Fix Bouncy Ride

[Bluemustang]

Thanks guys, I'll try playing around with more of the rebound settings and maybe the swaybars also as I think I may have them too stiff.

The one thing I saw mentioned (and just now found the huge BMR thread on) is about clocking of the bushings, which I definitely didn't do. I wonder if that could ultimately be the cause of this and if it's possible to do after the car being aligned.

Definitely could. The bushings need to be re-indexed at the new ride height. If not they will be in bind and the car will feel weird. It needs to be done at ride height with all 4 wheels on the ground. A drive on alignment rack or lift that can keep weight on all 4 wheels.

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[BmacIL]

Too much rebound damping slows the recovery of the wheel/tire out of 'bump', so the tire then crashes into the next little bump or unevenness harder than it would if the wheel/tire was permitted to recover to/toward its 'static position' a little more quickly.

I think the stiffer you go with the spring, the narrower the tolerance band between not enough damping and too much gets, at least as far as this ride quality matter is concerned.


Norm

Exactly this.

 

[Norm Peterson]

Gotcha, that all makes sense.

There is also the matter of shock force not returning to zero even when velocity instantaneously becomes zero. Or even not following the same path "back" that it took to go "up wherever".

Norm

 

[Norm Peterson]

The one thing I saw mentioned (and just now found the huge BMR thread on) is about clocking of the bushings, which I definitely didn't do. I wonder if that could ultimately be the cause of this and if it's possible to do after the car being aligned.

If the car drops any after reclocking the bushings, the alignment settings will have changed a little. Whether it'd be enough to matter depends at least on how much the car dropped (and perhaps to what it was set to by the previous alignment vs what works best overall for your driving).


Norm

 

[SteveW]

There is also the matter of shock force not returning to zero even when velocity instantaneously becomes zero. Or even not following the same path "back" that it took to go "up wherever".

Norm

Interesting. Add also these are twin tube (slower reacting) and very likely in a situation on my car beyond their designed valving. Can't wait to get rid of them.

 

[Roadway 5.0]

Thanks guys, I'll try playing around with more of the rebound settings and maybe the swaybars also as I think I may have them too stiff.

The one thing I saw mentioned (and just now found the huge BMR thread on) is about clocking of the bushings, which I definitely didn't do. I wonder if that could ultimately be the cause of this and if it's possible to do after the car being aligned.

For sure dial your swaybars back a hole or two if you have them full stiff, then go up slowly from there (if at all).

Very stiff swaybars, low rebound, and stiff(er) springs will be similar to going down the road on a 4’x8’ piece of plywood with elastic skateboard wheels.

 

[Nagare]

For sure dial your swaybars back a hole or two if you have them full stiff, then go up slowly from there (if at all).

Very stiff swaybars, low rebound, and stiff(er) springs will be similar to going down the road on a 4’x8’ piece of plywood with elastic skateboard wheels.

The stiff swaybars shouldn't affect ride quality on a straight flat road, but when you introduce any unevenness is when the issue comes up.

 

[Bluemustang]

The stiff swaybars shouldn't affect ride quality on a straight flat road, but when you introduce any unevenness is when the issue comes up.

Yeah but most roads aren't flat and straight. So it does matter quite a bit if you care about ride quality. And most people wouldn't complain about driving on a straight and flat road because it is straight and flat.

 

[Roadway 5.0]

The stiff swaybars shouldn't affect ride quality on a straight flat road, but when you introduce any unevenness is when the issue comes up.

Agreed

 

[Roadway 5.0]

Yeah but most roads aren't flat and straight. So it does matter quite a bit if you care about ride quality. And most people wouldn't complain about driving on a straight and flat road because it is straight and flat.

^^^ well said

 

[EFI]

Getting lots of good feedback here especially with the swaybars and clocking bushings which I will work on when I find some time.

Meanwhile did some quick testing of the rebound settings on my way to and from work today (same exact roads back and forth). On the way there I had both settings up to 1 full turn from soft and it was still quite "bouncy". On the way back I turned just the front all the way down to about 1/8 turn from full soft and that made quite a bit of difference. The front was more settled for sure, but now I could distinctly tell that just the rear was bouncy. Hitting a small speed bump at the same speed the front part of the car soaked it up nicely but then when the rear wheels hit the speed bump the whole rear end shot up like a cannon and crashed back down. This makes sense since I left the rear at 1 full turn since I didn't bring the jack with me to work

I'm starting to believe that too much rebound is causing this. I'm going to try later turning the rear down also to match the front.

 

[1bad66]

All this shock adjusting is for not if you don't clock the bushings first...You have to relieve the pre-loaded condition those bushings are in or you'll be chasing ghosts.

 

[Bluemustang]

All this shock adjusting is for not if you don't clock the bushings first...You have to relieve the pre-loaded condition those bushings are in or you'll be chasing ghosts.

Yeah. And I'd say generally good rule of thumb is to run slightly stiffer shock settings in the front than the rear. Going the other way will likely make the ride worse imo.

EFI dont be fooled into thinking small adjustments dont make a difference. Small increments.

 

[Roadway 5.0]

@Norm Peterson @BmacIL

I’m curious now if the critical damping point can be totally missed in a suspension system, but still give the feel of a good ride quality at lower speeds (< 50mph).

Is it possible that @EFI can have a limited oscilating ride by setting his rebound very low, as he said above, but he can also limit oscilation at a more aggressive setting as well (of course with a stiffer ride)? I’m picturing a wavelength with multiple nodes but I’m not sure how dampers would play into this, or if at all.

 

[Norm Peterson]

@Norm Peterson @BmacIL

I’m curious now if the critical damping point can be totally missed in a suspension system, but still give the feel of a good ride quality at lower speeds (< 50mph).

Is it possible that @EFI can have a limited oscilating ride by setting his rebound very low, as he said above, but he can also limit oscilation at a more aggressive setting as well (of course with a stiffer ride)? I’m picturing a wavelength with multiple nodes but I’m not sure how dampers would play into this, or if at all.

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

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