AEV procal error

[Jeep or Tacoma]

I just swtiched to 35's actual 315 70 17 which measure 34.69 say 34.75 for pro cal use. when I program the the new tire size in my speedometer is still 9 miles per off at 60 mph. so when my speedometer reads 60 I am actually doing 69. I have checked this 3 ways 2 with gps speedometers on my i phone and also outhouse signs with radar that always tell me to slow down. I can't figure out what to do. should I reset the speedo with a larger tire size that would match the 9 mph error. or is there something else I am missing .

 

[Comanche Scott]

Try going smaller, like around 33.25" to start. It's not the actual advertised tire diameter, but the rolling diameter, which is much less than 34.7"

I have a set of 315/70R17 S/T Maxx. Following the Procal instructions I measured the actual mounted size at normal pressure, and came up with a much smaller number. Somewhere around the low 33" size (can't remember exact #).
After inputting that dimension, the speedo is very accurate now based on GPS comparison.
Hope this helps.

 

[WininUtah]

I think CS is right, my Hankook MT 315/70R-17 measured in the 33" range when on the vehicle. Using the Procal formula the speed really close to GPS readings.

 

[jwilson2598]

Yeah, my Duratracs that are 315/70/17's and I measured them at 33.75", which when I set the ProCal to that it was just about dead on.


Sent from my iPad using Tapatalk

 

[oscar the grouch]

adjust in small increments until the speedo matches your GPS.


I think mine are at like 35.75 to get it right. for reference im on 37s

 

[1stDeuce]

Did you get this figured out? Judging by your error, it sounds like your not actually changing anything... 35's instead of ~30's would cause the speedo to read about 70 instead of 60.

I think it's not an "error", but rather a lack of actually re-programming tire size...
Call AEV if you can't figure it out, they'll help you.

 

[Jeep or Tacoma]

Yes I got it figured out had to drop the tire size to 33.5 the actual measured rolling size ( spot to spot painted is 34 .6") but dropping to the 33.5 puts everything exactly right