EcoModder Forum 5% larger tires (effect on odometer/MPG calculations?)

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08-13-2019, 10:39 AM   #31 (permalink)
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Quote:
 Originally Posted by hat_man Not confused so much as trying to see how it makes much of a difference in real world MPG numbers. If this 10 mile trip is your daily commute, then the difference is at most 2 tenths of a mile. About 1040 feet per day. So for an average work week the difference is 1 mile. Either 53 or 54 miles total. Even if you did this on 1 gallon of gas, how much more gas did you burn? Is it even worth calculating? If you only averaged 30 MPG, the difference in what you used is only 3.3/100 th's of a gallon. Just a hair over 4 oz for the week. Less than a dime at \$2.50/gallon for the week. Not much of a deal breaker. For an average of 30 MPG, to drive the two longer distances, it would take either 33 gallons or 33.66 gallons. \$1.65 extra to drive 1000 miles at \$2.50 a gallon. Again, not a huge meaningful difference. Precision is nice, but when converted to real world numbers, it seems like overkill.
You're right, at least for the average person out there in the world who may not even know how to calculate fuel mileage or odometer error.

However, for the non-average person, ie an ecomodder, here on this forum who does things to save, say, 5% on his/her fuel mileage, it often makes a BIG difference to achieve, say, 40mpg v only 38.

Enough difference between a frown :-( and a smile :-) to many of us.

In fact, that's why we're taking the time to participate here, no?

Edit addendum: I was referring to the OP's question in general. I see in the post I copied it is referring to much smaller differences than 5%. So, I guess it's all relative.

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Last edited by MeteorGray; 08-13-2019 at 10:55 AM..

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08-14-2019, 01:20 AM   #32 (permalink)
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Quote:
 Originally Posted by hat_man The way I'm seeing this is that Google maps rounds to the nearest tenth of a mile and GPS is to t he nearest hundredth? So Google adds 528 feet to every mile but GPS only adds 50 feet. So for every 10 miles Google shows it's actually 11 miles? Sounds a little extreme to me. Unless I'm not understanding what you are getting at. I can't imagine Google being 100 miles off for the 1000 mile trip I make to see my family in Myrtle Beach.
Maybe I was not clear (not the first time!). ...It's more like, hypothetically, I drive a distance & my odo measures it as 81.5 miles, Google says it was 85.6, and the GPS says 85.55...
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

 08-17-2019, 09:30 PM #33 (permalink) Master EcoModder   Join Date: May 2010 Location: Illinois Posts: 423 Oh Deer - '03 Ford Ranger XL 90 day: 33.16 mpg (US) Thanks: 50 Thanked 66 Times in 53 Posts Just out of curiosity with so many new vehicles having computer control and digital dashes, if the odometer is mis calibrated wouldn't the speedometer be off also? Wouldn't it use the distance traveled to calculate speed? If the ECU can be adjusted for tire size, could you "trick" the odometer by adjusting the tire size to compensate for the delta? __________________
08-19-2019, 11:59 PM   #34 (permalink)
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Quote:
 Originally Posted by hat_man Just out of curiosity with so many new vehicles having computer control and digital dashes, if the odometer is mis calibrated wouldn't the speedometer be off also? Wouldn't it use the distance traveled to calculate speed? If the ECU can be adjusted for tire size, could you "trick" the odometer by adjusting the tire size to compensate for the delta?
Yes. I think that's true. In fact, even on older cars like mine you can get aftermarket devices to spoof the speed sensor signal. For me, it is just cheper and easier to know how off it is and calculate the adjustment.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

 08-23-2019, 12:51 PM #35 (permalink) eco....something or other   Join Date: Jul 2009 Location: Colfax, WI Posts: 705 wood hauler - '91 Ford F-250 Team Pontiac 90 day: 18.97 mpg (US) Rav - '06 Toyota Rav4 Base 90 day: 26.52 mpg (US) Thanks: 36 Thanked 54 Times in 41 Posts I know our 2006 rav4 is off a bit and they are calibrated the same. There are several tire sizes offered and they don't bother to change it for each size. __________________ 1991 F-250: 4.9L, Mazda 5 speed, 4.10 10.25" rear
08-24-2019, 07:08 PM   #36 (permalink)
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Quote:
 Originally Posted by IsaacCarlson I know our 2006 rav4 is off a bit and they are calibrated the same. There are several tire sizes offered and they don't bother to change it for each size.
Yes. Same with the 1990s Civics. Different trim levels had different gearing and tire sizes but the speedo sensors all showed 60 mph at about 1025 RPMs of the sensor. Also, I think my speedo dial was painted slightly off center so that everythi g is reported 2 mph faster than it might have been. Precision instruments!
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

 08-25-2019, 03:29 AM #37 (permalink) eco....something or other   Join Date: Jul 2009 Location: Colfax, WI Posts: 705 wood hauler - '91 Ford F-250 Team Pontiac 90 day: 18.97 mpg (US) Rav - '06 Toyota Rav4 Base 90 day: 26.52 mpg (US) Thanks: 36 Thanked 54 Times in 41 Posts Yeah. I remember my physics teacher telling us about taking measurements and "estimating" the decimals or any smaller unit than indicated on the measuring device. I don't agree with it. I can easily measure to ~.0001" with my dial indicator that is marked to .001". Just like being able to tell if you are doing 56 or 57 when your speedometer is marked in 5's. __________________ 1991 F-250: 4.9L, Mazda 5 speed, 4.10 10.25" rear