Skip to content The load index of a tyre determines far more than comfort or handling in the commercial vehicle sector. For tractor units, swap-body trucks and long-haul vehicles, the correct load-capacity index is an absolute requirement for operational safety, roadworthiness and insurance cover. This article explains how to correctly read the load index on a tyre’s sidewall, which values are required for which axle loads, and what the consequences of choosing incorrectly can be.
Table of contents
- Basics: what does the load index mean for truck and commercial vehicle tyres?
- Reading the load index correctly on the tyre sidewall and in vehicle documents
- Load index table for truck tyres (excerpt with load capacity in kg)
- Calculating the required load index for trucks, vans and trailers
- Safety and legal consequences: what happens with the wrong load index?
- Influencing factors: air pressure, temperature, speed and duty profile
- Reinforced truck and van tyres: C, LI pairs, “Reinforced” and special markings
- Practical tips for drivers and fleet managers
Introduction: why the load index is decisive for truck tyres
In the commercial vehicle sector, tyres carry loads many times greater than anything a car tyre will ever handle. A standard 40-tonne truck distributes up to 27,000 kg across its trailer axles alone. The trailer axles of such a combination must reliably absorb these extreme static and dynamic loads.
The load index – also known as the load-capacity index, or internationally the Load Index (LI) – is the numeric code on the sidewall of every tyre. This figure states exactly how much maximum load per tyre, in kilograms, is permitted. While car tyres typically have load indexes between 80 and 100 (corresponding to 450–800 kg), truck tyres range from around 120 to over 170. That corresponds to a load capacity of 1,400 kg up to 6,500 kg or more per tyre.
The consequences of choosing the wrong load index are severe:
- Operational safety at risk: tyre blowouts at motorway speed with 40 tonnes on board
- Roadworthiness certificate voided: TÜV/DEKRA will refuse the periodic inspection
- Insurance cover at risk: recourse claims after accidents involving undersized tyres
- Fines and penalty points: police checks for axle overload
Below you’ll find everything you need to know about the meaning, reading and correct calculation of the required load index for your fleet.
Basics: what does the load index mean for truck and commercial vehicle tyres?
The load index is a number embossed on the tyre sidewall that, according to standardised European Tyre and Rim Technical Organisation (ETRTO) tables, corresponds to an exact load capacity in kilograms. In a typical truck tyre marking such as 315/70 R22.5 154/150 L, the figure 154/150 represents the load index – the double figure distinguishing single and twin-tyre fitment.
Single versus twin-tyre fitment
For truck tyres marked, for example, 154/150:
- First value (154): load capacity in single fitment – here 3,750 kg per tyre
- Second value (150): load capacity in twin fitment – here 3,150 kg per tyre
The lower second value for twin fitment accounts for increased heat build-up and the less favourable load distribution between the inner and outer tyre on an axle. Twin tyres share the load, but the friction between them generates more heat. This reduces effective load capacity by 10–20% compared to single fitment.
Typical LI ranges in the commercial vehicle sector
Vehicle type | Typical LI range | Load capacity per tyre |
|---|---|---|
3.5 t van | 109–121 | 1,030–1,450 kg |
Distribution truck 7.5–12 t | 120–130 | 1,400–1,900 kg |
Long-haul 18 t (4×2) | 146–154 | 3,000–3,750 kg |
Semi-trailer 40 t | 154–164 | 3,750–5,000 kg |
Heavy haulage/construction | 160–170+ | 4,500–6,000+ kg |
Load capacity applies exclusively under two conditions: correct, manufacturer-specified air pressure, and within the approved speed range (indicated by the speed rating, e.g. “L” for max. 120 km/h). |
Reading the load index correctly on the tyre sidewall and in vehicle documents
Correctly reading a tyre’s load index requires knowledge of the tyre marking and the relevant fields in the vehicle documents.
