Maybe I’m missing something here @Shatneyman and @Slingrazor but why would the width of the tire affect the speedometer?
well, the width is .8" wider,...agree, no need to worry,... diameter is .6" bigger, side wall is .3" taller, circumference is almost 2" bigger. Changing the rotation in the rear but not the front. Hope it made sense.
The tire height is changed. A 255 35 20 is 27", if I went with a 305 35 20 the height is 28.4". I'm only going to 275 35 20 which is 27.6"