Speedo ?
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Senior User
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Speedo ?
Is my assumption correct that since the speedo read teeth on its own wheel/gear, if I change the gear ratio I shouldn't have problems with speedo changing. Thanks for any help! By the way looks like I'm gonna go from 4.10's to 3.73's. Maybe I can pinch an extra penny of my fuel bill.
Elder User
Joined: Mar 2004
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From: Pasco, WA
It reads its own gear, so it shouldn't make a difference unless you change tire size. When I changed the tires from 215/85's to 235/85's, the mileage hardly changed at all, even though the new tires were almost 2" taller. In fact the towing mileage was worse. I switched back to 215/85's at the next change.
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Thanks for the confirmation. Am I making a mistake dropping to 3.73's. Currently I cruise 70 mph @ 2500rpm. If my calculations are correct 3.73's should have me cruising at just over 2100rpm. That should equal money in my pocket with out a big loss in pulling power. Thanks
Laughing Gas
Joined: Jun 2005
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From: Colorado
your computer actually converts the speed signal pulse from the speed sensor which is on the rear differential to vehicle speed based on an internal algorithm for gear ratio and tire size. I believe it can be reprogrammed up to six times.
Laughing Gas
Joined: Jun 2005
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From: Colorado
I run at about 2100 @ 75 with 285/75 16 tires and 3.55 gears with corrected speedometer, GPS and Ford APC module that displays RPM's to the single digit. FYi my Tach in the cluster is about 100 RPM's off from actual RPM's so dont trust that to be exact.
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Originally Posted by soutthpaw
I run at about 2100 @ 75 with 285/75 16 tires and 3.55 gears with corrected speedometer
