Woods

I know that this will be a controversial topic, but I'm really just trying to learn the technical benefits of different wheel sizes. Here are the reasons that I understand the whole looks deal, and that over the past ten years, lower profile tires have become more and more popular. So I get why someone wants to put 20's on.
What I don't know; the differences between wheel sizes in handling, mileage and off-roading.
I'm certain that the lower profile the tire, the "tighter" the handling of the vehicle. But for arguments sake, I'd like to know the real world differences between say, 15" to 17" wheels.
- Is there a difference in mileage (real world experience)?
- What is the difference in ride and handling?
I like the look and pricing of a small wheels and big meats. What are the advantages and disadvantages of each? Some may say that there's more sidewall to puncture on rocks. On the other hand, I'd rather punch a tire than crack a rim.

And let the flaming begin…

CJ2a

For the smaller differences like a 15" to a 17" when you are talking a tire that is 30+ inches in diameter, it's neglegable.

The real reason we've seen an increase in wheels from the mfrs is that it allows larger brakes. Disks are not quite as good as drums in raw stopping power so to improve brakes, we've increased the disk sizes and those no longer fit behind 15" wheels. Of course, it didn't hurt that the public seems to like the 'bling' factor in selling vehicles.

Frankly, I'm still in the small diameter narrow width camp. Off road, this usually prevents rocks from banging up your rims. However, it does reduce on-road handing a little, and in some cases can increase wear.

But then again, "Off-Road" in my book does not include "Flying Low" as far too many SUV drivers seem to think their vehicle is capable of doing on the highway.

Also remember that the real critical measurement that few people seem to think about is the offset or backspace (different ways of measuring the same thing) In my 1946 CJ2a I have about 4 inches between the outer edges of the bearings in my front hub. In the TJ, that is reduced to just over 2.5". While the bearings might be a better product, a poor offset places a lot of leverage on those bearings.

Hope that helps.

Killian

Also, when one goes from 15" to 17" they obviously add more weight (well, alot of the time). This is called rolling mass. More mass means more breaking needed to stop. Going from a tire made for the street to an off road tire (thicker sidewalls bigger lugs - as in a mudder) will also contribute substantial weight. The GY SRA's that come from the factory weighin about 40 pounds. the mudder that I plan to replace it with weighs about 52 pounds that's a 30% increase.
I know that strayed wildly into left field from your question; but bigger often means heavier.

Jake_Blues

It does, and this also adds to your unsprung weight, which is a bad thing as well. When you hit a bump, your tire, wheel, and any other unsprung mass is accelerated upward. Having less unsprung mass allows your suspension to do its job, keeping the wheels in contact with the ground.

My wheels are 17"x9". I chose this size because I needed a wheel at least 8.5 inches wide to meet the manufactuer's minimum for the tire I wanted to run. I know some will say you can undercut this, but I think the tire manufacturer knows more than I do about tires! I didn't want to run 15" wheels because some 15" wheels will rub the JK's brake calipers, and the 16" version of the wheel I wanted (Cragar Soft 8) didn't come wide enough. So I got the 17".

There shouldn't be a significant difference in milage as long as the overall tire diameter is the same. Smaller sidewalls will improve on-road handling, but will make the ride rougher since they won't flex as much to absorb small bumps. This is usually a bad thing off-road.

-E

Tjen97

There is also a big difference between steel and alum. In a Jeep, wheel sizes will not be noticeable, unless you take it on a track. In the end, larger wheels = more expensive tires.

Dean

Although I disagree with the opinions of some people regarding wheel size on this firum, I have to admit that Jake_Blues has the best argument for keeping rim diameter down, which is unsprung weight.

The suspension, axle, ball joints, etc.. all do better with a wheel that's close to stock size, so you'd do well with 17s or 18s. 20's would only be recommended if you're going to put some serious rubber (35s or more) or stay on-road.