geometry, toe -

Geometry: Toe

Setting the geometry on your vehicle is one of those things that for some reason, most people seem to ignore. Is it that nobody understands it? Is it that nobody knows the powerful potential of a proper setup? The public domain is full of misinformation, and tuners don’t really want to tell you what each setting does and why. Its a broad topic, so it will be split over a few articles, starting with Toe.

In this article I will explain how the setting of toe affects the handling of the vehicle, which will equip you with some knowledge as to how to set the car up to your requirements, whether that be for the road or the track.

Toe is adjustable at the front on all vehicles, and on most will also be adjustable at the rear. Toe is the angle the wheel is pointing if you look at it from directly above (you can think of steering as essentially toe angle changing). Thats why when your toe (tracking) is out, your steering wheel will often not be straight when the vehicle is driving straight ahead. At the front this is adjustable via the steering arms/track rods (interchangeable term) which you can make longer or shorter to change the toe. At the rear it can be adjustable in a number of ways – some cars have track rods at the rear, some have cam based adjusters and some require shims. The Motorsport Essentials Civic Cup Car has a cam adjuster on the lower rear suspension arms.

So why would we want to change this setting? Obviously it has to be set correctly in order to make the car go in a straight line. So do we just set all four wheels exactly straight? Not exactly….

The general rule is that increasing toe (tending towards toe in, wheels pointing towards the centreline of the car) will generally stabilise the axle you are adjusting. Decreasing toe (tending to toe out, wheels pointing outwards from the vehicle centreline) will make the axle less stable and more responsive to direction change.

Adjusting the front axle toe is useful for 3 basic reasons – ensuring the steering wheel is straight when the vehicle is travelling straight ahead, increasing turn in performance and ensuring straight line stability. Increasing or decreasing toe from 0 degrees will increase tyre wear – this is pretty intuitive. Any toe setting other than 0 means the tyre is scrubbing down the road.

Rear toe is extremely useful also. It must be set correctly to ensure the car travels in a straight line. Rear toe however has a profound effect on cornering performance throughout the turn in, mid corner and exit phases, and stability under braking. It is generally a far more powerful tool to adjust the handling of the vehicle than front toe.

Bearing in mind what we know about toe, lets talk through a basic road car setup and then a race car setup. I’ll use our Civic Cup Car as an example.

On a road car you need a setup that is safe and predictable, minimises tyre wear, and is very stable in a straight line (motorway!). As you may have guessed we will therefore not have any settings that are too extreme, as excessive tyre wear would be unacceptable. For the setup to be safe and predictable we will want to induce some understeer at the limit, and we won’t want the car to be too responsive. If you take a look at the factory settings, you will find that they are set exactly to achieve this:

Front Total Toe:0mm

Rear Total Toe:+2mm

Zero toe at the front will give a stable vehicle with minimal tyre wear. Some toe in at the rear will increase the tendency to understeer at the limit, and make it extremely stable under braking. You can afford to have this toe at the rear because a front wheel drive car doesn’t wear its rear tyres much.

On a race car you are interested in one thing only – performance. When setting toe you will generally be looking to make the car more responsive and dial out some of the understeer, while achieving a balance the driver is happy with. Therefore it would be sensible to suggest that we will decrease toe at the front of the vehicle to aid turn in performance, and decrease toe at the rear to change the balance of the car to tend to oversteer. This is exactly true, but also totally depends on the car. There is no ‘one size fits all’ setup despite what garages with their magic fast road setups might tell you. A typical setup for me in the Civic Cup Car at a weekend might be:

Front Total Toe: -2mm (Toe Out)

Rear Total Toe: -1mm (Toe Out)

The front toe helps with turn in – it means that as soon as you turn the wheel, the car darts towards the apex faster and more aggressively than with the road setup. The fact that the wheel might jitter in your hands a little down the straights, and the car is a little less stable is not a problem. On the motorway that kind of behaviour would be a nightmare.

The rear toe is a compromise – Toe Out at the rear makes the car very keen to rotate. In a front wheel drive car this is generally a good thing, as the sooner the car has rotated and is facing out the bend, the sooner you can get on the power. A front wheel drive car that doesn’t like to rotate can be extremely frustrating to drive, and potentially very slow if it affects your ability to get on the power early enough.

Under braking however this toe out makes the car extremely snappy. As the weight transfers forward, the car can sometimes aggressively want to spin, which can be a problem in certain tricky braking zones or especially for inexperienced drivers. Its also definitely not behaviour you want on the road.

The second problem is in high speed corners – with toe out, even at full throttle (which in a front wheel drive car should produce understeer) you can occasionally experience some oversteer which can be fairly aggressive. This can be detrimental to laptime, as big sideways moments scrub speed, and also difficult to deal with in terms of confidence in high speed bends.

A great example of this was at Snetterton this year – the final corner complex is a very long fast right hander (Coram) followed by a slower left hander (Murrays) onto the pit straight. While I was generally able to cope with the snappy oversteer in Coram, the difficult curved braking zone and change of direction into Murrays was very challenging, and resulted in me falling off the track. Despite this, I didn’t want to change the setup – the toe out was making the car perform fantastically well in the technical infield section, and I was concerned stabilising the car would lose more time here than I would by simply taking it slightly steadier through Coram and the entry to Murrays.

You’ll be pleased to hear this is all on video here.

Overall it is important to remember that no toe setup will make the car handle great. It is really up to you to decide what you want from your car and I hope this article helps you to understand how altering your toe might help you get there. Don’t go too crazy with it on the road – aggressive track setups on the road make the car feel rubbish, wear your tyres and can be dangerous if you are inexperienced. On a track car though, prepare to transform your experience!

Next setup article will be on camber….

Any questions or want something explaining in an article please hit us up, like the Facebook Page and remember there is a great video on how a front wheel drive car can slip and slide about here!