ATTN: Don't buy REAR Stoptech SS Lines!!

[WolfWings]

Originally Posted by CF-Shane

Take the Yaris for example: I see a solid beam rear axle with coil springs, and Toyota's marketing department sees a "tortion beam rear suspension".

There's a difference. The Yaris' "solid beam rear" actually appears to be under torsional load from what I saw, looking at it after I had my TRD rear sway bar installed. The fact that the 'solid beam' is a near-duplicate of the rear sway bar but attaches to mounts more-or-less one-bolt-higher than the sway-bar shows it actually is a torsion beam, not a true 'dead axle' design. The fact that there is no mount for a track rod/panhard rod (Suspension SP-62) shows that (at a minimum) the rear suspension is a twist-axle rear, which means that, yes, the rear beam is designed to be under torsional forces like a torsion-bar setup.

The only difference between a 'twist axle' rear and a 'true' torsion-beam rear is if the rear axle is two parallel (at rest) rods cross-linked or one single rod. The two parallel rods gain a minor design-engineering-simplicity advantage at a moderate complexity disadvantage. The single-beam is, in effect, two half-length torsion bars linked at the mid-point by comparison, and more math and proper design can let it perform almost well as the two-rod setup AFAIK, though it doesn't add as much chassic-rigidity as the two-bar setup. This is (I believe) why a rear sway bar is so noticable on the Yaris.

[CF-Shane]

Originally Posted by WolfWings

There's a difference. The Yaris' "solid beam rear" actually appears to be under torsional load from what I saw, looking at it after I had my TRD rear sway bar installed. The fact that the 'solid beam' is a near-duplicate of the rear sway bar but attaches to mounts more-or-less one-bolt-higher than the sway-bar shows it actually is a torsion beam, not a true 'dead axle' design. The fact that there is no mount for a track rod/panhard rod (Suspension SP-62) shows that (at a minimum) the rear suspension is a twist-axle rear, which means that, yes, the rear beam is designed to be under torsional forces like a torsion-bar setup.

The only difference between a 'twist axle' rear and a 'true' torsion-beam rear is if the rear axle is two parallel (at rest) rods cross-linked or one single rod. The two parallel rods gain a minor design-engineering-simplicity advantage at a moderate complexity disadvantage. The single-beam is, in effect, two half-length torsion bars linked at the mid-point by comparison, and more math and proper design can let it perform almost well as the two-rod setup AFAIK, though it doesn't add as much chassic-rigidity as the two-bar setup. This is (I believe) why a rear sway bar is so noticable on the Yaris.

Thank you for the explanation, you learn something every day and I stand corrected. I have found surprisingly little about the Yaris' rear suspension except for advertising jargon and was calling it as I saw it. Another thing I found surprisingly little information about was the availability of rear sway bars. So they make a huge difference on the car I take it?

[WolfWings]

Originally Posted by CF-Shane

So they make a huge difference on the car I take it?

Changed the car from being squirreley and 'squiggley' when in extended turning (sweepers or doing figure-eights around a pair of orange cones in a parking lot) to taking a quick 'set' under load and being very easy to control with throttle-adjustments and responsive to turning. Exactly what you'd expect from an unstiffened chassis suddenly getting properly stiffened, much more than just a rear sway bar would normally grant on a FWD car.

Without the sway bar the car felt like it was near-constantly under torque steer (the fuel cut-off deceleration causing it even under engine braking at highway speeds) but once I had the sway bar put on what I thought was torque steer turned out to just be how loose the rear chassis was magnifying things to very noticable levels.

Hell, without the bar I felt unsafe doing my figure-eight practices to get used to how the car handled. I couldn't get myself to break 25mph. Once I put it on I had to stop when my passenger/friend started complaining about the alternating side-to-side G-forces I was pulling off doing 35-40mph figure-eights for ten seconds non-stop. Car feels much more chuckable, very much like my 89' Corolla FX used to feel, or my 86' Civic Hatchback felt.