What we check, and what we don’t
Coverage statement — August 2026
This tool compares published specifications between the parts you pick. That is all it does, and knowing where that stops is as useful as knowing where it starts.
A checker that quietly implies it has thought of everything is worse than no checker at all. So this page lists both halves: every dimension the engine compares, and the questions it deliberately does not answer.
The short version
- It checks interfaces and published limits: whether two parts name the same standard, and whether a figure sits inside a range the maker published.
- It does not check anything about you, your riding, or the state of your parts: sizing and fit, ride feel, torque, wear and installation are all outside it.
- Where a maker publishes no figure, the matching check stays silent. Silence means we have nothing to compare, never that we checked and it passed.
How to read a result
Findings come in three tiers, and each means something narrow:
- Errors: won’t fit.
- Warnings: works, but check something. Often a named adapter, a shim or a spacer, or a maker’s own “not recommended” wording.
- Notes: things worth knowing that are not a fit problem.
When nothing fires, the tool says “No conflicts found”. It never says “all compatible”, and the difference is the point of this page: it means no conflict was found among the dimensions listed below, not that the build is guaranteed to work. The coloured dot beside a part means the same thing at pick time: green adds no new conflict, yellow adds a warning, red adds an error, grey means nothing is selected to compare against yet.
Inside the builder, the Why? control behind any finding names the rule that produced it, the parts it looked at, and where the figures came from.
What the checker compares
Every area below compares two things that are already written down: two named standards, or a figure against a limit its maker published. None of them is a judgement about how a bike will ride. Not every area applies to every bike type: the mountain, BMX, drop-bar and e-MTB builders each run their own rules over their own catalog.
Frame, wheels and tires
- Wheel size vs the frame and fork
- Axle standard
- Tire width vs frame and fork clearance
- Tire width vs rim
Drivetrain
- One drivetrain system
- Matching speed counts
- Shifter-to-derailleur actuation
- Chain, chainring and cog interface
- Cassette range vs derailleur capacity
- Derailleur mounting (UDH / full-mount)
- Cassette vs freehub driver
- Front shifting
- Shifter mounting on the bar
- Single-speed setup
- Gearbox drivetrains
- Belt drive
- Sprocket-to-crank drive style
- Bottom bracket, shell and spindle
Brakes
- Brake mounting
- Brake system and lever
- Rotor size vs the caliper’s own limit
- Rotor thickness vs the caliper’s design band
- Rotor-to-hub interface
- Rotor size vs the frame and fork
- Gyro / detangler
Front end and suspension
- Steerer tube
- Headset cups vs head tube
- Headset crown race vs fork
- Fork travel vs the frame
- Rear shock fit
- Frame and shock sold together
Contact points
- Seatpost and dropper diameter
- Handlebar-to-stem clamp
- Seat-to-post system
- Peg bore vs axle
E-bike systems
- Motor vs frame and crank
- Battery vs frame
- Display and controller vs motor
- E-bike approval on a part
Where a check goes quiet
Several of the areas above only fire when a maker has published the figure they need: a frame’s stated tire clearance, a caliper’s stated maximum rotor, a headset’s S.H.I.S. codes, and others like them. Plenty of makers publish none of it.
On a part whose maker publishes nothing for that dimension, the check says nothing at all rather than estimating. We will not infer a clearance from the tire a bike happens to ship with, or a limit from a part that looks similar. An invented number produces a confident verdict with nothing behind it, which is the failure this whole project is organised around avoiding.
The practical consequence for you: a clean result on a sparsely documented part is a weaker statement than a clean result on a well documented one. The part card shows which figures are sourced.
What it does not check at all
These are not gaps waiting to be filled in next month. They are questions a parts-interface checker is the wrong instrument for, and it is better to say so than to let a green result imply an answer.
