gear change( or 4t65e sprockets lol) odo accuracy help

[Kdog]

ok so if we have drive sprocket ratio of 1 (1.121094)[1] pulses per mile of 23536 (23430)[23536} calculated pulses per rev 25 (22.30078)[25] speedometer input pulses per revolution 9.117188 (9.117188)[9.117188] and trans revolutions per mile 2540 (2568.371)[2580.968] and after 68 miles odometer is off 2/10ths of a mile reading 67.8. and according to gps, speedo reads correct maybe 1mph under gps at higher speeds like interstate 75mph. no big deal i am just going 76 when my heads up display reads 75 so slow passing/speeding is the concern. how to correct this and should i use the mile markers on the road or gps to determine accuracy? numbers are oem in parentheses and number before parentheses is current setting or now modified number. i changed the output and input sprocket on the input shaft(trans from torque converter) to output shaft (shaft that drives diff thusly the 2 front tires) from a 37t drive sprocket on input from torque converter to 35 and the driven sprocket on output shaft from 33t to 35t. so my overall effective final drive ratio at cv axles from trans went from 2.93 final drive to 3.29 final drive. now a same car trans engine just non sc with a 3.29 final drive as they come with a 35t 35t config factory numbers are in the [] brackets above. i played with one number or table at a time and lowered trans rev per mile to 2540 and got it couple miles off to the 2/10ths it is now. i dont want to go to 2500 unless i know for sure this isnt affecting any other table lookups in vcm like idk ya know just to have peace of mind that tune is 100% correct as to right tables adjusted for my gearing change i wanna ask. (lower numbers = faster reporting or faster odometer climb hence the 2500 for correct odo if right table to adjust atleast for odo trans rev per mile lower is formentioned) ive spit this out chewed on it and thought long enough that i am not sure i know what 2+2 is rn. figured never hurts to ask for help and may get a clear duh fkn im idiot type explanation or answear. clear cut or not i wanna hear it please and thanks in advanced -Kdog-

[geep]

pop the speedo needle off and adjust use a fork under speed it lol

[geep]

on a serious note i think tech 2 can adjust the speedo on the cluster on the 04+

[vlad01]

I use the speedometer app on my phone and it's super accurate and it's free for all the main features. It matches the road side speed checks exactly at all speeds. I've had that app for many years and use it to check cars I haven't driven before so I know what the real speed is.

The old standalone GPS from like 15+ years ago are accurate too, most HUD and gps speedo units these days are deliberately out in the faster direction to cover their asses, usually 5Km/h exactly.

My cars are less than 1Km/h out or bang on, so I am happy not to mess with things. My cars need a signal correction module to adjust the speedo anyway and is not something I can do in the ECU or with the sensor gear as they are unique to the Aus market and they never made aftermarket ones with different tooth counts, I had used the VDO unit when I changed diff gears on one car where it was around 10% out after which worked great by the way, and on another car that was about 2% out, I changed to narrower and slightly lower profile tyre that not only got my speed bang on, it fixed the inner and outer guard scrubbing issues too, two birds, one stone I guess and a more common cheaper size to boot.

With the small % change you need, I'd say go for it, if the PCM allows the speedo to change accordingly, I'd just go for it. It should not effect anything that you should notice given the change is so small.

[Kdog]

thanks for the input yall. trying a new write rn ill update tonight