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Discussion Starter · #1 ·
I Have ordered a set of 33" Duratracs 295x65x18 for my sahara unlimited and want to know what the difference if any there will be on the speedo reading between those and the stock 32" tires
 

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I Have ordered a set of 33" Duratracs 295x65x18 for my sahara unlimited and want to know what the difference if any there will be on the speedo reading between those and the stock 32" tires
I put 35s on mine. This morning, I reset my trip odometer as I passed mile-marker 64. Not unexpectedly, my odeometer read 10.0 miles right as I passed mile-marker 75. So, I'm going 11 miles for every 10 miles my Jeep computer thinks. Also, when my speedometer reads 60 mph, I'm really going 66 mph. When my average mpg computer reading is 15 mpg, I'm really getting 16.5 mpg. And so on.
 

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kjeeper10 said:
MTH?

He reported 0 change I believe
Almost. I went to 33x12.5R15 and found using a GPS that my speedo was ACCURATE. I didn't try it when I had 32s, but logic tells me that it must have been inaccurate from the factory. In other words, I almost surely experienced a change, but as luck would have it the change was toward greater accuracy.

So for the OP I'd recommend the same. Use a GPS and figure it out. There are too many variables--how big are your current tires, really? How big will the new ones actually measure out to? And what is your computer actually programmed to?
 

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Almost. I went to 33x12.5R15 and found using a GPS that my speedo was ACCURATE. I didn't try it when I had 32s, but logic tells me that it must have been inaccurate from the factory. In other words, I almost surely experienced a change, but as luck would have it the change was toward greater accuracy.

So for the OP I'd recommend the same. Use a GPS and figure it out. There are too many variables--how big are your current tires, really? How big will the new ones actually measure out to? And what is your computer actually programmed to?
You should link these findings to the "why does my real life mpg's not match the advertised mpg's" threads. That would hopefully put an end to those that think the computer is the end all, be all of calculating your gas mileage, and never bust out the paper and calculator. :doh:
 

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MTH said:
Almost. I went to 33x12.5R15 and found using a GPS that my speedo was ACCURATE. I didn't try it when I had 32s, but logic tells me that it must have been inaccurate from the factory. In other words, I almost surely experienced a change, but as luck would have it the change was toward greater accuracy.
X2

I used a gps and was spot on. I did lose about 2 mpg & wonder if thats just more accurate now too.
 

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Discussion Starter · #9 ·
Thanks all. I will check it with my GPS when I finally get my Jeep.
Was supposed to be on the 3rd Jan, then the 6th Jan. Still no sign so far and now going to UK for 2 weeks so cant get my hands on it until the 20th at the earliest - The wait is killing me!
 

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I put 286/75R/16 Duratracs @ 35PSI on my 2012 JKU and the initial comparison with GPS showed it very accurate. Today I used a ProCal and put in the new tire size (though not too much different) per the instructions and now the speedo is 3mph higher than the GPS readout:confused:. I'll re-measure and try again but wouldnd't think it would have changed that much. Yes sounds odd that I'd mess with it if it was on but new to all this and trying the new kit to see how things work. Easy enough to change back.
 

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I know I'm kind of an old fuddy-duddy, but it's amazingly simple to test your practical tire size by zeroing it at one milemarker, and seeing how your actual miles compare to the readout. I assume the mile markers, in states other than Arkansas (just kidding), are pretty much right on. Maybe the GPS is too, but sometimes, mine is off a bit on distances to intersections etc ..., and I assume the GPS might not exactly track the vehicle's trajectory on some curves. In short, if you're getting wierd data from your GPS, you might want to check your odometer on a mile-marked highway.

For example, with my 35s, my odometer changes almost exactly 10 miles for every 11 miles I drive on the highway, which means my odeometer and speedometer now read pretty much exactly 10% low. I think this is the most-foolproof/easy method. Just my $.0.02.
 

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Discussion Starter · #14 ·
Beastmaster said:
No problem. :thumb:

I've gotten so many good ideas from this forum, it's nice I am able to contribute from time to time. :D
I know what you mean, there is so much info on here, I think it's actually adictive!
 
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