Position on the tyre
The load index appears directly after the tyre size and construction marking on the sidewall:
- Example 1: 385/65 R22.5 160 K
→ LI 160 for single fitment, speed rating K (max. 110 km/h) - Example 2: 315/70 R22.5 154/150 L
→ LI 154 single (3,750 kg), LI 150 twin (3,150 kg), speed rating L (max. 120 km/h) - Example 3: 235/65 R16C 115/113 R
→ C-rated tyre for vans, LI 115 single (1,215 kg), LI 113 twin (1,150 kg)
Relevant fields on the vehicle registration document (Part I)
Field | Content | Relevance for LI |
|---|---|---|
F.1/F.2 | Technically permitted total mass | Total vehicle weight |
F.7 | Permitted front axle load | Front-axle LI calculation |
F.8 | Permitted rear axle load | Rear-axle LI calculation |
15.1/15.2 | Tyres (axle 1/2) | Prescribed tyre size and LI |
Practical example: 4×2 tractor unit
A typical long-haul tractor unit has the following axle loads:
- Front axle (steering axle): 7,500 kg, two single tyres
- Rear axle (drive axle): 11,500 kg, twin tyres (4 tyres)
Front-axle calculation:
7,500 kg ÷ 2 tyres = 3,750 kg → at least LI 154 required
Rear-axle calculation:
11,500 kg ÷ 4 tyres = 2,875 kg → at least LI 146 (twin value) required
When converting fitments – for example from twin tyres to super-single – the LI must always be reassessed and re-entered in the vehicle documents. A single super-single tyre has to carry the load of an entire tyre pair, so it requires an LI 15–25% higher than the previous twin-tyre setup.
Load index table for truck tyres (excerpt with load capacity in kg)
The table below shows the load indexes relevant to the German truck market with the corresponding maximum load in kilograms for single fitment. The values are based on ETRTO standards and apply at correct tyre pressure.
Load index (LI) | Load capacity (kg) | Typical application |
|---|---|---|
120 | 1,400 | Light distribution trucks, 7.5-tonners |
121 | 1,450 | Reinforced van tyres |
125 | 1,580 | Municipal vehicles |
130 | 1,900 | 12-tonne chassis |
140 | 2,500 | Medium-duty trailers |
146 | 3,000 | Drive axle, distribution truck (18 t) |
150 | 3,150 | Swap-body front axles |
154 | 3,750 | Long-haul semi-trailers, steering axles |
156 | 4,000 | Heavy regional transport |
160 | 4,500 | Construction trucks, heavy trailer axles |
164 | 5,000 | Heavy haulage, reinforced trailers |
LI 204 | over 6,000 | Special vehicles, low-loaders |
Full load-index tables extend into ranges above 170 for special applications. For everyday fleet operations, values between 146 and 160 are the most relevant. | ||
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Note on using the load index table in practice
The table serves as a reference for fleet managers and drivers when buying tyres and checking existing tyres:
- Determine axle load from the vehicle registration document (fields F.7/F.8)
- Divide by the number of tyres (for twins: 4 tyres per axle)
- Choose a suitable LI with margin – don’t calculate right up to the limit
Recommendation: Always choose the LI with a safety margin of at least 10–15%. For a calculated requirement of 2,875 kg per tyre (which would exactly match LI 146), you should prefer LI 150.
For special applications, additional margin makes sense:
- Tanker trucks: liquid cargo causes dynamic sloshing → LI +2 steps
- Refrigerated trailers: factor in the weight of the cooling unit plus temperature effects
- Construction-site trucks: frequent kerb impacts and poor road surfaces → higher stress, which is why a reliable 24/7 truck tyre service in Germany offers international fleets extra protection against downtime
Calculating the required load index for trucks, vans and trailers
Calculating the required load index follows a simple principle: axle load divided by number of tyres gives the minimum load capacity per wheel. From this figure, you derive the appropriate LI.
Worked example 1: 18-tonne distribution truck (4×2)
- Permitted rear-axle load: 11,500 kg
- Tyres: twin fitment (4 tyres on the axle)
- Calculation: 11,500 ÷ 4 = 2,875 kg per tyre
- Required LI: 146 (3,000 kg) – better to choose 150 for margin
Worked example 2: 40-tonne truck with three-axle trailer
- Total trailer axle load: 27,000 kg
- Tyres: 3 axles with 2 single tyres each = 6 tyres
- Calculation: 27,000 ÷ 6 = 4,500 kg per tyre
- Required LI: 160 (exactly 4,500 kg)
For summer operation in southern Europe or long motorway stretches, you should factor in one additional margin step, since high temperatures can reduce load capacity by up to 15%.
