My question is concerning stock tire sizes versus aftermarket sizes for my 03 1500 QC 4x4.
The truck originally had 265/70R-17 michelins of some sort on it when I bought it used.
I just recently put Nitto Terra Grappler 285/60R-18's and wanted to just check my settings with the Superchips (3715).
The tuner asked me if I wanted to adjust tire size, and I said "Well, why not at least check...". The tuner then told me that the stock tire (OEM) size was 30.5", and my research on the Internet was saying that the Michelins (and the Nittos) are roughly 31.5" in diameter.
Is this true? I already changed the tire settings to reflect what the Internet was saying the outer circumference was on the Nittos, I just want to make sure that's correct.
If so, this means that for however long now my Speedo/Odometer has been giving inaccurate information. What would be the conversion factor, and how will this affect MPG, etc?
I think your right, 30.5 seems too big for the stock setting on 265/70/17 I thought mine were in the 29.? something range. I ran that setup for winter until recently going to toyo AT 295/70/17's. They are just under the stock 20's I have for summer.
I don't think I'd trust what the Internet says. Get a measuring tape out and measure the height of your tire and plug that into the SC. If the measurement was too big in the computer, you were going farther and faster than you really were. I was told it was about 5mph on the speedo from stock 20's to the 265/70/17 before I got my SC.
Checking the drivers door information panel, I noticed that the manufacturer's suggested minimum tire size is a 245/70-17.
Using a calculator and a tape measure just to be sure, this comes out to roughly 30.5".
Using an online tire size converter and comparing it with the new 285/60-18 Terra's this equals roughly a 3% difference in speedo and odometer. Both were causing the speedo to run to slowly.
I.E. when the speedo was indicating 58 mph I was actually travelling at 60.
Not much of a difference, but we'll see how it goes.
What you need to do is physically measure from the ground to the flat top of the tire with in 1/4" increaments. (31.25) This is the proper way to tune the SC product for the tire height:
Ron :rck:
I thought it was a teeny tiny bit off, even after the calculation/superchips change.
Rummaging around I did find a tape measure and you are correct, the Nitto's (when properly inflated) measure closer to 31.25" from ground to the top of the tire.
I'm going to get a buddy with an 05 QC 2x4 Hemi to compare speedo readings (hopefully his is correct) later today.
you can check what the stock config is .... put the truck back to stock ... then read stock config then there is a place you can verify what is in your PCM now .... you can also put the truck back to stock config and then if you re-tune skip over the tire part and it will NOT recalibrate your tire size ..... if you need any other assistance dont hesitate to ask
If you have a GPS try that to make sure your speedo is correct
I did check the stock configuration, it's set for a 30.5" tire (AKA the 245/70R-17 pizza cutters). Why did they (Dodge) in all of their infinite wisdom, put those tiny arsed little tires on that big ole truck? :crazy:
Using Ron, vandy535, slammed1, AIRRAM and everyone elses advice I did the actual walk-out-to-the-truck-with-a-tape-measure bit and they measure 31.3" properly inflated.
I did check the stock configuration, it's set for a 30.5" tire (AKA the 245/70R-17 pizza cutters). Why did they (Dodge) in all of their infinite wisdom, put those tiny arsed little tires on that big ole truck? :crazy:
Using Ron, vandy535, slammed1, AIRRAM and everyone elses advice I did the actual walk-out-to-the-truck-with-a-tape-measure bit and they measure 31.3" properly inflated.
Nope not nit picky .. you are alot like the rest of us ... we want it to be right
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