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This section covers toe on a racing car. It describes and explains how to measure, adjust and alter toe to suit the driver and the style of circuit. The section covering the different effects of toe is separated into 3 categories; front wheel drive, rear wheel drive and four wheel drive. A lot of the information in these sections is similar and is designed for the reader to read the section applicable to their type of car.
How to Measure
There are a few accurate ways to measure toe. One way, still used within Formula 1 and BTCC is a string and line kit. It may be old technology but it is highly accurate and can be done at a race track quite easily. Two poles are mounted at either end of the race car perpendicular to the wheels and the height of the centre point of the wheels.
Open wheel cars usually have holes drilled in the chassis to slot these bars through to save time and improve accuracy, kits such as the BG Racing string and line kit can be rigged up on a car at location and used with great accuracy also.
Once mounted a tape measure or steel rule can be used to measure the distance from the string to the front and back of each wheel. This will give the toe (in or out) in millimetres.
Another technique used at a racing track, especially within grass roots motorsport is using a toe rig. This is an easier to use technique to measure overall toe. A square frame is sat either side of the front or rear wheels across the width of the car. Two bolts can then be screwed in to touch the front of each wheel. The rig is then slid towards the back of the wheel. The bolts are then screwed in or out to touch the rim. The difference between the two bolt positions, front and rear, give a reading of the amount of toe in or out in millimetres. This technique does not give individual wheel readings but the overall across the front or rear wheels so is a less accurate technique.
If you are not at a race track then you can measure the toe of our vehicle with a 4 wheel alignment kit. This is often at a garage with a ramp and the laser equipment to carry out the measurement. The equipment is mounted to each wheel and then lasers shine onto the plates to give a reading of the amount of toe that each wheel has. The toe is often measured in degrees and minutes using this equipment.
One very crude way to see if a car is running toe is to visually check the tyre for tearing marks along the tread. This will tell you if your car is running any toe but will not differentiate between toe in or toe out.
For further information on measuring and adjusting toe check out our YouTube Video below:
How to Adjust
Depending on your application, there are different ways of adjusting toe, on anything from a standard road car to a Formula 1 car.
On a road car there are adjustable bolts that hold the toe arm to the rear subframe. These bolts are fitted with eccentric washers. If you rotate these bolts with a spanner, your toe will adjust in and out. However, you are limited in your adjustments by the range that the washer provides.
An upgrade that can be made to many road cars is an adjustable arm. This is where the arm that controls your toe on the rear hub can be replaced by an arm with a screw thread or shim pack to allow adjustment. These arms offer a lot more range in adjustment as they are built for purpose and are essential if you are competing within motorsport or want tuning freedom with your car.
Motorsport cars that are built for purpose, particularly open wheel racing cars sometimes have adjustable hubs where the hub can be moved away from the arms mounting point using shims. This technique does not alter the geometry of the suspension system such as bump steer or camber gain making it a near perfect method of adjustment.
The way to adjust the toe on the front wheels is mostly the same on any car, be it standard or a highly competitive, high budget racing car. This is by adjusting the tie rod end on a steering arm. This is the component that attaches to both the front hub and the steering rack. He body of the tie rod end can be turned on the thread to adjust the toe on the front wheels. This adjustment has a very large range even on a standard road car.
Effects of Tuning
The effects of running different types of toe on the front and rear wheels are different depending on whether the car is front, rear or four wheel drive. Therefore the effects have been broken into 3 categories, one for each, below. Within that category is a further breakdown showing the effects of a toe change on the front or rear wheels for that type of car.
Front Wheel Drive
Front Wheels
Toe Out
Running toe out on the front wheels of a front wheel drive car will increase the grip within the front tyres due to the increased slip angle in the tyre. This will increase the acceleration of the car due to the increased grip from the driven tyres. The tyre will also heat up faster due to the slip angle, meaning that the tyre will get to its most grippy point faster than if no toe was installed. However, running toe out will decrease the life of the tyre due to the increased stress on the rubber.
