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Superchips and KM2's
Anyone having issues with speedo correction with Flashpaq and KM2's The tires, as mounted, measure 34.5 tall but I am down to 33.50 as the flashpaq setting and it is still off by 2 mph at 75 mph.
Tuner is updated as of yesterday and tires have been pysically measured. If I set it at 34.5 as the actual measurements are this thing would be off by almost 5 mph. Actual speed is GPS, pace, and radar verified. Anyone else with similar issues or suggestions? I would guess that if I have to adjust the tire size to an incorrect measurement it would also screw with the auto's shift points etc. Thanks, |
Don't measure your spare and make sure your on flat ground when measuring the tire from the tread to the ground. It's certainly not perfect and since you have a GPS calibrate to that and don't be concerned what the numerical value is. The big thing is making sure your shift points are correct and proper speedometer calibration plays a big role.
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Did you set your gear ratio yet? What is your PSI? I haven't heard of KM2's being even close to their rated size. My 33's were an inch smaller at 40 psi.
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Originally Posted by planman
(Post 1255167)
I believe the correct way to measure tire height for a programmer is to measure from the ground to the top edge of the tire under normal load and air pressure.
I have used this approach with AEV ProCal, Hypertech, and Superchips programmers and my speedometers have been pretty close to exact GPS verified. I know the AEV ProCal instructions state in bold: Do not use the manufacturer's listed tire size. As your tire tread wears down, the height will get smaller and your programmer would need to be adjusted to get close to exact speedometer readings. Most 35s are probably somewhere between 33.5" and 33" tall when brand new under normal psi and load. Manufacturers provide measurements of unmounted tires. The actual height of the tires on your rig depend on wheel width, psi, weight of your vehicle, etc. The same tire on a 7" wide wheel on a 2 dr X with no top or modifications at 40 psi will be taller than on a 10" wide wheel on a 4dr with 1000+ lbs of accessories (bumpers, armor, winch, etc.) at 26 psi. |
Originally Posted by DESERT RAT
(Post 1255241)
The old fashioned way, which works, to find the actual diameter, taking into account the sidewall bulge, is to mark the tire and the ground at it's contact point, roll the jeep forward 1 revolution, line the marks up and measure the distance it has rolled. Using the circumference formula Pd (3.14 x diameter) you divide the rolled distance by 3.14. This is your real diameter.
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I just threw a level on top of the tire where it sat, and measured off the ground....
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Originally Posted by AK4Dave
(Post 1255273)
I just threw a level on top of the tire where it sat, and measured off the ground....
While on this subject, dont' forget that factory speedometers are not very accurate. Normally they are calibrated to be exact at around 55mph, which is the most important speed to get right,ticket wise!! so don't forget that when you check your settings with a GPS, only one speed will be dead on . The best speed to get right is the one you need the most, the speed limit you need to know the most !! |
I checked the speedo today with the GPS just to see if I needed to make any adjustments to the Flashpaq tire setting.
My Toyo 35" Open Country MTs at 28psi measure 33.25" height with the Jeep sitting in the garage. Using this number with the Flashpaq gave me what appears to be less than 1/2 mph difference between the speedo and the GPS at speeds of 60 to 80mph. This is more accurate than the Hypertech Max Energy, I usually had to add .25" to get it dead on (under 1mph deviation). |
Originally Posted by DESERT RAT
(Post 1255241)
The old fashioned way, which works, to find the actual diameter, taking into account the sidewall bulge, is to mark the tire and the ground at it's contact point, roll the jeep forward 1 revolution, line the marks up and measure the distance it has rolled. Using the circumference formula Pd (3.14 x diameter) you divide the rolled distance by 3.14. This is your real diameter.
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