924Board.org

[!tom]

So I've got a bit of a question on tire wear.

I put on brand new tires when I did my 5-lug conversion a couple years ago, as well as doing corner weights and an alignment. I've driven approximately 23,000 km or 15,000 miles (odometer is broken, so it's an estimate).

Corner Weights
Alignment Figures

Tires: 205/55R16 BFG Super Sport A/S

My right front tire is just about at the wear bar on the inside. The left front has substantially greater tread depth. Tire pressure has been 32 PSI the whole time.

Why the huge difference in tire wear?

You think there's any chance at a warranty? I haven't rotated my tires yet because I've been afraid of what might happen if I tried. . .
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78 924 NA
5-lug

[jason c]

Too much negative camber. Check for a worn wheel bearing, worn strut, worn control arm bushings and the camber adjustment. It is possible the eccentric bolt came loose causing too much negative camber. Its also possible the alignment wasn't done correctly to begin with. I highly doubt you'll get it warranteed, manufacturer will tell you the same thing I just did. The shop may do something for you if they sold you the tires and did the work.

[!tom]

Brand new bearings (8 bearings in all 4 corners) when I did the conversion, and that's the camber setting it was adjusted to when I had the alignment done. Less than that and it rubs (it still rubs a bit).

I got the tires from a tire shop and the alignment done at an alignment shop. Tire shop has never even seen the car.
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78 924 NA
5-lug

[jason c]

[!tom]

I was told the 5-lug bits came from a 931.

What I'm curious about is how the right front tire seems to be wearing out substantially faster than the left front tire. Camber is about the same, weight is about the same, caster is about the same. . .
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78 924 NA
5-lug

[jason c]

Tire pressure does effect wear, it does not cause inside-only wear (which is your complaint). Excessive tire pressure can affect the amount of width of inside wear when negative camber is present, it cannot cause inside wear without negative camber.Toe can cause inside wear but not if its only one wheel. Too much negative camber is the result you're seeing, the cause of the negative camber is what you have to find. Are you checking the camber with a gauge on a level surface or "eyeballing" it?

[!tom]

Camber was adjusted on a 4-wheel laser alignment rig and hasn't changed since being set.

I expect the insides to wear a bit faster than the outsides. I don't expect the right front tire to wear faster than the left front tire.
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78 924 NA
5-lug

[jason c]

I understand what is happening and what you expected, I get it. According to your readings you're .02 more on the right side, if your readings were correct and if they are still the same. Do the roads you most often drive on have crown on the left? You still haven't answered as to how you are checking camber, are you assuming it hasn't changed because you didn't touch it? It is possible there was movement since the alignment. It is also possible that the readings weren't correct. Even assuming all is as stated and nothing has changed, the slight difference in camber along with the crown of the road could cause the wear you are seeing, but if that is the case, you should also see a difference in wear in the rear.

[!tom]

You're suggesting 0.02 degrees camber difference between sides is significant. I had assumed it wasn't.

Let's run the numbers.

Left front has an angle of 1.4 degrees from horizontal. Tires are 205 mm wide. This means the effective radius of the tire is 205 * sin(1.4) or 5.0mm less on the inside than outside. Another way of saying that is the inside edge is 2.5mm less than the middle, and the outside is 2.5mm more than the middle.

Okay, I didn't expect that much.

Right front would be 205 * sin(1.6) = 5.7mm.

All else the same, I'd expect 0.7mm / 2, or less than 1/2mm difference in tread depth difference between left and right front tires due to camber alone.

Interesting. That's probably more than I was thinking.

I really should measure tread depth to get a handle on this, but eyeballing i'd guess the difference is probably 3 times that. But, eyeballing it is not very conclusive.

As far as crown, there's one section that I drive on regularly (probably around 1 km a day) that has a fair bit of crown, but everything else is normal, meaning a tiny bit of crown (not enough to get the car to pull to one side).

I replaced the strut mounts when I replaced the struts 6 or so years ago. I have no reason to believe the bushings are shot, nor is there any reason to believe any adjustments have adjusted since the alignment.
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78 924 NA
5-lug

[Rasta Monsta]

Not sure what you're arguing about. You have an alignment problem. . .you would be amazed how often alignment shops make mistakes. It needs to go back on the machine and they need to show you RF is still in spec.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[morghen]

[jason c]

You can lead a horse to water......

I'm saying there are several things that can lead to the excessive negative camber. A little of this and a little of that is all it sometimes takes. Any looseness or wear will automatically add negative camber. It is possible that the eccentric bolt was loose enough to allow some strut movement as well.
When was the last time the alignment machine calibrated? Was the runout done correctly? Are the bushings in the wheel heads to clamps loose? Did the heads get bumped during the alignment?
I have done more alignments than I can remember, all of the above is possible.
You can measure the difference in distance of the side to side angle but it doesn't translate to the exact same distance in tread depth because the majority of weight (pressure) is being applied to the inside, constantly. As the inside wears, only a minimal amount transfers towards the outside. It wears the inside faster. Even when the tire is worn to an angle, more pressure is still applied to the inside.

[musicalannette]

hi,

remember all the settings are for an "average usage".

a bit of cornering. a bit of strait road, white lines, maybee even a bit of track use.

assuming your settings are ok (and a change in one setting can affect the opthers), then i would guess you do a lot of strait road driving. this will wear the inner of the tyre.

if the roads not level (crown on the road) this might effect the tyres wear left to right.

hope this helps.

the best 4 wheel system i have seen, was a 4 wheel radio linked set, with 4 measuring devices, doing each wheel all the time. 1 adjustment and you could see the rest change (or not). it was about 15 years ago with a wireless 2.4ghz link to the pc. wifi/blutooth equivalent before it was around, the colours looked like bosche, nut i can remember exactly.
it was around 20000 pounds in uk sterling in around 2000. i remember the guy saying the 4 post lift had to be specially fitted to within 1/1.5mm!!
which really cost! it went as far as fitting weights in the car to simulate driver/passenger! i thought at 40 quid it was cheap! and thats all that place did. alignment. took about 30mins.
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....

[musicalannette]

Two things i would check.

1 the rack is centered. ( your tracking can be fine and all set up, but the arms that connect the rack to the upright might be different lengths.)

If there not the same, then it will change the toe -in one side to the other as you go over bumps.

2 all your bushes/balljoints are good and theres no movement.(it could all be good till you take it up the road, then it floats about due to play).

there free, but you might need a freind to look while you have a pri-bar in your hand (make sure the cars up in the air solid (dont try it on a jack).

hope this helps
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....

[jazz guy]