Fuel Economy on 17's

<in Spock voice>

It would seem logical bring extra fuel, if you insist in this irrational tendency to avoid timely refueling.

 

When one of you Five owners gets around to installing new tires could you please provide us with an update on your fuel economy. I'm trying to sort out the relative rolling resistance of the OE tire vs. aftermarket tires. I've got a feeling it's quite a bit lower than most aftermarket tires in this size.

 

I must be doing something very wrong, I have a set of MoMo Win Pros 17x7 on a 2012 with Michelin Primacy MxM4 LRR's that are same size as the factory 17 tires on prius for the forged wheels. I cannot get over 44mpg on the highway at around 70-75mph, and in town Im around 38-42mpg doing 17 miles one way mostly traffic lights with a short 65mph sprint for 3 minutes.

Granted the car has less than 2500 miles on it thus far, but even when I had the 15's on it for two tanks, I didnt hit 50 mpg

Is it possible weather is hitting it that hard? Bought it in November, we've bounced between 40-50 degrees.

 

You're right were i would expect you to be with winter conditions and that tire/wheel combo. many people fall below the EPA rating in winter, even with 15" wheels. Those 17s will really kill mpg in stop and go traffic conditions.

 

I guess, reading all the threads, and people saying 2-4 mpg loss with larger wheels, threw me off, I went ahead and bit the bullet because two wheels got curbed on week one (never let friends drive your car), and figured, why not go with some slightly bigger black wheels

Either way, it beats 17mpg I use to get on previous vehicle lol. I just was hoping to stay mid 40's even in city with electric assist.

 

It really depends on the conditions. In the summer I often see a 6mpg+ loss with 17s vs. my 15" Energy Saver A/S tires. You will be back in the 40s once summer comes back assuming you don't use your A/C too heavily. Winter blend fuel and cold temps kill mpg. Rolling resistance increases a ton when going from 90F temps to 30F temps!

 

Air density takes a bite too. Aero drag is directly proportional to air density and 30F air is 12% denser that 90F air.

 

Aye, I sorta lump aero into rolling resistance. That is not the right thing to do. I feel properly chastised.

 

20 lashes with a cold piece of grill blocking pipe insulation for you.

 

Above you said you've got 2500 miles on the vehicle. Full break-in doesn't occur until about 9 - 10K miles, and you'll see your mileage gradually improve past that point. Others probably put on their 17" wheels a bit later in the vehicle's life when they mention their 2-4 MPG hit. And yes, low temperatures, winter gas really hurt (block heater as your next mod?), but driving 70 - 75 also kills MPG. Try 60 - 65 MPH with the vehicle warmed up and see what mileage you get.

Short trips also suck under winter conditions.

 

Definitly. Here are my results based on the full tank records.

Short trip, summer mpg. 17" Michelin Primacy HP - 4.8 l/100km => 49 mpg (average temp. 20C / 68F)
Short trip, winter mpg. 17" GoodYear UG Perf. 2 - 6.91 l/100km => 34 mpg (average temp. -5C / 23F)

Short trip = 10 km / 6.2 mi
Tire size: 215/45/R17
Parked outside, no grill block, no EBH. A/C set to Auto at 18 deg C / 64F with A/C lamp OFF. Eco mode.

 

I just put on a set of Yokohama Avid Envigors (same size) that are supposed to be LRR per tires-easy.com: Yokohama AVID ENVigor 205/60R15 91H BSW - tires-easy.com

The 3 December tanks prior to the swap were 53 (492 miles), 53.1 (479 miles), & 55 (501 miles). Lifetime (3 years) is 54.7 (61445 miles).

I had an oil change and the CVT fluid drained & filled. That tank was 47.5 (441 miles).
I filled up just before getting the tires. That tank is 47.3 (300 miles).

tp was set at 50psi in the shop. I increased the tp to 50psi (at least) on the driveway in the freezing cold. OAT has been in the 30's F.

Under these conditions I would expect average to slightly below average FE, say 52-54.

