Thursday, 22 January 2015

Suspension Geometry - Introduction

(Image source: Balance Motorsport)

What I have seen is a lot of people buying a drift chassis and running it day in day out which is great fun, but they only ever change the wheels or body shells. What about everything that's going on behind the wheels and under the shell? There are plenty of components and moving parts under any body shell but this post will about suspension geometry.

What is suspension geometry?

Before we answer that question, we need to identify what suspension is and what is does. Suspension is a selection of different components all with different purposes such as arms, shock absorbers, roll bars etc. What it does is give the chassis it's handling characteristics as to how well the tyres are kept on the ground and how well it drives over humps and dips and around corners.

Suspension geometry then, is the collaboration of all these components working together and are set to specific angles and settings to create a well balanced chassis. Let's talk about some of the basic angles...


(Image source: FT86 Club)

The most commonly known angle is camber. The camber angle of either the front or rear wheels is viewed from the front or rear of the chassis and is seen as the tyre's lean. The top of the tyre leaning in towards the chassis is called negative camber and the top of the wheel lean out is positive camber.

(Image source: Gomog)

Camber is measured by angles and it is the difference between true vertical and the tyre's center line. As a general rule, more camber will give you less of a contact patch on the tyre and therefore give you less grip. The closer the camber angle is to true vertical, the more grip you'll have as the tyre is stood more upright. Most drifters have their camber set as slightly negative.

I should also mention that tyre choice and surface will make a difference; plastic tyres on concrete will wear down and eventually give you 0° or neutral camber. Plastic carpet tyres won't wear so camber angles will stay as what you set them to.


(Image source: Town Fair Tire)

Caster is another angle measured relative to true vertical but this time, it's viewed from the side of the chassis. It's not measured by tyre lean; it is measured at the pivot points on the wheel hub (or C hub) itself know as the kingpin or swivel axis and the angle created.

Although some chassis' come with adjustable caster on the rear, castor angle is mainly adjusted or changed on the front wheels. This is because the caster angle affects the steering; high caster angle will give better steering response and quicker steering but at the cost of stability. Low caster angle is the opposite; more stability but at the cost of quick and responsive steering.

If your chassis has option parts to change the caster, they will usually be set to be positive caster, this is where the the swivel axis leans towards the rear of the chassis as viewed from the side, negative caster is has the axis leaning towards the front and axis at 90° will be neutral caster.


(Image source: Quick Meme)

Toe is one of the most commonly spoken about angles. When is comes to real cars, if the car pulls to one side, people will usually say that the tracking is out meaning the toe is not correct. Toe is easily explained; stand straight and look down at your feet. If your toes are pointing in, you have toe in. If they are pointing out, you have toe out. It's very much the same on your chassis or even your real car!

(Image source: Lancer Tuners)

As opposed to the previous angles, toe is measured from above the chassis and not beside it. Front of the wheels pointing in is toe in (or positive toe) and front of the wheels pointing out is toe out (or negative toe) and is also measured in angles.

The effects of toe can vary depending on which axle we are talking about. Take a look at this table:

Front wheels
Rear wheels
Toe in
- Improves stability in a straight line
- More stability in a straight line
Toe out
- Reduces under steer when turning in
- More responsive steering
- Can be used to increase sideways, usually has negative effects

Most RC drifters (and even real drifters) will run close to 0° front and rear with a little toe out (0° up to -2°) on the front and a little toe in on the rear (0° to +2°). This will give the turn in and response up front with better sideways at the rear without it fighting all the time.


So there you have it; food for thought. Next time you're out drifting and "the car feels funny", think about what angles are present on your chassis and what you can change or adjust to make it handle better. When it comes to making changes, always remember the golden rule:

Only ever change one thing at a time

By changing multiple angles, you may end up having the chassis "fighting" itself making it completely worse and not know what caused it. Or the other side of that is that the chassis handles better but you're unsure what change made it better. If you want to adjust the camber, do so only on the front or only on the rear. Make a small adjustment and run it for a few laps and try to feel the difference. If it's better, make a note and leave it. If' it's worse, put it back to where it was and try something else. Do this with any adjustment and you'll find yourself making the correct tweaks in the minimal amounts to get a better handling chassis.

If you're happy with what you've learnt here, try the next step...

And as always, make sure you're having fun while you're doing it. This is supposed to be a FUN hobby!