1) Which setup is more fuel efficient?
2) Why have manufacturers gone with bigger wheels? Looks only?
3) Why do tire companies charge more for larger wheel sizes? Less rubber more money?
Looking for any input here, mostly out of curiosity.
Why do manufactures do it? Because they sometimes look better on the road. Lol, that's the quick summary.
Car And Driver's magazine article on the subject
Warning! Science Content.
Based upon the assumptions you've listed, I'll share my thoughts. By the way, good writeup on constraints. :nicethread:
Here are two assumptions I'll add to my explanation: tread thickness and sidewall thickness are the same for both tire sizes.
Which is easier to spin? The smaller rim size will be the easier of the two to get spinning, but not by much. The larger rim would have a larger rotational inertia, making it seem "heavier" to spin. Also, aluminum typically has a greater density than rubber does (upwards of 2 to 4 times). By that logic, the larger 17" rim size would be harder to change its angular momentum than the smaller rim size, the 16," because the wheel has more aluminum vs rubber. That last statement is a simplified claim, because I am assuming only solid cylinder and annular cylinder comparisons rather than the complicated star patterns that are common with aluminum alloy wheels. Think of dragsters, because they use tiny rims in comparison to their tire diameter. Check the Car and Driver article linked above.
Since only a small portion of the tire side wall would be added to accomodate the smaller rim, I would still expect the smaller rim to be easier to spin. The tire itself would be heaver, but the overall wheel would likely still have a smaller rotational inertia and be lighter than the one with the bigger rim.
If we were to use the above approach to gauge the wheel's performance, one could conclude a smaller rim would result in better fuel economy. However, tire flex has to be taken into account. The two tires have the same outer diameter, but the one with a smaller rim will likely flex, or bulge more between the rim and the ground. The tire flex robs energy from the system. Then again, its likely going to be a negligible difference, since the outer diameter of the tire is the same size, and that affects the gearing of the overall drivetrain from the engine to the road.
Tire flex also drops cornering ability, so perceived handling at high speeds is often improved with larger rims and smaller side walls. That's why Formula 1 and other race cars have a smaller side walls, bigger rims.
Cornering Force
Pros of larger rims?
-Looks better on many vehicles.
-Better Cornering at high speeds
Cons larger rims?
-impact durability. larger rims are more likely to be damaged from potholes and other bumps in the road. That's also discussed in the Car and Driver article as well.
-added inertia, heavier. Drops acceleration and felt torque.
-more expensive
-less offroad friendly than smaller rims
Pros of smaller rims?
-Straight line acceleration
-Better offroadability (I'll talk about that in a moment)
-Ligher
-Better fuel economy
Cons of smaller rims?
-Don't look as good with many vechiles
-Less cornering ability at high speeds
Now, to my offroadabiliy statement for rim sizes. Tire flex is often a benefit in certain offroad situations. Let's say I want to drive over terrain I'm likely to get stuck in if my tires are fully up to pressure (35 PSI). Let's go to an extreme: I let air out of the tires so there's only 15 PSI left. It is likely the smaller rim will allow the tire to flex more, allowing a larger surface area to touch the ground. This will prevent the vehicle from getting stuck and prevent punctures.
However, the difference between a 17 inch and 16 inch aluminum wheel would be negligible on most of the points I've brought up here. Now, if it was the difference between a 17" and a 20", that's when some of these points will become apparent. Again, I'd suggest reading the
http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested Cars and Driver article for more info.
Have a great day! :biggrin1:
-Spunk
