Testing MPG with 17s vs. 15s

I finished off the tank after swapping tires with Mike and with a little aggressive driving at 70mph as well as 65mph morning commutes the tanker indicated 50.something mpg. My morning commutes have been terrible since I stopped trying and even at only 65mph I saw 44mpg yesterday and 42mpg today. 50mpg is still totally achievable with the 17s even with my unfriendly commute but you really do have to nurse it along to maintain mid 50s whereas you don't even have to really try to get mid 50s with the Energy Savers. It can't decide if I want to switch back to my Ascends or just run the 17s out until winter.

 

This morning I kept my speed at 60mph and tried hard to keep mpg up but despite decent temps in the high 50s I was only able to achieve 46mpg for this 48mile segment. I was sitting at about 51mpg before I hit the large hill. At this point with the 15" Energy Savers I was over 60mpg with the same driving technique. With the Energy Savers I would end this segment around 53-54mpg. So I'm still seeing the average of about 3mpg loss vs. the AVID Ascend in the same conditions and a 6+mpg loss vs. the Energy Saver A/S.

I have to make a long trip up the coast this weekend so I'll likely swap back to the 15s today. I'm not sure I'll be putting the 17s back on. Anyone local want to buy a set of 17" wheels/tires and 15" AVID Ascend tires? LOL

 

The ride quality and noise is better on the Energy Saver A/S but the handling and steering feel is much better on the AVID Ascend. To me the Ascends feel like something in between the 15" and 17" tires. They ride sorta like the 17s. They are definitely harsher than the Energy Saver A/S but those tires feel well, mushy.

 

Weight for 15s:
AVID Ascend 195/65/15 = 21lbs
OE 15" Wheel = 15lbs?
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36lbs

Weight for 17s
Primacy MXM4 215/45/17 = 21lbs
Centerline RPM 17x7 = 15-16lbs
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36-37lbs

I never weighed the new setup on a scale but I have weight the 17" wheels with Kumho Ecsta ASX tires in the past and the weight was around 37-38lbs. The Kumhos are rated at 22lbs so this sounds about right. The OE AVID S33D is 18lbs so the OE combo should be about 33lbs. From what we can tell, weight plays a minor role in mpg for these cars. Otherwise the OE 17" 24lbs wheel would really kill your mpg. The OE Toyo Proxes A20 215/45/17 tires weigh 21lbs like the Primacy MXM4.

 

It is a common misconception that a 17" tire will not induce losses at highway speeds or that a LRR tire will not have much of an effect at highway speeds. My commute is 98% highway yet I can definitely see a difference between tires. I can watch my scan gauge and observe changes in real time as well. The Critic is correct in that LRR tires benefit you the most at lower speeds because RR plays a larger role in fuel economy than wind drag does at low speeds BUT it still plays a role at high speeds too. It is simply shadowed by aerodynamic drag. In city driving conditions I would focus first on the best LRR tire you can use and then weight. a good 16" wheel with the Energy Saver A/S or maybe the Ecopia EP422 would be a very nice combo for appearance, safety, performance and fuel economy.

 

You can do quite well with the 17s if you drive conservatively and choose the right wheels/tires. I mean you bought the car expecting 50mpg right? Well you can do that with the 17s if you try hard enough and your commute is not terrible. It seems like only a 2-4mpg difference between a good sets of 17s and the OE 15s. Socal has a bit of a different case because he is running a wider non-LRR tire so I'm sure he suffers a bit more of a hit vs. OE 15s. The pain beings when you start thinking about what you could get with a set of Energy Savers vs. 17s...... lol

Tell me this. How many miles do you drive each year? If it is less than 15,000 then just bite the bullet and get the 17s. The economic cost difference is quite low and could be less than $10/mo. depending on what tires you choose and their life expectancy. Just don't go running numbers vs. a 15" Energy Saver vs. the 17s or else the lifetime cost will be over $2,000.