WHY Is My Speedo.....Right???!?!

908 Views 3 Replies 3 Participants Last post by DurangoBeard, May 2, 2020

DurangoBeard

Discussion Starter · Apr 27, 2020

So i recently had gotten som 33/12.5/15 tires. Tired of getting flats on my used tires i decided to ground myself from off road until i could do the body lift and threw my good 33s on. Little trim here and there only rub at full bumpstop turns. Its been 2 weeks ive daily driven everywhere. My tranny still shifts fine even cruising at 80( i did a static balance so its a little vibration at that speed tbh) but my main concern was my speedo. I didnt want to get pulled over especially right now. Well my speedo isnt off and ive done nothing to it. Drove past 3 neighborhood speed limit things that tell u ur speed. And one police one that was down town. My speedo is on point. And for the life of me i cant figure out why. Its nice knowing its ok but i want to know why.
This is a stock 5.9 4x4 with 230k miles. I bought it 8k miles ago. Atleast 1k off road of varying degrees. During that whole time(b4 i knew better) i have 235s up front and 31s in the rear...then put these 33s on...could the computer learn itsself???

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daddyododge

· #2 · May 2, 2020

One of the factors in your antilock brake system (ABS), is TRPM, tire revolution per mile.
The truck came with a specific tire size programed into the ABS system. Changing tire size
changes the TRPM. To get the speedometer to read correctly, you have to take it to the
dealer, they can get the TRPM for your tire size and reprogram the ABS module.
Good Luck, daddyododge

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ajjacobs

· #3 · May 2, 2020

Hav you compared speedo to GPS?

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DurangoBeard

Discussion Starter · #4 · May 2, 2020

No but i will do that today after my fuel pump...i did not even think of gps...ill try that..
Ive read how and what im supposed to do the correct my speedo when its off....this post is about it NOT being off, as told by 1. Police and 2 neighborhood speed slow down ur too fast thingys...

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