Part of the tyre size are two digits that most motorists are unaware of or don't know what they mean. The two digits before the speed rating symbol as show in the diagram as 91V are the load rating. The load-rating is essentially the maximum weight the tyre can carry. Tyres have different load ratings but generally a tyre of the same size usually are the same. Lower profile sizes tend to have lower load ratings compared to higher profile ones. If you are considering changing your tyre size either up sizing or down sizing the load rating should be the same or higher than the original fitment. Fitting an incorrect load rating is seriously compromising on safety and can result in a serious accident. Load ratings can vary even when the size is the same as some tyres come as standard load ratings and others have been further strengthened. These types usually have the acronym 'XL' or 'RF' on the sidewall this means the tyre structure has been reinforced meaning it can more weight. The XL type are necessary for vehicles that carry more than 5 people and some estate vehicles that carry more wieght in the boot. A common car size 215/55/16 has a load capacity of 93 which reading of the chart equates to 650kg per wheel. Including the load of the vehicle anything extra including the passengers should not go over the 650kg or 1300kg (calculated for two tyres) over the axle distributed evenly. The same size 215/55/16 also comes in the XL version and this tyre has load rating of 97 which equates to 730kg, hence there is a clear advantage of 80kg per tyre. Generally speaking if you fit the correct size you should have the correct rated tyres but make sure as mentioned above you may need the XL and RF version read the load index rating as well before you make any purchase