Speedo Calibration Issue

[wreyns]

latest revision I've installed is 9r31, adjusted parameters too axle ratio 4:88 and tire size 33"
when my speedo is reading 60mph, gps shows me doing 46mph, so 14mph difference and it trips the service trailer brake and abs light within half a mile of takin off.
2008 Silverado 2500HD 6.0L gas with 4:88 gear and 33" tires for winter lol

[mikel]

how far off is the speedo with no changes made?

[wreyns]

With stock tune when the speedo reads 60mph the gps reads 52. So 8mph.

[wreyns]

So I've re-installed the diablo tune. Put in axle ratio 4:88 and set the tire size to 25.5" and the speedo is bang on and the service trailer brake and abs light have cleared.

[kevoscamaro]

Good job. Learn somethin new every day

[wreyns]

ok So I'm back on here with same problem as I original had except now I have installed my 37'" tires and the service trailer brake keeps tripping and abs I have tried all the previous steps that worked last time. but not as lucky this time so back to the drawing board