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WHEELS AND TYRES

WHEELS
- Alloy and steel wheels
- Magnesium wheels

TIRES
- Tire dimensions
- Speed rating
- Additional markings
- Tire storage
- Important to remember 



ROAD WHEELS

A road wheel is a circular metal part, holding a tire, or a tire with tube. The main purpose of a road wheel is to distribute the force of resistance evenly on the tires. They are also to improve the stiffness of the car when taking corners and to ventilate the brake system, e.g. brake discs/drums, calipers and brake hoses. Road wheels can be made of steel or aluminium and for the more demanding drivers there are high performance rims made of light and durable magnesium.

 

Alloy and steel wheels

Alloy wheels give the car a specific character and it is not only about a better or more elegant look. Alloy wheels last longer than steel wheels. Thanks to their construction and properties, alloys are less prone to deformation in case of large differences of the ambient temperature. What’s more, contrary to the popular belief, alloy wheels are more resistant than steel wheels. Also the weight of the wheels plays an important role. Thanks to the lower weight, both the comfort and the performance of the car are better on the alloy rims. Another significant advantage of alloy rims is that they are better at cooling the element of the brake system. 


Magnesium wheels

The main advantage of the magnesium wheels is their low weight. That’s why they were often installed in sports cars. However, mag wheels were less durable than alloy wheels and also less resistant to corrosion. 

 

TIRES

Tires are the only part of the car that has contact with the road. So the driving safety in any circumstances is dependent on a relatively small surface contact between the tires and the road. For that reason it is extremely important that the tires are in good condition and installed properly. There are mainly three types of tires for passenger car: summer tires, winter tires and all-season tires. In some countries it is obligatory to use only winter tires in winter. 




Tire dimensions

The manufacturers of tires put the markings on the sidewall. Here are some tips to understand the tire code:
- H – section height,
- B – section width,
- D – diameter of the wheel that the tire is designed to fit.

Tire dimensions can be provided:
- in inches,
- in millimeters,
- in a mixed format (mixing millimeters and inches).

For example, in the marking 165/70 - R14:
- 165 is the tire’s indicated section width in millimeters,
- 70 is the tire’s aspect ratio or profile. This is a ratio of sidewall height to section width (%),
- R stands for a radial tire (there can also be D for a diagonal tire),
- R14 is the diameter of the wheel in inches. 


Speed rating

Speed symbol indicates the maximum speed at which the tire can carry a load corresponding to its load index. 
 

Symbol  Speed [km/h] Speed [mph] 
 J  to 100  to 62
 K  to 110  to 68

 L

 to 120  to 75
 M  to 130  to 81
 N  to 140  to 87
 P  to 150  to 94
 Q  to 160  to 100
 R  to 170  to 106
 S  to 180  to 112
 T  to 190  to 118
 U  to 200  to 124
 H  to 210  to 130
 V  to 240  to 149
 W  to 270  to 168
 Y  to 300  to 186
 VR  over 210  over 130
 ZR  over 240  over 149

 

Additional markings

RF / Reinf. (reinforced) – with a higher load index
R/F / RFT – run-flat tire that resists the effects of deflation when punctured, and to enables the car to continue to be driven (at reduced speeds and for limited distances)
TL – tubeless tire
TT – tube type tire
Rear – rear tire
C – higher load rating  


Tire storage

The storage of tires requires particular care:
- tires must be thoroughly cleaned before storage,
- the perfect storage temperature is ± 10°C,
- stable humidity,
- tires should be kept away from oils, fats and heat sources. 


 

Important to remember

- The tires on the same axle should be of identical type and structure.
- The limit for minimum depth of the tread on the tires is 1.6mm.
- A tire with cracks or punctures is no longer suitable for use and should be replaced.
- A proper tire pressure must meet the tire manufacturer's standards. Tire pressure must be the same on the tires of each axle, but may be different on the front and rear axle. Too high or too low tire pressure will cause uneven tire wear.