Tire setting on SCT x4
04-12-2016, 11:57 PM
#21
Ford specs on speedo are +- 7 mph so at 70 you could be at 66.5 or 73.5 and be in spec. It's also a little known fact that cops wouldn't stop someone unless 5+mph over the limit. Last couple leo's I asked said they won't normally stop someone until they get between 7-10 mph over.
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04-13-2016, 12:12 AM
#22
Senior Member
so the sct x4 tire sizes actually do something? reason I ask is that my truck came with 245/75-17's ... I put the 295/70-17's on recently. that should be about 33.3" I've tried that setting, and up to 1.5" smaller or larger and nothing seems to change the speedo - it's always 5-7mph off (ie; 83 mph on speedo = 75 mph on GPS). I let it get to a speed and set the cruise then give it a few miles I was thinking the x4 wasn't actually communicating the tire size to the truck/pcm since smaller, correct, and larger than actual wasn't having any affect.
04-13-2016, 05:40 AM
#23
F150 Greenhorn
Just keep adjusting your X4 until you get the correct speed. I'm running 295/70R18 Trail Grapplers. Their website says 601 revs. On my X4 I ended up using 615 revs. The speedo is spot on with my GPS.
04-13-2016, 11:21 AM
#24
Senior Member
Thread Starter
Update, just drove to Pigeon Forge and back this week for vacation, speedo is off by 2, but odo is dead on, just like it was from factory, Guess it will stay that way. Lol
04-13-2016, 11:41 AM
#25
Senior Member
There will be a discrepancy when you are talking about a digital to analog conversion. Odo being digital and the gauge being analog. The best thing is to have the odo spot on and the speedo may be off.
04-13-2016, 12:29 PM
#26
Senior Member
ok thanks i'll keep trying - i'm downloading a speedo APP for my iPhone and will combine that with the garmin gps to make sure
just was weird that going 1.5" smaller, and an 1" bigger than my tire size had no apparent effect on the discrepancy - either way the speedo was still 7+ mph more than gps reading.
just was weird that going 1.5" smaller, and an 1" bigger than my tire size had no apparent effect on the discrepancy - either way the speedo was still 7+ mph more than gps reading.
04-13-2016, 04:51 PM
#27
Senior Member
Thread Starter
ok thanks i'll keep trying - i'm downloading a speedo APP for my iPhone and will combine that with the garmin gps to make sure
just was weird that going 1.5" smaller, and an 1" bigger than my tire size had no apparent effect on the discrepancy - either way the speedo was still 7+ mph more than gps reading.
just was weird that going 1.5" smaller, and an 1" bigger than my tire size had no apparent effect on the discrepancy - either way the speedo was still 7+ mph more than gps reading.
Measure the standing height, from ground to top of tire while loaded. That is your loaded Diameter, multiply by pi then divide by 12 to get your loaded rolling circumference in feet, then divide 5280 feet by your loaded rolling circumference to get your revs per mile.
Last edited by RajunKajun59; 04-13-2016 at 05:42 PM.
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04-13-2016, 05:06 PM
#28
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04-13-2016, 05:12 PM
#29
Senior Member
this will get you closer, than using the unloaded specs
Measure the standing height, from ground to top of tire while loaded. That is your loaded Diameter, multiply by pi then divide by 12 to get your loaded rolling circumference in feet, then divide 5280 feet by you loaded rolling circumference to get your revs per mile.
Measure the standing height, from ground to top of tire while loaded. That is your loaded Diameter, multiply by pi then divide by 12 to get your loaded rolling circumference in feet, then divide 5280 feet by you loaded rolling circumference to get your revs per mile.
thanks!
04-13-2016, 05:28 PM
#30
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this will get you closer, than using the unloaded specs
Measure the standing height, from ground to top of tire while loaded. That is your loaded Diameter, multiply by pi then divide by 12 to get your loaded rolling circumference in feet, then divide 5280 feet by you loaded rolling circumference to get your revs per mile.
Measure the standing height, from ground to top of tire while loaded. That is your loaded Diameter, multiply by pi then divide by 12 to get your loaded rolling circumference in feet, then divide 5280 feet by you loaded rolling circumference to get your revs per mile.
33x3.14159/12/5280=.0016362447