Monthly Archives: June 2011

Summer Tyres

The main characteristic of the summer tyre is excellent driving and braking performance on both dry and wet roads, in temperatures above freezing throughout the spring, summer, autumn and winter. A simple block-shape tread pattern ensures the tyre’s contact area remains as rigid as possible, ensuring maximium grip at all times by optimising friction with the road surface. If the tyre has any special indication on it, it means this tyre is for summer usage.

Winter Tyres

This type of tyre is suitable for snow and ice covered roads. The tread pattern features a heavily siped, fine-block design with grooves that are deep and wide, providing excellent driving traction and braking performance on winter road surfaces. The tread rubber used in winter tyres provides good friction characteristics and suppleness even in low temperatures. At present, winter tyre design is focused toward braking performance and driving control on icy roads. Recent developments in tyre pattern design and rubber technology have greatly improved winter tyre performance.

All-season Tyres

These tyres are designed to be used all year round to save having to change the tyres to suit the season. All-season tyre patterns are more complicated than those of the summer tyre because of the longer block-edge for winter usage. More sipes appear in the all-season tyre than summer tyre to improve the braking and driving performance by maximising the effect of edge. It is important to remember that in regions where winter temperatures are very low and heavy snow falls are frequent, braking performance will rarely be 100 percent so it is safer to use winter tyres. All-season tread designs will provide good all-around traction for varing road conditions, but still provide good treadwear and tyre noise characteristics.

Current tread depth legislation requires that car tyres must have a minimum of 1.6mm of tread in a continuous band throughout the central ¾ of the tread width and over the whole circumference of the tyre.

However, despite the law, it is generally recognised in the tyre industry that the legal limit is an extreme. Many tyre manufacturers state that they design tyres to function as well at 1.6mm as they do at 9mm (the accepted normal tread depth when new). That is a surprising statement for any tyre company to make, but some have said just that.

So, if a tyre performs as well at 1.6mm as it does at 9mm, what happens at 1.5mm? Is there a sudden drop in performance? Actually there isn’t, because industry testing has shown that when a tyre reaches around 3.5mm in tread depth, the level of performance in the wet, in particular, starts to deteriorate, as does its dry handling characteristics.
The recommended point for change is accepted Europe-wide as being 3mm. So much so that ministerial cars in the UK have their tyres changed at, you guessed it, 3mm.
Why then the current legal limit of 1.6mm? There are several arguments against the change, some of which you may question. One is that the sudden change from 1.6mm to 3mm would have a serious impact on the pockets of hundreds of thousands of motorists who are already struggling to keep their cars on the road. Another is that it would require changing all the tyre moulds in use to increase the tyre wear indicator depth to 3mm. And of course Europe plays a part, as there would not be universal implementation of 3mm tread depth, requiring double standards in production and possibly in policing.

The reality is that since tyres are now a global commodity it would almost require a global adoption of 3mm as a minimum. It doesn’t take an Einstein to counter the arguments against 3mm, but until the legislation is in place you can make up your own mind, scrape by on 1.6mm, or be safe on 3mm. Your choice.
Truck tyres currently have a 1mm legal minimum tread depth – which many are trying to drive up to 1.6mm – for exactly the same reasons as they want to see 3mm for car tyres.
Incidentally – you may wonder why the normal new tread depth is generally around 9mm. This is to do with the slip, ie distortion in a tyre block, and its level of hysteresis. If you take an eraser and holding it vertically, draw it across a desk, you will see that it distorts before it loses grip – that is what we call “slip”. If you increase or decrease the length of rubber you are flexing, the slip increases or decreases. It becomes obvious that too much slip would make a vehicle unstable. Remember that the compound is a compromise too and the ratio of slip to tread block and the compound used is all finely tuned. The industry norm is for car, van and SUV treads, 9mm.

Wheel Size

Two measurements, the Rim Diameter and the Rim Width, normally determine the wheel size. This is best explained with reference to the diagram shown on the right:

The ‘Offset’ of a wheel measures the distance between the wheel centreline and the wheel mounting face and is measured in millimetres. It is extremely important that wheels of the correct offset are used in order to maintain the correct track of the vehicles.

Offset can be Positive or Negative and is best illustrated in the two diagrams on the left. Most Modern vehicles are front-wheel drive, and as such generally require positive offset wheels. The main exception to this rule is 4×4 vehicles, which often use negative offset wheels.

It is, of course, extremely important that the clearance of both the vehicle body work and steering/suspension components are maintained. Failure to do so would most likely cause damage to both the tyre/wheel assembly as well as the body of the vehicles. Clearance is achieved by selecting a wheel of the correct size and type of tyre. Quality alloy wheel suppliers can give such information.

 Offset 

The ‘Offset’ of a wheel measures the distance between the wheel centreline and the wheel mounting face and is measured in millimetres. It is extremely important that wheels of the correct offset are used in order to maintain the correct track of the vehicles.

Offset can be Positive or Negative and is best illustrated in the two diagrams on the left. Most Modern vehicles are front-wheel drive, and as such generally require positive offset wheels. The main exception to this rule is 4×4 vehicles, which often use negative offset wheels.

Clearance

It is, of course, extremely important that the clearance of both the vehicle body work and steering/suspension components are maintained. Failure to do so would most likely cause damage to both the tyre/wheel assembly as well as the body of the vehicles. Clearance is achieved by selecting a wheel of the correct size and type of tyre. Quality alloy wheel suppliers can give such information.

Pitch Circle Diameter (PCD)

The P.C.D. can be defined as the diameter (in millimetres) of an imaginary circle drawn through the centre of the stud holes on the wheel and/or the vehicle wheel hub.

When new wheels are required, it is essential that they have the correct P.C.D. for the vehicle concerned.

Motor vehicle manufacturers use a central location collar on the stub axle hub in order to accurately locate the wheel. The wheel collar diameter varies, depending on the make of vehicle.

Many replacement allow wheel manufacturers use an adapter (spigot ring) to vary the diameter of the locating hole. In this way, a particular wheel can, by changing the spigot ring, be used on a variety of vehicles.

The adapter/spigot ring arrangement is illustrated in the diagrams to the left.

As an example, TSW Spigot rings should always be fitted without he tapered edge facing the vehicle hub. This is to allow easy and accurate location of the ring onto the hub collar. 

The P.C.D. can be defined as the diameter (in millimetres) of an imaginary circle drawn through the centre of the stud holes on the wheel and/or the vehicle wheel hub.

When new wheels are required, it is essential that they have the correct P.C.D. for the vehicle concerned.

 Wheel Location on Hub

 Motor vehicle manufacturers use a central location collar on the stub axle hub in order to accurately locate the wheel. The wheel collar diameter varies, depending on the make of vehicle. Many replacement allow wheel manufacturers use an adapter (spigot ring) to vary the diameter of the locating hole. In this way, a particular wheel can, by changing the spigot ring, be used on a variety of vehicles.The adapter/spigot ring arrangement is illustrated in the diagrams to the left.As an example, TSW Spigot rings should always be fitted without he tapered edge facing the vehicle hub. This is to allow easy and accurate location of the ring onto the hub collar.