Odometer correction for 215-85-R16 tires

warp2diesel · **Posted:** Sun Oct 11, 2009 6:45 pm

I did a bunch of driving this past week for work and determined the odometer correction factor for my 215-85-R16 ATR Cooper tries inflated to 45 PSI.
The correction factor is multiply the odometer reading by 1.115 for 215-85-R16 tires.
Stock tires the correction is 1.10 times the odometer reading.
Someone should figure this out for other tires and we should post it in the CRD Tech Section.

BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor.

gsbrockman · **Posted:** Sun Oct 11, 2009 9:07 pm

warp2diesel wrote:

I did a bunch of driving this past week for work and determined the odometer correction factor for my 215-85-R16 ATR Cooper tries inflated to 45 PSI.
The correction factor is multiply the odometer reading by 1.115 for 215-85-R16 tires.
Stock tires the correction is 1.10 times the odometer reading.
Someone should figure this out for other tires and we should post it in the CRD Tech Section.

BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor.

I'm a little confused here...............

1) Why should the correction factor for stock tires be trip odometer x 1.10 = actual odometer reading ?

2) I disagree with "BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor." Your actual fuel economy changes simply by correcting for the miles driven. A like percentage increase is "double dipping" if you add corrections for both odometer readings and mpg readings.

Greg

CRDMiller · **Posted:** Sun Oct 11, 2009 9:55 pm

Why not just get the tire mfg data on revs a mile at 40 mph and get your computer reprogrammed. it takes about 2 minutes to do, the flat rate is 30 minutes, don't be surprised if it takes longer though, dealers are re tarted.

geordi · **Posted:** Mon Oct 12, 2009 12:04 am

Revs per mile shouldn't change based on speed. The wheels on the bus go round and round... For the same number of times in a straight line at any speed.

warp2diesel · **Posted:** Mon Oct 12, 2009 7:35 am

gsbrockman wrote:

warp2diesel wrote:

I did a bunch of driving this past week for work and determined the odometer correction factor for my 215-85-R16 ATR Cooper tries inflated to 45 PSI.
The correction factor is multiply the odometer reading by 1.115 for 215-85-R16 tires.
Stock tires the correction is 1.10 times the odometer reading.
Someone should figure this out for other tires and we should post it in the CRD Tech Section.

BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor.

I'm a little confused here...............

1) Why should the correction factor for stock tires be trip odometer x 1.10 = actual odometer reading ?

2) I disagree with "BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor." Your actual fuel economy changes simply by correcting for the miles driven. A like percentage increase is "double dipping" if you add corrections for both odometer readings and mpg readings.

Greg

Correct the miles read before or after the MPG calculation to get the real number. But don't correct it twice or it will be wrong. Either way the the odometer is reading fewer miles than what you actually go. I never told the dealer so I could get extra warranty before the 36,000 came along.

TDIwyse · **Joined:** Fri Aug 14, 2009 7:44 am **Posts:** 91

A couple months into a recently purchased 06 liberty CRD and new to the site. Thanks for everyone's inputs to this site.

Recently changed the old stock tires to Cooper ATR 215-85-R16. I'm curious to know how you came up with the correction factors. I used my GPS on several long trips and it seemed to me with the stock rubber I was getting a correction factor of 1.055 and with the ATR's at 50 psi I'm getting 1.088. However the speedometer is almost dead on now.

Also curious if you noticed a hit in fuel economy. I seem to have lost about 6-8% on my back and forth to work, as well as highway driving. Unfortunately this was also about the time we were transitioning to winterized fuel here in Iowa which is throwing off the control of a seperate variable . . .

warp2diesel wrote:

I did a bunch of driving this past week for work and determined the odometer correction factor for my 215-85-R16 ATR Cooper tries inflated to 45 PSI.
The correction factor is multiply the odometer reading by 1.115 for 215-85-R16 tires.
Stock tires the correction is 1.10 times the odometer reading.
Someone should figure this out for other tires and we should post it in the CRD Tech Section.

BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor.

dirtmover · **Posted:** Mon Oct 12, 2009 10:12 am

Yeah, I've used a combination of GPS and highway markers and my odometer reads ~5% low and speedometer ~10% high for the stock setup. I also see a 20% drop in fuel economy over the winter months.

warp2diesel · **Posted:** Mon Oct 12, 2009 11:02 am

TDIwyse wrote:

A couple months into a recently purchased 06 liberty CRD and new to the site. Thanks for everyone's inputs to this site.

Recently changed the old stock tires to Cooper ATR 215-85-R16. I'm curious to know how you came up with the correction factors. I used my GPS on several long trips and it seemed to me with the stock rubber I was getting a correction factor of 1.055 and with the ATR's at 50 psi I'm getting 1.088. However the speedometer is almost dead on now.

Also curious if you noticed a hit in fuel economy. I seem to have lost about 6-8% on my back and forth to work, as well as highway driving. Unfortunately this was also about the time we were transitioning to winterized fuel here in Iowa which is throwing off the control of a seperate variable . . .

warp2diesel wrote:

I did a bunch of driving this past week for work and determined the odometer correction factor for my 215-85-R16 ATR Cooper tries inflated to 45 PSI.
The correction factor is multiply the odometer reading by 1.115 for 215-85-R16 tires.
Stock tires the correction is 1.10 times the odometer reading.
Someone should figure this out for other tires and we should post it in the CRD Tech Section.

BTW: If you use your odometer for fuel economy calculations, you need to increase your MPG by the same as the correction factor.

I drove on a route where I have driven many times and know the exact mileage. I verified this with Microsoft Streets And Trips and got the same. My Garmin GPS reports the same. Then I compared it to my odometer reading. This is not rocket science, just simple math as understood by Engineering Technicians, Engineers, Mathematicians, Chemists, Physicists, and Accountants, and even Bean Counters.

UFO · **Posted:** Mon Oct 12, 2009 11:10 am

I checked the speedo with 215/85/16s. It reads actual speed now.

TDIwyse · **Joined:** Fri Aug 14, 2009 7:44 am **Posts:** 91

Thanks warp2diesel. Just find it interesting that we're getting different numbers even though we're using the same process.

By the way, did you notice any difference in fuel economy?

warp2diesel · **Posted:** Mon Oct 12, 2009 2:12 pm

TDIwyse wrote:

Thanks warp2diesel. Just find it interesting that we're getting different numbers even though we're using the same process.

By the way, did you notice any difference in fuel economy?

I have my tires at 45PSI cold. Changing the pressure will change the rolling radius of the tire and effect how far they go per revolution.
When I picked up my CRD after the new tires were insalled, they had them at 32PSI and it drove like a mush bucket.
My speedo reads 1 1/2 MPH fast at 70 MPH, again, tire pressure will effect the number.
Since my trip included 1 1/2 hours of crawling in rush hour traffic on the Ryan Expressway in Chicago that would have normally taken 10 min, I did not bother to check my mileage.
I had a good laugh when a Chicago Cop zapped me with Radar when I was going 1 MPH and later when I was going 8 MPH, he must have been trying to warm up his coffee :lol:

Silverdiesel · **Posted:** Mon Oct 12, 2009 8:55 pm

Yup- I mention this size of tire on other posts and get "those are pizza cutters" kind of response.
But I really like how these 215/85's are working out-- 22K miles so far.
That 1.11 factor sounds about right-- and -------
If you think these awesome tall skinny tires will fail you offroad- Look what a set of 215/85's can do at MOAB!
http://www.lostjeeps.com/forum/phpBB3/vie ... hp?t=47078

Roland

TDIwyse · **Joined:** Fri Aug 14, 2009 7:44 am **Posts:** 91

Those are some beautiful pictures. Looks like it was a great time.

Do you have any comments on fuel efficiency impact with these tires? So far I'm impressed with their ride/handling/traction and think they look good on the liberty.

I'll have to recheck my GPS/odometer correlation.

