Tyres/ Tires and wheels should be viewed as the most important Performance Upgrade, not only do they affect the Cornering Grip, but also Braking and Acceleration abilities. Ultimately a road or race car is a combination of various components, designed to maximise the tyres contact patch with the ground.

Tyres/ Tires and wheels should be viewed as the most important Performance Upgrade, not only do they affect the Cornering Grip, but also Braking and Acceleration abilities. Ultimately a road or race car is a combination of various components, designed to maximise the tyres contact patch with the ground.

We will be looking at at wet/dry (all weather) applications for now to get a understanding of how tyres compare to each other. If you look at your tyre/tire sidewall, then you will see a serial of numbers on the side. Let quickly run through what all the numbers mean.  

The first number in the sidewall coding diagram above refers to the width of the tyre        (contact patch on the floor), the second number is the aspect ration of the tyre and the third is the diameter of the wheel. We then have the load and speed index figures, which you can view below for a more detailed explanation:

As the same suggest, each speed rating number codes related to a specified speed rating of the tyre, careful consideration needs to be taken into account when you upgrade your choice of rubber. 

Having a incorrect speed rating for your newly upgraded car could have serious consequences, especially if the tyre is not capable of the new founded top speed. The last thing you want is a high speed blow out, so make sure you have the right rubber for the job. Have a look at the table below to check you have it covered:

Each tyre also has a load index rating, indicating how much weight it can take, this shouldn't really be a issue as you want to be losing weight not gaining it. But again make sure you have the right rubber for the job as specified by the manufacturer:

A aspect ration is the relationship of the height of a tyre divided by the width, times 100 to represent a percentage. Generally speak the lower the aspect ratio, the better sidewall stability during corning forces and a more responsive driving experience in the corners.

A tyres coefficient of friction ( or CF) is a number which can be used in comparing different levels of pneumatic grip, tyres may have as a result of the molecular bonding between the tarmac and rubber compounds of their construction.

You may of been under the impression that a stationary tyre yields all its grip just sitting there, but as you will find out, there are different factors involved, which affects a tyres ability to attain maximum grip levels:

• Mechanical Grip from Suspension settings, including toe, camber and caster angles.
• Downforce levels.
• Tyre temperature, is it operating in it's design operation zone.
• Tyre wear rates, are they past their optimum.
• Tyre pressure, over or under deflated tyres can cause uneven contact patch with the road.
• Tyre compound, hard medium or soft construction material will yield different grip levels.

Slip Angle is the direction the wheel is pointing towards versus the directional travel of the tyre. Due to the fact the tyre is made of rubber, the elasticity of the material bends and stretches under different acceleration, braking and cornering forces.

This might seem like a negative situation from a performance point of view, but the tyre actually has increased levels of grip with a increase in slip angle, up to it's optimum range until grips starts to drop off. After this point the rubber will give up some of it's adhesion properties and begin to slide, resulting in a lower overall percentage of grip available.

Normally a narrower and taller tyre will have a larger slip angle peak, while wider and lower designs, will have less slip angle. It is also important to note that street tyre generally have larger slip angles then racing tyres. Street tyres peak grip levels will also decrease more rapidly pass the optimum slip angle level, compared to racing tyres.

Pitch Circle Diameter or also known as the Bolt Circle Diameter (BCD) is the measurement of the the circumference of the centerline of the wheel nuts/ bolts. The measurement can be expressed in millimeters or inches and will also indicate the number of Wheel nuts/ bots as the first number.

The wheel offset is the distance between the hub mounting surface and the wheels centerline. The offset is normally measured in millimeters of ET ( German derived word "Einpresstiefe", meaning press/insertion depth) and is engraved or stamped in the wheel itself. This measure translates into three different types of offset: