How to Build Your Own Gravel Bike: Parts and Build Order
Building a gravel bike is mostly a matching job. The frame and fork set the standards for the headset, bottom bracket, brake mounts, wheel axles and tire clearance, and every other part has to agree with them. Confirm those standards before you order anything, then assemble in this order: frame prep, headset and fork, bottom bracket and crank, brakes, drivetrain, wheels and tires, cockpit.
Standards to match before you buy
Start with the frame and fork. Get the frame size right first, using the gravel frame size guide, then ask the maker for the headset code, bottom bracket shell, brake mount type, axle spacing and maximum tire size. Everything else follows from those answers.
| Check | What has to agree | Numbers to know |
|---|---|---|
| Headset | Fork steerer, head tube bore, headset type | Standards are not interchangeable. A ZS44 headset suits a 1-1/8 in steerer and a head tube bore of 43.9 mm. A tapered fork uses two codes, for example ZS44/28.6 on top and ZS56/40 below. (Park Tool headset standards, SHIS) |
| Bottom bracket | Frame shell type, bottom bracket, crank spindle | English threaded (BSA): about 33.7 mm shell, and the drive-side cup has a left-hand thread. T47: threaded, about 46 mm shell. PF41 (BB86, BB92): 41 mm bore. PF46 (PF30, BB386EVO): 46 mm bore. PF42 (BB30): 42 mm bore. (Park Tool bottom bracket standards) |
| Brakes | Frame and fork mount, caliper, rotor size | Measure bolt-hole spacing, then use the checker below. (SRAM caliper mounting specifications) |
| Wheels | Frame and fork axle spacing, hub, axle diameter | On a thru-axle hub, measure from end cap to end cap and note the frame spacing in the form 142×12. Check with the hub and frame makers if unsure. (Park Tool) |
| Drivetrain | Shifter, derailleur, cassette, chain, freehub body | Stay inside one maker’s compatibility chart. SRAM 12-speed road cassettes such as XG-1270 need an XDR driver body, and XD cassettes fit an XDR driver with a 1.85 mm spacer. SRAM’s 1×12 XPLR setup lists Flattop 12-speed chains and 10-44T or 11-44T cassettes (XG-1271, XG-1251, PG-1231). (SRAM road compatibility map) See freehub body types for the wheel side. |
| Cockpit | Handlebar clamp diameter, stem clamp diameter | They must match. Common road bar sizes are 25.4, 26.0, 26.4, 31.8 and 35 mm. Measure the bar where the stem clamps it with a metric caliper. (Park Tool) Bar width is a separate choice, covered in how to measure handlebar width. |
| Tires | Frame and fork maximum tire size, rim width | Use the maker’s stated maximum, not a guess. The tire size chart explains why a nominal size can mislead. |
Shimano publishes its own compatibility charts for GRX and road parts. Use those when you build Shimano, and do not mix shifter, derailleur and cassette across ranges without checking.
Brake mount and rotor checker
Measure from the center of one caliper bolt hole to the center of the other. SRAM’s spec lists the frame spacings as 34 mm for flat mount, 74 mm for post mount and 51 mm for IS. Forks are 70 mm for flat mount, 74 mm for post mount, 51 mm for IS and 34 mm for a thru-bolt fork.
Mount and rotor checker
Enter the spacing and weight, then press the button.
The rotor sizes come from SRAM's road, gravel and cyclocross column of its rotor chart, by system weight. Flat mount and thru-bolt mounts need 5 to 7 mm of mounting bolt thread engagement, and post mounts need 9 to 13 mm. SRAM warns that too little engagement can let the caliper come off the bike. If the frame has one mount type and your caliper is another, see which disc brake adapter you need.
Build order
- Prepare the frame. Check that the disc brake mounts are flat and clean. Park Tool's DT-5.2 facing set is made for IS, post and flat mount brake mounts, and shops use it when a mount is not square.
- Headset and fork. Press in the headset that matches the head tube code from the table above, seat the crown race, and fit the fork. Leave extra steerer length until the cockpit height is settled, because a steerer cannot be lengthened.
- Bottom bracket and crank. Install the bottom bracket that matches the shell. On an English threaded shell the drive-side cup has a left-hand thread, so it tightens in the opposite direction to a normal right-hand thread.
- Brakes. Mount the calipers with the right bolt length and thread engagement, set up the levers, and bleed or fit the hoses by the brake maker's instructions.
- Drivetrain. Fit the derailleur, shifters and cassette, then size the chain with the chain length calculator and index the gears.
- Wheels and tires. Mount the tires, confirm clearance at the fork, chainstays and seatstays, and check that the rotors sit centered in the calipers.
- Cockpit. Fit the stem and bar, then the levers, grips or tape. Set the final steerer length last.
Every bolt on a build has a torque limit set by the part's maker, usually printed on the part or in its manual. Use a torque wrench and follow those numbers, particularly on carbon parts. Where the maker gives no figure, ask them rather than guessing.
Suryashankar Dasgupta founded Wise Wheeling. He has been cycling for more than 20 years, on geared and single-speed bikes, across many kinds of terrain. His guides cover bike repair, fit and gear, and each one is checked against manufacturer manuals, Park Tool and other primary sources before it’s published. Read how guides are made: https://wisewheeling.com/editorial-policy/