The dynamic effects of toe out will give the car faster steering, meaning that the car turns in faster with less steering input from the driver, which is ideal for a tight, winding course with multiple direction changes, similar to Monaco GP. This increased response means that the high speed stability of the car is reduced and can feel twitchy in long fast corners.
Toe In
Running toe in on the front wheels of a front wheel drive car will again increase the grip within the front tyres due to the increased slip angle in the tyre. This increases the acceleration of the car due to the increased grip in the driven tyres. The tyre heats up faster due to the slip angle, which means the tyre gets to its most grippy point faster than if no toe was installed. However, running toe in will decrease the life of the tyre due to the increased stress on the rubber.
The dynamic effect of toe in reduces the responsiveness of the steering. This means that the car requires a larger steering input from the driver for the car to change direction. This makes the car more stable at high speeds and makes the car feel planted through long fast corners. This set up is perfect for new drivers within motorsport or for drivers who do not have fast reaction times. This set up is perfect for race circuits similar to Silverstone.
Zero Toe
Running zero toe on the front wheels will increase the life of the tyre. Therefore, this set up is commonly seen within road going cars where tyre life is important. That said, tyre life can be of great importance within long races such as endurance racing, so running a set up close to zero toe can be beneficial as your tyres last longer on track. Furthermore, the top speed of the car is increased due to having less drag to overcome the power of the car.
The dynamic effect of running zero toe on the front wheels is that the car is no less or more stable in different corners and will respond evenly in short or fast corners and the behaviour of the car will be more dependent on other aspects of set up and geometry.
Rear Wheels
Toe Out
Running toe out on the rear wheels of a front wheel drive car will reduce the acceleration and the top speed of the car. This is because these wheels are not driven so are being pulled around the track. Therefore, any extra grip in the rear tyres translates into increased drag, therefore slowing the car down in a straight line. However, the slip angle does generate heat within the tyre faster, generating maximum grip faster, which is ideal for short races.
The dynamic effect of running toe out on the rear wheels effectively shortens the wheel base of the car. This happens due to the toe out, rotating the car on corner entry allowing the car to turn in faster and tighter. This effect feels similar to oversteer, without the loss of grip, and makes the car more nimble, ideal for tracks with multiple quick direction changes. However, this effect does make the car feel more unstable through high speed corners.
Toe In
Running toe in on the rear wheels of a front wheel drive car will also reduce the acceleration and the top speed of the car. This is the same as above due to these wheels not being driven so are being pulled around the track. Therefore, any extra grip in the rear tyres translates into increased drag, slowing the car down in a straight line. However, the slip angle does generate heat within the tyre faster, generating maximum grip faster, which is ideal for short races.
The dynamic effect of running toe in on the rear wheels lengthens the effective wheel base of the car. This is because the loaded rear wheel during cornering is already pointing in the direction of the corner. This means it works against the steering input and rotates the car more slowly. This increase in control makes the car more stable through long high speed corners. It is especially effective when used on a sort wheel base car like a Honda Civic.
Zero Toe
Running zero toe on the rear wheels of a front wheel drive car will increase the acceleration and the top speed of the car. This is because the tyre is rolling in its most efficient direction and will therefore generate minimum drag. This reduction in drag force can be used to propel the car forwards instead making it faster in a straight line. Furthermore, the tyre life will be increased due to the reduced stress. However, the tyre will take longer to heat up, so will not generate as much grip as early on in the race.
The dynamic effects of zero toe are that the car will feel neutral to control through tight and long fast corners meaning that the driver does not have to alter their driving style if there is a mixture of styles of corner on the track.
Rear Wheel Drive
Front Wheels
Toe Out
Running toe out on the front wheels of a rear wheel drive car will decrease the acceleration and top speed of the car in a straight line. This is due to the front wheels not being driven so any extra grip generated by toe will increase the drag on the system. The life of the tyre will also be reduced which is not ideal for endurance racing. However, the tyre will warm up faster getting to operating temperature sooner in the race.
