speedometer/mileage help
 

First post here please be kind. just got my sencond xj and already got in trouble. did a 3" bds lift and ridding on 32.5x11.5 tires on stock 15"alloys. have't calibrated speedo nor do i know how. was figuring i'm only about 5 over but after reading a few threds on here i realize that it's more of a ratio size/rotation to determine speed and the trip odomiter. as i'm figureing it my milage is alot more than it's reading and my speed must be a lot more help any one running a similar setup please let me know how fast 60 is and how far 275 miles actually is. (that 275 is what i'm averaging on a take. can you say17-18mpg. and if my milage is more i'll be topping 20mpg. ask me how but help me out. already got a speeding ticket for 15over. oops

i'm running 31x10.5x15 and my spedo reads 4mph UNDER what GPS reads.

265s (31.7) my mph at 60 is 5 over so speedo says 60 but gps says im actually doing 65. don't know about the other part.