Load Index (LI) and Speed Rating (SI) - complete guide;
Markings like 205/55R16 91V end with a number and a letter that tell you how much load the tyre can carry and how fast it's allowed to go. Below we explain every number, letter and extra code you'll find on the sidewall.
What is the Load Index (LI)
The Load Index is a numeric code between 60 and 140 that defines the maximum load a single tyre can carry at its maximum permitted speed. The number maps to kilograms via the standardised ETRTO (European Tyre and Rim Technical Organisation) table.
Example: a 205/55R16 91V tyre has LI 91, meaning 615 kg per tyre. Across four tyres that's 2460 kg - the full laden weight of a typical mid-size car with passengers and luggage.
LI → kilograms (common values)
| LI | kg | LI | kg | LI | kg |
|---|---|---|---|---|---|
| 70 | 335 | 85 | 515 | 100 | 800 |
| 75 | 387 | 88 | 560 | 103 | 875 |
| 80 | 450 | 91 | 615 | 107 | 975 |
| 82 | 475 | 94 | 670 | 110 | 1060 |
| 83 | 487 | 97 | 730 | 116 | 1250 |
Our tool uses the full 60–140 table internally when checking fitment. When you see "91 (615 kg)" on a model page, that kg figure comes from this table.
What is the Speed Rating (SI)
The Speed Rating (also called Speed Index) is a letter at the end of the sidewall code that defines the maximum speed the tyre can sustain at its rated load.
SI → km/h
| SI | km/h | Typical vehicle |
|---|---|---|
| N | 140 | spare wheel |
| P | 150 | SUVs with off-road tyres |
| Q | 160 | winter tyres, SUV |
| R | 170 | light commercial |
| S | 180 | city cars and small saloons |
| T | 190 | family cars |
| H | 210 | most mid-size and large cars |
| V | 240 | sport and performance |
| W | 270 | high performance |
| Y | 300 | high-performance and supersport |
| ZR | over 240 | older V-rated sport tyres |
Each higher letter covers every lower one - a Y-rated tyre is legal on a car that requires H. The reverse is not true. A T-rated tyre (190 km/h) must not be fitted to a car whose manufacturer requires V (240 km/h), even if you never plan to reach those speeds - it's illegal regardless.
How to read the sidewall
A full dimension and category marking looks like this:
205/55R16 91V XL
- 205 - tread width in millimetres
- 55 - sidewall height as a percentage of width (aspect ratio)
- R - radial construction (standard)
- 16 - rim diameter in inches
- 91 - load index (615 kg per tyre)
- V - speed rating (240 km/h)
- XL - Extra Load, reinforced tyre with increased load capacity
Extra markings that confuse people
- XL (Extra Load)
- Reinforced tyre. Carries 10–15% more than a standard tyre of the same size. Mandatory on most SUVs.
- RFT / ROF / SSR / Run-Flat
- Tyre with reinforced sidewalls. Lets you drive up to 80 km at 80 km/h after pressure loss. Used instead of a spare wheel.
- M+S (Mud + Snow)
- Tread pattern suited to mud and snow. Legacy marking; for certified winter use the "3PMSF" symbol is required.
- 3PMSF (Three-Peak Mountain Snowflake)
- Alpine snowflake. Tyre tested and certified for winter conditions. Mandatory in Croatia from 15 November to 15 April.
- ZR
- Legacy marking for speeds over 240 km/h. Today usually paired with a specific SI letter (e.g. 245/40ZR19 98Y).
Law and limits in Croatia
Per the Croatian vehicle technical regulations:
- Tyres must have LI and SI equal to or higher than the manufacturer specification.
- Minimum tread depth: 1.6 mm for summer, 4 mm for winter.
- Winter equipment mandatory 15 November – 15 April (M+S or 3PMSF + chains).
- Tyres older than 10 years are not recommended regardless of tread.
What SI do I need on Croatian roads?
Your tyre's speed index must at least match the legal speed limit on the road you drive. In Croatia this means H (210 km/h) for the motorway because a tyre running at its rated maximum overheats and loses grip - always leave headroom.
| Road class | Speed limit | Minimum SI |
|---|---|---|
| Motorway (autocesta) | 130 km/h | H |
| Expressway (brza cesta) | 110 km/h | T |
| Open road (out of town) | 90 km/h | T |
| Urban road | 50 km/h | not a constraint |
Note: winter tyres often carry a lower SI than the summer set (e.g. T instead of V). This is allowed if a sticker stating the winter tyre's maximum speed is placed in the driver's field of view. Always cross-check the vehicle manufacturer's spec.
Frequently asked questions
Can I fit a tyre with a higher load index?
Yes. A higher LI is always safe. Note that higher LI often means a stiffer sidewall and higher price, which can affect ride comfort.
What if my tyre is XL but the manufacturer didn't require XL?
Allowed and safe. An XL tyre carries more than a standard tyre of the same size - you can't break anything. Just adjust pressure (typically +0.2 bar vs the standard-tyre recommendation).
Can I replace tyres on just one axle?
Not recommended. Different tread depths or speed ratings between front and rear change vehicle handling, especially in corners and in the wet.
How do I know which LI/SI my car requires?
On the sticker on the driver's door jamb or in the owner's manual. Or - find your car on TrebamGume and you'll see the factory values.
Are winter tyres always the same size as summer?
Not necessarily. Manufacturers often allow a narrower winter size - it grips better on snow. Constraints: overall diameter ±3% and LI/SI compliant.
Can I drive with tyres rated below the legal SI?
This is a technical violation under the Croatian Road Traffic Safety Act. Beyond the fine, in case of an accident your insurer can deny coverage because the vehicle did not meet technical requirements. Exception: winter tyres with a lower SI together with a visible in-cabin speed-restriction sticker.
Why H on the motorway when the limit is 130 km/h?
T (190 km/h) would technically suffice, but a tyre at its rated speed overheats, grip drops, and the risk of blowout on hot asphalt rises. H (210 km/h) leaves an ~80 km/h safety margin over the legal max - this is the industry standard for European motorway driving.
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Enter make, model and year - we'll show every factory tyre size with LI, SI and recommended pressure.
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