The dynamic effects of toe out will increase the agility of the car, making it turn in faster and sharper with less steering input from the driver. This makes the car navigate through a tight; twisting course faster makes it feel nimble. Toe out also means that the car feels less stable at high speeds and though high speed corners due to the twitchy nature of the set up.
Toe In
Running toe in will also decrease the acceleration and top speed of the car in a straight line. This is due to the front wheels not being driven so any extra grip generated by toe will increase the drag on the system. The life of the tyre is also reduced due to the increased stresses on the rubber. However, the tyre will warm up faster getting to operating temperature sooner in the race.
The dynamic effect of toe in is that the car feels more stable at high speeds and during high speed cornering. This is due to the car requiring larger steering inputs from the driver to turn, giving the car a more planted feel. This does reduce the agility through tight, slow corners but the trade-off is especially worth it for new or unconfident drivers.
Zero Toe
Running zero toe will increase the straight line acceleration and top speed of the car. It will also prolong the life of the tyres out on track or on the road. The disadvantage to this set up means that the tyre takes longer to warm up to operating temperature to generate maximum grip.
Running zero toe will make the car feel relatively stable in a straight line at high speeds. It will also make the car feel more neutral when taking long sweeping corners and slower tight corners. It leaves the feeling of the steering and the responsiveness of the steering in the hands of the Ackermann geometry as well, which can be a good thing for a race car where the Ackermann geometry has been designed for purpose.
Rear Wheels
Toe Out
Toe out on the rear wheels of a rear wheel drive car will improve the acceleration of the car but decreases the top speed due to the increased grip and drag force. It will also reduce the life of the tyre due to the increased slip angle. The acceleration is increased as there is more grip available from the tyre due to the toe putting a greater slip angle into the rubber. This allows more power to be transferred to the ground without spinning the wheels, allowing the car to accelerate faster. The tyre will also heat up faster getting to its most effective level of grip faster.
Toe out on the rear wheels will make the car more nimble and faster through tight sections, making it feel as though it has a shorter wheel base. This effectively makes the car have a higher tendency to oversteer so is a set up used by smooth drivers who can be light on the throttle. Toe out will also make the car feel less stable through high speed corners due to the feeling of oversteer occurring at the rear wheels.
Toe In
Toe in on the rear wheels improves the acceleration of the car due to the increased grip levels allowing more power to be put through the tyre without spinning the wheels. However, the top speed of the car is reduced due to the increased drag from the tyre. The tyre heats up faster when running toe in as the rubber is stressed, generating heat, getting the tyre to operating temperature much sooner in the race; this in turn reduces the lifetime of the tyre.
Having toe in at the rear wheels will increase the high speed stability of the car round long fast corners and makes the car feel as though it has a longer wheel base. The increase in high speed stability is comforting for new drivers who are not used to a nimble car that is sensitive to steering inputs. Toe in does mean that more steering effort is required from the driver through tight corners which can slow the car down through tight sections. Toe in on the rear wheels can also give the car a tendency to understeer due to fighting the want to oversteer and increasing rear end grip which can overcome the grip of the front wheels.
Zero Toe
Zero toe on the rear wheels will reduce the acceleration capabilities of the car but will increase the top speed of the car due to the tyre rolling in its most efficient direction. This also means that the life time of the tyre is increased but it takes longer to heat up to its operating temperature.
Zero toe makes the car more stable in a straight line at high speed and stops the rear end of the car from shifting around. It also gives the car a similar feel through fast and slow corners and leaves the dynamic feeling of the car down to other aspects of set up and geometry.
Four Wheel Drive
Front Wheels
Toe Out
Running toe out on the front wheels of a four wheel drive vehicle will increase the grip and the acceleration of the car but will reduce the top speed. This is due to the toe out generating a higher slip angle in the rubber, in turn generating more grip. This increase in grip allows more power to be put through the rubber by the engine without spinning the wheels. However, the increase in grip force reduces the top speed of the car due to increased rolling resistance. The tyre will heat up faster, getting to operating temperature sooner but reducing the life of the tyre.
