17" Vs 15" gas mileage

Yes, it's mainly from rolling resistance and diameter difference rather than unsprung weight.

 

I haven't read this thread carefully, but yes, the 17" wheels are known to cause a slight mileage hit.

Regardless of wheel size, what mileage are you expecting and why?

 

In EU the 17" version is rated the same as the 15" in town and combined. +0.1L/100km higher in suburban/highway. Which makes sense since at higher speeds, rolling resistance will be greater. That said, it seems there is no practical difference, as long as they are properly inflated...

 

I have a 2011 Prius III and just switched out to 17 inch Eagle 192s with Michelin Pilot A/S 215/45/17. I have followed this thread for some time and am generally hearing that folks are taking a significant MPG hit for this mod. I have only run 1 tank through but am discouraged as went from about 47 to about 42-43mpg. Handling is much better than with the 15s. Are there ant secrets here? Tire pressure? The 17s look and feel much better and I guess this is the price.

 

Unfortunately I have not experience 15" rims on a Prius but I have over 8500 miles with the 17" and stock drivetrain. Summer time I average about 56mpg calculate, 48mpg calculated in winter. Grille blocking helped alot, 51mpg winter with heater 53mpg in winter no heater. Best trip 72mpg in 40 miles in autumn no AC. Worst trip 45mpg with heater on high, no grille blocking. Driving habit plays a big role, even if you don't notice being a lead foot. I admit that I feather the pedal a lot to get the mileage into the high 50's but not light enough to hold up traffic.

 

I wouldn't be surprised if the newer tires have higher rolling resistance then the stock tires coupled with the effect noted at Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires.

http://priuschat.com/forums/gen-iii.../65496-17-wheels-effect-mpg-2.html#post909868 (the PDF is in UK gallons on a totally different test)

 

To Gail, don't jump to conclusions about reasons just yet. A lot of things affect the mileage you get compared to EPA 'estimates'. There are some great post here for people newly coming to awareness of MPG. Read a bit, practice a bit, experiment a bit. See what happens to your mileage. Try not to get overwhelmed by the minutia that many people here are involved with.

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Should be easy enough to test. Rolling resistance is mostly not speed dependent, weight mostly affects mileage in frequent stopping situations, and aerodynamics affects mileage most in long runs, yes?

 

Cwerdna gave you good advice and some great links. Those will help you to understand why your MPG dropped.

You also went from a tire (Ecopia EP20?) with a revolutions per mile of 833 to one with a rating of 844. This is the take home message:

The Michelin Primacy MXM4 would have been a better choice for LRR.

Yes and no. The higher wheel/tire weight is a larger factor in frequent stop and go situations than it is on the freeway. Rolling resistance however, is a factor at all speeds but is worse on the freeway as higher speeds equals more friction. Here is a snippet from Tire Rack:

 

I have a prius III with the 17" stock wheels and tires. I also have a set of aftermarket 15" wheels mounted with Michelin X ice2 winter tires. I average 45mpg around town with both setups and on 300 mi trips up to the mountains, I get 40mpg on both setups. Considering the high rolling resistence for a winter tire, I am surprised the 17" setup isn't better than the winter tire setup. The winter tires are 10mm narrower.

It's hardly scientific but I think unsprung weight is a huge factor. It takes a lot of energy to move that extra weight up and down over all the bumps on the road.

 

In EU the Prius is rated with only 0.1L/100km difference whether you buy it with 17" or 15" rims. Which means in real life there is practically no difference...

 

I too have the Michelin Pilot A/S. I drove straight from the dealer to the tire store to get rid of the 15s for the 17s, so I don't have much to compare it to. I hate the 15s they put on these cars. They had to go if I was going to drive this car. I think the hit in MPG was pretty significant.

 

Makes sense. 17", greater energy required to rotate, lower MPG.

Most drivers that I know who own a V came from a BMW or other euro car. 46mpg to them is heavenly.

 

My experience is similar to JJLawyer: I've just switched back from 195/65R15 Michelin XIce (on steel Corolla rims), to our stock Michelin Pilot 215/45R17, and haven't noticed any significant difference. Considering the XIce is a snow tire, I'm wondering what would happen if I swapped to something like Ecopia EP20 in 195/65R15 size.

One other factor: the Outside Diameter of the 17" combo is smaller, I believe making about 1~2 percent difference in revolutions per mile, for example.

 

I recently put 17" aftermarket wheels withe the Michelin Primacy MXM4 in the 215/45R17 size. The first four tanks of fuel with the stock EP20's in 15" size averaged a calculated 49 MPG. The next four tanks of fuel were with the new setup and I averaged a calculated 46 MPG. Driving conditions exactly the same and weather the same. I agree that looks are definately worth 3 MPG

 

Each tire is different. Some 17" tires are rated at high revs/mile than the stock 15s and some are lower.

 

I'm curious to see this exact setup on your Prius, as the American Eagle Series 192 is very close in design to the original Prius V 17". The only drawback is the ET38 mm which would make it stick out 12mm more.

If you could, please provide as many photos as you can. Thanks!

 

Granted, I read through this rather quickly, but I never saw any mention of specific tire pressures. If you're running tire pressures set by the dealer, you're probably in the low-mid 30psi. Increase the psi to 40 - 42 and you should see a marked improvement in mileage. I personally run 42f 40r, and now that the weather has warmed up, I'm seeing an average of about 52mpg on a Prius V with 17" wheels.

-edit-
To add to the above...my friend has a gen II Prius with 15" wheels. He recently replaced his old tires with new Kumhos from the dealer. His mileage went from 51ish to upper 40's...regardless of how he drove the car. He checked the pressures, and they were in the mid 30's set by the dealer. He then increased the pressures to 42/40 and is now back in the low 50mpgs.

 

Factory 17"s weigh more. More weight costs more energy in starting and stoping.

 

I run 42f/40r on my 17's as well, but I still only average about 47mpg (caluclated), or about 50mpg by what dashboard says.

My dealer had actually set the tire pressure way to low, about 26psi both front and rear. I have no idea why they set them that low but mine didn't stay that way for long.

 

Yeah...I'm simply going by what my dash is telling me. I'm sure I'm around 48/49 or so when actually calculated. Next time I fill up, I'll see what Fuelly calculates the actual mileage to be.

The disparity in our mileage can obviously come from a multitude of factors...driving distance, elevation changes, number of stop/go's, weight of your foot, wind, temperature, etc. I'm sure given the exact conditions, our cars would be within 10th's of miles in mpg.