Manufacturing tyres is a tedious process and maintaining uniformity in the quality and construction can be difficult sometimes. There is always a margin of error that results in variation of parameters like radial runout, lateral runout, force variation and imbalance can also affect a vehicle’s ride quality.
If the mass is not distributed uniformly in a rotating object then it gives rise to balancing issues. Match mounting of tyres and rims is a process in which the tyre’s installation position on the rim is specifically selected to minimise final force of imbalance.
For match mounting the tyre, the simplest method is to align the tyre’s lightest spot (dot mark on the tyre) with the wheel’s heaviest spot.
A common norm in the industry is that OE tyre suppliers are required to mark the high point and the OE wheel manufacturers have to mark the low point. This allows car manufacturers to match mount tyres and rims simply by aligning the two markings. The wheels still require balancing but the amount of balancing weight added is reduced.
In the recent times, car manufacturers use temporary tags instead of permanent marking to specify high and low point on the tyres and wheels. These are removed before the vehicle is put to use but this means that there is no match mounting markings for future reference.
Earlier, the common rule of thumb was the stem hole on the standard wheels indicated optimum place for match-mounting tyres. However, with the rise in popularity of styled steel wheels and alloy wheels, the position of stem hole is decided based on the wheel aesthetics rather than being a uniformity indicator.
Moreover, after being used for several thousand kilometers, it is less likely that the original marked runout will remain the same.
When installing replacement tyres, match-mounting is a important procedure to follow. If the markings are provided on the wheels and tyres, then it is best to align them. However, the most accurate way is to use the tire balancer machine that is capable of measuring wheel runout and tyre force variation before the tyre is mounted over the wheel.