If i am going with 31s or 32s how bad will it set off my spedo if at all

 

Year and drivetrain please

 

Indicated Speed x (New diameter/factory diameter) = actual speed with the new tire diameter

Example: 60 MPH indicated x (35"/28") = 75 MPH actual with the larger 35" tires in place of the stock 28's.

You can use a similar calculation for any other speed point or diameter ratio. Be aware that many tires sized in inches like "31" or "32" are often actually 1/4 ~1/2" smaller than the label implies. Don't ask me to explain that.