Trip Computer / Odometer Accuracy - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

brillo · 01-21-2014, 08:32 AM

I was cruising along the highway and decided to see how accurate our odometer / trip computer was via the mile markers to kill some time. Over several observations, my trip computer was consistently below by ~.1 miles compared the mile markers as I was driving. Can that be correct? I would think that the trip computer would be dead on accurate as far as calculating mileage. I have different tires than stock but they are the same size (225/45/17). The area was quite flat as well.

Are mile markers accurate? 10% seems too high in terms of inaccuracy.

Grimlock · 01-21-2014, 08:51 AM

Check Tire Rack to see how many revolutions per mile your new tire has compared to the original. Even tires of the same size can vary on revs per mile. Also, it could be an air pressure difference could cause that as well.

brillo · 01-21-2014, 09:04 AM

revolutions are the same for both and the tires are pressurized to 35psi.

DarkSunrise · 01-21-2014, 09:20 AM

Quote:

Originally Posted by brillo

I was cruising along the highway and decided to see how accurate our odometer / trip computer was via the mile markers to kill some time. Over several observations, my trip computer was consistently below by ~.1 miles compared the mile markers as I was driving. Can that be correct? I would think that the trip computer would be dead on accurate as far as calculating mileage. I have different tires than stock but they are the same size (225/45/17). The area was quite flat as well.

Are mile markers accurate? 10% seems too high in terms of inaccuracy.

225/45/17 is not stock size. Stock is 215/45/17.

brillo · 01-21-2014, 09:22 AM

Quote:

Originally Posted by DarkSunrise

225/45/17 is not stock size. Stock is 215/45/17.

that was a mis type on my part (not enough coffee). my tires are 215/45/17.

DarkSunrise · 01-21-2014, 09:33 AM

Quote:

Originally Posted by brillo

that was a mis type on my part (not enough coffee). my tires are 215/45/17.

Ah ok, I see it's in your signature too. I'm out of ideas then, although I did hear manufacturers tend to set their odometers conservatively bc they had gotten sued in the past for odometers that recorded too many miles.

IronSean · 01-21-2014, 10:18 AM

Did you just check one mile at a time? Or did you get a total over multiple miles to be a bit more accurate? I'd be more concerned if it said 9.0 miles after 10. If it's just showing 0.9 every time you hit the mile marker it could actually be something like 0.98 miles per mile marker which isn't as bad.

993Fan · 01-21-2014, 11:02 AM

I wouldn't be surprised if the road markers themselves are in error. I doubt they used GPS coordinates to locate them, especially if it's an older road. More likely, they were located by somebody using the odo in his pickup truck with worn tires...

humfrz · 01-21-2014, 11:12 AM

Quote:

Originally Posted by IronSean

Did you just check one mile at a time? Or did you get a total over multiple miles to be a bit more accurate? I'd be more concerned if it said 9.0 miles after 10. If it's just showing 0.9 every time you hit the mile marker it could actually be something like 0.98 miles per mile marker which isn't as bad.

I agree.

I think you would need a longer distance (larger sampling) to get an accurate reading......

wrxneffect · 01-21-2014, 11:20 AM

There is always going to be some error with any measurement device. I have no idea what the specs are for the trip computer. Maybe +/- 10% is to be expected, I hope not though. Plus there is also the error associated with the measurement of the mile markers themselves as others have mentioned.

Sounds like you should drive more awesome miles in the car to find out.

01-21-2014, 08:32 AM	#1
brillo Senior Member Join Date: Nov 2011 Drives: 2013 Firestorm FR-S Location: Houston Posts: 506 Thanks: 18 Thanked 77 Times in 64 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	Trip Computer / Odometer Accuracy I was cruising along the highway and decided to see how accurate our odometer / trip computer was via the mile markers to kill some time. Over several observations, my trip computer was consistently below by ~.1 miles compared the mile markers as I was driving. Can that be correct? I would think that the trip computer would be dead on accurate as far as calculating mileage. I have different tires than stock but they are the same size (225/45/17). The area was quite flat as well. Are mile markers accurate? 10% seems too high in terms of inaccuracy. __________________ 2013 Firestorm FR-S, MTX, build date 1/13.

01-21-2014, 09:04 AM	#3
brillo Senior Member Join Date: Nov 2011 Drives: 2013 Firestorm FR-S Location: Houston Posts: 506 Thanks: 18 Thanked 77 Times in 64 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	revolutions are the same for both and the tires are pressurized to 35psi. __________________ 2013 Firestorm FR-S, MTX, build date 1/13.

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01-21-2014, 08:51 AM	#2
Grimlock Senior Member Join Date: Dec 2011 Drives: BRZ and NA Location: Annapolis, MD Posts: 878 Thanks: 46 Thanked 270 Times in 167 Posts Mentioned: 11 Post(s) Tagged: 2 Thread(s)	Check Tire Rack to see how many revolutions per mile your new tire has compared to the original. Even tires of the same size can vary on revs per mile. Also, it could be an air pressure difference could cause that as well.

01-21-2014, 10:18 AM	#7
IronSean Member Join Date: Jan 2014 Drives: 2006 Toyota Camry Location: Canada Posts: 38 Thanks: 16 Thanked 10 Times in 8 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Did you just check one mile at a time? Or did you get a total over multiple miles to be a bit more accurate? I'd be more concerned if it said 9.0 miles after 10. If it's just showing 0.9 every time you hit the mile marker it could actually be something like 0.98 miles per mile marker which isn't as bad.

01-21-2014, 11:02 AM	#8
993Fan Senior Member Join Date: Nov 2013 Drives: 2014 DGM BRZ MT Location: SoCal Posts: 188 Thanks: 1 Thanked 120 Times in 57 Posts Mentioned: 3 Post(s) Tagged: 0 Thread(s)	I wouldn't be surprised if the road markers themselves are in error. I doubt they used GPS coordinates to locate them, especially if it's an older road. More likely, they were located by somebody using the odo in his pickup truck with worn tires...

01-21-2014, 11:20 AM	#10
wrxneffect Senior Member Join Date: May 2012 Drives: 13 BRZ Ltd 6MT(sold), 03 WRX (RIP) Location: USA Posts: 110 Thanks: 23 Thanked 31 Times in 24 Posts Mentioned: 1 Post(s) Tagged: 1 Thread(s)	There is always going to be some error with any measurement device. I have no idea what the specs are for the trip computer. Maybe +/- 10% is to be expected, I hope not though. Plus there is also the error associated with the measurement of the mile markers themselves as others have mentioned. Sounds like you should drive more awesome miles in the car to find out.

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