How does a tire change technician determine whether a tire is out-of-round because of a tread separation etc?

You raise an age old question one that I've looked into hundreds of times. The easiest way to determine tire run-out is to put the car on jack-stands and turn on the ignition in low gear. With a white china marker or white chalk and a piece of 2x4 to guide the chalk or marker observe the tread as it slowly spins. In my book if a tread runs out more than .090 the only wheel / tire balancer that is able to correct the problem is a Hunter GSP 9700 Force Wheel Balancer. Go to Hunter wheel balancers and check this machine out. There's a box to fill in your zip code to find shops in your area who have these machines. It's by far the most complete system on the market. It senses bent wheels and out of spec. tires before the actual balancing takes place. A force wheel exerts 1,400 lbs on the tire as it spins to re-produce road spinning weight. The weights are added to the center-line of the hub flange first then any small clip-on weights are added if absolutely needed.

This machine corrected an out of round condition on a new set of front tires that had previously been spun balanced on a Coats machine. Before they were re-balanced on the Hunter GSP-9700 they were checked as is first! What an eye popper. The previous balance job was completely unacceptable. They were done using the force wheel and the vibration was gone for good as I put the tires and wheels back on the front of the car.

My question to you is: How much out of round tolerance is allowed on any new tire. I have yet to find that very simple question out.

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RE:

How does a tire change technician determine whether a tire is out-of-round because of a tread separation etc?

I know that an out-of-round tire vibrates the car badly the faster you go and yet can still be dynamically balanced perfectly on the technician's spin balance machine.

Balancing a tire doesn't cure an out of round or separated tire, nor will it keep it from shaking. A tire is under a great amount of stress, and if it isn't round it will shake no matter what you do. Usually you can tell by looking at it, you will see a bulge in the tread or sidewall; other times, when it is still early, you can see where a spot or area of the tread is worn down too far in relation to the rest of the tire. When that happens, throw it away.

This isn't an answer. I just bought a 2015 Silverado and noticed a strong vibration at 70 mph. Called service for an appointment,, stated my concerns and found out that all 4 tires were out of round and needed to be replaced. This was from factory with 24 miles on the truck when I bought it. Not sure if it sat in the dealer yard too long or they just had a bad batch of tires.

As the other have stated, it is easy to see a tire that is out of round, or distorted due to tread separation. I have seen tires that were S shaped when viewed straight on due to separation. Brand new tires can be out of round. A dial indicator is used while the tire/wheel is mounted on the vehicle or balance machine to determine the amount the tire is out of round. Most manufacturers call for a spec of less than .080" out of round to minimize vibration. This is not very much. Sometimes it can be corrected by rotating the tire to a different location on the wheel and re-checking it. In some cases the out of round condition is due to the wheel. The wheel would have to be replaced in that case. In a few cases, the run-out can be due to radial run-out of the hub bolt pattern. A stack up of tolerances in each component. If the hub run-out is .030, the wheel run-out .050 and a tire run-out of .060, and all are assembled in the worst position, the total run-out would be .140. You would have a vibration even though the tire is balanced. By aligning the components for the best outcome, the run-out can be reduced to .020. I hope this answers your question.

A seperated tire can sometimes give a visual clue. It can show in what some call an "egg". It is a bubble on the tire, any size any location. Even inside the tire where you cannot see it. The egg is the spot where the metal wire has broke, seperated and deformed the surface.

These can almost always be spotted visually, either with an inspection of the tire or by observing it on the balancer.

ASE Certified Automotive Service Manager working in the tire industry

Tread seperation is easily spoted. Simpley roll the tire (inflated) and watch for the wobble.

some well equiped tire shops have a "road force ballance" and it puts pressure onto the tire tread as it is being ballanced