Worked example 3: 3.5 t van
- Typical tyres: 235/65 R16C 115/113 R
- The “C” indicates a commercial tyre with a reinforced carcass
- LI 115 single = 1,215 kg, LI 113 twin = 1,150 kg
- Sufficiently dimensioned for a permitted total weight of 3,500 kg
Additional factors to consider
Beyond the calculated minimum requirement, other aspects also play a role:
Factor | Effect | Recommendation |
|---|---|---|
Poor road surfaces | Impact loads +20% | LI +1–2 steps |
Temperatures >35°C | Load capacity -10–15% | Check summer tyres |
Continuous 90 km/h operation | Increased flexing | Step up pressure checks |
Load peaks | Short-term overload | Choose a higher LI |
Safety and legal consequences: what happens with the wrong load index?
An undersized tyre load index triggers a cascade of risks – technical, legal and financial. Fleet studies show that more than 30% of commercial vehicle tyre failures are due to undersized load-capacity ratings at full load.
Technical risks
Under sustained overload, the following happens:
- Sidewall overheating: carcass temperature can rise above 100°C
- Belt delamination: the steel plies separate from the rubber
- Structural failure: high-speed blowouts at 90 km/h with 40 tonnes on board
A blown drive-axle tyre on the A7 at full load can cause an uncontrolled lane change, loss of vehicle control, and severe damage to the vehicle and cargo. Especially in metropolitan areas such as the capital region, a 24/7 truck tyre service in Berlin can help you get back on the road quickly after such an incident. ADAC data shows that around 25% of serious truck accidents are tyre-related.
Legal consequences
Violation | Consequence |
|---|---|
LI below minimum requirement | Roadworthiness certificate voided |
TÜV inspection | Inspection sticker refused |
Police check | Journey prohibited, vehicle taken out of service |
Overload class 4 | €75–150 fine + 1 point on the Flensburg register per axle |
Repeated violations | Up to €500 and more |
Insurance aspect
The most critical point for transport companies: after an accident, insurers examine the tyres fitted. If the investigation finds that the fitted LI was below the required load capacity, the motor insurer can:
- Reduce or completely refuse the payout
- Pursue recourse against the operator
- Terminate the policy with immediate effect
A documented case from Bavaria in 2022: a 32-tonne truck with LI 148, on an axle load requiring 3,200 kg per tyre, suffered a blowout. The cargo’s integrity was destroyed, and the damage came to €250,000 – borne by the operator.
Influencing factors: air pressure, temperature, speed and duty profile
The load index printed on the tyre sidewall applies only under ideal conditions. In real-world operation, several factors influence the tyre’s actual load capacity.
Air pressure
- 22.5″ truck tyres, tandem/trailer: typically 8.5–9.0 bar
- Steering axles: often 7.5 bar
- Effect of underinflation: 0.5 bar less = 10–20% lower capacity
Underinflated tyres are especially critical in long-haul operation. Increased flexing leads to significant heat build-up, gradual carcass damage, and ultimately failure – often with no warning, meaning a mobile 24/7 truck tyre service in Germany is needed to get the vehicle safely back on the road quickly.
Temperature
Condition | Effect on load capacity |
|---|---|
Normal operation, 20°C | 100% |
Summer operation, 40°C ambient | -10–15% |
Southern Europe, peak summer | Up to -20% |
For every 10°C rise in temperature, effective load capacity drops by 5–8%. On long motorway stretches in southern Europe, carcass temperature can run 30°C above ambient temperature. |
Speed and duty profile
- Continuous 90 km/h operation: higher centrifugal forces require a 10% buffer compared to urban traffic
- Construction-site vehicles: frequent kerb impacts and off-road stretches increase impact loads by 20%
- Scheduled long-distance coaches: constant loads, lower margins sufficient
The letter after the LI – the speed rating – indicates the maximum permitted speed. Typical values:
- J: 100 km/h (construction vehicles)
- K: 110 km/h
- L: 120 km/h (standard long-haul)
- M: 130 km/h
- ZR: over 240 km/h (car tyres only)
Reinforced truck and van tyres: C, LI pairs, “Reinforced” and special markings
In the commercial vehicle sector, various markings and variants exist that go beyond standard car-tyre distinctions such as “XL”.
