Tuned Suspension - What is it???

[Whiteyprius]

I know how to tune a radio; I know how to tune a guitar. I know what tuned exhaust is - but what on earth is a tuned suspension system? My '08 Touring came with it, and I'm darned glad - I guess! C'mon PC'ers, help me.

[Boo]

I think it involves stiffer struts/shocks, springs, and stabilizer bars than the standard Prius.

But, one unanswered question that has been posed here (I can try to find the thread later) is whether all the struts/shocks, springs and stabilizer bars are stiffer on the Touring Prius

I asked my Toyota dealer's service and parts departments several times by email, telephone and in person:

Exactly what parts do I need to convert my standard Prius' suspension into the Touring Prius' tuned suspension?

Haven't gotten a decent answer yet. My Toyota dealer is by far the worst dealer I've ever dealt with.

[Boo]

Here's the prior thread on the subject of what parts are needed to convert a standard Prius' suspension into the Touring Prius' tuned suspension:

Touring Suspension Parts Research

[donee]

Hi Whitney...,


Tuning a Mass and Spring system such as a car suspension is the process of selecting spring constants, and damping rates (shock absorber valving) so that the wheel resets to the road as quickly as possible after hitting a bump. The goal is to maintain the pressure between the tire and the road at the undisturbed level, or greater, through-out the tires progress over the road surface discontinuities.

Think about a heavy ball hanging from a spring. Push up on the ball and let it drop. It oscillates up and down. Your car is the same thing, only rather than having a extension spring, its upside down with a compression spring. The ball and spring system does not have a shock absorber, so it vibrates for a very long time. If your car did not have shock absorbers (dampers in european and engineering terminology), the car would bounce up and down for a long time. Each time the car went high in this response, the pressure between the road and tires would get small, and traction poor. In a turn, the car would slide at this point.

A tuned suspension is setup so that when a bump happens, the wheel follows the bump, and rebounds to the road nearly instantly, and the car does not oscillate. If there are side or accelleration loads on the tire during the bump, the car continues to track down the road as steered, and does not slide sideways, within the capabilities of the tire.

[RonH]

Originally Posted by Whiteyprius

I know how to tune a radio; I know how to tune a guitar. I know what tuned exhaust is - but what on earth is a tuned suspension system? My '08 Touring came with it, and I'm darned glad - I guess! C'mon PC'ers, help me.

A car's suspension is basically composed of springs, masses, and dampers of one sort or another. So, theoretically, any suspension is tunable, that is the combination of spring constants and damping factors resonates at a specific forcing frequency and has certain Q, the narrowness of the frequency response. Normally you want your suspension to be detuned. Not going boing-boing down the road. I had a Corolla that did that on a certain patch of freeway at a certain speed. An old trick is to push down on the fender and watch whether it bounces or not to check the condition of your shocks. "Tuned" is marketing speak for stiff which really means the resonant frequency is well above that which might be encountered.

In another sense, a car will sway when going through a turn and will rock back and forth when negotiating an S curve. If the suspension is "tuned" right the turning forces will be out of phase with the swaying forces and cancel. The car will seem to go through the turns on rails, up on its toes as they say. Obviously, this condition exists for only certain values of turning radius and speed and car. Watch a NASCAR race as the pit crew inserts and turns a crank in the rear fender, changing the tuning of the suspension as the tires wear or the track condition changes. At a certain speed and banking no tuning would be needed as the suspension forces would be neutral.

Hope that helps.

[RonH]

Originally Posted by donee

Hi Whitney...,


Tuning a Mass and Spring system such as a car suspension is the process of selecting spring constants, and damping rates (shock absorber valving) so that the wheel resets to the road as quickly as possible after hitting a bump. The goal is to maintain the pressure between the tire and the road at the undisturbed level, or greater, through-out the tires progress over the road surface discontinuities.

Think about a heavy ball hanging from a spring. Push up on the ball and let it drop. It oscillates up and down. Your car is the same thing, only rather than having a extension spring, its upside down with a compression spring. The ball and spring system does not have a shock absorber, so it vibrates for a very long time. If your car did not have shock absorbers (dampers in european and engineering terminology), the car would bounce up and down for a long time. Each time the car went high in this response, the pressure between the road and tires would get small, and traction poor. In a turn, the car would slide at this point.

A tuned suspension is setup so that when a bump happens, the wheel follows the bump, and rebounds to the road nearly instantly, and the car does not oscillate. If there are side or accelleration loads on the tire during the bump, the car continues to track down the road as steered, and does not slide sideways, within the capabilities of the tire.

Good description from a time-domain perspective: the impulse response's (bump), rise time (instantaneous return) and overshoot (bouncing). Mine was in the frequency domain: resonant frequencies and Q's. In passive linear systems (masses, springs, dampers) they are equivalent. An interesting exception, which is why I'm belaboring this, is active suspension which adjust its parameters (stiffness, damping, its kind of hard to change mass!) as conditions change on a moment by moment basis. Is it raining, is a tire sliding, no problem for the micro-controller. I think they banned them in formula one racing to slow the cars down and make driver skill more of a factor.

[Whiteyprius]

Thanks to all who replied! - I think I understand now - I'm also glad that I don't have to make that conversion - sounds like not much help from your dealers!

[qbee42]

Originally Posted by Whiteyprius

I know how to tune a radio; I know how to tune a guitar.<snip>

Yes, but do you know how to tunafish?

Tom

[Boo]

Supplementing RonH's and Donee's good answers above (and correcting an error in my answer):

Ken1784, in the Touring Suspension Parts thread, made the interesting point that the Touring Edition's rear springs are actually softer than those on the standard Prius; evidencing that the suspension's performance depends on the totality of its parts (shocks, springs, stabilizer bars, and even tire stiffness).

[David Beale]

Short answer, the shock rates are set with the spring rates in mind for the handling/ride you want.

Be aware as well that a "tuned suspension" isn't the same every time. You could tune the suspension for an extremely soft ride or for best handling (the normal meaning). If you were the Mythbusters you could even tune it for maximum bounce.

Usually you choose the spring rate for the ride or handling you want, then choose the shock dampening to ensure the motion stops after 1/2 cycle. There is no "right" way however. It depends on what you want, and there are always compromises. A "best handling" setup usually rides pretty rough, for example.