Selecting Springs and Anti-Roll Bars - Part 2


In Part 1, we established how we might select springs and anti-roll bars using the Racing Car Technology Weight Transfer Worksheet™ (WTW).  We can choose the springs and anti-roll bars by trying different spring rates and anti-roll bar diameters in the spreadsheet, to come up with the Suspension Frequency, Balance and "Roll rate" we want.

In Part 2, we'll look at some of the finer points of selecting anti-roll bars.

How Big Can We Go With The Anti-Roll Bars?

As long as the car was balanced, stiffer ARB’s would always be better for grip, wouldn’t they?

In terms of roll stiffness, yes.  In principle, we can never have too much roll stiffness, as long as the car is balanced'  (See Selecting Springs and Anti-Roll Bars - Part 1)

The problem is, with very stiffer ARBs, the stiffness difference between front and rear of the car is dissipated in the torsional twist of the chassis.  We could make a change to the anti-roll bars, and nothing happens to the balance of the car.

For the ARBs to be affective in changing the balance of the car, we need the torsional stiffness of the car to be 2 x (front roll stiffness + rear roll stiffness).

To make this super roll stiffness work, we need a specially designed racecar, such as the Mygale Formula Ford, or the Mygale FIA F4.  When we do the Weight Transfer Worksheet™ (WTW) calculations for these cars, the ARBs are so stiff, they don’t roll at all – less than .1 degrees per lateral G.  (“Degrees per lateral G” is the so-called “roll rate”, one of the results we get in the WTW.)

With a super roll stiff car, the turn in is great – like a go-kart.  And you don’t need squillion dollar shocks. Australian F4 specifies the Sachs non-adjustable shocks.

But the Mygale designers (make that all race and road car designers) still want the cars adjustable for balance.  We can see from the WTW calculations, about half of the roll stiffness is dissipated in the chassis.  The ARBs have a greater range of lever arm adjustment to allow for this.  As far as mechanical balance is concerned, all drivers within the range allowed for.  There is no need for any driver to deviate from that.

Old thinking says that these cars should not work.  But in fact, in Formula Ford, the high roll stiffness Mygale chassis was dominant upon its release in the mid-2000s, and remains so, up to the present day.

Practicalities in setting up production cars with higher centre of gravity and lack of torsional stiffness preclude super stiff roll resistance, but we can certainly go with bigger bars than we might have thought possible a while back.

Learning What You Need to Know…..
The Way Forward to Improving Your Race Car

To get a handle on what we need to know in amateur racing, we could attend the high-end seminars and read the books on vehicle dynamics.  But really, this is for pro-racing race engineers.  There’s not a lot of trickle down stuff for us.  How will we digest it all?  Or for most of us, even do the maths?

Rather than get too theoretical, we’re in-the-trenches doers.  We believe the best way to learn something is to roll up our sleeves and get our hands dirty.  This is how we first discovered our technologies around grip and balance.

We want a starting point for grip and balance – our “baseline set-up”.  From there, we need adjustable roll stiffness within sufficient range (usually with front and rear anti-roll bars), such that we can initially get the car to understeer, and then tune out the understeer with stiffer roll stiffness adjustment at the rear.

Can We Get A Good Set-Up By Testing at the Track?

To identify our baseline set-up by driving the car at the race track, there are two immutable truths we need to address….

Firstly, it’s not possible to drive the race car in isolation, and say if more grip will be available with different springs.  Hardly any racers out there have sufficiently tested with different springs, to be able to say they have optimized what they've got.  The cost is too high and there is too little known about what to shoot for.

The driver should be able to pick if the car has a balance problem - but there are many issues that will blurr the line between understeer and oversteer.

• Instead of diagnosing understeer, the driver and/or his team are unable to identify the source of the “front end grip problem”.
OR…
The car is allowed to oversteer, because the driver “prefers oversteer”.

• Lateral chassis and suspension stiffness is lacking.  In cornering, vertical movement at the tyre contact patch is resisted by a bit of a blancmange, instead of nice stiff suspension.

• Torsional chassis stiffness is lacking in a lot of cars.  Sports cars without a roof, for instance.  MGBGT with fixed roof will be a bit stiffer, and therefore require a greater split of front roll stiffness vs rear roll stiffness to balance the car, compared to the soft top version.

So, with the Weight Transfer Worksheet™ we can:

Select springs based on the natural suspension frequency we choose on our suspension stiffness scale – around 80 CPM for road cars, to 170 CPM at the top for race cars (non-aero).  We can choose best grip for racing or best grip vs ride compromise for road performance.

Choose the mechanical balance we want for understeer/oversteer.  For our baseline set-up, we want Front Weight Transfer Distribution (FWTD) of 5% more than the front static weight. 

Who’s This Program Best For?

Even if you already have a race winning car, most times, we find there is still more to come.   For instance, we found a few tenths in David Stone’s Mazda MX5 with rear shock development this year, ONLY because we knew where the neutral steer balance of the car was, and could therefore identify the oversteer tendency inherent with the old shocks.  (They were too stiff, even on the softest setting).  With just that small improvement in lap time, David can maintain dominance over fast-improving competitors.

If you’re running midfield or running some seconds slower than the equivalent cars (the cars and drivers you benchmark yourself against), you have potential to pick up much more.  Possibly seconds per lap.  Most likely, with this course, you’ll blow your PB times away, and hopefully catch the other guys.

Even if you don’t think you want to make any changes to your car right now, if performance driving or racing is your thing, then the course gives you invaluable insights into the mechanism of handling and what suspension set-up can mean for you, as you progress further with your driving and racing.

Whether you want to do the set-up on your performance road car, or consider a full development program for your circuit car.....

Get the Insights and Tools You Need to Go Faster and have more Fun….

If you're interested to learn more about how you can choose the springs and anti-roll bars you need for best grip and balance, then check out our training course here....

"Get More Grip and Balance, the Suspension Set-Up You Need to be FAST"
All on-line course.  Get support within the course.  All your questions answered.