I just got some new Falcon 912's P195/55/R16 put on, then got the MPG computer flashed to get it more accurate, and reset to 0. After a few days (all highway) I'm still sitting at around 27.4 MPG on the dash. Old tires gave more like 34.7 MPG.....

Questions:

1. Does the larger diameter of the tires effect my speedometer calculations or the on-board MPG computer accuracy?

2. Could it be that they are 'directional' tires, larger, and likely more heavy dragging the car down?

3. Is the near zero temperatures effecting fuel economy?

4. Combination of the re-flash, larger tires, throwing off MPG computer, frigid weather, etc.?

Just want to get that puppy back into the 30's.... thanks.

 

1) yes by about 5.2-5.4% (depending on how you look at it). Having larger tires means you are actually traveling faster and further than the speedo/odo is reporting.

2) not sure about it being directional or its affect. But, yes, they seem to be heavier so it will bring down your mpg.

3) yup

4) I have no idea what your reflash was. I know there's an official software update to make the obc mpg more accurate... and then the unofficial ecu re-flash to change other things. That being said... the re-flash could also be affecting your mpg too.

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Are they questions or are you asking a single question with multiple choice answer? Cause #4 makes it seems like an "all of the above" answer.

 

#4 all of the above.

Recheck tire pressure.

 

I've got General Altimax Arctic 185/65 Snows on the car with Acura 15" Alloys. i'm running slightly larger diameter than stock and my last tank (1st tank with the snows on) was 31.89mpg. 2nd tank so far however has been in the high 30's (Probably end up 35-36ish).

Your tires are Wider than stock (More rolling Resistance), and also larger in diameter(Heavier and throws off the speedo/odo). both of these mean lower economy.

We just got our 1st decent snowfall here in VT so I'll see how the Generals work. supposed to get 6" by the end of the day but it could be more.

~SB

 

Are you guys just reading what the computer says? Because I look at the MPGs the computer says and then I do it the old fashion way..... Miles/gallons. and it is always a little off from one another. So since you are get such different readings on the computer I would say for sure that the tire size is effecting the reading on the computer.

Thats is my simple way. You would also need to determine percent wise how much your tires are off from the orginals and add that into the equation b/c with big or small tires you miles will be slightly off as well so there for you would need to know the percent to get the most accuate reading possible. Of course there are other things that effect MPGs in the winter(like if you start your car 10 mins before you leave ect.)

 

Thanks for the replies. I guess the reason it feels like the sky is falling with regards to my MPG is the culmination of each one of those factors all being introduced within the same week.

Larger tire diameter throwing off the calculations by 5%, added weight, larger contact patch, ambient air temperatures well below freezing, plus the tires probably need air. Just thought 27.4 was pretty low.

I’ll put some air in the tires and hope for the best, maybe try a manual calculation.

 

lol...of course tires will have an effect on your fuel mileage!
You will lose a few mpg because of the winter tires and even more in the cold temps.
winter tires are designed to grip the road and ice, more friction hence lower fuel mileage.
Summer tires, more free wheeling, less friction and better fuel mileage.
You're best bet is to use winter tires in the winter, summer tires in the summer. The tires will last a lot longer, all season tires are decent but nowhere good as having a set of strictly summer and winter tires.

 

Then you should have gone with 175 section tiresthat have the same diameter.

 

Yeah, the 195's are a bit big
the honda dealers are installing 175 65 15 on 2009 honda fits base and sports, 2009 and up
who really cares what your display is, your most accurate method is your fillups cost per liter or gallon and your odometer reading (trip) between fillups.

 

With the 185/65's I'm about 1.9% over what the stock tires would give so most all of my calculations since the tire change are about .6mpg low. Unfortunately, there's no way for my phone app "gasuplogger" to take this into account.

The 195/55/16's are almost the same as the 185/65s (running on 15's) as far as the wheel diameter so mpg will be about .5-.7mpg off (on the low side. Depending on the Weight of the wheel/tire setup, it might or might not make a difference (weight wise). likely not that much either. The wider tire with the winter tread pattern will likely drop it a mpg or two as well. add in the temp difference and you're slowly eating away at your economy. (although you aren't really eating away as much as would seem as the distance you are traveling is acually 1.9miles/100 you travel than what the odometer states so for every 100 miles you think you travel (by the odo) you actually travel 101.94.

