Identify your RS125
- Read the plate, then the casting.
- A 1998 registration can be a Rotax 123 or a 122.
- The sample plates on the full page are made up.
VIN and engine
Read the plate, then the casting.
A 1998 registration can be a Rotax 123 or a Rotax 122. The number plate will not tell you which. This decoder uses only the positions the research brief defines, and it marks every other year letter To verify.
The reading will appear here. Nothing is sent anywhere.
Where the number is
From the MP model on, the plate is on the frame to the right of the headstock. Early GS, LA and MP00 bikes have the number stamped on the frame, sometimes with a sticker and no plate.
- Positions 1–3
- ZD4 means Aprilia from the MP model on. GS and LA numbers start GS or LA instead.
- Positions 4–5
- Model code: GS, LA, MP, SF, PY, RD or RM.
- Position 6
- Variant. The brief’s examples are 0 for open and A or B for restricted. MPB uses B for the bee-tail generation, so it is not a complete key.
- Position 10
- Model year, from the MP model on. The sourced letters are in the table below.
Year letters the brief lists
| Code | Model year |
|---|---|
| 1 | 2001 |
| 2 | 2002 |
| S | 1995 |
| T | 1996 |
| V | 1997 |
| W | 1998 |
| X | 1999 |
| Y | 2000 |
| A | 2010 |
| B | 2011 |
| C | 2012 |
2003–2009 and 2013 onward are not in that table. ISO 3779 has letters for them. The decoder shows the ISO year and marks it To verify until it has been checked on a known RS125 plate. S is 1995 in the brief and also 2025 in the ISO cycle. T is 1996 and also 2026. On a new four-stroke, do not assume the two-stroke reading.
Position 9 is not defined in the brief. North American VINs use it as a check digit. That has not been confirmed for these Italian plates, so the decoder does not check it.To verify
Rotax 122 or Rotax 123
| Rotax 123 | Rotax 122 | |
|---|---|---|
| Casting | Left rear, by the engine number | On top of the left crankcase, by the cylinder |
| Carburettor | Dell'Orto VHSB 34 | Dell'Orto PHBH 28, or VHST 28 on the Euro 3 bike |
| Ignition | SEM | Nippondenso CDI, then the EFI Technology ECU |
| Where you find it | Extrema / GS, and much of Europe and the UK until about 1997–98 | Italy from 1995, then the later two-strokes through 2012 |
The Derbi D50B0 is the RS50 engine from 2006, not either of these, and not the four-stroke RS 125. The four-stroke is the 124.2 cc Derbi GPR125-derived engine in the RS4 and the current bike.
1998 liveries
| Check | 1998 Rossi replica livery | Chesterfield schemes |
|---|---|---|
| Livery documented for 1998? | Yes. Listed by rs125.it and Decalmoto. | Not as a 1998 scheme. Sources list Chesterfield for 1994, Biaggi Chesterfield for 1995–96 and Chesterfield for 1999–2005.To verify the build year against the first registration, or a later rebody. |
| Likely engine | Rotax 122 and PHBH 28, since Italy switched to the MP and the 122 from 1995.To verify on the bike. | Either a GS with Rotax 123 and VHSB 34, or an MP with Rotax 122.To verify |
| How to confirm | VIN should start ZD4MP with W in position 10. Look for Rotax 122 cast on top of the left crankcase by the cylinder. | A frame number starting GS, not ZD4, means a GS. Look for Rotax 123 cast at the left rear by the engine number. |
| Bodywork | 1996–98 shape. MP0 and MPA used the GS fairing shape, round headlight, digital temperature gauge. | The same 1996–98 shape if it is an MP or a late GS. |
| Power | Italian spec may be open, around 22 kW. Not learner-legal at full power. | UK bikes were often sold restricted to 15 bhp. Check for the powervalve or a blanking plate. |
| Paperwork | If it is not yet UK-registered: over 10 years old, so exempt from MSVA. NOVA within 14 days, then a V55/5. | MOT and V5C as normal, if it is already registered here. |
Sources
- Differences between Rotax 122 and 123 (opens in a new tab) — Hartrusion
- Modellübersicht RS 125 2T (opens in a new tab) — Hartrusion
- Storia e modelli (opens in a new tab) — rs125.it
- RS 125 replica decal sets by year (opens in a new tab) — Decalmoto
- Aprilia model list (opens in a new tab) — Motorcyclespecs
- RS50 D50B engine (opens in a new tab) — Pedparts
- RS 125 (1995–2012) review and buying guide (opens in a new tab) — MCN
Research brief dated 24 October 2026. Where this page says “the brief”, that is the sourced master plan behind the first edition.