Adjusting for speedo/error...? - Fuelly Forums

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Old 02-09-2013, 11:40 PM   #1
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Adjusting for speedo/error...?

My snow tires are apparently slightly smaller than my OE summer wheels...
My speedo reads 100km/h when GPS indicates 95...
5% error.

How is this effecting my mileage and can I change something in my profile to adjust for the difference?

Thanks
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Old 02-10-2013, 01:18 AM   #2
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You can't. I brought this up about 2 months ago when I realized that the odometer on my scooter is off by 12% when compared to GPS.

You can see that thread here: http://www.fuelly.com/forum/1146/Odo...helpsuggestion

Unfortunately, I don't think it's a feature they plan on implementing.
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Old 02-10-2013, 02:02 AM   #3
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You need to find out the difference in circumference of the tire relative to stock, and then multiply your odometer readings by that value when you submit a fill up.
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Old 02-10-2013, 03:29 PM   #4
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I do it by hand, using a simple calculator. Though now that I got new winter tires on the YARDIS, the issue has gone.
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Old 02-10-2013, 05:18 PM   #5
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>My speedo reads 100km/h when GPS indicates 95...

Incidentally, you will find this on many vehicles. The speedo is often designed to read high compared to the actual speed (to reduce the possibility of it reading low, and getting the driver convicted of speeding offences).
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Old 02-17-2013, 03:56 PM   #6
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If your speedometer is reading faster than your actual speed by 5% then your odometer is reading 5% more miles than actually driven. Thus your mpg will seem to be 5% better than actual. To correct this divide miles driven (say 350 mi.) by 1.05 ( percent error) equals 333.33 actual mi. For a vehicle like mine with oversized tires I multiply my miles by 1.08 (8 percent error) because I'm going faster than speedometer indicates. I hope that clears it up.
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Old 02-17-2013, 04:06 PM   #7
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Is it true though that your odo will be 5% out too?

Could it be that they manufacturers know they over read on the speedo, but display mileage correctly?

Maybe count mile markers on the road and see.
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Old 02-17-2013, 04:43 PM   #8
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>Could it be that they manufacturers know they over read on the speedo,

>but display mileage correctly?

You are correct. The manufacturers try to set up the system so that the speedo reads high but the odometer read accurately (i.e., there is a deliberate bias set on the speedo).

If you change your tyre size then this will affect both readings - you are supposed to then adjust your ECU so that the odo is correct again (and hence the speedo will read high again).

>... multiply my miles by 1.08 (8 percent error) because I'm going faster

>than speedometer indicates. I hope that clears it up.

That is mistaken - you will need to check your miles driven via a GPS. If you try to do it via the speed alone, you will be caught out by the manufacturer's deliberate bias.
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Old 03-01-2017, 10:51 PM   #9
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speedo error need adjustment box on app

just joined this app and i also have a vehicle with different tires on and a 7% under speed ,Its a great site but seems an easy fix for the site to put in a box that allows for an increase or decrease in speedo error?
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Old 03-02-2017, 05:33 AM   #10
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That would be nice, currently I just multiply my miles by my odometer offset before I enter my fuelups. Honestly, I think that's probably an advanced feature that would create more confusion among users than the problems it would solve for the few like you and I that would actually use a feature like that.
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