Intermission 1 – Sway Bar Top Tips
Since the whole purpose of this pilot is to try to standardise tuning for Beam, here’s the first in a series of “How to Tune” which will go a long way to explaining the way I critique how cars drive.
As I mentioned before, sway bars and their effect don’t really show up on the Automation metric. In fact most of the metrics they change are more to do with the roll angle which affects “comfort”, and literally the weight balance on the car which is miniscule compared to what they really do. The handling graph similarly will not show the effect because that’s all about static velocity, mid-corner grip.
What do sway bars do anyway? They limit the amount of body roll your car has by limiting the amount of relative suspension travel between each wheel. In my over-simplified way of thinking about it: the grip between the tyre and the road is related to the opposing forces of the road on the car, and the car on the road, but the forces are transmitted through the tyre, then the wheel, then the suspension, then the frame of the car. This means that any time there is any give, there is a loss of immediacy in the transmission of those forces. This is important for road applications, because if everything was perfectly rigid, then any bump you encountered on the road would result in airborne projectile motion, which is obviously bad for grip because then the tyre is not in contact with the road.
So in a sentence, you want to maximise the contact with the road, but also minimise the delay in response otherwise everything gets really wobbly and unpredictable. That’s fine if you’re driving a rock-crawler at 2mph along a boulder trail because you need suspension travel to get through that, but for this challenge, you want to strike the right balance so you can drive fast, change direction etc. and generally feel engaged with the road.
Keep in mind that the racing wisdom is that for the best balance, all else being equal you will want the inside wheel to be barely touching the road mid-corner. Too stiff and the inside wheel loses contact, too loose and you will lose response, precision. Then, there is also the balance between front and rear: within reason, stiffer sway bars on the rear will encourage faster response and an oversteer balance. On the front, it will make the steering more direct, but it will generally encourage understeer. But this must also take into account the weight distribution and the character of the car in the first place. Either way, tuning sway bars is the broad brush stroke on the balance of how a car handles, so this part is generally done first before going to springs and dampers (because those are all about how each individual wheel traverses over bumps and that varies a lot per surface).
Now, I already button-holed Ornate about the handling of his car among other things. Without giving too much away I’m going to home in on the sway bars because it’s a perfect example for what I want to demonstrate. Below is the G force, the simple brake thermals and the weight distribution chart you can find in the UI in Beam:
If you want a graphical representation of what this means, see below:
As you can see, the rear right wheel is cocked. Some people (I’m looking at you, Knightophonix), love this because it gives a certain lairiness to the handling and in fact it is a common attribute of FWD hot hatches of a certain era. That’s precisely the application in which it kind of works, within reason (you’ll see later), as it does encourage the car to get tail happy which means you can actually accelerate through a corner harder and not have the nose run wide as is a FWD car’s wont.
However, up front, is this:
In this kind of situation where there is a big mismatch between the front and the rear, one of two things can happen: 1) the body flexes 2) one wheel stays on the ground and the other lifts off. To put it simply, as this is not a ladder chassis, 2) happened. What this really means is that the car loses responsiveness up front and the lag in steering response actually can literally drag the rear out of line. If you want a demonstration of what this means, try running a moose test and you’ll find that aside from feeling like a bus, you can also actually get the Akuna Sprinter HF to swap ends by simply turning side to side.
This is not exactly desirable behaviour.
For something that is sharper and more balanced and will change directions briskly, let’s look at my reference car, complete with inferior suspension components:
As you can see the weight transfer between the wheels when turning maximally at a static velocity is far more even. The sway bars are not ultra stiff, and they don’t need to be. They’re just where they need to be that I can get the rear end to go light if I lift off/brake while cornering and then straighten up with throttle. In this car that happens to be 1400 and 1200 N/m respectively. I could probably get it to turn even harder and sharper if I stiffened the rear sway bar, but this is how I like it.
If you have Beam I encourage you to play with the set-up while looking at that app, and throwing the car around several corners under different circumstances. If you don’t have Beam, then you should start by more-or-less matching the weight distribution and then go from there depending on the drivetrain and, well, other factors.