I know most of the reviews here are against the Pirelli P-Zero Nero, and I completely agree after owning this set. They have 23k miles on them, have been nothing but trouble with vibrations.

So I'm trying to figure out a bad brake vibration on my car yesterday. All suspension bushings are in perfect shape, either replaced or show no signs of age (specifically the front lowers). The front rotors have less than 0.003 inch runout--they're not the issue. The brake shudder I have is in the steering wheel, not the brake pedal.

I get to looking at the tires--3 are fine, showing about ~50% tread life and no odd wear. The front right tire is cupped in the center, and some of the tread is down to the wear indicators and some is not. These tires have never been over inflated, so the cupping is bizarre to me. And the non-round wear pattern? I've never seen this.

The tire shop looked at them, rated the 3 good units at 70% tread, the one bad at 40% and will replace under pro-rated warranty with 33% off the list price. It seems to me this tire is defective somehow, shouldn't Pirelli be honoring a better warranty? I can't see how anything on my car would make one tire wear this way (and it was rotated, so not the suspension being out).

 

A picture of the worn tire would be helpful.

 

+1 on DonsXJ8's comment

On the face of it Id guess you had an inflation issue on the one tyre but just a guess without more info and pics

The PZero is a very soft tyre and will wear quite quickly. It wont take long for an inflation issue to show up like you have seen. An alignment, bearing or bushing issue will normally effect both sides not one tyre

I have spent a fortune on replacing PZero's over the years and have since given up and gone to a Khumo which I am very pleased with. Yes it has a harder compound and is not as good on the track but is as good on the road is 1/4 of the price and lasts longer.

The other side of the coin for me is track days. Yes I would like the Pzero fitted but a better and cheaper option is a spare set of rims with semi slick track tyres which again is cheaper and far more sticky than Pzero's

Cheers
34by151

 

You keep saying " brake shudder " , " brake vibration " , is this occurring whilst your braking only ?

Cheers ,

 

No, there's always a vibration, but it started to get magnitudes worse while braking over the past month or two. I have pretty much given up on these tires staying balanced for more than 2 miles outside the tire dealer. They have road forced them every time I've complained, replaced one tire after a few thousand miles, but they just never seem to be consistent. Every change of the weather bring some new vibration.

The brake shudder was not consistent either (to begin with). Sometimes it would be gone completely. Now it's pretty much every time I brake, and doesn't seem to vary with speed. I spent this past Saturday checking the brakes and suspension. The brake "shudder" is not in the brake pedal, but the steering wheel. Initially I suspected the front lower control arm bushings, bought new ones, but there's absolutely nothing wrong with the originals.

Unfortunately I don't have a picture of the worn tire and won't have time to take the tire off before tomorrow when the new tire arrives. It's possible the tire was slightly over inflated for a while, causing the cupping. But the out of round wear is what has me stumped. I can even hear it while running down the road (the tire noise warbles). This is most certainly the last set of Pirelli tires I will buy. I'll sooner go back to Conti.

 

I would do this ,

Take off the damaged tyre (front right) , swap it with the spare , drive the car .

You should now have little to no vibration while driving but the brake shudder may still be there , particularly at higher speeds .

 

So you suspect brake or suspension issues causing the shudder?

 

No doubt the badly worn tyre is causing a vibration .

To eliminate this , remove the suspect tyre , that should bring you back to a level playing field .

In my opinion what you have described sounds like " tyre scalloping " ,
the more you drive the worse and louder it becomes . ( this by the way is common with a worn or defective shock absorber )

Brake shudder will be easier to test with out tyre vibration .

This would be my starting point before I tackle the suspension or brakes

Cheers ,

 

Good advice. I decided against going with a new Pirelli yesterday (for several reasons) and just had them rotate, balance, and check the odd tire for out-of-round.

The tire shop did see the odd wear one the one tire, with some of the wear indicators being flush and others having tread, but said on the road force machine it turned perfectly round. Regardless, this tire is on the back axle now. Front tires are even and balanced. Most of the road vibration is gone, but the brake shudder did not change at all.

My next step is to pull the front left rotor (which measured 3-5 thousands of runout) and index it, see if this gets runout closer to zero. Maybe the simple solution is the answer here. If that does nothing, then I'll replace the front lower bushings.

