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.
"Wade had sized the front-wheel arches for larger tires but left the rear arches alone since only the drive wheels need to be bigger to get the ratio effect. The mixed tire sizes, though good for speed, would be perceived by the computer as a dire safety hazard." Got Hybrid? - Over 130 mph This is one reason I think they were working against the stock software.
could be telephoto compression but the rears actually look larger here. There isnt any EXIF meta data in the image. This car is lowered about as far as it will go, thats somewhere around 4"
I put a fine grid on it in PhotoShop. As near as I can see in the picture, the center of the wheel front and rear wheel covers are the same distance above the contact point of the tires. There is lot of telephoto in that picture because the mountains in the rear don't look nearly that high when you are there, so the ties could be the same size or the rears slightly bigger according to the limits of my 1/2 arsed photo interpretation. I suspect that picture was taken without the bigger wheels on the front.
looking harder when the back door handle is wider than the front one .... it has to be telephoto compression at work this was a crop from a larger image BTW surprising how pretty the car is when 1" off the deck
its interesting looking at the Gen 3 forum, where nobody seems to give a hoot about this, and here where we comb over the same thing time after time. I want to do something like this soon, so figuring the data points between wheel sizes and tyre weights is going to be important. Im not so fascinated by losing 3-5 MPG, but if I can avoid it with better wheel tyre choices I think I should try.
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.
Justin, I have some pretty 17 inchers that come stock on my CT. I may have to offer them in trade for your butt ugly 15 inch tyres.
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.
My last long trip I averaged a bit over 50 mpg on the 17 inchers, so I am inclined to think the car is good for 60 mpg driven the same way if 15 inchers are used. Btw, what other considerations are involved in downsizing a tyre besides pad position ?
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.
You know, I have my '04 Prius. This would be a quirky and amusing test Do I just measure the radius out to the caliper ?
Yup. Now I order you to go swap wheels with your 2004. Then drive around and report back after a couple hundred miles!
Sir, yes Sir ! It will have to wait until my car arrives though. For the moment I have a courtesy loaner. Fwiw, I expect to see the same percentage differences you have reported; I am just curious how much of the EPA difference between the CT and the G3 Prius is tyre related.
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.
yes that would be great data thinking further out, the lightest 15x6 wheels are Racing Hart CP-035R at a mere 7.9lbs
