Correcting Speedo w/ SCT tuner for 37" tires - Ford Powerstroke Diesel Forum
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Old 11-23-2011, 08:33 AM
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Correcting Speedo w/ SCT tuner for 37" tires

I just installed Innovative Xtreme Street tune and the first question on my SCT was how many tire revs per mile to correct the speedo. It was set at 629 but my 355/60/20 Nitto's should be 565 per their website (I hand calculated and got 577) so I'm thinking 570. Problem is the tuner won't go below 600. It will allow lower than that in the tune options for the shifts points but not for the Speedo correction. SCT and Innovative weren't much help. Anyone know if the parameters for the Speedo can be lowered? Thanks!
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Old 11-23-2011, 09:57 AM
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Did the tune writer ask you what your tire diameter was when he wrote the tune?? They can put that tire rev per mile in the tune and should have done that when they wrote it to make sure the transmission shift points are right.

Not sure what to tell you though about the tire rev per mile not being able to go below 600 revs per mile.
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Old 11-23-2011, 10:57 AM
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Unless something has changed with SCT, I don't think you can correct your speedometer with one. The tire size and gearing adjustments are for shift points.

Last edited by Snake; 11-23-2011 at 11:01 AM.
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Old 11-23-2011, 11:05 AM
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Yes you can adjust the speedo by changing tire size. I have done it with my SCT SF3 with TSD tune. I know I calculated like 629 revs per mile for my tires but had to actually input like 642 revs per mile to get my speedo to agree with GPS. This was with 33in terra grapplers.

I do believe it is a new feature because I have heard from others saying the same thing that they couldnt correct their speedo. Hope this helps.
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Old 11-23-2011, 11:13 AM
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SCT WILL NOT CORRECT the the speedometer on a 6.0. It doesnt have the capability. All it corrects is shift points.
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Old 11-23-2011, 11:22 AM
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Quote:
Originally Posted by Dave View Post
SCT WILL NOT CORRECT the the speedometer on a 6.0. It doesnt have the capability. All it corrects is shift points.
Well that is funny then. Because when I change the tire size on my SCT SF3 before loading up my TSD SPD tune, the speedo changes compared to the engines rpm and my speedo will either be closer to or farther away from agreeing with my GPS.

SO you can say that it doesnt change the speedo reading compared to actual speed over ground all day long and I will say that it does, because my unit actually does. I am sorry I dont know the reason why it does. Maybe it is because the latest version of the firm ware allows it. IDK. But at the end of the day, my unit does recalibrate the speedo if I desire it to.
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Old 11-23-2011, 11:57 AM
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SCT Tire Size Adjustment Doesn't Seem To Work?

On the above link (on page 3) shows Matt from SCT talking about the feature becoming available in June on the X3. Before the tune I was off about 6mph at 50 and now my Speedo is only off 3 at 50 but a correction is definitely made with the SCT. Just wish I could adjust down further than 600. Maybe that stock sensor can only be adjusted so far?
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Old 11-23-2011, 12:01 PM
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No I dont think it has anything to do with the stock sensor. I would say it must be the device. If there is indeed nothing you can do electronically, you could always do a gear swap to get back to the same speed. I know you could take your truck in and have them change the ECM to read the speed correctly.
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Old 11-23-2011, 12:19 PM
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Thanks for the reply. To answer your previous question Eric from Innovative did ask my tire size and the shift points are adjusted for the 37's. I'm waiting for a call back from them to see if the speedo revs per mile can be adjusted any lower with their tune or if 600 (which would be about right for a 35" tire) is the limit for adjustment with an SCT. For those with an X3 or SF3 and 05-07 trucks try to update your firmware if you're unable to adjust your speedo....
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Old 11-23-2011, 12:27 PM
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Quote:
Originally Posted by windrunner408 View Post
Well that is funny then. Because when I change the tire size on my SCT SF3 before loading up my TSD SPD tune, the speedo changes compared to the engines rpm and my speedo will either be closer to or farther away from agreeing with my GPS.

SO you can say that it doesnt change the speedo reading compared to actual speed over ground all day long and I will say that it does, because my unit actually does. I am sorry I dont know the reason why it does. Maybe it is because the latest version of the firm ware allows it. IDK. But at the end of the day, my unit does recalibrate the speedo if I desire it to.
Of course vehicle speed changes with RPM. Thats the whole point of adjusting shift points

That doesnt mean your speedo is correct though. SCT cannot correct the speedo on a 6.0 It doesnt have the necessary hardware to do it.
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