As an aside, I also thoguht about the scalloping as a result of a bad shock (from an old automotive encyclopedia which illustrates tire wear issues), but I've never felt anything wrong with the shocks, and this tire was in several locations on the car. And now that the shop says the tire is round, it almost seems like Pirelli made a round tire that wasn't symmetrical. I may look for a replacement P Zero that has 70-80% tread and replace it with that, so then I won't have another odd set of tires on the car.

 

You can still balance an out of round tyre ( will use more lead weight's ) , what you can't stop is the noise/vibration from the uneven tyre wear . Any way , you seem to have fixed that .

As far as brake shudder goes , you need to remember , the faster you drive the worse the shudder becomes (DTV) .
Don't play with it , just have the rotors machined , do both sides , not just the left . you might also check the pads for wear at this stage .

If your car is an XJ8 L 2006 the front rotors should measure 326 mm in diameter .
If they are , your MINIMUM THICKNESS IS 28 mm , do not go below this limit , if need be replace the rotors .

FYI ,

DTV " Disc Thickness Variation " or more commonly known as ( " Disc Run out " ) is not always detectable with a dial gauge .

.15 microns ( 0.015 mm ) is enough to cause or start the cycle of brake shudder .

Given that there are 25.4 microns to one thousand of an inch you can see why it's very hard to measure or detect .

Any way good luck with that .

 

Well, last time I had measured some runout on the front left and none on the front right. Today, I measured the left again and this time carefully bolted the rotor down. Absolutely zero runout with my dial indicator. Not even a flicker.

You make a good point about a thickness variation in the rotors. However, I replaced these rotors and pads around Christmas (not that it excludes them). The thing that leads me back to bushings is that this vibration is mainly in the steering wheel, and it does not change frequency with speed. I've had runout issues on a previous car, and that vibrated the brake pedal badly.

Since I have the new lower bushings already, I think I will replace those and see where I am. I guess there's no definitive way to judge those front lower bushings without just taking the arms off the car?

 

Got around to the front lower bushings on the car today. The old ones were a little bit softer than the replacements, but not horribly worn out (see photos below). That said, after replacing them the brake shudder is 80% gone, and the front end is much tighter. I may be extra picky about the remaining vibration because I'm looking for it.

Really not sure what it could be, unless as you mentioned, it's a thickness variation with the rotors. I just don't feel anything at all in the brake pedal, it's only the steering wheel that shudders (side to side).

I found no issues with the front end to speak of--all the ball joint boots are fine, no play that I could detect. Nothing with the bearings. The lower rear bushing (hydro) look great, no free play either. Upper A arms look great. I think I will go ahead and get it aligned, since I changed lots of suspension parts, see where that puts me. Not expecting it to fix the vibration though. The only other thing would be the tires? Maybe the way they grip it causes them to grab unevenly? Not sure.

 

Hello again ,
You will need to do the wheel alignment , before you do , try this ,

Find a smooth straight dry road

Drive the vehicle at 20 mph , then only just touch the brake pedal , there should a slight
to no vibration coming through the steering wheel .

Now drive the vehicle at 40 mph and again only just touch the brake pedal , your steering wheel will be vibrating .

If that is the case you need to machine the front rotors .

Good luck with that .

 

As mastersid said in one of his note's above, I would take a hard look at that right shock. If it's bad, it could be letting that tire and wheel bounce up and down causing that tire to wear unevenly........also shaky steering wheel and brake.

 

Thank you, yes they are definitely worth checking. I know how to diagnose a typical shock, but how do we go about that on these cars? (when the shock defaults to firm with the power removed).

 

I knew you would ask me that--;-(
You'll have to wait for someone with a lot more smarts, answer that, but just as a 2 cents'er, I would think that if the shock itself was in fact bad, it wouldn't revert to firm when power is removed. One other thing I can think of, is possibly an "oil" wet shock.
Beyond that I can't answer the question. I do know however, that regardless of how well balanced a wheel and tire are, with a bad shock it will bounce along as one drives and will wear a tire in different ways.
If you come up with an answer, let me know.

 

Haha, sorry--no worries, I will see what the FSM says about checking shocks. I haven't really noticed any uncontrolled rebound when I go over road or speed bumps. If the car has gotten softer, it hasn't been enough for me to notice while driving. Still handles well, too.

I will probably see what I can do about the rotors first. If I can eliminate the thickness variation as causing the issue, then I will look at the shocks.