Quote:
Originally Posted by Ni87
Thanks again for all the input. My question is why doesn't having a low profile tire help with economy? Like someone said the trains have steel wheels for efficiency and we have air more for the cushy ride. Wouldn't the lower profile make for a harder more effienct tire?
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Maybe it does, maybe not. This isn't data I'm in possession of.
What I can say for certain is that rotating mass is a big deal whenever you have to change speed - 10 extra pounds of weight in your tires has a
lot more impact on the amount of fuel it takes to get up to speed, and the amount of brake wear needed to slow you down, than 10lbs in the car. This is because the rotational inertia formula is mass times radius
squared.
Or, in other words, tires with larger circumferences have exponentially more inertia than those with smaller diameters, while the rotating speed only goes up linearly. So, it's doubly important for this to get a light weight (narrow) tire if it has a larger circumferences. And for low pro tires, to keep the same wheel diameter they need to have larger diameter rims, so all of the weight of that metal is farther out, meaning exponentially more rotating mass again.
A narrower tire also has less aerodynamic drag, which is highly important at higher speeds.
Whatever the truth is about aspect ratio and width vs rolling resistance, the highest fuel economy cars have all had narrow, lightweight tires.