Z'mnypit

iTrader: (58)

It seems no matter what I do I cant get my speedo to read right with the 4l80e. Ive tried the values from different tunes from trucks that came with the 4l80e and Ive gotten close but not quite. Its reading about 5mph off and its driving me nuts. Ive got the 2-3 shift set at 33mph and my speedo will read 40mph when the 2-3 occurs so its about 7mph off. If I put the correct tire size in there it goes way off. Im using 25.70 for the tire size and 3.73 for the gear ratio. The tire size thats on there is 295/35/18 BFG KDW 2's. If you put that through the conversion you get 26.10. Below are the values I have entered:

Current tire size: 25.70
Gear: 3.73
Calculated Tire: 24.09

General VSS Pulses Per
mile: 117094
Rev-Trans: 40.0000

Final Drive Ratio
Ratio: 3.73
Trans Revelutions/Mile: 3122.9295

Anybody have any suggestions or different values to try?

RedHardSupra

iTrader: (1)

measure the actual radius of your tire (center to ground) and use that for radius. there's quite a bit off difference in tire sizes on top of weight of the car squishing the tire, and the pressure and temperature of the air in the tires, so it's just easiest to measure it.

Z'mnypit

iTrader: (58)

So measure from the center of my rim to the ground then multiply by 2? Or would it work if I measured form top of the thread to the ground?

RedHardSupra

iTrader: (1)

the two methods (center to asphalt vs asphalt to top of the tire) are NOT equivalent, that's where the problems stems from. tire, while normally it would be a circle, it is squished on the bottom. that's why the center-to-aslphalt distance is the effective radius.

Z'mnypit

iTrader: (58)

Sorry to sound stupid, but if I put the radius in I measured which would be 13.xxxx how is that going to make it right. The PCM will think they is a half of a tire there. Once again sorry for my ignorance.