Tire Diameter Change In Fuel Log?

[Blue Angel]

Just wondering if anything has been considered to add a variable in the fuel log input for a change in tire diameter?

An easy way to effectively make your car's gearing taller is to increase your tire's diameter. For example, going from a 25" tall tire to a 26" tall tire will effectively give you a 4% increase in "gearing".

The issue with this comes when logging fuel data. Your car's odometer has no way to compensate for the change in tire size so your reported distance will be 4% shy of your actual distance travelled.

Is/has there been any thought of adding this feature to the fuel log? I may decide to put taller tires on my car for winter driving next year, but if I do so it will get complicated to track mileage with the fuel log.

[MetroMPG]

I'm dealing with the same thing in my Firefly owing to a transmission change. I've been correcting my "trip odometer" distance prior to entering the fill data in the fuel log.

[D.O.G.]

I'm running oversized tyres on my Mazda.
Checking odometer milage against my GPS, shows a 5.7% difference.
I simply multiply my odometer figure by 1.057 when entering a fuel log.

[user removed]

I forgot to do this with my Ranger when I went from 14 to 15 inch wheels. I use a 19.9 mile trip I do about 4 times a week to check the distance and compare the two. The Ranger was off by 2.6%. The Kawasaki with a 15 (versus 14 stock) front sprocket was off by 7.14%.

Since the fuel log uses actual distance travelled I just bump the odometer reading by the correction amount, to get the actual distance within 1/200th of exact distance.
The calculation is based on the average recorded distance of at least 10 different vehicles over the last 8+ years of driving-riding that route, both ways.

On the Ranger, I found my reciept when the wheels and tires were changed which was 12/11/12 and my fuel log showed a refill on 12/12/12, so I just used the +2.6% correction on every log entry after that point to get it correct and current.

regards
Mech

[Blue Angel]

I guess it's not that big a deal to do here, as you input the distance travelled instead of the odometer reading. Capturing the correction factor in the notes seems easy enough.

I have an app on my iPhone called "Fuel Log" that I use at the pump while filling, and I also use the Fuelly page, both of which are set up to capture your odometer reading. I know I have the choice with the app to configure it the other way (distance travelled on tank), but I made the mistake of setting it up the odometer way as it was a brand new car. I'll have to look into the Fuelly page and see if I can change it.

[jakobnev]

I just recalculate the Pulses Per Mile-value on the MPGuino.

[Blue Angel]

Originally Posted by jakobnev

I just recalculate the Pulses Per Mile-value on the MPGuino.

The MPG-what? I have factory installed, perfectly optimistic fuel computers inflating my ego... why would I pay more to feel worse about my mileage?

[Diesel_Dave]

Depending on the vehicle, it can be done in software. I changed my tire size with a tuner. I know in a lot of cases a dealer can do it for you. It's a fairly common thing to do with pickups, as there are folks out there who put on huge tires and still want a reasonably accurate speedometer.

[Blue Angel]

Originally Posted by Diesel_Dave

Depending on the vehicle, it can be done in software.

I will be looking into this. I have HPTuners and I know the tire size can be set for my Corvette, but I'm not sure about the Cruze. If that's the case I'm all good and just need to update the tune whenever the tire size changes.

[gone-ot]

Regarding the GM Chevrolet 2013 Cruze, below are the OEM tires and their respective "engine revolutions @ 50 mph" (EPA value: N/V). Notice however, that regardless of the rim diameter, they ALL are roughly about 35(A) or 38(M) engine rev's per mile at 50 mph vehicle speed for the same Final Drive Ratio (FDR), except for the ECO and LS models:

6-SPEED AUTOMATIC (FDR = 3.53:1):
• P215/60R16 (Firestone)....N/V = 36.5 (LS, FDR = 3.72:1)
• P215/60R16 (Firestone)....N/V = 35.1
• P215/55R17 (Goodyear).....N/V = 34.9 (ECO)
• P225/50R17 (Continental)..N/V = 35.4
• P225/45R18 (Michelin).....N/V = 35.4

6-SPEED MANUAL (FDR = 3.83:1):
• P215/60R16 (Firestone)....N/V = 38.7 (LS, FDR = 3.94:1)
• P215/60R16 (Firestone)....N/V = 37.6
• P215/55R17 (Goodyear).....N/V = 30.8 (ECO)
• P225/50R17 (Continental)..N/V = 37.9
• P225/45R18 (Michelin).....N/V = 37.9

Source: GM to EPA document, "Application for Certification 2013 Model Year", page 62: http://iaspub.epa.gov/otaqpub/displa...d=29809&flag=1