[NatDogg]

I'm a few thousand miles shy of 100k miles on my 2000 ZX3. I was having terrible highway speed vibration, so I took it in to NTB and they noticed some pretty bad diagonal wear on my rear tires. It was so bad that I was shocked I never noticed it and it makes me think that the tires were not rotated properly.

Anyway, the NTB guy recommended that I replace the shocks and struts as well as the tires. New tires solved the problem, but do the shocks need to be replaced or is a diagonal wear pattern on the rear tires a common wear pattern if the tires aren't rotated frequently enough? The shocks and struts are still OEM btw.

Also, I've found the few posts in the forums that talk about a TSB for inner edge tire wear and an SSM for diagonal tire wear that recommends just adjusting the toe on the rear tires.

So, bottom line: should I be replacing the shocks and struts?

 

[nomad327]

Usually struts at that mileage have seen better days, and you sure could replace them. I tend to go with them until I get a leaker or have an obvious driving problem. The thing I would do, especially with brand new tires, is get a full four wheel alignment done by somebody with a good machine. My experience with tire wear in patterns is that it's caused by bad alignment. Bad shocks are supposed to cause a skipping wear pattern as I recall, but I have never actually witnessed it.

 

[WuNgUnSVT]

By 'diagonal', do you mean camber wear? The tires is more worn on the inside than the outside?
I believe Ford made optional (TSB?) camber arms to decrease the rear camber out a degree...
I had this done on my SVT after some terrible camber/flat spotting on my tires (actually Ford replaced 3 of my tires after 15,000Km because of how bad this was)...
I now rotate my tires every 5000Km and don't have any more issues (but the camber arms helped big time!)

 

[NatDogg]

By 'diagonal', do you mean camber wear?

I mean I had diagonal stripes of worn tread across the tires. This little drawing shows what I'm talking about.

Most of the information I've found on the internet says diagonal tire wear is most likely cause by bad toe alignment.

The only TSB on tire wear is the inner edge tire wear problem:

Suspension - Rear Tire Inner Edge Wear
Article No.
03-13-5

07/07/03

SUSPENSION - REAR TIRE INNER EDGE WEAR
FORD:
2000-2004 FOCUS

ISSUE
Some vehicles may exhibit rear tire inner edge wear.

ACTION
If a vehicle exhibits rear inner edge tire wear, and the rear camber reading is beyond the negative end of the specification (max. -2.2 Wagon, -2.3 Sedan & ZX3/5), then install revised +1.0 degree rear Upper Control Arm(s). Refer to the following Service Procedure for details.

There is one other post on these forums with a description of an SSM that talks about diagonal wear:

I found this SSM. Hope it helps

17591 2000-2004 FOCUS - DIAGONAL WEAR OR CUPPING ON THE REAR TIRES
SOME 2000-2004 FOCUS VEHICLES MAY EXHIBIT DIAGONAL WEAR OR CUPPING ON THE REAR TIRES. TO SERVICE, PERFORM VEHICLE ALIGNMENT AND ADJUST THE REAR TOE SETTING TO A REVISED NOMINAL SPECIFICATION: REAR TOE INDIVIDUAL NOMINAL +0.19 DEGREES (TOLERANCE RANGE OF +0.11 TO +0.32 DEGREES) TOTAL NOMINAL +0.38 DEGREES (TOLERANCE RANGE OF +0.30 TO +0.56 DEGREES). SEE WORKSHOP MANUAL SECTION 204-00 FOR PROPER REAR TOE ADJUSTMENT PROCEDURES.

I think SSM's are Ford internal bulletins? They must be because I can't find that particular bulletin anywhere.

Anyway, I guess the question really is: how can I tell if this tire wear was due to poor tire rotation, bad struts/shocks, or improper rear toe setting? I don't want to have to replace something or adjust the toe setting when it doesn't need it.

The NTB guy said "they" recommend strut and shock replacement every 50,000 miles, which seemed excessive to me.

 

[WuNgUnSVT]

That's the wear I had on my tires...but not quite as diagonal as that...
It was like flatspotting...same as that, but more perpidicular...and worn more on the inner edge than normal.
AND they installed the revised arms on my car...which got rid of the problem.

I'd be trying to force Ford to do this work if I were you...

 

[NatDogg]

Well my tires weren't worn on the inside more than usual. It was pretty much all across the tire. The middle portion actually looked more worn than the edges, but it was definitely a diagonal pattern. Bad camber will put the wear on either the inner or outer edge, correct?

Also, I called the shop and asked to see my alignment report. Rear Toe settings as follows:

+0.26 Left
+0.29 Right
+0.55 Total

So it's within tolerance.

I've got new tires on there now so if I take the car in they wouldn't see the wear pattern I'm talking about. How long do you think I can let this go before I start to see whether or not this is still an issue?

 

[NatDogg]

Also, Rear Camber as follows:

-0.15 R
-0.17 L

Camber isn't out of spec and camber isn't adjustable on the rear tires right? That's why they install the revised control arm?

 

[WuNgUnSVT]

I'd think 10,000 miles would be plenty. Make sure you look VERY closely for the wear pattern. You don't need to be buying more tire!
How often did you rotate before? You might of had worse inner wear if you didn't rotate as often.

 

[NatDogg]

I rotate every other oil change, but sometimes I can stretch my oil changes to 5k miles. I'm thinking someone didn't rotate the tires when they said they did.