The two basic systems
- Through-bolt (usually 3–15 mm per side): the plate sits between hub and wheel, the wheel bolts pass through both. You need longer wheel bolts – by the plate thickness.
- Bolt-on / hub-mounted (usually from 15 mm): the spacer is bolted to the hub with its own bolts, the wheel is then fixed to the spacer with the stock bolts. Wheel bolt length stays the same.
Bolt length and thread engagement
New bolt length ≈ stock length + spacer thickness Thread engagement ≥ 1 × thread diameter (M14 → 14 mm)
The engagement rule of thumb applies to steel hubs. Bolts that are too short engage too few threads; bolts that are too long can bottom out and never clamp the wheel. The exact value is in the spacer's certificate.
Centering
From roughly 8–10 mm, spacers have their own centering spigot that extends the hub centering outwards. Thinner spacers usually do not centre – the hub spigot must then still reach into the wheel.
Legal requirements in Germany
- Only use spacers with an ABE or part certificate (Teilegutachten).
- The combination of vehicle, wheel and spacer must be covered by the certificate.
- Usually an inspection under § 19 (3) StVZO is required; ABE parts without conditions only with the ABE carried in the car.
These values drive the calculator. Legal limits are binding, guidelines and orientation values help you assess.
| Rolling circumference vs. stock | -2 % to +1.5 % | Guideline | VdTÜV-Merkblatt 751 |
|---|---|---|---|
| Speedometer lead | 0 to 10 % + 4 km/h, never below real speed | Legal | UN-R39 / § 57 StVZO |
| Rim width for the tyre | Approved range per ETRTO table | Guideline | ETRTO Standards Manual |
| Load index | at least the value in the papers | Legal | § 36 StVZO / COC |
| Speed rating | at least the papers' value (winter tyres: sticker) | Legal | § 36 StVZO / COC |
| Wheel cover | 30° ahead to 50° behind the wheel centre | Legal | VO (EU) 1009/2010 |
| Track widening | check closely above ±2 % | Orientation | Orientierungswert |
| Remaining fender gap | ≥ 5 mm | Orientation | Orientierungswert |
| Remaining strut gap | ≥ 5 mm | Orientation | Orientierungswert |
| Thread engagement | ≥ 1 × thread diameter | Guideline | Faustregel (≥ 1 × d) |
Try it: enter your values in the calculator and see what changes live.
Open calculatorGeneral information without warranty – no legal advice. Vehicle documents, certificates and the inspector are authoritative.