(This video was shot on the weekend of the Singapore GP. Examples of driver confidence refer to Sebastian Vettel's qualifying performance at Singapore and Cameron Waters first up win in V8 Supercars at Sandown.)
You don’t get too far in racing before you realize, the results and satisfaction you get depends to a large degree on your suspension set-up. It’s no fun fighting an ill handling car. Sometimes it can sap your confidence too.
Maybe you’ve been making progress, but now you’ve plateaued out. There’s no better kick start than sorting your suspension set-up. With more grip and better balance, it'll be just what you need to get you moving forward again.
Maybe set-up has always been on your radar, but there is so little information out there. Where do you start?
First up, you should always have your own input into what’s done to your car, even if somebody else does all the work. You can master the basic principles involved, and guide the process. If you’re mostly responsible yourself, then it’s the same deal. Your knowledge about set-up will guide you.
The idea is to look for best improvement in lap time for the work you do on the car. Put time and resources into those areas that offer greatest improvement.
One of my friends in racing, Radek Kolbabek, is an expert in race car suspension tuning, using the Dynatune-XL spreadsheet tools. He reckons, the key to fast lap times is a high degree of driver confidence.
It’s really hard to argue with that.
Some of our clients have used their new suspension set-up to great effect, improving seconds per lap.
As a rule, they feel the difference, and go faster, straight off. Particularly in the faster corners, where they had previously felt some instability. The sort of thing they’ll say is “The grip was incredible. I felt it particularly at turn 6 (or whatever)".
What we're talking about here, is the extra stability that enables the driver to push harder. It’s in the corner entry and corner exit where the greatest gains are made.
All of this speaks hugely of driver confidence. The car feels planted.
It’s not only a mental thing.
It’s the relationship between the driver, the car and the track. Grip and balance together, helping the driver create the extra speed.
So, if that’s our aim, and we want our car to deliver for us, what are our priorities for race car handling development?
Race car handling is not that hard to understand. It’s possible to build a conceptual view about how things work, a “mindset” that guides you.
But, there’s so much misinformation out there, seriously influencing what we learn, and negatively impacting on our ability to make the best decisions. So, we need to cut through all of that. We need to know when the info presented to us, is not right or not useful.
We’ll show you a very basic understanding about how handling works, using simple tools like our Weight Transfer Worksheet™ (WTW). What are the priorities, where your time and effort can deliver the greatest gains?
Deciding on spring and anti-roll bar stiffness (spring rate) is your number one priority to get more grip at the tyres and better balance for understeer/oversteer.
In many circumstances, spring and anti-roll bar rate selection is based on the experience of those making the decision, mostly without any theoretical basis. So, it most likely ends up being a bit of a guess.
In the aftermarket, anti-roll bars and springs are offered separately. If the balance works out under these circumstances, it's a fluke. You can see what balance you've got before you buy, with the Weight Transfer Worksheet™.
When you check out some of the categories of racing with spring rates fixed by the rules, you see the problem. One category, recently revised, has a spring option that is way too stiff. Another has a set up that's too soft, and on standard anti-roll bars, giving away about a second a lap. Another with decades long history in Australia, has rear springs softer than standard and no rear anti-roll bar. Mid corner, the cars have massive roll at the rear.
Sorting out the baseline set-up is at the centre of what we do at Racing Car Technology.
We choose springs and anti-roll bars in our Weight Transfer Worksheet™, optimizing for the type of racing, or performance driving the car will be used for.
Next, we do our baseline set-up in the workshop. Then we can go to the track, knowing we have a good starting point for grip and balance.
If you were originally running in the midfield, and your car was a long way from a good set-up, then the gains can be seconds per lap.
If you have a race winning car, chances are your set-up won’t be that far off. Gains are more likely less than a second per lap. But gains of even a few tenths of second per lap can be huge when you are already on lap record pace. It may be enough to keep that edge you have on your competitors.
It’s all about getting the suspension build right in the workshop.
A good race car set-up will have sufficient bump and rebound travel, and smooth operating suspension (reduce friction and binding).
The procedure for ensuring proper suspension travel is the same for all types of suspension. However, coilovers with adjust-ability makes it easier to achieve the bump and rebound travel you want.
A proper race car suspension build is quite a lot more than just removing and replacing the parts.
We need an understanding about set-up that helps us make sense out of all the suspension tuning options available to us.
Let’s look at three of the basic areas of performance improvement…
Aero, Less Weight and Lower Centre of Gravity…..
What could be more important in the “physics of racing”?
1. Aero downforce for more grip.
2. Less weight for faster acceleration, braking and cornering.
3. Lower centre of gravity for less weight transfer and therefore, more cornering grip.
Of all the improvements we can make to the cornering performance of the race car, aerodynamics is a standout. If you have aero freedoms in your class of racing, then this is clearly where some serious gains can be made.
