Fix Bouncy Ride

[BmacIL]

I think this may be getting into "flat ride" behavior, where you'd want to match front and rear frequencies to road speed and wheelbase. With low amounts of damping, it's important to get the spring rates "right" for some range of speeds. With high amounts of damping, the front and rear oscillations are damped out more quickly, so there's perhaps greater tolerance for suspension frequencies that wouldn't be a good match in an undamped analysis.

Some years ago I put these flat-ride plots together for a 3500-ish lb 108" wheelbase car. These and similar ones have been used as illustrations here and there.

Rear ride frequency 1.17 x front ride frequency, not too far above the 1.10 factor that's commonly referenced. 10% critical damping - think worn-out shocks/struts. Lots of motion, but the pitch (front displacement minus rear displacement) dies out fairly quickly. Perhaps more importantly, pitch jerk (think in terms of front-to-back head toss where lack of being constant means it's harder to keep your neck muscles "in sync" with the pitch.

Here's a badly mis-matched frequency set with the front ride frequency higher than the rear. Let's also give it worn out front shocks and OE-replacement-ish rear shocks. Lots more pitch jerk, and the vibrations are slow to decay.

But let's take the above example and throw a lot more damping at it. It'll ride pretty firm, maybe even 'hard'. But the vibrations and the pitch/pitch jerk decay very rapidly. The first half-cycle or so is always a "bust"; not much you can do about it when the front is moving and the rear has no more than just gotten started.

Norm

What I'm finding now, Norm, is that the best RF balance for sharpest/best track handling with these cars is typically pretty far from the ideal for flat ride. Obviously you made a good point that with proper damping it can be controlled very well. On the S550 it seems to be in the 2-2.5x higher front range than rear. For me this has been difficult to get as it flies in the face of theory, but I have come up with a few physics based theories as to why this is true.

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[Norm Peterson]

Obviously, there's a lot more to this than any single item or aspect. I'd be interested in your thoughts.

By PM or email, if you prefer.


Norm

 

[Roadway 5.0]

I think this may be getting into "flat ride" behavior, where you'd want to match front and rear frequencies to road speed and wheelbase. With low amounts of damping, it's important to get the spring rates "right" for some range of speeds. With high amounts of damping, the front and rear oscillations are damped out more quickly, so there's perhaps greater tolerance for suspension frequencies that wouldn't be a good match in an undamped analysis.

Some years ago I put these flat-ride plots together for a 3500-ish lb 108" wheelbase car. These and similar ones have been used as illustrations here and there.

Rear ride frequency 1.17 x front ride frequency, not too far above the 1.10 factor that's commonly referenced. 10% critical damping - think worn-out shocks/struts. Lots of motion, but the pitch (front displacement minus rear displacement) dies out fairly quickly. Perhaps more importantly, pitch jerk (think in terms of front-to-back head toss where lack of being constant means it's harder to keep your neck muscles "in sync" with the pitch.

Here's a badly mis-matched frequency set with the front ride frequency higher than the rear. Let's also give it worn out front shocks and OE-replacement-ish rear shocks. Lots more pitch jerk, and the vibrations are slow to decay.

But let's take the above example and throw a lot more damping at it. It'll ride pretty firm, maybe even 'hard'. But the vibrations and the pitch/pitch jerk decay very rapidly. The first half-cycle or so is always a "bust"; not much you can do about it when the front is moving and the rear has no more than just gotten started.

Norm

Norm, I owe you a beer. Thanks for answering my question—in spades.

 

[Radiation Joe]

What I'm finding now, Norm, is that the best RF balance for sharpest/best track handling with these cars is typically pretty far from the ideal for flat ride. Obviously you made a good point that with proper damping it can be controlled very well. On the S550 it seems to be in the 2-2.5x higher front range than rear. For me this has been difficult to get as it flies in the face of theory, but I have come up with a few physics based theories as to why this is true.

The e-46 in my sig was 480 lb/in wheel rate front, 240 lb/in rear. Best balanced car I've ever owned. The spring rates were recommended by Ground-Control.

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