Odd tire wear


#1

I’ve encountered a curious tire wear issue that warrants some feedback thoughts from the collective. I recently replaced all 4 tires on the wife’s Saab because of the tire issue shown in pictures below. The inner edge of the tires wore clear through to the cords on 2 of 4 tires and the other 2 were close Pictures show one cored, the tread used and the 3rd worn but not corded. In 27,000 miles, long before hitting the wear bars. These are Khumo Ecsta LX Platinumtires and the second set of tires to do this.

The last set of Khumo Ecsta ASX tires went 35,000 miles but failed before the wear bars appeared. I used the same model ASX tires on the Mustang and had no issues like this. I drove the heck out of them, put 25,000 miles on and sold them with tread left.

The first set of OEM Michelins did not wear like this but got extremely noisy as they reached time for rotation. Rotate in a X pattern and they were quiet for a while but they wore evenly.

The car is in alignment except the rear has 1/4 degree more negative camber than Saab specs out, but it has been at the max limit when new and its sagged a bit over the years. Rear toe is a touch more than I prefer at 0.44 degrees toe in but in spec at 0.42 +/-0.2. The front is spot on at 0.20 degrees toe in and 0.75-1.0 negative camber on a spec of 0.28 +/- 0.08 toe in and -0.9 +/-0.5 camber. I ran much more aggressive camber on the front of the Mustang, -1.5 for the street and -2.25 for the track with way more caster than the Saab.

Is it the tires? Is it the car? Anybody else have similar experiences with these tires or manufacturer?


#2

You might have to watch the car go around corners. I imagine that the tire is trying to fold under the car. Something has to be broken. Not true but it is my first thought and struts would be my first guess as to where to look and then anywhere there is a bushing. That isn’t much help but I haven’t been under a car in years.


#3

So how old is the Saab and how many miles are on it?
Looks like a typical negative camber issue to me. This can come from tired old springs combined with your having the camber a tad more negative than spec.

I’d start with a close look at that sagging you mentioned. As I know you’re aware, wheels will intentionally go to negative camber as they move upward of the “new & static” suspension position in order to keep the track constant. With the springs sagging, it’ll be constantly leaning toward that condition.


#4

Very odd indeed! The missing chunk is really different, almost like something took a bite out of the tire? Take a good look at the wheel wells and suspension parts with the car up on a lift. I’m wondering if something could be contacting and/or rubbing on the affected tire(s)?


#5
I'm wondering if something could be contacting and/or rubbing on the affected tire(s)?

+1 Look for a shiny surface.


#6

No rubs anywhere 'cause that’s what it looks like to me, too.

I forgot to mention, I had the front end completely apart to check everything at 101,000 miles and 15 years of age.

I replaced the control arms/bushings/ball joints because the ball joints are un-grease-able and were a tad loose. The rest got replaced for age alone although everything looked great. Replaced the stab-bar links because they were a tiny bit loose and some minor clunking. I took the strut assemblies apart to replace the jounce bumpers because they were pounded to dust and 1 inch shorter (midwest potholes with a lower Aero-model ride height). The struts were fine; no leaks and hand-stroked great. Same for the steer bearings and mounts. Back together it was quiet and felt like a brand new car.

Did a rear inspection next. Everything looked and felt tight. Measured up just fine except for the little bit out camber. I’d expect more than just the inner shoulder to be worn if camber was the issue. That’s the head-scratcher. The wear across the face was just about perfect. I can probably force the camber out by loosening the bolts and drawing it up with a ratchet strap and then tighten to get it into spec. I’d like less rear toe, too.

It doesn’t roll much at all even when I drive it, let alone the wife!


#7

I’m still going with tired springs.


#8

All 4 tires are like this. Do you rotate the tires frequently. If not, do the rear tires get this way while on the rear?

What I am suspecting is that you do rotate the tires frequently and that is making the bad part and I suspect that the bad part is a bushing on one of the front trailing arms (aka, drag link), if this car uses trailing arms.

I am not familiar with Saabs, but some cars use the anti-sway bar as a trailing arm as well. The sway bar goes through the lower control arm and has a pair of bushings between the sway bar and the control arm. One of these bushings could have disintegrated or just pulled through the control arm, or the nut came off.

Edit: The trailing arm could have a bad bushing at either the control arm or the front cross member of the frame, the one below the radiator. A center bushing on the sway bar could also cause this in the case of the sway bar serving as the drag link.


#9

I noticed that you didn’t replace your tie rod ends. Try this. with the car on all four paws, have your wife turn the steering wheel back and forth about a quarter turn each way while you look at the various suspension parts. You will see any parts that are slipping the two sides, like a loose tie rod end. Watch the tires and make sure they move in sync.

The hardest part to detect will be the inner tie rod ends as they are covered by the rack bellows. If one or both of these are loose, the tires won’t move quite in sync, one will move before the other. For this, it might be best to jack up the front and move one tire left and right while watching the other. They should move in sync.

This is the bogus test that some mechanics use to sell tie rod ends, ball joints, wheel bearing etc because the customer only notices one wheel moving and doesn’t see that the other wheel is moving in sync, just like it should.

BTW, you might want to take the wife out to dinner before you do the on the ground test, just in case she might get ideas while you are lying on the ground in front of the car.


#10

Have you checked the edge of the lower spring pads on the struts? Offhand, it looks like the tires have been rubbing on the strut spring pads.

What year model SAAB and what size are the tires?


#11

This looks like too much camber. 2 thoughts:

If the camber is over 1 degree, then this tends to cause tire wear issues.

Most published alignment specs are too wide - by half - and it appears that Saab’s specs are, too!


#12

2001 Saab 9-5 Aero sedan (lower ride height, bigger brakes) Factory tire size always used; 225/45/17. No rub marks at all front or rear and it still has the factory front struts. Rear shocks replaced 66K ago (a leaker at 35K)

Part of the reason for rear camber being over 1 degree negative, I’ve been told, is the car has a tendency to oversteer in quick transitions and that isn’t acceptable in the US market.

I’ve experienced camber wear on other cars at over 1(and sometimes over 2) degree negative and that always shows the inner tread blocks to be worn more than the outers. These aren’t, only the shoulder. I’ve read a few comments on forums about this type wear on Khumos on Saabs as well as other cars.

No disrespect to @CapriRacer for the disagreement, I highly value his opinion as a tire engineer and racer.


#13

I agree that it is not a camber issue. OK4450 could be right in that even though the tire is the OEM size, that does not mean that it is exactly the OEM size. There is some variance in actual sizes and often quite a bit of variance in the tread width. The tread on a Pirelli P7 tire in that size is over an inch wider than the same size Michelin Premier. One tire may rub where another would not.