Saturday, 1 June 2013

TGM tires, and ply placement

Truth be told, my last post on the rF2 tire model a while ago was written in frustration. Looking back on it, I do stand by everything I said, but I'm back to trying to work with it. I have absolutely no in engine results yet, but I have got some nice findings in the construction. Notably in the ply distribution.

I find it helps me personally to simplify tires down to two parts; Sidewall and Ring (Or surface?). Although these are compressed and stretched by the same forces at broadly similar times, they've got different requirements. Having your ply upright in the sidewall (as per Radial Ply tires) gives great structural strength in the sidewall, as the ply is compressed/stretched as the sidewall becomes taller/shorter in motion.

The ring doesn't become narrower as the tire is loaded, however, so a horizontal ply in the ring doesn't really do anything. Just because there's no movement in it for it to react to. There's far more movement in the ring's circumference however. Remembering that the circumference of a circle is Radius x Pi, any compression in the tire's radius will bring about a greater compression in its circumference.

Having some ply deviate from the horizontal axis (as per Cross/Bias Ply), the ply in the ring will be contorted by changes in circumference, and reach accordingly. Without using this, you'll get a tire which's surface balloons out at speed or with pressure changes very dramatically.

Though, if I'm honest, I didn't figure this out for myself. It's present in ISI's Corvette tires, as well as many others.

This graph shows the different layers present in the front C6R slick tires across its profile, from one corner on the rim right round to the other. The legend on the right follows the naming scheme used in engine (it's vague, I know). This summary of the layers in the Corvette tires illustrates the different ply layers present. The two red ply layers are present across the entire profile of the tire. However, the yellow and green layers are present in the middle under the surface, and don't spread all the way up the sidewall.

The two red ply layers are oriented at 82 and 98 degrees, which is more or less lateral as we'd expect with a radial ply (90 degrees being 100% left-to-right). The green and yellow in the middle are oriented at 23 and 157 degrees, much closer to a longitudinal orientation. This makes a very significant effect, as this is what a generic tire with and without these layers looks like doing about 150mph.

Yikes! I want a bigger contact patch than that at 150mph! There's also the issue that some cars aero parts are very sensitive to ground clearance. And having these tires lift your car up 4cm is enough to make a Formula 1 front wing and diffuser useless.

Oh yes, one last thing. I did say I wouldn't be touching this tire model until I had an easier and quicker way of making the tires. Well... That's what I'm experimenting with! But more on that later. :)

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