I found some wheels that someone sold off their Ranger, and they are the right bolt pattern, but 15"

Does that affect your speedometer? What would I need to do to have these wheels instead of the 14" on there currently?

 

What affects your speedo is the overall diameter of the wheel and tire together. The size of the wheel wont matter if you get a tire size that matches the height of the tire you have now. I would imagine you would want taller tires to go with your 15" wheels so if you do go that route then yes, it will affect your speedo slightly.

 

depending on the year you might have to run spacers up front. i have heard that newer 15 inch rims rub on the TTBs of older Rangers.