Hi guys,
I have a very noob question. I've only ever ridden on the stock 15' rims (not the steelies), and I was planning on getting new shoes. My question is, if I were to compare the same set of rims in 15" and 16" sizes, would there be a noticeable loss in mpg because of the added weight? Or would there be a small gain in mpg because the larger wheels would translate to less rpm's?

Basically 16"s would be nice, but if I'd lose any mpg, then I'm fine with the 15"s.

I know that its kind of hard to answer that question without the weight etc, but I was just was curious about the physics behind it.

Thanks!

 

Extra unsprung weight translates into less mpg.

Larger diameter tires = higher overall gearing and more mpg if you're driving for mileage. If you drive like you stole your xB, larger diameter tires and higher gearing work against performance, and you may get worse mileage pushing your box harder.

It's not as simple as 15" v. 16". The stocker 185/60R15 tires are 23.7" in diameter with 44 psi sidewall pressure rating. You might think replacement 205/50R16 tires with their 24.1" diameter and 51 psi rating might get better mileage. Your engine is turning fewer rpms, and there's less rolling resistance with the 16s. Maybe so, maybe not. The 16s are 20 mm. wider, .8" more rubber to push on each rotation. How hard is the tread compound to meet the company's wear rating? How sticky are the tires to meet the company's traction rating? Did you know one company's wear rating doesn't relate at all to another company's wear rating?

How aggressive is the tread pattern? How heavy is the tire/wheel combination? What if you go for 35, 40, or 45 series tires in 16"? What if you go to 215 or 225 wide tires? It gets complicated real fast, and there's no way to know how your changes will affect your mileage.

 

Check this out.
http://www.miata.net/garage/tirecalc.html
If you can keep the diameters within a reasonable difference from stock and run a wheel that's as light or lighter than the stock wheel, you're not going to see a real difference.

 

if you can find some mag lite rims that'll help you out also weight wise...

 

I run 16" wheels ( Niche Serpants) , 205-50-16 Zeix Tires and see no difference between my 15" stock rims and tires and the 16".

I run 32 psi in 15" and 40 psi in the 16".

Hope this info is useful to OP.

 

The thinner tires would be lighter. You just need a lightweight wheel.

 

ya I was wondering the same thing If I was to go to a set of 15 x 8's

 

my 18's and 15's are close in weight but I get better mpg's with the 15's

 

high mileage tires definitely help... but, overall if u do a lot of city driving, you'll want lightest combo