Tires and Odometer Variance

[21cExp]

I just got a question about mileage in my van, and it got me thinking about something I've been meaning to look into.

I've been measuring my dash odometer against the yard stickers along the interstate and against my GPS and see that it's off.

Not a tremendous amount, but enough that over longer distances it skews my mileage records for runs, my fuel mileage figures, and my planned maintenance intervals. That bugs me, of course.

Is this just a tire thing, you think, or is there a way to adjust the odometer to be more accurate? New odometer cable, or grease it perhaps, or some other way to effect the way it reads?

Do the Scan Gauges do their figuring off the dash mileage, or have a direct way to read mileage?

I'm running Michelin M&S2's in the size recommended for my '08 GMC Savana.

 

[purgoose10]

This might help.

Using Performance Monitor : Linear Logic : Home of the ScanGauge

If your running the size tire that the vehicle calls for there should be no variance. Scan guages measure throught the loop or electronically.

This might also help.

http://tire-size-conversion.com/tire-size-calculator/

 

[OntarioVanMan]

I just got a question about mileage in my van, and it got me thinking about something I've been meaning to look into.

I've been measuring my dash odometer against the yard stickers along the interstate and against my GPS and see that it's off.

Not a tremendous amount, but enough that over longer distances it skews my mileage records for runs, my fuel mileage figures, and my planned maintenance intervals. That bugs me, of course.

Is this just a tire thing, you think, or is there a way to adjust the odometer to be more accurate? New odometer cable, or grease it perhaps, or some other way to effect the way it reads?

Do the Scan Gauges do their figuring off the dash mileage, or have a direct way to read mileage?

I'm running Michelin M&S2's in the size recommended for my '08 GMC Savana.

Really?...that sure seems like picky butt stuff...like 20 or 30 miles over 10,000 will make a difference? even 1/10 of a mile over 10 miles is like a mere 10 miles total over a thousand...or 100 miles or 10,000....hope you are going to caculate or subtract when them tires spin in the winter time really skewing your totals.....LOL.....just poking ya...

 

[RETIDEPXE]

I have the same w/ my M2 but I don't want to spend the money to have the computer re-calib'ed, yea, cheap I know. Use the yard sticks for a set amount, say, 10 mi.s, and compare to your dash odom. Figure the percentage, my is 2% off, or .2 more on the odom in 10mi.s, 2 in 100, 20 in 100, 2000 in 100,000. I figure my maintenance intervals are procrastinated by at least 2% over so now I'm even.

The speedo will be off by 2%, so when showing 56mph, your doing about 55, showing 102mph, doing 100.

Ur '08 GMC will not have a speedo cable.

 

[mjmsprt40]

It's nearly impossible to get a dashboard odometer to be spot-on, we just live with the variance. Even if you could get it exact, say with brand-new tires, over time your tires will wear and there will be a variable.

We haven't had speedometer cables since the mid 1990s, no help there. Today it's all done electronically, though the sensor does feed from the same place the cable used to run from on the transmission.

 

[OntarioVanMan]

It's nearly impossible to get a dashboard odometer to be spot-on, we just live with the variance. Even if you could get it exact, say with brand-new tires, over time your tires will wear and there will be a variable.

We haven't had speedometer cables since the mid 1990s, no help there. Today it's all done electronically, though the sensor does feed from the same place the cable used to run from on the transmission.

thanks..that was my point.....the variance is not worth the effort..one would be better served...
If you had a tail wind out of Laredo and it improved your fuel mileage by 3% with all northernly miles traveled...what would be your NEW...CPM and your lowest acceptable rate?

 

[xiggi]

I doubt anyone figures wind into their acceptable rate. That just might be a bit extreme.

Sent from my Fisher Price ABC-123.

 

[21cExp]

Ha...well, it's mostly something I do when bored driving longer stretches at night or with no scenery, wondering why it's doing it, what causes it, and how it might be remedied.

And sure, the variance is worth the effort. Nailing down problems and realizing how to solve them is great fun for me, actually.

I know I can make the simple calculations to be able to record true miles driven per run, but my mind says "lets fix this so ya don't have yet another thing you have to do in daily life."

It's actually off more like 1.8 miles for every 60. Which, for this last trip, makes it close to 40 miles different than it should be.

I don't currently run Scan Gauge but wondered if it would be more accurate or if its pulling from existing on board figures.

As for tail wind and figuring it into the figures, perhaps if I could get OVM to stay behind me for a long run I'll get statistically better figures. Ha!

Thanks for the links and info; much appreciated.

 

[purgoose10]

I don't currently run Scan Gauge but wondered if it would be more accurate or if its pulling from existing on board figures.