My last calculation was 220 miles with 6.89 gal used from the odometer which comes out to 31.93. if I recalculate using actual miles traveled 220*1.0194 then divide that by the 6.89gallons, I get 32.55mpg. a .6mpg increase. (the 195/55/16 should use 1.0182 instead of the 1.0194 - also, for reference, the Fit base 175/65/15's would use .998 as the multiplier)

~SB

 

You guys kill me. Of course your mileage will decrease in winter with snow tires. The cold means the car is running less efficiently. You are running the heater and defroster(with the a/c compressor cycling on). There is also added resistance from driving in snow,and dragging snow in the wheel wells and tire treads. Despite the decrease in MPG,it's still way ahead of alot of vehicles. The glass is half full.

 

Thanks for your input. I would like to point out a few inaccuracies in your reply just to clarify things a bit. First of all I purchased all season tires, so your first point doesn't apply to my situation. Second, I am not using the rear defroster or AC (I disabled the AC from automatically engaging on defrost mode as well). Last, I have not driven through any snow. I agree that initially a cold engine is not working very efficiently, but the engine warms up quickly and stays that way for my long commute each day, one could make the argument that the engine actually runs more efficiently in overall cool weather, right?

 

I believe the OEM tire size is 185/55/R16 in the US for the GE8...

 

Exactly. Yep I need to clarify that my new tires are all season. I would definitely go the route you did with the Acura wheels and smaller tires for winter, especially living in VT. But since my all seasons were bald, I decided to just get a good set of replacement all seasons to get me through winter in STL.

 

I numbered each question in an attempt to make it easier to answer/reference back to, but yes #4 ended up being an all of the above option as well.

I received the Honda software update to correct the MPG computer inaccuracies. No ECU flash.... I wish!

 

It may have been better to do each one separately and check out the results each time. But new tires and re-flashing, and then throw in extreme weather all at the same time leaves you wondering and guessing which one of those is contributing the most or least. They are all contributing, but which one is doing what is all but lost. When it gets warmer out, at least you'll know what that part of the equasion was contributing. Good luck this winter- for all of us!

Dan

 

Im so confused, winter tires cost money far more money than the mpg you are losing. more important to stay out of ditch than care about mpg.

 

They do... and they don't... , if the average person will put new tires on the car at 45,000mi, someone who runs dedicated winter tires, will not need to replace theirs until 60,000 miles. (given that you run winters for 4 months out of he year. for 5 months you'd run until 63,500 miles)

Using the 45K tire interval with 4 Months of Winter driving above; someone who keeps their car for 10 years averaging 15K miles per year on all seasons alone would have gone through 3 full sets of All seasons and be 1/3 of the way through their 4th set of tires. someone who runs dedicated Snows in the winter would have gone through 1 set of All seasons, 1 set of summer's, one set of snows, and be on their 2nd set of summer tires & snows. While the dedicated summer/snow tire individual is on their 5th set of tires, the 2 sets of summer tires they bought were likely cheaper overall than the 2 sets of all-seasons purchased by someone who doesn't change. (Plus, the 2nd set of summers & Winters are still fairly new).

In the end, a dedicated summer/winter tire person will end up paying more but in the long run it's probably not much more than $100-200 including mpg differences (unless: you have to have the wheels/tires stored, don't have dedicated winter wheels, your car has VSA & Requires TPMS sensors - all off these will incur additional costs). The benefits are obvious, safer tires & better performance all around and your summer wheels remain in better condition longer, but there is that slight additional cost. It depends on what's important to the driver/owner.

~SB

 

I was referring in general to the thread, and not so much specifically to your post. You are correct in the above response. I forget that the weather here is not the rule. We received approximately 4 feet of snow last week,with more this week (and there's more to come). I'm also with you on the cold engine being efficient once it warms up,and possibly being more efficient at operating temp in cold weather. On a sidenote,I have lived in the Syracuse area for the past 17 years (originally from Manhattan) and have never felt the need to purchase snow tires for any of my cars. I came here with a rear wheel drive 8 cyl no ABS vehicle,and once I bought a more current front wheel drive ABS one I was fine. I have had primarily FWD vehicles,and 2 with AWD (including my last one prior to the current Fit). I personally do not see the need to drive with snow tires in the winter,and we get ALOT of snowfall here! Sorry to get off track,and to the OP for misconstruing his first post. I just get a little weary of al the snow tire talk. The only winner I can see there is the snow tire dealer.

 

OEM tire size on All fit sports is 185/55/16. you do NOT want low profile winter tires.
The WINTER tire size recommended for the fit sport is 175/65/15! It's virtually the same diameter, but you will need a set of different wheels obviously.
I highly recomment these if you drive in snow or ice, your fit will become a 4x4 with these, I have the michelin x-ice II, they are awesome!