My Ultra Racing rear sway bar install

[Loren]

Originally Posted by Sandwash

I've had my Yaris for only 2 weeks now and am considering getting rear sway bar. Very much appreciate reading of pro and con opinions although as can be expected am no less (or more) certain as to sway bar's net effectiveness. Question arises as to relative inexpense of sway bars, especially if produced in mass numbers, and why it is Toyota wouldn't include the sway bar as stock item if it in sum total better overall handling may be realized?

Automotive design and engineering is all about compromises. The general public, especially the "commuter car" market, wants a car that is comfortable and handles predictably. Basically, they want an appliance. A couch that they can drive to work.

For these reasons, cars like the Yaris are designed with fairly soft suspension that handles most road conditions "comfortably" and the car is designed to handle predictably and safely. Predictable and safe handling for the average idiot driver means understeer.

Enter the rear swaybar. A rear swaybar's purpose is to increase rear roll stiffness. Increasing rear roll stiffness has a lot of effects, but the most obvious is a reduction in body roll and an improvement in steering response, which the "performance-minded" driver likes... but the general public might actually prefer the car to be less "twitchy" and prefer a little body roll that allows the suspension to lean in a turn instead of making THEM lean in a turn.

Increasing rear roll stiffness also changes the handling bias of the car and makes it less prone to understeer, or more prone to oversteer. The stiffer the rear of the car is made, the more likely it is to oversteer in an emergency maneuver. Toyota doesn't want the liability of putting the average idiot in a car that could oversteer unexpectedly, so they design their cars to understeer predictably.

Now, if Toyota wanted the rear roll stiffness to be greater on the Yaris... they wouldn't have fit a swaybar to it, anyway. It adds weight, complexity and expense, things that are considered greatly in the design of such a car. Even if they used the TRD/Ultra Racing design (a beam axle reinforcement rather than a true anti-sway bar), it would still add at least 7 parts to the car, one of them being a bar that requires complex forming and welding and heat-treating, the others being a pair of bolts, nuts and washers. (if they put a REAL swaybar on the car, the part count would be at least 3 times as many with brackets, end links, bushings, etc.) No, if Toyota wanted to add more stiffness to the back of the Yaris, they would simply have designed a stiffer beam axle assembly that allowed less twist or they would have fitted stiffer rear springs... either of which would create a compromise to the level of comfort that the car was designed for.

Um... what was the question again?

[Sandwash]

Thanks for your thorough and thoughtful response. You're right, most people want that couch they can drive to work so Toyota would not be so compelled; and, thinking about it you're correct - there would be other engineered approaches a manufacturer would take.
And, do you have a rear sway bar and would you hesitate in recommending one for whatever reason? Again, thanks--