Skip to content
Technical Reference

Bike Parts Compatibility: Tires, Bottom Brackets, Wheels, Disc Brakes and Cassettes

By Cycle99 Editorial Team ⏱ 7 min read 📂 Technical Reference

Short answer: a part fits when the interface numbers match, not when the names sound alike. This guide gives a decision tree for five areas: tires, bottom brackets, rear wheels and axles, disc brakes, and cassettes with freehubs. Each tree ends at one decisive number and points to a deeper guide. Seatposts, stems, headsets, handlebars and pedals are not covered here (see the last section).

The method behind every tree

  1. Identify the interface. It is the surface where two parts meet: a tire bead on a rim, a crank spindle in a bottom bracket, an axle in a dropout.
  2. Read or measure the number that defines it. Prefer a marking or a manufacturer specification over your own caliper reading, and use the caliper to confirm.
  3. Check the secondary limits. A matching diameter can still fail on width, length or clearance.
  4. If sources disagree, trust the maker of your frame or component. Several Sheldon Brown pages cited below are dated, so treat them as background and confirm against current maker documents.

Names are the main trap. Sheldon Brown calls this Brown’s Law: sizes that look mathematically equal but are written differently usually are not interchangeable. His example is a 26 x 1.75 tire (559 mm bead seat diameter) versus a 26 x 1 3/4 tire (571 mm).

Decision tree: tires and rims

  1. Read the ISO/ETRTO size on the tire sidewall, written width-diameter, for example 40-622. The second number is the bead seat diameter (BSD).
    • BSD differs from your rim’s BSD: it will not fit. Stop here, whatever the inch or “C” name says. Per Sheldon Brown, 700C and 29 inch tires are 622, while 26 x 1.75 is 559 and “27 inch” road tires are 630.
    • BSD matches: continue to step 2.
  2. Check width against the rim. Sheldon Brown’s general guideline is a tire width of 1.45 to 2.0 times the rim’s inner width.
    • Outside that range: look for a different width.
    • Inside it: continue to step 3.
  3. Check clearance in your frame and fork. A shared BSD is not a guarantee: Brown’s own example is a 20-622 road tire and a 38-622 hybrid tire, which he calls “less-than ideal replacements for one another” although a rim that fits one would work “after a fashion” with the other.
  4. Buy the inner tube by the tire’s ISO/ETRTO size.

Go deeper: Gravel Tires Explained and Flat Tire? Here Is Exactly What to Do.

Decision tree: bottom brackets and cranks

  1. Look into the bottom bracket shell.
    • Threads inside the shell: threaded standard. Go to step 2.
    • Smooth bore: press-fit. Park Tool groups these by bore diameter, for example PF41 (BB86, BB92 and related names), PF42 (BB30 and BBright Direct Fit) and PF46 (PF30 and BB386EVO). Confirm the exact name in the frame maker’s documentation; Park Tool’s article gives no measuring procedure and advises asking the bike or component maker or a professional when unsure.
  2. For a threaded shell, measure shell width and identify the thread.
    • 68 mm (or 73 mm) wide, about 34.8 mm thread (1.37 in x 24 TPI): English (BSA/ISO).
    • 70 mm wide, 36 mm thread: Italian. Sheldon Brown notes Italian shells are larger in diameter and other cup sizes fall right through them, while Italian cups are too large to start in an English shell.
    • 68 mm wide, 35 mm x 1.0 mm thread: French or Swiss. Sheldon Brown labels French obsolete and used on older French bicycles. The Swiss thread is the same as French, but its fixed cup is left-threaded. Do not guess between them; check the cup direction.
    • Anything else (Raleigh, T47 and others): use the frame maker’s specification.
  3. Check that the crank spindle suits the bottom bracket. Park Tool lists spindle sizes including 24 mm, 28.99 mm and 30 mm; adapters exist for some combinations.

Forcing a wrong cup is the classic way to damage a shell. Crank removal and bottom bracket installation need specialized tools; if you do not have them, a shop can do it. A creak after fitting often traces here: Why Your Bike Creaks and How to Fix It.

