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Discussion Starter #1
hey guys, i upgraded from the stock tires to 35 inch tires. best i could tell the stockers were about 30 inches call, and my new tires are about 33.75 inches tall. its throwing my speedometer off im sure.. when i got my sct i was under the impression it would alter my speedo as well. but when i change the size on the sct it doesnt seem to make any affect on my speedo. if i got stock tuning or the sct tuning i still sit exactly at 2000 rpms at 70 mph. for a 33.76 diameter tire,, what revs per mile should i have it set at?


i may be wrong,, but this is how i figured i was suppose to do it.

33.75 times pi is 105.975. im gonna round to 106.

so 106 is my circumfrence in inches.

a mile is 5280 feet. that times 12 (inches in a foot) is 63360 inches in a mile.

63360 divided by 106 is about 597 or 8 revs per mile.

Does that sound right?????

If the sct doesnt actually affect my speedo,,, and my only option is to take it to the dealer,,,,, do i need to tell them a specific number??

thanks guys.
 

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You need to go to a dealer to get the speedo recalibrated. The SCT will reprogramm the trans so it shifts properly. Keith
 

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Discussion Starter #4
i still need to know what you guys think i should tell the dealer to flash it too?
 

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I think the lowest revs per mile the dealer can recal for is 600 or close to that. 35's are the largest tires the dealer can do. Keith
 

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MAFIA #8
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5,567 Posts
yeah it isn't necessarily a flash just tell them you need to have it recalibrated for your larger tire size.
 

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Pursuit Interceptor
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735 Posts
Ask the dealer to recal the ABS module for the new tires. I have asked why the SCT doesn't do this and was told the liability of screwing up the ABS was to great for the aftermarket guys to worry about.
I would look at the manfacturer's web site for the rotations per mile for your tire. They sometimes list the revolutions in the specs of the tire. If not go with the 601 value. If the dealer has a problem with that suggest to them using the OEM 20" wheel and tire combo value. It's hit and miss with the dealers so good luck on that end. If I remember right the Superlift Tru-Speed will adjust the ABS and speedo. I'd call Superlift first on that one.
 

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Like said above..SCT wont change your speedo ..and the dealer can only adjust up to 35's..

you need something like this..I don't have one..(don't care that much) but there are quite a few people on FTW that have them and say that they are the best speedo correction module that they have ever used..

http://www.fmdkinc.com/truck.htm

here are a few pics of my buddy Scott's truck..while he was installing the speed wizard

http://fordtruckworld.tenmagazines.com/gallery/COTTS4x4/698833.jpg
http://fordtruckworld.tenmagazines.com/gallery/COTTS4x4/698832.jpg
http://fordtruckworld.tenmagazines.com/gallery/COTTS4x4/698831.jpg
 
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