Silverdiesel wrote:

Yup- I mention this size of tire on other posts and get "those are pizza cutters" kind of response.
But I really like how these 215/85's are working out-- 22K miles so far.
That 1.11 factor sounds about right-- and -------
If you think these awesome tall skinny tires will fail you offroad- Look what a set of 215/85's can do at MOAB!
http://www.lostjeeps.com/forum/phpBB3/vie ... hp?t=47078

Roland

Silverdiesel · **Posted:** Fri Oct 16, 2009 2:25 am

Moab,Ut to Phoenix, Az is approx 460 miles - my EVIC was reading 29 .8 Avg MPG on the way back - so with that 1.11 factor looks like approx 33 MPG on those pizza cutter tires- yep great handling, smooth stable ride, great acceleration ( at least compared to a 3.8 JK ) and off road or on=NO rubbing!

BTW-- Hats off to fellow LOSTER AZKJ that had that JK and he was my trail partner and comrade for our Moab trip and he was quite invaluable in trail layout and friend as with his planning/guiding we would have never packed sooo much in the two short days we we were there!

Roland

AZKJ · **Posted:** Fri Oct 16, 2009 6:45 am

Silverdiesel wrote:

Moab,Ut to Phoenix, Az is approx 460 miles - my EVIC was reading 29 .8 Avg MPG on the way back - so with that 1.11 factor looks like approx 33 MPG on those pizza cutter tires- yep great handling, smooth stable ride, great acceleration ( at least compared to a 3.8 JK ) and off road or on=NO rubbing!

BTW-- Hats off to fellow LOSTER AZKJ that had that JK and he was my trail partner and comrade for our Moab trip and he was quite invaluable in trail layout and friend as with his planning/guiding we would have never packed sooo much in the two short days we we were there!

Roland

No fair!!! Your comparing apples to oranges!!! LOL... You have to admit I kept up with your CRD, even if I had to drop down to fourth on the uphill side of the highway!!! Mileage??? Oh well, at least ya didn't see any stinky black smoke coming out of my exhaust, and not to mention no worrying about dust, cool down times, glow plugs and all that other silly diesel stuff etc etc....

Thanks for the kudos on putting the Moab trip together!! Are you ready to go again?? I hear Baby Lion's Back AND Fins 'n' Things calling.....

flash7210 · **Posted:** Fri Oct 16, 2009 9:19 am

I too have the 215/85 tires.
Compared to my GPS, the ODO reads about 3% low. So for every 500mi
I should be getting 515mi actual.
I dont know what tire my speedo/odo is calibrated for and I dont know
how accurate my GPS is, but thats what I've calcuted.

Here in FL, few trails are hard packed. Mostly soft sugar sand.
My pizza cutters dont give me a whole lot of confidence, but I have never
gotten stuck. :wink:

Also, at 70mph on the speedo, my GPS show 72-73mph.

AZKJ · **Posted:** Fri Oct 16, 2009 11:15 am

Here's the scoop on your pizza cutters and a link to check yourself (I think I got your stock size correct)...

http://www.1010tires.com/TireSizeCalcul ... ion=submit

* Info provided by your friendly Gasser Guy....

warp2diesel · **Posted:** Fri Oct 16, 2009 1:52 pm

With the stock tires when it read 63 I was going 60MPH
With the 215-85-R16 tires when it reads just shy of 61 I am going 60MPH.

AZKJ · **Posted:** Fri Oct 16, 2009 4:25 pm

warp2diesel wrote:

With the stock tires when it read 63 I was going 60MPH
With the 215-85-R16 tires when it reads just shy of 61 I am going 60MPH.

You might want to check your speed and speedo with a GPS unit. With your speedo reading 63mph with stock tires and you actually going 60 mph indicates somethings not reading correctly.

UFO · **Posted:** Sat Oct 17, 2009 12:30 am

Using mile markers between Denver and Moab today, Yokohama Geolandar HT/S at 45 psi, my odometer measures 4.2% low, over a 300 mile stretch. I didn't calculate mileage yet, but I expect 28 or so as I set the cruise to the limit, 75mph most of the way.

Odometer correction for 215-85-R16 tires

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