Free tool · ITV Canary Islands
Tyre equivalence calculator: will it pass the ITV or does it need homologation?
Enter the size on your registration document and the one you want to fit. I'll tell you instantly whether it's equivalent (±3% diameter), how much your speedometer will deviate, which rims the tyre admits per ETRTO practice, and which alternative commercial sizes exist.
Tyre on your registration document
Tyre you want to fit
Indices (optional, refine the verdict)
Found after the size, e.g.: 91V
M+S tyres: a lower speed rating than the document is accepted as long as it's Q (160 km/h) or higher.
Outer diameter
632 → 634 mm
Diameter difference
+0.38%
Speedometer
≈ 99.6 km/h
At a real 100 km/h, your speedometer will read ≈ 99.6 km/h.
✓ Equivalent size: no homologation needed
The diameter variation is within the ±3% allowed by the Spanish reforms manual. Remember the load index and speed rating must also be equal or higher than your document's, and the rim must match the tyre's profile.
Admissible rims for the new tyre (ETRTO practice)
For a 225 mm width, the admissible rim well is 7″–8.5 inches (ideal: 7.5″–8"). If your rim is outside that range, the assembly isn't valid even if the diameter matches.
Equivalent commercial sizes (within ±3%)
Common catalogue alternatives equivalent to 205/55 R16, on the same and adjacent rims:
| Size | Diameter | Diff. % |
|---|---|---|
| 205/55 R16 | 632 mm | +0.00% |
| 225/50 R16 | 631 mm | -0.08% |
| 225/45 R17 | 634 mm | +0.38% |
| 195/65 R15 | 635 mm | +0.41% |
| 245/40 R17 | 628 mm | -0.65% |
| 205/50 R17 | 637 mm | +0.78% |
| 205/60 R15 | 627 mm | -0.78% |
| 215/45 R17 | 625 mm | -1.04% |
| 185/65 R15 | 622 mm | -1.65% |
| 195/55 R16 | 621 mm | -1.74% |
Guidance tool based on the Spanish reforms manual and ETRTO practice. The final decision always rests with the ITV station; suggested sizes are common European catalogue sizes — confirm availability with the manufacturer. In doubt, send me your registration document and I'll confirm for free.
The 4 legal equivalence requirements
Under the Spanish reforms manual applied by ITV stations, you can fit a tyre different from your document without homologation if it meets all four at once:
- Outer diameter within ±3% of the original.
- Load index equal or higher than the document's.
- Speed rating equal or higher (M+S accepted from Q/160 km/h).
- Rim matching the tyre's profile (ETRTO ranges in the table above).
If any of the four fails, fitting that size is a modification: it needs an engineer's project, certificate and an ITV inspection. I prepare everything online across the Canaries.
Frequently asked questions
Does the calculator replace the ITV's judgement?
No — it's guidance. The final say belongs to the ITV station. But it applies exactly the same rules from the reforms manual, so an 'equivalent' result with correct indices normally means no problem. In doubt, send me your document and I'll confirm for free.
My size exceeds 3% — what now?
Fitting it is legal if homologated: I prepare the technical project, and with the garage certificate you pass the ITV and the size is recorded on your document. The whole procedure is online.
What if I fit non-equivalent tyres without homologating?
ITV rejection, possible fines and — most seriously — your insurer can dispute claims after an accident. Given what homologation costs, the risk isn't worth it.
Does it work for 4x4s and camper vans?
Yes, the logic is the same. For 4x4 sizes in inches (e.g. 31×10.5 R15), multiply inches by 25.4 to get millimetres — or send me the size and I'll check it.