Whether the bike fits you
Nothing here reads your height, your inseam, your reach or your riding history, and nothing compares frame geometry between builds. Frame size, stem length, bar width, crank length and saddle position are all fit questions, and this tool has no opinion on any of them. A build can be entirely conflict-free and still be the wrong bike for your body.
How it will ride
Suspension setup, tire pressure, damping, whether a gear range suits your local climbs, whether a wheelset is stiff enough for how hard you ride: none of that is modelled. The one place ride behaviour is mentioned at all is fork travel, where a maker states the travel a frame’s geometry is drawn around; even there the tool reports the maker’s figure and the direction of the change, not what it will feel like.
Torque, fasteners and small hardware
No torque figures are held in this catalog, and nothing checks them. Bolt lengths, headset spacers, axle end caps, brake hose and cable lengths, chain length, spoke lengths, bearing sizes: the small parts and cut-to-length pieces an assembly actually needs are not modelled and will not appear in your running total.
Wear, condition and age
Every check runs against a part as its maker describes it new. A worn cassette, a stretched chain, a rotor thinned by use, a fork due for service or a frame with a history: none of that is visible to the checker, and a rotor thickness check reads maker design figures, never a wear limit.
Installation, tools and workmanship
Whether a job needs a press, a facing tool, a specific bottom-bracket socket or a shop at all; whether an internally routed frame is pleasant to build; whether the parts were installed correctly: all outside. Two parts that pair correctly on paper can still be assembled badly, and a creak is a symptom of installation, torque or wear rather than of two incompatible parts.
Rules, safety approvals and legality
Race regulations, e-bike class rules and local law, helmet and protection certification marks, and whether a bike is legal to ride where you ride it are not checked. The one adjacent thing the engine does read is an explicit maker statement that a part is not approved for e-bike use, and the absence of such a statement is never read as approval.
Price, stock and where to buy
Prices are catalog figures for comparison, not live quotes; nothing here knows what a retailer is charging today, what is in stock, or what a shop will bill for labour. Confirm the price and availability at the retailer before you buy.
Rules we considered and did not write
The bar for adding a rule is manufacturer documentation plus tests, and it is deliberately high in both directions: a false “won’t fit” is as bad as a false “fits”, and both are worse than a missing rule. A rider who is wrongly told a part is incompatible buys the wrong thing just as surely as one who is wrongly told it is fine. Two worked examples:
- Crank chainline against frame standard (Boost vs SuperBoost): rejected. SuperBoost frames are commonly ridden with Boost-chainline cranks, so the obvious rule would fire a false error on builds people ride every day. It needs real per-frame data and domain-expert input before it could be written honestly.
- An adapter note for an oversize rotor: deferred. A rotor over the native mount size already produces a warning; adding a second line naming adapter brackets is a refinement, not a missing safeguard.
Where two of a maker’s own sources disagree, the more conservative figure is the one used, and the conflict goes to review rather than being resolved by whichever page loaded first.
What the numbers are
Specifications, prices and weights in the catalog are approximate sample data unless the row carries a ✓ Verified badge. Verified means that figure was checked against the manufacturer’s own published page, with the source linked and the date recorded. Interfaces always come from the maker, and a reputable third-party measured weight is accepted for weight alone and labelled as measured. Prices are MSRP; a sale price, where one is recorded, only ever appears labelled as a sale price. The builders carry a ✓ Verified only filter, and a line under each catalog stating how much of that category the filter is hiding.
A verified badge is a claim about the spec, never about the fit. Two parts with verified specs can still be a poor idea together for a reason no published figure captures.
If something here looks wrong
Wrong verdicts matter more to us than missing features. Where a builder offers a Report a wrong verdict link on a build, that is the fastest route to a rule being looked at, whether one fired that should not have, or one you expected stayed silent.
For anything load-bearing (brakes, steering, suspension, anything you would rather not discover on a descent) confirm the spec on the maker’s own page and, where it matters, have a mechanic check the build. This tool is a planning aid; it is not a substitute for either.