Tyre Slip Angle Know-How for Racing Drivers

Uncategorized Dec 20, 2019

In this article, get a deeper understanding of these all important "tyre slip angles". Learn how the race car turns a corner, how the tyre slip angle are created, and what it means for you in driving and controlling the race car.


When you turn the race car into the corner, the forward momentum of the car generates a lateral force at the front tyres, forcing the generation of what we know as "tyre slip angles". 

Tyre slip angles are a property of the pneumatic tyre that allows the creation of substantial lateral force at the tyres, and in so doing, allows the car to turn. 

If you just presented the steered road wheels to the road road rushing by without slip angles, it's a bit like presenting the wing on an aircraft without an angle of attack. For the aircraft, no lift. For the race car, no lateral grip. (If we had steel treads, for example, there would be no slip angles, and insufficient friction available to create any significant cornering force on an asphalt road surface .)

Why should you, as a racing driver, be interested in tyres slip angles?

  • Tyre slip angles help explain a very subtle rotation motion of the race car that is important for the racing driver's feel for controlling the car. In the corner entry, at the rear of the car, as grip and therefore tyre slip angles build, the side walls of the tyre twist in order to accommodate the tyre slip angles. 

    This is a brand new concept that explains the nose-in or drift attitude of the car in the corner entry. For many years I have not had this explanation. It is now released with full details in my online training "The Physics of Race Car Handling".

    Please read further and see how understanding tyre slip angles can really work for you in your racing. Get a real appreciation of what is behind your car control skills. 


It’s often thought the tyre slip angle is an indication of the tyre losing cornering grip – that the slip angle is formed by the tyres “slipping” or “sliding” on the pavement. 

The truth is, the slip angles indicate the tyres are making grip. In fact, building grip with increasing slip angle (up to the point where grip levels off and then reduces). 

In response to the lateral force being applied, the tyre contact patch does distort significantly.

However, to make grip, the majority of the rubber in the contact patch has to stay keyed in to the road surface, as the slip angles are building.

At racing speeds, racing drivers build grip in the tyre as fast as possible and then hold the tyre at peak grip, until ready to release the car in the corner exit. 

For the tyre represented in this diagram of Lateral Grip vs Slip Angle, peak grip is reached at around 6 degrees of slip angle.

If the driver pushes harder and/or friction at the tyre contact patch reduces, the grip area of the contact patch reduces in size, causing grip to fall away.

The tyre is no longer able to support the grip level asked of it. The lateral force of cornering overcomes the tyre grip availability, until the driver, by counter steering, takes action to reduce the cornering lateral load, and return the tyre into the grip zone.    


The tyre slip angle is generated by the road wheel being forced sideways and stretching the sidewall of the tyre.  

The steered angle of the wheel is a little greater than the actual direction the wheel is traveling in. The difference between the two is the slip angle, α, as shown in the diagram.

The cornering force is applied at the axle, and the reaction force at the contact patch is shown as  "cornering grip" in the diagram.

Note how the bag of the tyre is stretched sideways, as shown above in end view.  You can see the tyre contact stays gripping the road, while the cornering force applied at the axle forces the wheel outwards.

The tyre contact patch and the wheel now rotate in different planes. The tyre rubber feeding into the contact patch is stretched sideways and then relaxes again. This sort of side step action causes the tyre to drift sideways a little. The forward velocity of the tyre and this so-called side slip velocity are resolved into the actual velocity representing the path the tyre contact patch is travelling. (see diagram above.) 

It's clear that the degree of separation between the  plane of the wheel and tyre determines the slip angle required at any point in time. More flexible side walls lead to higher slip angle. 

Tyres with greater flex in the side wall operate at higher maximum slip angles. Tyres with less flex in the side wall (e.g. low-profile tyres) are more responsive. They build grip quicker. But they are also “less forgiving” than tyres with a bigger bag. There’s less warning for the driver at the limit of grip.


Note in the drawing of the slip angle, that the position and direction of travel of the tyre contact patch is the of Here's another diagram showing the tyre slip angle that illustrates the twist in the tyre sidewall. As The side wall twist is needed to accommodate the difference between the direction of travel of the tyre contact patch and the direction of travel of the road wheel. 

The road wheel is forced outwards from the turn to form the tyre slip angle, as discussed earlier.

This tyre is turning right. 

The contact stays aligned with the instantaneous direction of travel, as cornering force and slip angle build. The twist happens in response to the tyre slip angle. The twisting force in the sidewall can be felt through the steering and will have an influence on the steering torque - called the aligning torque. . 


Starting from the straight ahead, and no tyre slip angles, as you turn the steering wheel to initiate cornering, tyre slip angles start building immediately, then build quickly, subject to your speed of turning the steering wheel.

The diagram above shows Cornering Force (lbs-force), or grip level on the Y axis versus the Tyre Slip Angle (degrees) on the X axis.

In this example, grip builds initially in a fairly linear fashion.  Around 4 degrees the rate of increase reduces, peaking at around 6 degrees of tyre slip angle, and then falls away. 

Note also that vertical load on the tyre increases the grip potential.  If we doubled the vertical load from 900 to 1800 lbs, for sure, we’d increase the grip a lot, but not quite double it. The "tyre (vertical) load sensitivity" is the key concept behind "roll stiffness" distribution, which is our main tool for adjusting the "steady state" balance of the car. 

The situation shown here, where grip level is fairly constant between 5 and 8 degrees, is typical. The shape of the curve varies with tyre vertical load as shown. With maximum weight transfer mid corner, the outside tyre delivers most of the cornering force, but inside tyre grip is still important in achieving best overall grip at that axle.

Maximum grip for this tyre is generated at around a slip angle of 6 degrees.  Tyres where maximum grip is achieved around 3 or 4 degrees will be peakier at the top of the graph.  Such tyres, making maximum grip over a smaller range of slip angle, can be considered a “less forgiving” tyre. 

Note from the Author:
I have revised this article on the 23/11/2021. The concept of the tyre carcass twisting in response to the lateral force and slip angle building at the tyre contact patch is something I had not addressed in the earlier version of this article.