Thinking of getting 17s but i dont want to lose mpg's

I believe the UK test was flawed which is why they concluded a 1-1.5mpg difference. Other real life testing shows otherwise.

 

You believe it was flawed--based on what? Seems to me Toyota would use the government-mandated test, no?

 

Ahhh. Unique perspective. The rest of the world uses:
Round-off error - Wikipedia, the free encyclopedia
I think you really mean that you think the uncertainty of comparing mpg's is in the 2-3% range???
On-the-road mpg depends on a lot of factors but if you could hold the important ones constant I think you could do better than 2-3%. EPA ratings are lab tests under highly controlled conditions so if they are expressed to 1mpg, I would hope that they are repeatable to <1mpg. It's fundamental in science that you do not express your results to an accuracy that they do not merit (significant digits).

 

I believe it was flawed because the results do not appear accurate. Everyone that has bothered to test the idea in a somewhat rigorous way, or in my case repeatedly over 5yrs, has observed a larger difference than the UK results would let you believe. I will be the first to admit that I drive a GenII and my results cannot be directly applied to the GenIII but to assume that there is a barely perceptible difference, or rounding error, in mpg between the 15s and 17s defies logic and observed results.

A government mandated test? What does that mean in the real world?

 

depending on how many miles a year the OP drives the difference between 52mpg and 47mpg can cost hundreds over the lifetime of the tires.... I agree, however, in the grand scheme of things it's not a huge deal and unless you drive a lot of miles per year, the saving is only in the realm of a hundred or so dollars/year depending on the price of your replacement tires.

 

At least it is something that can be compared because all tests are done under the same conditions. Would you prefer that Toyota test under one set of conditions and GM under another? Or multiple tests (we already do two) under identical conditions yielding a mass of results that we would have to wade through? Not to mention the costs of doing them.

I do believe that there is a difference between 15" and 17", and that real world numbers are interesting and somewhat useful. But unless variations are eliminated in things we know make a difference, such as temperature, tire pressure, wind, terrain, etc., comparing the results is tough.

The most careful "real world" test I have read of involved two Insight-I owners who wanted to compare the mpg of two different tires, OEM and something else (I forget). They met and drove both cars at different speeds in both directions over the same flat stretch of road. Then they swapped wheels and repeated. A lot of work!!!

 

I have a Gen-2 and upgraded from the 15" to the 17". I lost about 5-6 mpg loss after the upgrade. Was it worth it? Depends on what you're looking for. If you want strictly fuel economy, I think the sacrific is pretty heavy since -- I went from about 50.5 down to 46.4, that's about 10% !!! Looks wise, I think it's outstanding and I'm willing to pay to play. The 17" tires will also cost you more when it comes time for replacing.

 

But this makes no sense given that the ~1.7-1.8 mpg loss was calculated using the same (European equivalent of EPA) test on the 15"-wheel Prius and 17"-wheel Prius. Same test = same or roughly similar variables.

 

I get it--you don't agree with me. How many ways do you want to say it?

 

I don't either but I still like you.

 

I think one of us is confused, do you have the rotating weight of the c and Gen3 tires/wheels?

The Effects of Rotational Inertia on Automotive Acceleration

 

While the extra weight doesn't influence fuel consumption significantly, it does have a large effect on acceleration and deceleration.

 

Takes a lot more work to spin a heavier or wheel/tire combo, regardless of size. The 17" wheel/tire is A LOT more heavy than the standard 15s. I found that out when doing the swap. I did read once somewhere that the standard 15s were designed to be very low in weight, designed just for the Prius with fuel economy in mind.

 

Find the lightest wheel you can that fits your visual taste and attempt to marry it to a LRR tire. All you can do is attempt damage control. If you are like me...you get the wheels you want and then pray.

 

The OEM 15s on the GenII were 15lbs. I believe the GenIII wheels were 15-16lbs. Even though my 17s are very light, 15-16lbs, the tires are much heavier at 21lbs vs. 17lbs for the OEM 15.

 

Just a crass generalization but a modification that reduces mpg's on a hybrid is a downgrade.

I'm not sure if it has been mentioned but you should also factor in the higher cost of 17in. tires.

 

I try to think of it as downgrade in terms of cost and fuel efficiency but an upgrade in terms of aesthetics and personal satisfaction.

Things in life is rarely just black and white.

 

:kiss:

 

Interesting article on upsizing in caranddriver.com, once in the site then search for upsizing.

The forum does not allow me to post a link, apparantly I need 5 posts before that feature is enabled (spam filter I guess)