SUSPENSION SECRETS – HOW TO TUNE TOE SETTINGS
Matthew Cowley from Suspension Secrets is back with his second guest article here on the BRSCC website, as this time he takes us through a guide on how to tune the toe settings on your car which, as it turns out, are rather vital when it comes to affecting the car’s handling, response and even straight-line speed! Pay attention and take notes…
In our previous article, we took a look at how best to prepare for a test day and what to measure on the day to provide the best feedback possible in order to make the best changes possible to your set up in order to improve performance. Following on from that article we will be taking a look at adjusting and tuning toe angle and how different settings affect handling.
What is toe?
Toe angle is the angle of the wheels when viewed from directly above. If the front of the wheel is pointing in towards the centre line of the car then it is called toe in (positive toe). If the front of the wheel points out towards the outside of the car, then this is called toe out (negative toe). Toe angle is effectively a static setting that steers the wheel in a chosen direction. Toe is most often set evenly side to side; for example, both rear wheels will share the same toe setting as each other and both front wheels will have matching settings. The front and back axle often have different settings to each other though.
How to measure toe
Toe angle can be measured in a few ways. One of the best ways that is highly accurate and provides a reading independently for each wheel and can be performed in your garage or at the circuit is by using a string and line kit. A string and line kit can be set up on the car and squared off with the centre line of the axles. A string is then passed down each side with the kit set properly and a measurement can then be taken from the front and back edges of the rim to the string. The difference in the readings is your toe setting. For example, if the back edge of the rim to the string reads at 67mm and the front edge of the rim to the string reads at 65mm then that wheel has 2mm toe out; as 65mm-67mm=-2mm.
Another technique is to use toe plates. These are very quick and easy to use and are a great tool to carry trackside for fast adjustments between sessions. They do however rely upon you knowing your settings exactly beforehand. This is because the plates tell you the overall difference between the two wheels but they do not tell you what the individual toe is at each wheel. If you already know that your wheels are set to 1mm of toe out each then the plates will read at 2mm toe out overall. Therefore, with even adjustment side to side and the overall reading now saying 3mm toe out overall you know that you now have 1.5mm toe out per wheel. If you do not know your settings then it is quite easy to adjust toe with the plates and set different wheels at different settings which has very negative effects on handling.
The final main method of measuring toe is using a laser alignment system. These vary from hunter systems that are often fixed and calibrated to a situated 4 post ramp down to easy laser trackers that work in a similar way to toe plates but instead of using tape measures, a laser is used against a gauge placed against opposing wheels. The laser displays the overall toe angle of the two wheels. The main issue with laser systems is that if they are not calibrated accurately then they will read incorrect toe settings and there is no simple way of double-checking the settings.
How to adjust toe
Toe adjustment on the front wheels is a straight forward process. The steering arm (or tie rod) can be turned making it shorter or longer in the tie rod end, in turn altering the toe angle of the front wheel.
At the rear, toe adjustment varies for different styles of suspension systems. For many multi-link suspension systems using a rear subframe and suspension arms to mount the hub, an offset adjustment bolt will be mounted to either the subframe or hub. This can be rotated to adjust toe within a set range of adjustment. For trailing arm systems, the trailing arm mounting plate can either contain slots or have them inserted to allow the beam to be adjusted inboard or outboard to set toe. For fixed beam rear axles, adjustment is more difficult. Adjustable shims can be purchased to be inserted behind the bearing which will set toe in fixed increments.
Alternatively, aftermarket adjustable suspension arms can be used that will offer adjustment in the length of the toe arm which will provide a wide range of adjustment and allow fine increments of toe change to be possible at the wheel.
Toe has a large effect over the handling and response of a chassis and is a relatively easy area of geometry to adjust.
Toe settings and handling are a very subjective area that relies a lot upon a person’s driving style and personal preference for how they like the car to handle. We will, therefore, use some general advice below on how to adjust toe.
Toe out on the front wheels is a common setting as it will help to improve turn-in response and help to reduce understeer. For technical circuits, toe out is a very popular choice due to the lower speeds and the frequent changes in direction resulting in the need for a positive turn in. However, toe out will also create instability in the steering at high speed which can be unsettling for a driver as the steering wheel tries to change direction without driver input. For this reason, toe in is a setting commonly used on the front wheel s for high-speed circuits such as Spa or Silverstone. This setting will make the car more prone to understeer though but the increase in stability ultimately provides a higher top speed due to driver confidence allowing them to push harder in the faster sections.
Toe out on the rear wheels is a setting seen often on FWD platforms. This is due to FWD cars often being plagued by understeer, the toe out at the rear wheels helps to rotate the rear of the car into the corner, steering the front of the car towards the apex and reducing understeer. Too much toe out will cause the car to begin oversteering and will become more difficult to drive. Toe out at the rear, similar to the front, will cause instability at high speed. This must be taken into account when using this setting as it makes the car more prone to oversteer through long fast sections which can result in large crashes as the rear snaps around.
Toe in is a much more common setting on the rear of cars, especially on RWD platforms, as it reduces their tendency to oversteer and provides the car with high-speed stability making the car handle in a much more stable manner allowing the driver to push harder and faster.
Toe in or out on the front and rear wheels will produce a constant slip angle in the tyre which will generate heat within the carcass. This is particularly helpful for sprint races as it causes the tyre to heat up much faster, helping the tyre to operate at maximum grip at an earlier stage in the race. However, this can also cause the tyre to degrade and wear faster which means that toe should be carefully managed for endurance racing as tyre life is a very important factor as well as all-out grip and tyre performance. Too much toe can cause the tyre to overheat and begin delaminating, it can also tear the tyre compound and cause the tread to begin splitting or graining.
For more information on suspension set up, tuning and geometry head over to our website linked below for free suspension information.