Vehicles carrying higher loads need a higher load rated tyre and a higher inflation pressure. You can refer to the manufacturer's handbook. The tyres will carry the marking RF (Reinforced) or XL (Extra Load) The markings for low profile tyres differ slightly.
Example: 185/60 R 14 79 H
- 185 – 185 millimetres nominal section width
- 60 – Sidewall height is 60% of tyre nominal section width (standard tyre is 82%)
- R – Radial
- 14 – Means it fits 14" diameter wheel
- 79 – Load index
- H – Speed rated to 130mph
The 'aspect ratio' (percentage of sidewall height to tread nominal section width) – low profile tyres have a lower aspect ratio meaning more tread is on the road.