Quote:
Originally Posted by CapriRacer
The reason I asked the question is that I am confused about why you would think wide tires and narrow tires would be different when it comes to tread radius. Perhaps if I answer your question, it can serve as a basis so you can answer mine.
Let’s start with an assumption that in the contact patch, a flat belt is needed to get an even pressure distribution. That means that the tread thickness is the same shoulder to shoulder. Remember this is an assumption, which we will revisit later.
If I measure the tread radius when the tire is completely unloaded (commonly called Freestanding), I can get a value – and I can translate that back to the radius in the mold, because I know the relationship between freestanding and molded tire shapes.
But what if my initial assumption about the belt needing to be parallel to the road surface is wrong? I can add or subtract rubber as needed. And I don’t even have to change the tread depth. I can change what we tire engineers call the undertread – the rubber between the bottom of the grooves and the top of the belt. The net result would be I’d get a different freestanding tread radius.
What if it takes different freestanding tread radii for different tire sizes? Well it doesn’t matter, I just do the same thing for each size.
In the old days, that was time consuming, because you’d have to build tires. But today, we can do that in virtual space – lots easier and faster. And, of course, once its been done for one tire line, the same thing can be applied to different tire lines.
So back to the question I asked, why do you think there is a difference between wide tires and narrow tires when it comes to tread radius?
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Before I related it to tread radius, let's discuss the relative integrity of, IE, the 195-75R14 off my 1981 Buick and the 225-50R17 off my 2010 Honda.
The Century's tire consists of a narrower action surface(tread) spanning two taller sidewalls.
The Accord's tire consistes of a significantly wider tread, spanning two shorter sidewalls.
Going by my gut again, Capri, with the wider tread, something - either the tread's construction itself, its free-wheeling shape, or, what fills the tire to maintain the tread's shape integrity and thus equal force across its contact patch - must be changed from what worked for that narrower Buick tire.
Please tell me what that is. If not a change in the tread radius(what you illustrated with the green line), then something else. Just tell me what that is, or what combination of properties.