One reason to inspect your tires closely every time you rotate them
 

Due to front-end feathering wear, even when I know the suspension is properly aligned, I rotate the tires in an H-X-H-X pattern every 4K miles, such that the tire sits on all four positions coming back to the original position at 12K miles. Since I statically balance the wheel-and-tire assembly after mounting the tires myself, I test dynamic balance by driving at speed, where, if I did a good job on static balance, I rarely, if ever, get wobble at speed.
https://www.yotatech.com/forums/atta...ic_balance.jpg

Last week, after doing a brake job, I had a wobble at speed, which, I thought might be the tires being unbalanced, so I moved them in position for a week and just put them back where they belong today.

Normally, I inspect the tires by trying to pull out of each tire 100 pebbles and stones and broken bits of debris out of the sipes, where I generally get over 50 but rarely near 100 for each tire.
(The reason for counting is that it's a boring job - so trying to get to 100 makes the job slightly less boring.)

While I often find pebbles and even sometimes some glass shards stuck in the sipes, today I found this little metal nib embedded in the two front tires that I had moved to the rear temporarily last week.
https://www.yotatech.com/forums/atta...1&d=1518920059
When I teased out that little nib, I was surprised to find the same-shaped sharp-tipped shard of metal about 1/4 inch long in both tires!
https://www.yotatech.com/forums/atta...1&d=1518920059
If this tiny plate of sharpened steel isn't the perfect wedge to eventually wear into the tire to make it slowly leak, I don't know what else is!
https://www.yotatech.com/forums/atta...1&d=1518920059

So the lesson learned is to always inspect your tires closely at every 4K mile rotation, where I recommend you overcome the admittedly boring task by counting and trying to remove 100 bits of debris, one of which may be something like what I found today!

Nice find! Had a flat on my 4runner a couple years back, threw the spare on and headed to the tire shop to get it fixed. Couple blocks before the shop I notice a clicking noise from the spare I just put on. Pull into the tire shop to inspect and find, I kid you not, a 5/8" bolt stuck in the tire. Not one of my best days. :( But hey It was an excuse to throw on a fresh set of KO2's. :D

Thanks for that anecdote, where, likewise, when I've found a nail or bit of glass or sharp chunk of metal that I might have gotten it simply from something I did differently recently, like driving on the shoulder (when I stopped to help someone at the side of the road) or when going to, of all places, a tire shop, where they're often in an "industrial" complex, replete with all sorts of sharp things lying on the ground just waiting to stick to our tires.

Sometimes it might be better to park at the curb and WALK to the tire shop to get something (I buy those pull-through patchplugs from them to repair tires from the inside out).

The startling thing about this shard is that it was so tiny that I'd never have seen it unless I had my fact to the tire, as the protruding end was the size of a pinhead and, the oddest thing, was that it had a twin in the other tire! (I actually found the twin first, but didn't snap a picture of it until I found the same thing in the second tire!)

I'm wondering if it is the leftover from a construction staple of some sort, where the staple could have been whole at the time it embedded in the tire, but the rest broke off?

Anyway, the point here is the PSA of inspecting your tires to get from 50 to 100 objects out of the sipes, some of which could eventually work their way into the rubber enough to cause a very slow leak.