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Discussion Starter · #1 ·
Hi, all. I recently decided to replace the Nitto tires on my 215,000 mile MDX. I put the Nittos on with 160,000 miles, so they've been great for 55,000 miles. I rotated them regularly - thinking last time I did it was about 10-15,000 miles ago. Never noticed any odd wear on any tires. Today I went in for a new set of Michelin Premier LT tires (nice, so far), and was shocked and amazed when they showed me the rear tires I'd been driving on (and just finished a 7,500 mile road trip on, no less)... Portions of the tire didn't look nearly as bad as the photos, though the uneven wear was obvious all around. There was no sign of any rubbing on the fender liner or anywhere else where these tires could have possibly contacted anything.

For the life of me, I can't imagine what did that to the inside of the rears. I've seen odd wear on front tires with bad alignment, or with some really ham-handed driving and/or under-inflation. But to have plenty of tread above the wear bar, AND to have the inside edge of the tires scrubbed down to the point the wires show... I'm at a loss (but really happy I pulled the trigger on an "early" tire change). Could it be a rear alignment problem? Seems to roll and handle just fine, but I suppose there could be something bent or otherwise out of line...

Thoughts?

 

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Blown rear shocks with no gas charge and/or heavy loads in back will make the rear squat, and when the MDX squats its rear, it rolls the rear tires onto their inside edge. ( Induced negative camber ). Check your shock absorbers. The rear shocks should have been replaced multiple times by 215k miles, unless your roads are a whole lot better than mine.

And if you are towing, check the tongue weight.
 

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Discussion Starter · #4 ·
The tires have been inflated correctly. I replaced the rear shocks 6-8 months ago (and the old ones I pulled off were pretty much fine), which is about the time I rotated the tires (meaning the wear all occurred with the new shocks installed).

I guess I need to check the alignment... I'm guessing that it would be a gross misalignment to cause wear like this. The odd thing is that the wear is ALL on the last couple inches of the tire, and I'd expect an alignment problem to cause scrubbing across the entire tire, not just the very edge. I could see a lot of negative camber causing this kind of wear (and have seen lots of vehicles set up that way by boy racers), but my wheels are really vertical.
 

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So I guess that takes us to defective tires or occult rubbing, which AFAIK would be unusual at the rear but could happen during full suspension compression if the tires are oversize and/or installed on non-stock wheels. Are the tires and wheels OEM size, including offset of the wheels? Is that wear pattern all the way around the tire?

But how does this fit with all the wear happening after the shock swap and wheel rotation? Are the shocks OEM? Changing shocks is pretty easy on 1st-gen, and I can't think of anything offhand that could rub if it isn't installed correctly, but take a close look at anything that might rub when the suspension compresses.

Do you have about 4/32 of tread left overall? I have seen scrubbing of the inner edge when my tires get to the end, but nothing this extreme.
 

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Discussion Starter · #6 ·
The unusual wear was all the way around, though worse in some places than others - but seriously more worn out than the rest of the tire(s), which still had at least 10,000 miles of tread left on them. I'd say half of the circumference of each of the rear tires was worn down well below any hint of tread, and in a couple places to the steel cord, while the other half of the circumference still had enough tread to look more or less OK in a (too) quick inspection.

The tires and wheels are aftermarket, and larger than stock - 255/55/18. That said, there's no sign of any rubbing anywhere underneath the car (something the tire techs looked for as well). I think the first place that tires would rub would be the fender liners, which would burn through long before this kind of damage was done to the tire. But as I said, there's no apparent damage anywhere.

The shocks are (IIRC) KYB shocks - definitely aftermarket, but "not junk". And the ride quality is just fine as well.

There was about 4/32" of tread left - the really freaky part was that the wear wasn't at all spread out across the face of the tire, but there was a pronounced "lip" at the edge of the unusual wear. It's hard to imagine misalignment causing that specific kind of wear pattern, rather than a more gradual scuffing that leaves less tread depth from inside to outside.

I'm usually a pretty fair automotive detective, but this has me stumped.
 

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Discussion Starter · #8 ·
I had a four wheel alignment done a couple years ago (with the same size tires). I went back to check the results, and found that the specs the alignment shop used don't match those in the factory service manual.

The camber on the rears was -1.0° on the left, and -1.6° on the right. The "spec" the alignment shop used looks to be centered on -1.0°, so the left one looked perfect and the right was off a bit.

Looking at the spec in the MDX factory manual, I see the actual specs are: -0°30', plus or minus 45' (which could be reformatted to -0°75' to +0°15').

I'm still astonished that I got the wear I did from the camber being off that much (a quarter degree on the left, almost 1 degree on the right). I suppose it might have changed in the last couple years (considering I put over 50,000 miles on the car since then).

I'm thinking the prudent thing to do is to install adjustable upper control arms (aka "camber kit"), and have a new alignment done before I put any real miles on the new (expensive) tires. Oh, and stand over the technician with the actual specs this time... ;-)
 

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Discussion Starter · #9 ·
Just ordered a couple Moog adjustable control arms.
https://www.rockauto.com/en/moreinfo.php?pk=3638358&cc=1429118&jsn=15

They were on sale, just a few bucks more than the no-name control arms available elsewhere (and a whole lot less than the typical "performance part").

My plan is to lift the rear, take off the wheels, and measure the angle of the hub face, then to install the adjustable arms, and crank them out to cant the hubs out by difference between the results of the last alignment and the factory spec. I've got a cool app on my phone that allows me to use it as a very sensitive level.

And then I'll get it aligned "for real", of course... ;-)
 

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Discussion Starter · #10 ·
Well, it only got to around 100° by late morning, so I drug a patio umbrella around to my driveway and dug into swapping out the upper control arms with adjustable units.

FWIW, the Moog control arms I got (part number K100106) are nicely built, and look pretty sturdy. One thing I did notice though is that their "shortest setting" is pretty close to the length of the originals. So these aren't going to be a good choice if you're trying to set up loads of camber for track day performance (like anyone would really do that on an MDX). ;-)

I took my best guess at setting the length, but ended up having to adjust it with the wheel down and tire on the ground. Not really a big deal, as long as you work out which way to turn what (including the adjuster and the lock nuts). It was about as easy a job as you can imagine, so I didn't bother taking photos. I used a pickle fork to remove the old UCAs since I wasn't ever going to use them again. Getting the bolts in wasn't difficult at all - it's easy to tweak the angle of the hub to push the UCA bushing into alignment with the bolt.

So after doing a quickie camber alignment (shooting for -0.3° using an angle finder app on my phone), I should be good to go. At least until I get a 4-wheel alignment done after I do my struts in a few weeks.

 
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