Same here. When I switched form Sasquatch tires to 37" Toyos my speedometer is dead on now.How much bigger? I noticed my speedo was more accurate after going 2" larger. Went from 2 mph slow at 60 to 1 mph fast.
it’s actually required to read NOT LOWER than the actual ground speed.It is required by law for speedometer to read higher. I don't know how much higher but none the less, higher.