Tuning to recalibrate for tire size

[cableguy_hd]

Do you input what the mfg says the tire height is or actually what it measures? May sound dumb but my 275 65 20 say they are 34" tall but don'teasure that. I put in for 33.75" but I sure do get to 50 mph pretty damn quick now it just doesn't feel that I'm going that fast. Been throwing a knock code too. 91 SC tune with 93 octane. Gonna go back to stock and see if it stops. Not sure why it's happening either. All I did was install the tune increase top speed and tire size.... Sorta confused

 

[cableguy_hd]

I put in 26 gal on 93. I have a 32 gal tank that had 89 in it. Could the last 6 gal of 89 cause the knock sensor to go off? Just thought about that....

 

[Ronan]

Mine measure a little under 33 and I have it set to 32. Use a gps to compare your speed and calibrate it accordingly. Worked for me. I use the waze app.


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[Ramrt1]

I use to set it by the height but now go by the over all tire setting which is 285-45-22. I couldn't get the exact tire height at times so I put in the numbers and press apply and the computer adjusts for it.

 

[cableguy_hd]

I just did the gps thing and I'm about 1.5 mpg high. I think if I get the tire size down to the actual 33" they measure that'll correct it. Just hoping the knock code is from the 6 gal of 89 I need to finish running through.

 

[oe542bob]

My personal experience with tire diameters advertised vs. actual. I have a 2003 Dodge Ram 3500 4X4. Purchased oversize tires, BFG KO's. I have a Smarty tuner for it, which allows you to adjust for different tire diameters.
I put the diameter from BFG that was shown for my tire size. After some time I was noticing that my speedo was reading high by about 3 mph. This was using those portable speed signs that the police use in certain areas to warn drivers of their speed. Also places where there is road construction.
So I took a level resting on top of the tire, held it level, then measured the distance to the garage floor. Readjusted the tuner to that measurement. Speedo is right on now.