The leading cars in World Time Attack, give away 20 to 30 kph in top speed on the main straight, yet post unbelievable lap times, with the extra grip available from the downforce. So, if you’re allowed to fit a front splitter and a rear wing in your class of racing, you should most certainly do that, and optimize as much as possible.
But in most amateur racing, if you have no aero, or if everybody has a similar limited aero package, then you probably won’t give it much thought. Best to recognize though, just how much of a big deal downforce is.
Minimizing weight should become an automatic part of our thinking in race car development.
Where we can take out weight easily, without affecting strength, it’s a no-brainer. Mostly, we'll be looking for incremental gains that are harder to achieve.
We need to balance the benefit of less weight against the need to improve or retain lateral and torsional stiffness.
Lateral stiffness is very important for generating cornering grip. For example, fitting a strut brace between the front strut towers can improve response, where the standard car has been weak in that area.
Torsional stiffness becomes an issue when you have a “roll stiff” race car – stiff springs and anti-roll bars. If the chassis and suspension is not stiff enough, it will dissipate the difference in the “roll stiffness distribution” between the front and rear of the car. The anti-roll bars will no longer be an effective set-up tool in balancing the car for understeer/oversteer.
Force, Mass and Acceleration
We know there is an exact relationship between Force, Mass and Acceleration.
Net Force on the car = Mass x Acceleration
If we reduce weight (or mass), there is less mass to be accelerated.
For a given mass, the net force gives rise to acceleration in a particular direction. So, for any given grip level at the tyres, we can accelerate and brake faster. And we can corner faster.
The lighter car can corner faster?
Yes, that’s right.
Visualise the car at constant speed in a constant radius corner. This is so called “steady state cornering”.
For steady state cornering, the forces of drag (or braking) and forward drive (or accelerating) cancel each other out in the diagram. So, the “lateral force of cornering” is the net force acting on the car.
The concept of steady state cornering is important in our thinking about set-up. For example, we calculate steady state weight transfers when we determine the balance of the car for understeer/oversteer (using the Weight Transfer Worksheet™).
The cornering force gives rise to the lateral acceleration the driver feels inside the car.
Force of Cornering = Mass x Lateral Acceleration
The force of cornering is equivalent to, and limited by, the grip available at the tyres. So, for any given level of grip at the tyres, the lighter weight car can corner faster, same as the lighter car can accelerate faster and brake better in a straight line.
Note on the Lateral G as per the data logger: We think of the lateral G as being our de-facto measurement of cornering force. For our fixed weight race car, higher lateral G does represent more grip (or cornering force). But remember, a lighter car can corner faster ie more lateral acceleration, for the same maximum cornering force. Vice versa for a heavier car.
In a lateral G test on the skid pad performed by Sports Compact Magazine, 14 race cars (including open wheelers) faced off in what they called the “g Masters”. A superkart flogged the lot of them (no suspension, bouncing around on the asphalt surface), because of substantially less weight than any other vehicle.
How big a deal is centre of gravity height? Fortunately, we can do some easy calculations to get a handle on it.
In this photo Craig has launched the car off the kerb. He can control the car (open up the steering if necessary), to ensure the car will not approach roll over.
With four wheels on the ground, the rollover tendency still happens. In cornering, weight is transferred from inside wheels to outside wheels.
Commercial vehicles, like trucks and buses, have a high centre of gravity, In some road situations, especially emergency maneuvers, they can roll over.
For cars generally, we have a lower centre of gravity height such that tyre grip will max out before roll over occurs. In steady state cornering, there will be a maximum amount of weight transfer associated with maximum grip.
Looking at the picture of Craig Lowndes, it's clear - if we have lower centre of gravity, or wider track, we’ll transfer less weight, and therefore we’ll corner faster before grip is maxed out.
The equation for total weight transfer for steady state 1G cornering, (1G lateral acceleration) is:
Total Weight Transfer = Weight x CofG Height / Track
Assuming a 1350Kg car with 530mm CofG height and 1500 track, the weight transfer works out to be 477Kg.
If we lower the CofG Height by 10mm to 520mm and then the weight transferred at 1G steady state cornering is reduced to 468Kg.
This indicates if we lower the car by 10mm, it would be able to corner faster - ie it would be cornering harder by the time it got to transferring the original 477Kg. The improvement in lateral acceleration is around 2%. The new lateral acceleration is 1.02G.
So lowering the car 10mm offers a useful improvement in performance, indicating we should run our race car as low as possible.
If we calculate what the equivalent track increase would need to be, it works out around 30mm. For most racing we can’t increase track that much. So we'll get less benefit chasing track width than we'll get from lower CofG.
So, lowering the car as much as possible is a big deal. If there is no rule restricting how low we can go, then the limitations are:
• The suspension must bottom out on the bump stops before the chassis contacts the ground.
• We must retain sufficient bump travel.
• The roll centre height will go lower, especially with McPherson strut suspension. We should recover roll centre height as much as possible. Methods of doing this: Use extra length (tall) top ball joints for double A arm suspensions. Use RC height adjusters for strut suspensions.