Originally Posted by Hittnthebz

The rim diameter does not affect the speedo reading. The tire size is what affects this so if you have tires sized 195/50/15 and switch to tires sized 195/65/15, your speedo reading will be affected. This is just an example so I know that it wont be much, if it is even noticeable at all. I just want to make the point that if your truck comes with 17 inch wheels which will have a big sidewall, you can keep the speedo reading the same as the 17's when using 23 inch wheels by having low profile tires. The thinner sidewall compensates for the excess wheel size. Some online wheel/tire distributors have a program on their website that will recommend tire sizes so you stay within this margin.