As for tail wind and figuring it into the figures, perhaps if I could get OVM to stay behind me for a long run I'll get statistically better figures. Ha!

Thanks for the links and info; much appreciated.[/QUOTE]

It might help with OVM behind you. They say there's less drag with hot air. LOL!

 

[Moot]

It's actually off more like 1.8 miles for every 60. Which, for this last trip, makes it close to 40 miles different than it should be.

Could be a GM thing. My 04' is also exactly 3% off. Every time I fuel, I reset the "B" tripometer. At that time I would frequently run loads that transferred at a Con-Way terminal in Des Plaines. I would fill up at the Flying J, south of the Beloits. With my old van it was always 75 miles. My new van showed 77 miles. I too did the mile marker thing, which roughly confirmed the 3%. Later that year I got a ScanGauge and for every 100 miles on the ScanGauge my odometer and tripometer showed 103 miles. When I got a GPS it jibed with the ScanGauge.

I don't currently run Scan Gauge but wondered if it would be more accurate or if its pulling from existing on board figures.

I don't know where the ScanGauge gets it data, but I believe it to be accurate and can't understand why the odometer is off and the ScanGauge isn't. I would highly recommend a ScanGauge. I don't leave home without it! Type ScanGauge or Scan Gauge into the E.O. search machine to find several previous threads touting the wonders of the ScanGauge.
http://www.expeditersonline.com/forum/truck-talk/22305-scangauge-revisited.html

Don't sweat the 3%. Your fuel mileage will look slightly better but your overall mileage will be higher come resale time. I've got 673,374 miles on the odometer when in reality the van only has 653,731 miles. If I were to sell it today, that extra 20,201 miles would probably knock the price down about $1.99.

 

[21cExp]

Could be a GM thing. My 04' is also exactly 3% off. Every time I fuel, I reset the "B" tripometer. ... Later that year I got a ScanGauge and for every 100 miles on the ScanGauge my odometer and tripometer showed 103 miles. When I got a GPS it jibed with the ScanGauge.

I don't know where the ScanGauge gets it data, but I believe it to be accurate and can't understand why the odometer is off and the ScanGauge isn't. I would highly recommend a ScanGauge. I don't leave home without it! Type ScanGauge or Scan Gauge into the E.O. search machine to find several previous threads touting the wonders of the ScanGauge.
http://www.expeditersonline.com/forum/truck-talk/22305-scangauge-revisited.html

Don't sweat the 3%. Your fuel mileage will look slightly better but your overall mileage will be higher come resale time. I've got 673,374 miles on the odometer when in reality the van only has 653,731 miles. If I were to sell it today, that extra 20,201 miles would probably knock the price down about $1.99.

Yep, that's exactly the info I was looking for, whether or not Scan Gauge ends up reading the same as the dash or gets its info in some other way. Good to know it is in line with both the mile markers and GPS.

Naw, it's not a huge difference, but over time adds up and makes a difference when figuring six and twelve month averages for fuel mileage based on total consumption, as well as all miles driven and cpm.

Good info man, thanks. Now to decide which Scan Gauge to purchase...

 

[BobWolf]

Keep in mind there are several factors in place.
First, the Engine Controll Moduel and Transmision Controll Moduel programs are not living in real world they compute thousands of electrical inpulses a seccond, sort them out and display the closest average posiable.

In otherwords, the TCM and ECM dont realize wheeel spin in snow, rain or mud, they dont know if your tires are worn, underinflated, a bad tank of fuel unless it raises hell with your vehical. It just reads an impulse from the pickup on the transmission.

If youre milage is down check the tire size and if the size starts with a P for passenger or LT for light truck. You want LT or light truck tires they are rated as a 10 ply due to the tougher sidewalls. Passender tires will wrinkle a few thousandths of an inch under a load you waste power, and load capicity. Also diferent tire brands have diferent hardness to the tread rubber.
I like BF Goodrich for cars and light truck harder compound and decent wear.

Also check with your GM dealer and find out what larger size tires are available for your van. Typicaly you can run one size up and one size down both width and overall diameter if you show only one size on the door. Opt for the one size up. The trick is getting this through the untrained idiot youre trusting to install your tires.
Your spedo might be off by 2 to 5 mph however thats the reason cops dont bother you unless you are seven over.

Summit racing sells a calibration tool made by Super Chips but at 350 to 400 bucks for the tuner it might be cheaper to have the dealership dial it in for you.

Bob Wolf.

 

[westmicher]

Actually, the main reason most odometers read less than actual is an unpublished rule issued by the IRS to automakers... so drivers who claim mileage are screwed out of 3-5% of their mileage deduction. The savings are going to pay for Obamacare!