Racers hate losing money buying the wrong stuff for their race car and then having to fork out more money for the right part.
A case in point is buying suspension springs. How do you know what spring rates to order?
Parts suppliers, shock absorber and suspension specialists, and car preparation shops are likely to make a the choice for you, unless you say what you want.
Yet, even with very experienced people making the decision, most racing car spring selection is little more than informed guess work. It doesn't need to be that way.
In racing, it's the stiffness of the spring
What we’re showing you in the video is a unique way of measuring suspension stiffness. We’ve called this simple test the Racing Car Technology Bounce Test™.
The recognized measure of suspension stiffness is the "suspension frequency". Or as I call it in the video, "spring frequency".
What we are after is the spring rates we need to achieve our desired suspension frequency.
For a new race car, an important early decision in the design process is the choice of front to rear weight distribution.
Equally, if we are racing an existing car it’s important to know what our weight distribution is, so we can make decisions about the suspension set-up of the car.
How do we measure weight distribution?
If we have the corner weights, we can determine the weight at the front and rear axles as a proportion of the total weight. E.g. We may have 53% of the total weight at the front axle, leaving 47% of the total weight at the rear axle.
How does weight distribution affect the balance of the car? What is the effect of more front weight? Or more rear weight?
To get answers to these questions, let’s look at the problem from the vehicle dynamics engineer’s perspective. They are trained in the application of a universal simple model of handling known as the “bicycle model”.
Here is a schematic diagram describing the main features...
The details of anti-roll bar operation are discussed in our blog article, “Anti-Roll Bars. A Good or a Bad Thing?”
As indicated in that article, there’s much more to anti-roll bars than simply reducing body roll.
In this blog I want to focus on two super important characteristics of anti-roll bars in suspension set-up for racing…Suspension Stiffness in Roll and How You Get More Grip With Stiffer Springs and ARBs.
Suspension Stiffness in Roll
The anti-roll bar adds to suspension stiffness in roll i.e. In cornering, both the spring and the anti-roll bar contribute to the suspension stiffness as seen at the tyre contact patch.
I’m going to quote a vehicle dynamics expert here, so you don’t think I am making this up:
“Typically, a bigger bar on the front improves the perception of nimbleness, (agility), as it makes the outer tire work harder in the first half a second or so (of initial turn-in).” Greg Locock – Engineering...
In racing, it’s often thought the tyre slip angle is an indication of the tyre losing cornering grip – that the slip angle is formed by the tyres “slipping” or “sliding” on the pavement.
The truth is, tyres build grip with increasing slip angles up to the point where grip starts to level off, as shown below in the slip angle vs grip diagram.
It's important to understand a little about how grip is created at the tyres.
A steering control input from the driver results in the forward momentum of the car being counteracted by frictional forces acting at the tyre contact patches, and so creating tyre slip angles at the contact patches as the car starts to turn and build cornering grip in the tyres.
Tyre slip angles are a property of the pneumatic tyre that creates the lateral force and allows the car to turn. (If we had steel treads, for example, there would be no slip angles, and insufficient friction available to create a...
On a show of hands, I don't think there'd be many hands up. Certainly not mine. We can always keep learning in this absorbing sport.
How much do we need to know about the physics of race car handling?
There are two sides to this:
So, Race Car Handling and Suspension Set-Up is a pretty thorny subject. Right?
I’m having a crack at it in my new E Book “7 Little- Known Hacks – Your Pathway to Race Car Handling Mastery”
I’m especially not making it hard to...
It’s no good making random adjustments to your race car set-up at the race track. You'll most likely get lost with the changes you make, and end up not making the car any faster.
Magazine articles, "cheat sheets", and generalized advice you get on set-up from internet web sites, are particularly unhelpful. No wonder the general impression most racers get is that handling, as it applies to set-up, must be very complicated.
Even someone highly experienced both as a driver and a set-up engineer cannot tell what you need straight off. They can't just jump in your race car, do some laps, and then say you need XYZ springs and anti-roll bars.
What you need is a baseline set-up. The set-up we know is close to optimum. Then in testing, you and/or your team, can decide what changes you’ll try.
At Racing Car Technology, the baseline is the set-up we can do in advance in the workshop, then go to the track knowing we are in the set-up...
Here's the full version of TRE's video of this tarmac rally car on their 7 Post shaker rig:
TRE Dynamics are technical partners with Ohlins DTC, Germany.
You can see in the video, the shaker rig forcing vibrations in the suspension. About half way through, they show you a "track replay". The actual suspension movements from the track are reproduced.
Best dynamic grip comes from minimizing the tyre load variation, minimizing disturbance, minimizing vibration at the tyre contact patch. (Note the difference in shaker rig testing for road cars. The required set-up will be a compromise between ride quality - least disturbance for the driver and passengers - and best grip - least disturbance at the tyre contact patch.)
To minimize disturbance at the tyre contact patch, you need the required "natural suspension frequency" or "suspension frequency", as we regularly call it.
The "natural suspension frequency" is the vibration of the suspension...
Race car handling is about optimizing the behavior of the vehicle in response to the driver inputs.
So, if we're going to truly understand vehicle dynamics, we have to look at it from both a vehicle setup and driver control perspective at the same time:
At the bottom of the diagram, the car is traveling slowly. The car can turn sharply, but there is no rotation of the vehicle about its own axis.
In the middle diagram, cornering at racing speeds, there is rotation as the driver turns in. Then, as the car takes a set in the mid corner, the rotation stops. The race car has adopted a nose-in attitude, as shown by the "vehicle slip angle", β.
In the top diagram, the rotation has not settled by the mid corner. The rotation keeps on going and the car has gone in to a spin, as indicated by the now much larger vehicle slip angle.
The interconnection between the vehicle dynamics and...
Weight Transfer Part 3: How Does the Driver Control the Race Car?
This is the final part in our “Weight Transfer” series. See Part 1 and 2 home page /blog
Summarizing what we discussed in Parts 1 & 2:
Nowadays, “weight transfer” thinking is commonly used to describe what the racing driver is doing. The driver is said to manage or control the weight transfer. The “rate of weight transfer” is considered important. And as discussed in Weight Transfer Part 2, the driving coach Rob Wilson talks weight transfer almost exclusively when he describes what he is teaching to drivers.
Talking “weight transfer” with respect to race driving is a fairly recent phenomenon. Most of the authors of books on handling don’t talk about weight transfer in the context of the driver controlling the car.
My major sticking point with weight transfer thinking is that drivers cannot feel...
What do these three F1 racing drivers have in common? Kimi Räikkönen, Valtteri Bottas and a young Nico Rosberg (when he drove for Williams in 2006).
They’ve all been coached by Rob Wilson – “the F1 drivers coach”. He’s also coached many other professional drivers, racing in just about every pro racing series around the world.
Rob knows weight transfer. Most times, when he is talking about driving, he’s talking about weight transfer. He says that “the rate at which you transfer weight”, is just about the most important thing you do in a race car.
For a quick look at what he does, check out this video with Formula E driver, Karen Chandok. It shows Rob's great sense of humor as well:
2017 Belgium - Rob Wilson Driving School
Rob is teaching smooth introduction of the steering brake and throttle so as to maintain maximum grip. From that...