Tire randomly developed a flat spot

Tire engineer here: Flat spots on a tire are indeed a rarity on modern tires. Without actually looking at your tire, even perhaps cutting it apart to check the condition of the belt packages. I can only conjecture a few possibilities.

1. The belt package is damaged in the area of the flat spot leading to less rigid support behind the tread rubber.
2. The side wall belt package is damaged in the area of the flat spot leading to less support of the tread. The side wall belt package is much like a reverse link-bar suspension bridge. Designed to suspend between the two sides of the rim from bead to bead. As the tread meets the road, load forces travel along the sidewall belt package to the rim and the combination of sidewall belt package and air provide an equal but opposite force. Its secondary purpose is to dampen some of the varying amplitude/changes of the load forces. For this reason, I would never buy a used vehicle with low profile tires that was not designed by the vehicle manufacturer to use low profile tires. Unless the vehicle is designed with a suspension to handle the increased amount of volatility of road forces passing thru the rim into suspension, the tire is basically beating the suspension to death.
3. This last one is a little harder to explain and can itself have several underlining causes: Consider a car with tires on the rear a different tread diameter than the tires on the front. At any vehicle speed, the smaller tread diameter tire is rotating faster than the larger tread diameter tires. Now imagine a portion of the larger tread diameter tire is worn to a slightly smaller diameter than the rest of the tire. The moment that smaller diameter patch contacts the road, two things will happen singularly or together. The slower moving rubber as is contacts the road wears faster as it tries to accelerate the rotation of the wheel. This condition will accelerate the wear of the tread low spot.

I don't believe your vehicle suspension is a cause, but I would recommend, for safety reasons, that you change out the tires if you notice it's getting more pronounced.

For what it's worth, I had a Goodyear tire randomly develop a flat spot within a month of new installation on 2015 Limited.

OpticonBill made some good points - I'm also from OEM world, advanced manufacturing so I spent a lot of years working through some of the vehicle development issues. Indeed, major changes to suspension impact forces as a result of sidewall reduction. However, what I know from tire engineers is that they do, in fact, flat spot. Typically we're talking from sitting on a lot. At 70 degrees the flat spotting that isn't permanent will be gone within 1/2hr of driving. The rest is there for good. Just what I've been told when asked directly to the tire engineers I know.

What sounds odd to me is the pull you mention. I wouldn't expect a flat spot to cause this. And I also was curious how you saw the flat spot. I didn't think you could typically actually see them.

mobile314 said:

Has anyone had experience with a tire that randomly developed a flat spot from one day to the next?

I don't think it matters in this circumstance but it's a 2019 Ford Expedition Max Limited Stealth. Daily driven by the wifey on the highway every day. I say that because I've been a shady tree mechanic long enough to know that if your vehicle sits for an extended period, it will develop a flat spot. She said she didnt hit any curbs, didnt slam the breaks and didn't hit any major pothole.
So googling and search the forum on this issue is tough because I am only getting results for flat spot from sitting to long. But its so strange. From one day to the next, it developed a bad vibration. Truck was pulling to the right. Wasn't hard to find the flat spot. I would say there is about 45% tread left on the tire. I hate to just buy one new tire versus getting them all done when its good and ready. Ive read stuff where guys have over inflated the tire for a 100 miles and apparently fixed it to some extent. Granted its the wife and kid school and sport truck, Id rather not risk it.
Anyways, Ive never heard of a tire randomly disforming so I thought I would throw it out there and see if anyone had experience with that on any vehicle.

Click to expand...

Hi All- Seen this before. Not likely a "flat spot" on this tire... flat spots happen as a result of locking up the brakes or a large, high duration "spin" where the vehicle ends up facing in a different direction. Many many years in the tire business makes me suspect a "Tread Separation" which means the tread and the carcass are separating from each other... This results in visible bulge or growth under the tread. It may be as small as 1/8" inch high or could approach one inch. I promise you you would notice this problem. Usually causes a vibration which could also make the vehicle "pull" to the left or the right. This condition cannot be fixed or balanced out. The tire must be replaced. It will eventually deform and wear enough that you'll see the steel belts under the tread. Let us know what you find... Ernie

The factory hankrooks will flat spot after a day or two, though I’ve noticed it I’m pretty sure overnight. Absolutely hate these tires. Hate. So I can totally see some random brand doing that. However, these ****** tires will roll back out after a few miles.

The only flat spots I’ve ever actually seen were on a classic I had. Tires were in the car when I got it. After about six years I had to replace them as they were old and you could see the flat spots as you spin the wheels around with it on jacks.

With your tread worn that much you will most likely at least need to replace 2 tires. Replacing one will probably cause issues with the dif because the difference in tread compared to the other tires is too great.

mwar99 said:

With your tread worn that much you will most likely at least need to replace 2 tires. Replacing one will probably cause issues with the dif because the difference in tread compared to the other tires is too great.

Click to expand...

While it's preferable to replace both, I think the diff design can handle such a small difference without failing.