The mpg difference 15s vs. 17s

Q1: I don't know of anyone with a really wide 15" tire that is monitoring their MPG closely. Those that have upgraded to a 205 tire do complain about a mpg lose but without any serious measurements it is hard to say how much they have really lost but it does seem to be about a 4mpg loss when compared to a 185 tire.

Q2: I think the rotational mass distribution would have an effect on mpg as you go larger in wheel size. So a skinny 17" tire will likely get less mpg than the a 15" tire of the same width.

Q3: If I did gain anything from lowering the vehicle I have not really been able to detect it but I admit to not really doing any serious tests.

Since I have swapped back to the 17s (due to inbound rainy weather) I have been applying the same driving speeds and techniques I had used when I had the 15s on and I have posted two 49-50mpg tanks. I attribute this to slowing down to 60mph (freeway) and 55mph (rural roads) which is what I had been doing with the 15" tires. The same techniques will net 55-57mpg with the 15s. It just depends on how much city gliding I can do. Since I drive approx. 92% highway, 5% rural road and 3% city, my variables are quite a bit less than those who drive a reversed pattern and much deal with variable city traffic.

What I notice between the two tire sizes is the effort require to move forward from a stop and the length I am able to glide. There is more effort require to get moving and when going into passing mode on the freeway. The 15" tires just feel, well, lighter and easier to get going. When gliding, the 15" tires want to just keep rolling and rolling. I can glide nearly a mile or maybe more depending on the road surface. With the 17" tires they glide fairly well but you can feel a bit more resistance and I cannot glide quite as far. I have not tested the actual lengths but if I let of the gas at the same point while approaching a stoplight on my regular commute pathway, I notice I drop speed faster with the 17s than I do with the 15s.

As or the picture below, we would need more information on the actual weight and dimensions of the wheels and tires they have on that car. That may have went larger for a number of reasons and I doubt fuel economy even factored into their decision.

 

But 4 wheels are require to keep the car stable at high speeds.

 

I always wondered why some cars like the Corvette came with larger rear wheels.

 

I did it again...

I swapped back to my 15s today.

I performed the same techniques on my 17s the day before and saw 50.2 mpg at the end of my commute. Today I saw 60.6mpg with the 15s. Temps are in the low 50s with heavy fog on both days. No wind to speak of. The damn 15s are butt ugly but they sure do roll well. Yeah for the orange peel tires!

This is a 98% highway commute at speeds of 60 mph. Average speed on the SG2 says 47mph.

 

LOL you know I'm a sucker for pretty wheels.......

I have often wondered what the CT and the new Camry would get on 15" tires. I bet the CT could top 50mpg pretty easily if it did. I wonder if the 15s would clear the brakes.

 

Wow, nice!

That is really it. The CT shouldn't be significantly heavier than the Prius so a good 15" tire should have more than enough load capacity. I wish you lived closer so I could let you borrow my wheels to see how much of a difference they make. I would think a good 195/65/15 would work great as long as there are no clearance issues with the smaller wheels.

 

Yup. Now I order you to go swap wheels with your 2004. Then drive around and report back after a couple hundred miles!

 

Ok, we'll have to wait but if you can do it we will have some potentially very interesting information! If you could test the 04 with the 17s that would be awesome.

 

Get off my Kool-Aid, man! I'm first in line. : p

I'm teasing but serious. LOL