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CapriRacer · 07-28-2013, 10:32 AM

Just an FYI:

The belt in a steel belted tire is a layer of parallel steel cables encased in a rubber matrix that runs at about a 15° angle to the circumference. In other words, the steel in the belt is NOT circumferential and does not PREVENT the center of the tread from growing - it only restricts it.

In passenger car tires, there is typically 2 steel belts - one "angle left" and one "angle right" - BUT these 2 belts are insulated from each of by rubber and can move relative to each other.

So as inflation pressure is added, the center of the tread bulges out - a large amount for the first bits of inflation pressure and the amount decreases as more and more pressure is added. The important thing to remember is that it doesn't stop. More inflation pressure results in more growth at the center of the tread - albeit in small increments at higher pressures.

Where this gets complicated is that tire wear is more affected of other things - and some of those things can counter the tire's tendency to wear at the center. Driving style has a major affect. Severe cornering tends to wear the shoulders of the tread. So if you combine strong cornering with high inflation pressure, the result could be even tread wear.

Plus, the construction of a tire (meaning the flatness of the belt relative to the loaded profile within the tire's structure) can affect the evenness of wear - and tire manufacturers do adjust this as they get data from their returns. It is not uncommon for some radial tires to develop shoulder wear due to poor placement of the belts - but fixing these sorts of things requires increased cost and increased rolling resistance - and sometimes that is not acceptable.

Put a different way, tires aren't always designed to wear evenly. In many cases, uneven wear results in things that are more desirable. For example, tires supplied to vehicle manufacturers have to meet rolling resistance requirements and since these tires don't carry a treadwear warranty, it's OK if they wear out in the shoulders first. In fact, one of the tricks tire engineers use to get low rolling resistance is to take rubber out of the shoulder - and that results in worse shoulder wear.

Bottomline: Increasing inflation pressure TENDS to cause wear in the center of the tread, but there are enough other factors that can overwhelm this tendency - so you need a large sample size to see this tendency.

07-28-2013, 10:32 AM	#25 (permalink)
CapriRacer Tire Geek Join Date: May 2008 Location: Let's just say I'm in the US Posts: 796 Thanks: 4 Thanked 393 Times in 240 Posts	Just an FYI: The belt in a steel belted tire is a layer of parallel steel cables encased in a rubber matrix that runs at about a 15° angle to the circumference. In other words, the steel in the belt is NOT circumferential and does not PREVENT the center of the tread from growing - it only restricts it. In passenger car tires, there is typically 2 steel belts - one "angle left" and one "angle right" - BUT these 2 belts are insulated from each of by rubber and can move relative to each other. So as inflation pressure is added, the center of the tread bulges out - a large amount for the first bits of inflation pressure and the amount decreases as more and more pressure is added. The important thing to remember is that it doesn't stop. More inflation pressure results in more growth at the center of the tread - albeit in small increments at higher pressures. Where this gets complicated is that tire wear is more affected of other things - and some of those things can counter the tire's tendency to wear at the center. Driving style has a major affect. Severe cornering tends to wear the shoulders of the tread. So if you combine strong cornering with high inflation pressure, the result could be even tread wear. Plus, the construction of a tire (meaning the flatness of the belt relative to the loaded profile within the tire's structure) can affect the evenness of wear - and tire manufacturers do adjust this as they get data from their returns. It is not uncommon for some radial tires to develop shoulder wear due to poor placement of the belts - but fixing these sorts of things requires increased cost and increased rolling resistance - and sometimes that is not acceptable. Put a different way, tires aren't always designed to wear evenly. In many cases, uneven wear results in things that are more desirable. For example, tires supplied to vehicle manufacturers have to meet rolling resistance requirements and since these tires don't carry a treadwear warranty, it's OK if they wear out in the shoulders first. In fact, one of the tricks tire engineers use to get low rolling resistance is to take rubber out of the shoulder - and that results in worse shoulder wear. Bottomline: Increasing inflation pressure TENDS to cause wear in the center of the tread, but there are enough other factors that can overwhelm this tendency - so you need a large sample size to see this tendency. __________________ CapriRacer Visit my website: www.BarrysTireTech.com New Content every month!