A6 front tire wear on edge

99 A6Q 2.8. My front tires are showing excessive wear on the outside edges of the tread. In fact, I feel the need to replace them, even though the center of the tire still has about one-third of the useable
tread left. Air pressure, cold, is ~32 psi. The dealer says this wear is "normal". I can't help but feel that something is wrong in the front end.
Any thoughts or comments?
Howard Delman
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Its the byproduct of being able to turn your wheel while stopped, try and get into the habit of pulling away or at least start moving before you turn the wheel, this will elliminate most of the tyre wear
hth
Ron
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The dealer insists that Quattro front tires wear out the outer edges much faster than the center of the tread. Can other Audi owners confirm this?
Howard Delman
Howard Delman wrote:

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How many miles have they done? -- Doug Ramage
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Have you had the alignment/geometry checked recently - using proper laser equipment? I used to have mine done about every 12-18 months (15,000 -20,000 miles). -- Doug Ramage
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Rune Skigelstrand wrote:

Absolutely. The OP's pressures of 32 psi (approx 2,3 kPa) are similar to what I used earlier on, and I got same problem. Handling also had that distinctly squishy North American feel, too.
On 205/55-16 tyres (for an A4 weighing about 1500 kg), I've used 2,9 kPa (just over 40 psi) and found it too harsh, but tread wear was nice and even. On this car I now have the tyres to 2,7 kPa (38 psi) and it's a good compromise.
Make the appropriate translation for your tyre dimensions, car weight, and load, and you'll probably still find that you need to increase your air pressure by about 20% compared with what you have today, to get even tyre wear (and good handling).
Robert
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I am sure the decrease in contact area is not linear.
Otherwise, increasing by 100% would mean the car is suspended in mid-air? :) -- Doug Ramage
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Fair point! Doubling the pressure halves the contact area, so a 20% increase in pressure reduces the contact patch by 16.66667%!
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Peter Bell - snipped-for-privacy@bellfamily.org.uk

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Peter Bell wrote:

Your statement is complete rubbish. That's not the way radial tyres work. If what you said were true then one would expect much more wear in the middle of the tread, compared with the edges, once values over ca. 2,5 kPa are used. You have to go *way* over that to get any symptoms like the ones you describe.
Very doubtful you've ever tested your theory.
Robert
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... but subsequently corrected that to 16.66667% less rubber on the road.

Why?
I didn't know that I'd described any symptoms. I merely pointed out that increasing pressure reduces contact area

My theory? No, I've never set up any experiments to test it. It's based on simple physics/mechanics. If you take the weight carried by a single wheel (in pounds), and divide the weight by the tyre's inflation pressure (in pounds per sq. inch), this should give you the area of rubber in contact with the ground (in sq. inches). As inflation pressure increases, I would expect the contact patch to become shorter, but not to vary significantly in width (within the range of pressures which would be sensible).
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Peter Bell wrote:

Beginning to see what you're driving at - you are right, that a tyre will have its contact patch area reduced if more air is added to it (you are of course indicating the contact patch measured longitudinally - I thought you meant the contact patch measured laterally)
But I doubt that the relationship between contact patch area and pressure is linear.
A tyre being loaded by side forces (turning) will deform to a greater or lesser degree, depending on the tyre pressure. At lower pressures, the deformation
will cause the outer tyre's sidewall to contact the pavement more, causing wear in that area, which is what the OP had commented.
At higher pressures, this problem is reduced, though at a small price to the straight-line stopping characteristics. But with today's much wider tyres, this is usually not a problem.
A car moving in a straight line will always deform the tyre ever so slightly due to the toe-in employed to improve handling characteristics. A higher tyre pressure should reduce the amount of deformation and thus the amount of wear on the outside of the tread.
----8<----- cutting ----

Quite right. The width of the contact patch will not decrease significantly, due to the cords running along the circumference of the tyre.
Would you agree that higher pressures might cure the OP's problem? (once he gets new tyres, that is ...)
/Robert
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Peter Bell wrote:
---8<---cut

You are quite right of course. Elegantly put. The dimensions of pressure are (in SI terms) kg/m2. Thanks for the insight, I now understand what my 6th form physics teacher was trying to tell me - 27 years later ;-)
---8<----cut

Don't agree there, regardless of what theory may tell us. My empiria showed me that a higher tyre pressure fixes the problem of outer edge tread wear, without sacrificing braking effectiveness, and gave me better cornering as a bonus.
Anybody else reading this try more air to fix uneven tread wear? What results did you get?
/Robert
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[Snip]

You must be younger than I am, then - I left 6th form in 1972. I must say that the relationship between inflation pressure and contact area only struck me in recent years. This then put paid to the idea of 'getting more rubber on the road' by fitting wider wheels/tyres - unless the tyre pressure is reduced with the wider tyre, all that happens is that the contact patch changes shape.

Yes, the essential cause of outside edge wear is the tyre squirming sideways during hard cornering such that the shoulder of the tyre rolls under and makes heavy contact with the road. Of course, it is the outside edge of the more heavily-loaded wheel which bears the brunt. Increasing pressure stiffens the sidewall, reducing the squirm. Whether this can entirely eliminate uneven wear across the tyre will depend on other factors such as suspension geometry and roll-stiffness. Note the 'won't necessarily' in my previous post!

Yes, I have, and there's no doubt that it will improve matters. Don't forget that increasing pressure reduces rolling resistance and, within reasonable limits, reduces tyre wear anyway.
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wrote:

So what -- sideforce is not just a matter of contact patch. As you incresase the pressure (within reason) the extra stiffness in the side wall increases cornering force, despite the (slightly) smaller contact patch. Ask anybody who races on street tires.
You can carry this too far, however. Above about 45 lb (most street tires) cornering force will start to drop off, as the sidewalls are now too stiff to allow the tread to stay flat on the road.
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