National Motorsport Academy

Gaining Lap Time: Chassis Alignment & Suspension Geometry

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Here are some ways that you and your race engineer can gain lap time! Starting with Chassis Alignment and Suspension Geometry

For my next few blogs I am going to take a look at some of the dark arts that gain lap time. This is exactly the type of thing that we work towards in the core modules of our motorsport degree courses. Whether you are a Race Engineer, Weekend Warrior, part-time tinkerer – the holy grail and most satisfying part of working on a race car comes when those lap times drop. So, let’s get cracking!

The Bet

“If it was that easy everyone would be doing it” is what my editor said when I proposed these subjects. So the challenge was set, the bets agreed. We bet big here at the NMA! And I am going to win! So that’ll be an upgrade to 24 chicken nuggets at the ‘Golden Arches’ for me 😊

Gaining lap time is not just about turning up and going faster than you did last time. If you can do that then well done you! But for mere mortals, you will need a plan, some processes and some solid methodical thinking and working.

I have broadly based these pieces on one that was written by the fantastic crew at Demon Tweeks, who, as we all know are experts in the products that we need and no mean racers themselves. Their new catalogue will be out and ready to pick up at the Autosport show in January as always.

Chassis Alignment and Suspension Geometry

Corner weights for chassis alignment

It can be easy to assume that it is possible to just start the engine, head out onto the track and expect the car to handle just as you would like it to. However, there is nearly always some “hidden lap time” to be found in optimising the chassis geometry. This is especially true if the race car you are in started life as a road vehicle.

The first place to start is with the corner weights, in other words, ensure that the car is sitting properly with the weight correctly distributed on each corner as well as front to rear. By having a balanced car you will have way less instability under braking or on cornering – this creates confidence and confidence creates gains in lap time.

Corner Weights

Getting the correct weight distribution on your car can be achieved via the use of a set of corner weight scales. This allows you to accurately see how much of the cars weight is situated over each corner of the car. You may find that you have uneven weight distribution between the left and right sides of the car.

Just a quick tip, make sure that you do the corner weights with the anti-roll bars disconnected as they can seriously impact the readings!

 

Camber, Caster & Toe

The other way for Race Engineers to ensure that they are getting the most out of the chassis is to adjust the suspension geometry in terms of camber, caster and toe. These parameters are all about how and how much of the tyre tread surface is touching or interacting with the track surface. To read an in-depth explanation of these terms, hit this link.

  

 

 

 

 

 

To start off with camber, this is the angle of the tyre that is measured vertically. Camber is used when setting up a car to counteract the forces encountered when cornering and allow more of the tread surface of the tyre to be in contact with the track.

With perfectly vertical being measured as zero, a tyre which leans inwards at the top is measured as negative camber, while the opposite, where the top of the tyre leans outwards, is measured as positive camber.

Most race cars will be set up to run with negative camber, as this allows the outside tyre, to where the weight is shifted on turning, to achieve a larger contact patch due to the cornering forces. The end result of this being improved grip through the corner.

Although adding negative camber increases the grip through corners, it is worth bearing in mind that it will have a side-effect. In this case, a car with a large degree of negative camber will have a smaller contact patch when driving in a straight line. While this will lessen the rolling resistance of the tyre, it will also mean that braking stability and performance will be reduced and it will be harder to get the power down. Adding camber will also increase the wear on the inside edge of the tyre as well as adding additional heat through greater friction.

 

The other major change that can improve the performance of the car is by adjusting the toe. This is a measurement taken as if looking directly down on top of the tyre. If the tyre is perfectly parallel, then there is zero toe on the car. If the leading edge of the tyre is pointing towards the middle of the car, this is known as toe-in, while the opposite is known as toe-out.

Typically you would add toe-out on the front axle to compensate for an effect called “camber thrust”, which is where a free rolling tyre on an angle will follow a curve rather than a straight line. Adding toe-out will adjust the slip angle to be more natural and combat this tendency.

Toe-in is more commonly used on the rear of the car as it creates understeer, which is particularly useful when trying to tame a car that suffers from excess oversteer on corner exit.

As with camber, the drawbacks are increased wear and heat, but adding toe will also result in more drag in a straight line as the tyre is being dragged across the track surface.

You will notice that although I mentioned caster as one of the three parameters, I have not dealt with it. This is because caster is normally something that is pretty much fixed whilst you are at the track. Adjustment is not easy and not having a clear reason to do so can introduce some really unpleasant side effects if you do not know what you are doing – ask a Jeep owner about the death wiggle if they have modified them for big time off-roading!

What would you like to see us cover?

In the New Year we will look at a couple of other lap time gainers but in the meantime, if there are any specific topics that you’d like to see us cover in this blog series, just get in touch or comment on Facebook post!

To Race Engineers, Motorsport Marshals, Support Staff, Drivers and Students in this crazy industry – have a relaxing off-season because it all starts again in the new year!

 

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