Decision tree: rear wheel, axle and spacing

  1. Find the frame’s rear spacing and axle type from the frame maker (or the old wheel’s markings). Spacing is the distance between the dropouts.
    • Quick release: go to step 2.
    • Thru axle: go to step 3.
  2. Quick-release frames: match the hub’s old locknut dimension to the frame spacing. Sheldon Brown’s spacing crib sheet is a dated, general guide that associates 120 mm with 5-speed and track hubs, 126 mm with 6- and 7-speed road, 130 mm with 8- to 11-speed road, and 135 mm with mountain bikes and disc-brake road bikes. A modern bike’s real spacing comes from its maker.
  3. Thru-axle frames: match both the spacing and the axle.
    • 142 mm versus 148 mm: these are two different rear hub widths (SRAM’s Boost 148 is a wider standard than 142). Do not assume a 142 mm wheel fits a 148 mm frame or the reverse; check the frame maker’s specification.
    • Axle itself: thru axles are typically 12 mm in diameter with some 15 mm and larger. Per Sheldon Brown they are not generally interchangeable between makers because hub width, thread pitch and head or lever seat vary. Order by the axle’s part number and test-fit it before relying on it.
  4. Spacers cannot fix a spacing mismatch, and a misaligned thru-axle frame or fork generally cannot be rebent (Sheldon Brown’s thru axle page).

Safety. Wheel retention is structural. Never ride with a loose wheel, a thru axle that does not fully engage, or cracked or deformed dropouts. If a wheel will not seat without force, have a shop inspect it. Go deeper: How to True a Bicycle Wheel.

Decision tree: disc brake mounts and rotors

  1. Confirm the bike uses disc brakes. If it has rim brakes, none of this section applies.
  2. Identify the frame or fork caliper mount. Shimano’s compatibility documentation names three codes: S for International A-standard, P for post mount, and D for flat mount.
    • Caliper and mount types match: go to step 3.
    • They differ: you need an adapter listed for that exact combination. Shimano’s adapter charts cover post mount calipers on 140, 160, 180, 200 and 203 mm direct-mount forks and frames, International A-standard, and flat mount (ø140/160 and ø160/180 mounts). Each adapter fits specific rotor and frame combinations, so use the chart rather than guessing.
  3. Check the rotor size against the mount and the brake maker’s limits. Shimano’s charts show the frame or fork type and the rotor sizes (within ø140 to ø220 mm across its adapters) that pair with each adapter. Flat mount frames are listed as ø140/160 or ø160/180, which is a range tied to the mount, not a free choice. Rotors on a given bike must stay within the limit set by the frame or fork maker.
  4. Check how the rotor attaches to the hub (six-bolt or Centerlock) before buying a rotor. Wikipedia’s brake overview lists both among the common rotor mounts.

The maximum rotor size is set by the frame or fork maker, so check their specification. Stop and see a professional if you are unsure of the mount type, if any adapter or bolt does not seat properly, or if a brake feels spongy or weak after a part change. Go deeper: How to Service Your Own Brakes.

Decision tree: cassette, freehub and drivetrain

  1. Identify the freehub body on the rear hub.
    • Shimano HyperGlide (HG): takes HG cassettes. Spacers handle width differences between speed counts; follow the instructions packed with the cassette.
    • SRAM XD: takes XD cassettes. SRAM states XD keeps the hub spacing and flange locations of 8-, 9- and 10-speed HG freehub bodies.
    • SRAM XDR: road version, 1.85 mm longer than XD and matching 11-speed road HG spacing. SRAM says XDR drivers accept XD cassettes when a 1.85 mm spacer is installed behind the cassette.
    • Shimano Micro Spline: a different 23-spline interface for Shimano’s 12-speed mountain cassettes. It is not interchangeable with HG, and may need a new freehub body.
  2. Match speed count across shifter, rear derailleur, cassette and chain. Sprocket spacing narrows as speeds increase (Sheldon Brown shows 5.0 mm spacing for a 7-speed SRAM freewheel).
  3. Check the derailleur’s published capacity (largest and smallest sprocket) rather than assuming.
  4. Within one speed count, brand and generation still matter. The component maker’s compatibility chart is the authority.

Go deeper: Understanding Bike Gearing, How to Service Your Rear Derailleur and How to Maintain Your Bike Chain.

What this guide does not cover

Seatposts, stems, headsets, handlebars, pedals, derailleur hangers and e-bike parts (batteries, motors, controllers) are not covered here. The same method applies: find the interface, find the number, check the secondary limits. Parts that carry load or steer, such as forks, stems, handlebars and seatposts, should be checked by a professional if a mismatch is suspected. For fit rather than parts, see How to Fit a Bike Properly.

Sources

Last reviewed: October 2026.

More in Technical Reference