ppritchard

Getting a bumpy feeling, similar to what an almost flat tire would feel like.

Tires are all fine though.

We've been replacing suspension parts and it was feeling a lot better until
this sudden issue.

Any thoughts on a bumpy feeling issue?

Thanks for any ideas.

Gringo Grande

iTrader: (97)

What suspension parts have you replaced? I had the same issue...started at Deals Gap last year and would randomly surface. I just replaced EVERY bushing in my car but haven't driven it yet.

I can tell you when replacing my rear bushings the ones that were so shot that a child could easily move were: Pillow ***** (all), rear end links and rear toe links.

Edit: Should be noted I experienced this issue with both illuminas + tein springs and also with tein coil overs.

ppritchard

Replaced upper and lower control arms front and back
Replaced front sway bar links
Replaced suspension cradle bushings

Suspension was feeling pretty good until this bumpity surfaced.

7dust

iTrader: (14)

Check for an out of round tire. Jack the wheel up and give it a spin and look for out of round.

Bad wheel bearing will do the same thing.

96fd3s

diff mount bushings i rekon
does it go away under hard acceleration?

ppritchard

replaced the diff bushings already.

Never really checked the wheel bearings.

thanks

dimondjack

Not convinced that a wheel bearing will cause a "bumpity".

Wheel bearings typically "groan", and the noise will go away when you unload that side of the car.

If you messed up your alignment with the bushing replacements you could be wearing your tires in a really messed up way. I had a car with a bad alignment which put HUGE waves in the tire. The tires essentially turned in to a decagon (or something like that) with many flat spots instead of being round.

ppritchard

Had the alignment done with the parts change.

What about the tire balance, could we have spun off weights?
They are flat mounted on the inside of the wheels.

DaleClark

iTrader: (55)

Most likely it's the tire. Easiest way to diagnose is remove the tire and roll it along the ground at slow speed, watching the surface of the tread. If you see a bump or shift, the core of the tire is separating.

Had this happen on my daily driver a while back. I thought it was all kinds of crazy stuff until I found it. New tires and done.

If it's a rhythmic bumping that increases/decreases with speed, it can ONLY be something that rotates. Suspension and bushings only do weird stuff if they're bad when you are working that bad bushing. Something that changes with speed has to be rotational, period.

BTW, hope you're going to Deal's Gap! Meet me in person and pick my brain

Dale

dgeesaman

iTrader: (7)

If it's a tire then move the wheel to another corner of the car and see if the bumping moves with it.

David

1QWIK7

iTrader: (33)

Does the car sit for long periods of time??

If so, the tire(s) prob has a dead spot(s) in it. That will cause the "bumpy" feel when driving. Even though the tire pressures are correct (or at least within normal spec).

That said, did you check tire pressures?

MazdaSpeedDan

iTrader: (4)

Have you checked to see if your tires have weights

N1atMax

iTrader: (4)

Mine had a bumpity from 47 to 53 mph. I got a good tire tech to take his time and propely do a dynamic balance and it is gone.

Dynamic balance

Dynamic balance describes the forces generated by asymmetric mass distribution when the tire is rotated, usually at a high speed. In the tire factory, the tire and wheel are mounted on a balancing machine test wheel, the assembly is accelerated up to a speed of 300 RPM or higher, and sensors measure the forces of unbalance as the tire rotates. These forces are resolved into static and couple values for the inner and outer planes of the wheel, and compared to the unbalance tolerance (the maximum allowable manufacturing limits). If the tire is not checked, it has the potential to wobble and perform poorly.[1] In tire retail shops, tire/wheel assemblies are checked on a spin-balancer, which determines the amount and angle of unbalance. Balance weights are then fitted to the outer and inner flanges of the wheel. Dynamic balance is better (it is more comprehensive) than static balance alone, because both couple and static forces are measured and corrected.

The dynamic balance can only be conducted if the driver comes to the garage and has the garage check for imbalances. With the existing sensors found in many cars, however, the imbalance can be estimated in real time, as seen in a recent SAE paper: sensors such as the ABS wheel speed sensors were used to detect an imbalanced tire or tires in real time [2].

[edit] The physics of dynamic balance





Physics of tire imbalance
Mathematically, the moment of inertia of the wheel is a tensor. That is, to a first approximation (neglecting deformations due to its elasticity) the wheel and axle assembly are a rigid rotor to which the engine and brakes apply a torque vector aligned with the axle. If that torque vector is not aligned with the principal axis of the moment of inertia, the resultant angular acceleration will be in a different direction from the applied torque. Whenever a rotor is forced to rotate about an axis that is not a principal axis, an external torque is needed. This is not a torque about the rotation axis (as in a driving or braking torque), but is a torque perpendicular to that direction. If the rotor is suspended by bearings, this torque is created by reaction forces in the bearings (acting perpendicular to the shaft). These reaction forces turn with the shaft as the rotor turns, at every point producing exactly the torque needed to keep the wheel rotating about the non-principal axis. These reaction forces can excite the structure to which they are attached. In the case of a car, the suspension elements can vibrate giving an uncomfortable feel to the car occupants. In practical terms, the wheel will wobble. Automotive technicians reduce the wobble to an acceptable level when balancing the wheel by adding small weights to the inner and outer wheel rims. Balancing is not to be confused with wheel alignment.

ppritchard

Car does not sit. Driven daily.
Weights are visible, but not sure if "all" of them are there.
Air Pressure checked and set

Will go for the tire tech and balancing.

Thanks

RotaryRX-007

You don't generally loose weights. They're on there pretty good.

So you drove the car after the bushing change and it was OK at first, then it got bad?

Re torque your lug nuts? I've done it before....

ppritchard

Yes, was fine after suspension work.

I'll check the torque on the lug nuts.

1QWIK7

iTrader: (33)

Constant bumps in the road can make you drop some weights. Not necessarily the first good bump but over time.

Def check torque specs. I torque mine at 85 ft lbs.

gracer7-rx7

iTrader: (16)

Kinda sounds like a blown shock. Visually inspect the shock to see if there is any wetness around the top or on the shock body itself.

djseven

iTrader: (56)

Could be a bent wheel as well.

gracer7-rx7

iTrader: (16)

Also, what wheels are you using? Are they hub centric?

ppritchard

Same wheels we have had for years.
Still, when we get them balanced we can check wheel integrity too.

Shocks appear dry.