2016 Prius Two MPG changed after switching 15" rims to factory 17" ones

they are not tested individually.

 

The 17" rims for 2016 are pretty light I think. While they look bulky a lot of it is plastic filler pieces. That said, you still have the wider tread.

What tires did you have on the 15", and now on the 17"? That could also be a factor.

@Danny Please, please, please look into the posting delay, it's back: attempting to post, it'll crunch away for about 20 seconds, then quit. When you attempt to post a second time it usually goes smoothly. Well except sometimes it ends up being a double post.

 

The non- touring Level 3 and 4 have a handicap ... the moonroof. It adds weight so they perform as badly as the touring.

Bob Wilson

 

They don't test every combination of options - the VOLVO V40 has 7 optional wheels, BMW 120 has 8 optional wheels. And that's just wheels.

 

I reject his line of thought -- at least to the extent hat it tends to absolve Toyota of a moral responsibility for their legal fraud.

The 17" wheels on the Prius are not sold "a la carte" but rather as a key feature of two specific models - the Three Touring and the Four Touring -- which are each listed with thier own MPG estimates, estimates that are exactly the same as their other non-Eco models.

In other her words, they show the full line's MPG as a special line item in their advertising material for those specific models in exactly the same way they show Softex seat material.

But it's worse than that. Toyota is well aware that MPGs are a KEY selling feature, and one that is used to justify the cost premium for the Prius. They also know that looks matter.

So what does Toyota do? The use the 17" wheels in virtually all of thier advertising even though they know it has a real negative impact on MPG.

They are making a very conscious decision to present the look of the 17" tires, and the mpg benefit of the 15" tires together. (Ssssh, no one will know).

By not bifurcating (I have been wanting to use that word since I joined) these two "Unique Selling Propositions" the slick folks in their marketing department have been able to have their cake and eat it too.

Legal, of course. Shameful?

Very much so from my personal perspective.

 

it's no different than things like a moonroof, which add weight, drag and reduce mpg's. it isn't a toyota issue, it's an epa issue. if it's an issue at all.

 

The EPA has thought long and hard about how things that add weight can impact mileage. That is why a car company that offers a model with significantly heavier features must have it recertified.

Toyota is gaming the system.

Toyota know full well that the cars they feature in all this adds won't get the same MPG as the rest.

The consumer be damned -- they are playing by the rules, so screw the average guy who is buying a car.

After all, 2 or 3 MPG shouldn't matter!

 

Two questions in my mind:
(1) Is the difference the OP saw real? Is the circumference of the 17" Goodyears he put on the same as the OEM 15" tires? Is this an odometer error?
(2) If it cost nothing to switch from 17's to 15's to gain 2-3mpg, would you do it? How important is appearance vs mpg to you?

 

1) The 17's OD is slightly less than the 15's, so the car will think you've actually gone a little further. The difference is trivial tho.

2) Just personal, I'm not enamoured of the 2016 17's, black with silver plastic inserts.

 

Manufacturers have been getting put on the hot seat the past few years after reports of unachievable ratings. The C-Max and HSH immediately come to mind. I had a HSH and it became apparent real quick it did not come close to the rating on the sticker. As far as Prius goes, unless it's a significant shortfall as Consumer Reports found with the C-Max I doubt there will be any repercussions for Toyota.

 

This is not a surprise.
Rotational inertia is real, figure skaters spinning easier when closer to the center is not an illusion.

As you move more of the weight towards the outside of the circle, you have to push harder to maintain the same speed, so 17 inch wheels use more energy than 15 inch wheels, even if the total weight is the same.

 

as well there shouldn't be, until the epa decides those 2-3 mpg are important enough to change the rules.
every business takes advantage of the rules as best they can, and why shouldn't they?

 

In Europe, models with 15" get 70 g CO2/km with/without a sunroof, those with 17" 76 g CO2/km, independent on the trim levels.

Car makers ALWAYS game regulations.

Jan

 

if you have a problem with that you can always write to EPA. why knows, maybe there is some whistle blower money in this?

 

I wonder how a Two with 15s would compare to a Three/Four Touring with 17s, though. Weight is within 5 pounds, and the Li-Ion battery may make up for some of the inefficiencies of the 17 inch package by allowing more EV operation.

A Two with 17s is what I would expect to be the least fuel efficient configuration, though.

Out of curiosity, any trouble with rubbing (especially when hitting a bump during a tight turn)? The Three/Four Touring has a slightly slower steering rack, with less steering lock available, presumably to prevent that. The stock 17" wheels have 10 mm more offset, meaning that the 20 mm of additional tire width is all pushed into the wheel well, rather than 10 mm outside, 10 mm inside.

 

Additional questions came to mind:
(3) Which Goodyears does the OP have? Tire Rack lists 6 Goodyears in the stock 17" size, and none of them are OEM. Only one, Assurance Fuel Max, is LRR like the OEM Prius tires. If the OP has non-LRR Goodyears, the rolling resistances could be much higher than for his OEM 15" tires. And even if two tires are both "LRR", their rolling resistances can differ. Not to mention likely differences in rolling resistance between 15" and 17" tires.
(4) Weights: I was unable to find weights for the OEM 15" and 17" rims, but aftermarket 17" rims on Tire Rack appear to be 1-3 lbs heavier in general than 15" rims. As for the tire weights, the OEM 15" Bridgestones weigh 18lbs and the OEM 15" Dunlops 16lbs according to Tire Rack (no listing for Toyos). The OEM 17" Dunlop is 20lbs, and the 17" Goodyear Fuel Assurance is 19lbs. The non-LRR Goodyears were 20-23lbs. So it appears that the OP's 17" wheel/tire combination may be at least 2 lbs heavier than what came on his Prius, much of the additional weight being located further from the center where it has a greater effect on rotational inertia. However, at steady speeds (highway) greater rotational inertia might have less effect because the angular momentum doesn't change much?
(5) I couldn't find revs/mile for everything, but the OEM 15" Dunlop shows 836rev/mi and all the 17" Goodyears listed 848rev/mi, which would mean that the 17" Goodyears would appear to give 1.4% HIGHER mpg than the 15" Dunlop.

So lacking more info it's inconclusive.

Underpinning all of this is that the EPA numbers are not a guarantee of what one will get on the road so it's best to just leave them out of the discussion and focus on why the OP saw the numbers change.