Truss Rod & Neck Relief
The adjustment everyone fears, demystified — and the one rule that keeps you safe.
A guitar neck isn't meant to be perfectly straight. It needs a slight forward bow — called relief — so the strings have room to vibrate without hitting frets. Too much relief and the action gets high in the middle of the neck; too little (or a back-bow) and you get fret buzz in the low positions. The truss rod, a steel rod inside the neck, controls this curve by counteracting string tension.
The one rule
Quarter turns only — and never force it. If the truss rod feels very stiff, won't turn, or makes cracking or popping sounds, STOP immediately and take it to a tech. A broken or seized truss rod is one of the most expensive guitar repairs there is — often more than a mid-range guitar is worth. Everything else about this job is low-risk; forcing the rod is the one way to cause real damage.
How to check relief (the capo test)
- Tune to pitch. The neck must be under normal string tension — loosening the strings changes the curve you're trying to measure.
- Capo the 1st fret. This takes the nut out of the equation.
- Hold the low E down at the last fret. The string is now a perfect straight edge along the fretboard.
- Look at the gap at the 8th fret — between the bottom of the string and the top of the fret.
| Relief at 8th fret | Metric | Imperial | Who it suits |
|---|---|---|---|
| Standard target | 0.25mm | 0.010" | Factory spec — start here |
| Low relief (flatter) | 0.15mm | 0.006" | Light-touch players — less forgiving |
| High relief (more bow) | 0.35mm | 0.014" | Heavy strummers, slide players |
No feeler gauges? A credit card is about 0.76mm thick — roughly 3× the target gap. If a credit card slides under the string easily at the 8th fret, you have too much relief. If there's no visible gap at all, the neck is too flat or back-bowed.
Which way to turn
Adjusting from the headstock end (modern Fenders; Gibsons under the truss rod cover — two or three small Phillips screws hold the little plate on):
| Problem | Turn | Effect |
|---|---|---|
| Too much gap (excess bow) | Clockwise — tighten | Straightens the neck, less relief |
| No gap (flat or back-bowed) | Anti-clockwise — loosen | String tension pulls more bow in |
- Turn a quarter turn. That's a significant adjustment — resist the urge to do more.
- Wait 10–15 minutes for the neck to settle. Wood responds slowly.
- Retune, re-measure, repeat until you're in the 0.20–0.30mm zone.
Vintage-style Strat necks adjust at the heel instead — you may need to loosen the strings and remove the neck to reach it. Same targets, more faff.
Why necks drift
Wood moves with humidity and temperature. Dry winter air pulls moisture out and necks back-bow (buzz appears); humid summers bow them forward (action creeps up). This is normal — even expensive guitars need seasonal relief tweaks. It's maintenance, like tyre pressure. A room at 40–60% relative humidity keeps a neck happiest; in dry climates a case humidifier genuinely helps.
Relief comes first
Relief affects every other measurement — it's step one of the setup order for a reason. If you adjust the truss rod, re-check your action and intonation afterwards.
Guided, with diagrams
GuitarDoc's setup workshop walks the capo test step by step, with animated diagrams showing exactly which way to turn for your guitar type — and warns you before the mistakes that cost money. The workshop is free, offline, no account.
Coming soon to the App StoreMore guides: Setup order · Action height · Fix fret buzz · Intonation