Lean Less

Any enthusiast worth his salt knows that tires have arguably the biggest impact on a vehicle's handling. Obviously, however, there are chassis dynamics that extend beyond the realm of tires. Once you increase the traction threshold at the road surface, then you may be ready to take the next step in…

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Time for Throwback Thursday. Just stumbled across this article deep in the list of stories on our site. Thought I'd bump it up on the forum because the tech info is SO good.

It's missing a couple of important points, or doesn't emphasize them enough.

1. TLLTD is a ratio. It's the relationship between the front and rear sway bars. This isn't quite clear enough in the article. If you don't grasp that, you'd probably end up with the same common mistaken theory that since stiffening the front bar leads to decreased traction on the front, and stiffening the rear bar leads to decreased traction on the rear, that softening both leads to improved grip at both ends. This is not usually the case.

2. Boundary cases. If you have too much body roll, you can run out of suspension travel at one end or the other. This can lead to surprising handling changes. For example, take a car that corners on the bumpstops at both ends when stock. Add a big front sway bar. In our example, let's say this particular car no longer bottoms out the front suspension but still bottoms out the rear. You cut down on overall roll, but now you have an effectively higher spring rate in the rear so you'll have increased oversteer.
   There's also the other case, where you start to lift wheels in the air. Once you've gone in to tripod mode, all remaining weight transfer will happen at the other end.

3. Body roll gives important cues to the driver. It makes it a lot easier to judge cornering speed. Read all of the various interviews from Dave Coleman on this one. You also have to let your suspension breathe and move to be able to absorb bumps - and if you can't absorb them, then you lose traction over them. Over-stiff sway bars will also have an effect on the ride, you'll get increased head toss over one-wheel bumps and you'll start to feel more harshness - but they do definitely give a big change in handling for a minimal change in ride overall.

Here's another take on some of the same info. It uses FRC instead of TLLTD, and the boundary cases are covered in later chapters. Handling theory chapter from How To Build A High Performance Mazda Miata

I know this is supposed to be a pretty basic primer, and it definitely is a good one, but there is still one thing that I felt was missing on the topic of (why roll is 'bad') maintaining the contact patch. Suspension geometry also plays an important roll(). I've seen this concept somewhat misapplied to the FRS/BRZ vs Miata debates, where the Miata seems to be overly criticized for its body roll. This criticism neglects the fact that the double wishbone suspension on the Miata also loses considerably less camber in roll than the strut suspension on the FRS/BRZ. So it's not as critical to control roll as tightly on a car like the Miata as opposed to a car like the FRS/BRZ.

And with solid axles, roll doesn't cost camber at all!

But all the kool kids are removing their sway bars to reduce weight and compensating with increased spring rates, which has the added effect of limiting yaw and pitch.

This is the kind of hardcore tech I would love to see more of. Thanks GRM!

TL/DR

kidding good stuff

is it true that if an inner rear tire comes off the ground, a stiffer rear bar won't make any difference, because lifting the tire is the most it can do and there's no further resistance?

Once a wheel is off the ground you have 100% weight transfer at that end. All remaining weight transfer will take place at the other end of the car. The sway bar at the lifted end is no longer part of the equation.

So yes, but not quite in the way you described.