brands. (confidence high). Manufacturers measure the seat tube to different reference points, so two brands' '54 cm' can differ by a couple of centimetres; height plus a brand's own chart is more reliable. [8] [9]
- Battery watt-hours alone do not predict e-bike range. (confidence medium). One source only. Makers quote ranges for the same battery that vary enormously with assist level and terrain, from heavy continuous assist on hills to light intermittent assist on flats. [4]
- Federal and most state e-bike laws agree a sub-750 W motor that stops assisting by 20-28 mph is still a bicycle. (confidence high). CPSC's product-safety definition and the 41-state model law use the same 750 W and speed-cutoff logic, just split the cutoff into three classes. [1] [2]
- 700C and 29-inch wheels share the same 622 mm rim diameter; only the tire differs. (confidence high). '29 inch' is industry marketing for a wide tire on the same 622 mm bead-seat diameter as a 700C road rim; width and intended use still rule out most swaps. [6] [7]
- Bottom bracket and press-fit standards are not interchangeable without an adapter. (confidence medium). One source for the exact shell widths. Named standards (BSA, Italian, BB30, PF30 and others) differ in shell width and bore diameter and are a frequent parts-buying mistake. [10]
- Suspension fork travel ranges have grown; what counted as a downhill fork decades ago is now a cross-country number. (confidence medium). 80 to 100 mm was once the downhill standard and is now the cross-country norm; current downhill forks run 200 mm or more. [15] [14]
- Mountain-bike subtypes like cross-country, trail, enduro and downhill are defined by riding style and travel, not by a strict standard. (confidence medium). No standards body sets these boundaries; brands and reviewers use the same travel number differently depending on the bike's intended use. [14]

## References

1. [16 CFR Part 1512 - Requirements for Bicycles](https://www.govinfo.gov/content/pkg/CFR-2023-title16-vol2/xml/CFR-2023-title16-vol2-part1512.xml) (regulator). Supports: bicycle and e-bike legal definition (750 W, 20 mph); sidewalk bicycle defined by seat height; handbrake stopping-distance test; drive chain tensile strength.
2. [PeopleForBikes, Model Electric Bicycle Legislation (Jan 2020)](https://peopleforbikes.cdn.prismic.io/peopleforbikes/3686d20b-5695-47c1-b0c7-ffe06402be55_Model-eBike-Legislation-Jan2020.pdf) (standards body). Supports: Class 1, 2, 3 e-bike definitions by wattage, speed cutoff and throttle; Class 3 path restrictions and age/helmet rule.
3. [PeopleForBikes, Electric Bicycle FAQ (Aug 2023)](https://peopleforbikes.cdn.prismic.io/peopleforbikes/2a558ca4-943a-4220-ad6a-bf3e8f4ed30b_ebikeFAQ_August_2023.pdf) (standards body). Supports: 41 of 48 states use the three-class system; why Class 3 is capped at 28 mph; Class 1/2/3 throttle versus pedal-assist distinction.
4. [Wikipedia, Electric bicycle](https://en.wikipedia.org/wiki/Electric_bicycle) (primer). Supports: EU pedelec 250 W / 25 km/h cutoff; US Class 3 750 W / 45 km/h; e-bike range varies hugely for the same battery.
5. [Wikipedia, Pedelec](https://en.wikipedia.org/wiki/Pedelec) (primer). Supports: EU 250 W motor power and 25 km/h cutoff for pedelecs; S-pedelec treated as a moped, not a pedelec.
6. [Wikipedia, ISO 5775](https://en.wikipedia.org/wiki/ISO_5775) (primer). Supports: 622 mm BSD equals 700C; 584 mm BSD equals 650B; 559 mm BSD is most mountain-bike 26-inch; at least six historical 26-inch sizes exist.
7. [Sheldon Brown, Tire Sizing Systems](https://www.sheldonbrown.com/tire-sizing.html) (enthusiast community). Supports: 622 mm is '29 inch' marketing for a wide 700C tire; 584 mm is '27.5' marketing; 559 mm is most mountain bikes.
8. [Sheldon Brown, Revisionist Theory of Bicycle Sizing](https://www.sheldonbrown.com/frame-sizing.html) (enthusiast community). Supports: frame seat-tube length is measured to different reference points by different makers.
9. [Wikipedia, Bicycle frame](https://en.wikipedia.org/wiki/Bicycle_frame) (primer). Supports: typical medium frame sizes 54-56 cm road, 46 cm mountain; carbon fiber, aluminum, steel and titanium frame properties; chromoly is a chromium-molybdenum steel alloy.
10. [Wikipedia, Bottom bracket](https://en.wikipedia.org/wiki/Bottom_bracket) (primer). Supports: threaded BSA shell widths and press-fit standards are not interchangeable.
11. [Wikipedia, Bicycle gearing](https://en.wikipedia.org/wiki/Bicycle_gearing) (primer). Supports: a 3-chainring 8-cog drivetrain has 24 nominal but 16-18 distinct gear ratios; cassettes typically run 5 to 12 sprockets.
12. [Wikipedia, Groupset](https://en.wikipedia.org/wiki/Groupset) (primer). Supports: Dura-Ace/Super Record/Red as top-tier; Claris/Veloce/Apex as entry-tier road groupsets.
13. [Wikipedia, List of Shimano groupsets](https://en.wikipedia.org/wiki/List_of_Shimano_groupsets) (primer). Supports: Shimano road hierarchy order: Dura-Ace, Ultegra, 105, Tiagra, CUES/Sora/Claris.
14. [Wikipedia, Mountain bike](https://en.wikipedia.org/wiki/Mountain_bike) (primer). Supports: suspension travel now up to 200 mm; 1x drivetrains up to 13-speed; hardtail and full-suspension definitions.
15. [Wikipedia, Bicycle suspension](https://en.wikipedia.org/wiki/Bicycle_suspension) (primer). Supports: 80-100 mm travel now common for cross-country; downhill forks typically 200 mm or more.
16. [Wikipedia, Bicycle tire](https://en.wikipedia.org/wiki/Bicycle_tire) (primer). Supports: tubeless setups reduce pinch flats and use sealant to stop leaks.
17. [Wikipedia, Thru-axle](https://en.wikipedia.org/wiki/Thru-axle) (primer). Supports: thru-axles use M12 threading and resist disc-brake ejection forces better than quick-release.