I also had an alignment done. The only value that was changed was the front toe. It is now 0.10" on both sides. It was 0.03" left & 0.01" right. I did not have any abnormal tire wear on the original set.

I'm still looking for the gremlins that took my FE. So far the alignment & traction battery are the only things I've ruled out.

The car does seem to handle better when cornering but I haven't played much. It does not glide as before. I have to keep the HSI bar further to the right in the power region to maintain speed. I also have less acceleration down the hills . I hope & expect to get a couple mpg back when the tires break in.

I did a system check of the 12v battery after the car sat for four + hours today. Voltage was 11.3 & 10.9 with the headlights on per the nav screen. The ScanGauge showed 11.8 & 11.3 respectively.

I know the 12v is on the low side now. Was it low before the service or did the CVT drain stress it?

Normal commuting is 30+ miles and 1:15. This last tank also included a trip to Totowa, NJ, short hop commuting, and the return. Historically I take a bit of a hit or make average on trips to North Jersey.

Suggestions & advice are welcome.

 

Jim,

The AVID Envigors are not really a LRR tire. May I ask why you went with that size tire? It's even smaller than your OE 17" and the handling is only marginally better than the 195/65/15 that comes OE on the Prius. If you want max mpg I would suggest dumping those AVIDs for a set of Energy Saver A/S 195/65/15 or Ecopia EP422s. I assume your speedometer is also off, more than it was from the factory. The OE 17s are even smaller than the OE 15s and your new tires are even smaller. If you are dead set on that tire size you can look into the Goodyear Assurance Fuel Max or Continental ProContact with EcoPlus. Both tires have a longer warranty and offer somewhat better fuel economy. Goodyear just had a $80 rebate available.

Your battery voltage is low IMO. It may or may not be affecting your fuel economy, however. Since you will have to replace it soon anyway why not do it now?

 

F8L, I'm on the same size tire as the OEM: P215/45R17. I used that page for the description. Because the new tires are the same size I didn't think to check the speedo against the Garmin. Will do that tomorrow & post the specs when I can read the sidewall in daylight.

When I asked for LRR tires these were mentioned as they are advertised as LRR & were said to be made of that LRR compound. Whatever page I read (I don't have it bookmarked) seemed to confirm what he told me. I'm going to score this as "I was misled & confused".

Since the FE hit is bothering me it's going to be a loooong 60000 miles before the next set. I'm going to talk to the shop tomorrow.

I started shopping for a battery (like I needed another thing to do) and will be getting a Yellow Top delivered.

Thanks for the help.

 

Gotcha.

They consider them LRR but like a lot of performance-oriented tires, they fall short on fuel efficiency.

Can you swap them for something else? The Ecopia EP422 is a good fuel efficient choice. Unfortunately nothing matches the FE of the OE 17s but what can you do?

Should you keep the tires know that they will get better after they break in.
Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires

 

Just the thread I was looking for.

Based on this, the easy thing to do is increase my tire pressure. Other threads addressed 15" wheels but with 17's, I was worried about excessively harsh ride due to profile. With that, what pressure are you guys running and still tolerable?

Look forward to better MPG as I break-in my tires and car.

 

I'm running our OEM Michelin Pilots (215/145R17) at 36 psi, all 'round, at present. Even there it's semi-harsh going over speed bumps (which I hate with a vengeance). I've tried higher, around 40 psi, which I'd use a starting point for 15", but it's pretty rough with speed bumps and pot holes.

The sticker in the door jamb says maybe 35 psi for 15" and 32 psi for 17", something like that.

 

I'm asking what's the consensus on increased PSI in tires to get better mpg and acceptable ride quality.

 

Well, I thought I answered that question (36 psi, in my case). I'm pointing out the pressures on the sticker just to note that the 17" pressures are lower.

 

Sorry, my mistake.. I thought 36 is the recommended pressure.. I just looked, it's 33F 32R. With the increase to 36, what gain mpg did you get?