The dynamic effects of running toe out on the front wheels will make the car feel more nimble and will be more sensitive to steering input from the driver making the car feel twitchy and slightly unstable at high speeds. However, at low speeds through tight corners, the car will change direction faster and smoother making the car faster.
Toe in
Running toe in will also increase the grip of the front tyre by the same amount as toe out in a straight line. Likewise the top speed of the car will be reduced for the same reasons as mentioned above. The tyre will also heat up to operating temperature sooner due to the extra work being done by the tyre in a straight line which is ideal for short races. This will in turn reduce the life time of the tyre on the vehicle which is why road cars run as close to zero toe as possible.
Dynamically, toe in will make the car feel more stable at high speed and feel more settled through high speed corners. This is because the wheels require more input from the driver before they change direction. At high speeds this can make the car feel more planted and give the driver more confidence to go faster. However, the car is less nimble through low speed corners.
Zero Toe
Running zero toe at the front wheels can reduce acceleration due to the reduction in straight line grip in the tyre. However, due to the reduction in grip, the rolling resistance of the car is reduced, allowing the car to have a higher top speed. Furthermore, the life time of the tyre is increased as it is rolling in its most efficient direction. However, this does mean that the tyre takes longer to warm up by simply driving the car.
Having zero toe in the front wheels means that the responsiveness and feel of the steering is controlled more by the Ackermann geometry and the caster settings of the car which are sometimes designed around a zero toe setting to get the best grip from the tyre during cornering. Also, the high speed stability of the car is improved in a straight line as the wheels are not pointing in different directions to each other.
Rear Wheels
Toe Out
Having toe out on the rear wheels of a four wheel drive car will increase the acceleration and reduce the top speed of the car due to the increased slip angle of the tyre and therefore the increase in grip and drag available from the tyre. The increased slip angle will also heat the tyre up faster, getting the compound to operating temperature sooner in the race which can be highly beneficial in short races. This in turn reduces the life time of the tyre.
Running toe out on the rear wheels makes the car feel as though it has a shorter wheel base; making it more nimble through tight slow corners, having the ability to change direction much sooner. Toe out also gives the car a tendency to oversteer which some driver prefer to control as oppose to understeer when racing. Toe out makes the car feel slightly unstable at high speeds through long fast corners due to the feeling of oversteer and a more loose rear end.
Toe In
Running toe in on the rear wheels will increase the acceleration and reduce the top speed of the car due to the increased grip within the tyre. The increased grip generates more rolling resistance which is a force that engines power must overcome. Therefore, less of the engines power can be used to generate a top speed for the car. The extra grip will also heat the tyre up faster, getting the compound to operating temperature faster. However, this also reduces the life time of the tyre.
The dynamic effects of toe in at the rear wheels are that the effects of oversteer can be reduced and the high speed stability of the car can be improved. This works because the rear tyre that is put under load during cornering (the outside tyre) is already pointing in the direction of travel, therefore fighting the urge for the rear of the car to rotate. This makes the rear of the car feel as though it has a longer wheel base but also improves the stability through a long fast corner. However this does mean that the car feels less nimble and responsive which can be a negative factor through slower, twisting corners. The less snappy nature of this set up is ideal for new drivers or less confident drivers.
Zero Toe
Having zero toe in the rear wheels could reduce the acceleration potential of the car, allowing the rear wheels to spin more easily due to the reduced grip. However, these reductions in grip and therefore drag, increases the top speed of the car due to the tyre rolling efficiently. Furthermore, the life time of the tyre is increased as it does not have to work as hard. However, this means that the tyre does not heat up as fast on circuit.
Zero toe in the rear wheels also means that the straight line stability of the car is improved making the car feel more planted at high speeds. It also means that the car has a similar feel through slow and fast corners leaving the cornering behaviour of the car more to other aspects of geometry and set up.