C-rated tyres for vans and light trucks
The letter “C” stands for Commercial and marks tyres with a reinforced carcass for vehicles under 7.5 t permitted total weight. C-rated tyres typically carry a double LI figure:
- Example: 225/75 R16C 121/120 R
- Meaning: LI 121 single (1,450 kg), LI 120 twin (1,400 kg)
LI pairs for twin-tyre fitment
For all truck tyres fitted in twins on drive or trailer axles, the pair principle applies (e.g. 154/150):
- First value: maximum load in single fitment
- Second value: maximum permitted load in twin fitment
The lower twin value compensates for:
- Increased heat build-up between the tyres
- Uneven load distribution (the inner tyre often carries more)
- Mutual deformation effects
Load range and ply rating
Heavy truck tyres are additionally classified by carcass strength:
Load range | Ply rating | Application |
|---|---|---|
E | 10 | Standard long-haul |
F | 12 | Heavy-duty applications |
G | 14 | Construction, heavy haulage |
H | 16+ | Extreme loads, low-loaders |
Notes for fleets
Strict rules apply when switching between different tyre types:
- Switching from C-rated to truck tyres: only with the vehicle manufacturer’s approval
- Super-single instead of twins: the single LI must carry 1.8 times the dual load
- Run-flat tyres: rare in the commercial vehicle sector, but TPMS has been mandatory for new fleets since 2024
Recommendation for long-distance tractor units and swap-body trucks: choose tyres with a sufficiently high LI and matching load range. Any savings from cheaper, tightly dimensioned tyres are more than eaten up by higher wear, failure risk and potential damage.
Practical tips for drivers and fleet managers
Correctly handling the load index is not a one-off decision but part of ongoing fleet management. The following points summarise the most important measures.
When purchasing new truck tyres
- Systematically check the LI against maximum axle load + 20% margin
- Check the DOT number and production date (no older than 3 years if held in storage)
- Obtain manufacturer approvals for special applications
- Keep documentation for TÜV inspection and insurance
During ongoing operation
- No mixed fitment: different load indexes on the same axle are not permitted
- Check tyre pressure: at least weekly, mandatory before long trips
- Use TPMS: modern systems have been proven to reduce failures by 40%
- Visual inspection: check the sidewall for damage, cracks or bulges, and if anything looks off, contact a 24/7 mobile truck tyre service in Germany right away
Driver training
Include the following topics in regular training sessions:
Topic | Learning objective |
|---|---|
Reading tyre specifications | Driver can identify LI, tyre width and speed rating |
Recognising overload symptoms | Hot sidewalls, unusual handling |
Performing pressure checks | Correct use of the pressure gauge |
Winter vs all-season tyres | Differences in load capacity and approval |
Economic aspect
The optimal load index isn’t just a safety question. Correctly sized tyres with the right air pressure lead to:
- 10–15% fuel savings through optimal rolling resistance
- Longer mileage through even loading
- Less downtime through fewer breakdowns
- Lower insurance costs through documented compliance
Conclusion
The load index on truck and commercial vehicle tyres is not an optional technical detail, but a legal and safety-critical foundation for any professional fleet operation. Choosing the correct load-capacity index, matched to axle loads, duty profile and environmental conditions, prevents tyre damage, protects your roadworthiness certificate, and guards against recourse claims.
For fleet managers and drivers, the rule is: systematically check axle loads against the required LI at every tyre purchase. Build in margin for temperature, load peaks and route profile. Document the tyres carefully – in the event of a check or a claim, this documentation is worth real money.
The correctly chosen load index is the foundation for safe, economical and legally compliant tyres across the entire commercial vehicle sector.
