Correct Tire Size Adjustment-Revs Per Mile (RPM) - Ford Powerstroke Diesel Forum
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post #1 of 19 Old 05-21-2008, 04:33 PM Thread Starter
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Correct Tire Size Adjustment-Revs Per Mile (RPM)

All,

If you have 35" tires or bigger I highly recommending you set your RPM's on your tuner in the options screen to match your specific tire size. Your changes will overide what your vendor had put in there.

I have had custom tunes from two different vendors now that set the RPM much less than the actual RPM for my tire size. I told them I have 35'' tires when having my custom tunes built and they we way off.

Once I made the change, I immedieatly noticed better shifting and MUCH quicker downshifting. That dreaded Lag is gone...you know..the one where you slightly give it more throttle and nothing happens...this is seperate from the know turbo lag.

Now while going 40+ MPH and when pressing the pedal it downshifts right away and takes off..! Much improved! If you have that lag also, and have large tires identify what your RPM's is for the tire and get it as close as you can on your tuner. Incriments of 5's is as close as you can get unless you call have your vendor do it. It's much faster just to make the change yourself.

I have Toyo Open Country M/T Tires and mine are 35x12.50x20 which is 592 RPM per Toyo's website. I selected 590 RPM on my tuner and it made a noticable difference.

Here are some other Toyo sizes:

35X12.50R17LT = 596 RPM
35X12.50R18LT = 593 RPM
35X12.50R20LT = 592 RPM
37X14.50R15LT = 566 RPM
37X13.50R17LT = 560 RPM
37X13.50R18LT = 560 RPM
37X13.50R20LT = 560 RPM
37X13.50R22LT = 560 RPM
37X13.50R24LT = 561 RPM
All 38's on 16/17/19/20 inch rims are 550 RPM


If you have a different brand you will most likely have to look up your tire makers website to identify actualy RPM for your brand.


Hope this helps, I just wanted to share what worked for me.



-Evan

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post #2 of 19 Old 05-22-2008, 04:15 AM
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thanks, ill have to refigure mine out and see what i have in there now. although i dont think i can adjust my Rev's per mile myself. ill see if i can have Vivian redo the tunes for me.


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post #3 of 19 Old 05-22-2008, 08:05 PM
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I think you have to have an XCal 3 to change the tire size yourself. I tried to do it on my XCal 2, and there was no way to do it. I'll get Vivian to change mine when I get a new tune this summer to see if it works.

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post #4 of 19 Old 05-23-2008, 04:19 AM
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Vivian reurned my email and said i am able to adjust it myself. i hope she remembers i have the Xcal2. ill see what i can do tehn if i cant ill ask her to redo a tune for me.


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post #5 of 19 Old 05-23-2008, 03:51 PM
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so if you have an Xcal2, you are able to change your revs per mile. it is inthe change parameters options before you install the tune. i changed mine but havent driven it yet. ill post again after i drive it to update any noticeable changes.


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post #6 of 19 Old 05-24-2008, 07:31 PM
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so i have given it a good amount of drive time since i made the change in the rev per mile. i completely agree with the first post in this thread. up shifting, downshifting, way better. just drives better IMO.


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post #7 of 19 Old 05-24-2008, 08:48 PM
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Quote:
Originally Posted by Rwalker View Post
so i have given it a good amount of drive time since i made the change in the rev per mile. i completely agree with the first post in this thread. up shifting, downshifting, way better. just drives better IMO.
Thanks, Rob, I'm going to try it.

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post #8 of 19 Old 05-24-2008, 08:50 PM
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no problem.


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post #9 of 19 Old 05-24-2008, 09:06 PM
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I just went out to the truck and changed mine, so I'll let you know how it turned out tomorrow.

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post #10 of 19 Old 05-24-2008, 09:14 PM
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its tons better!!!!!!!


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