I'm planning on putting some 30 inch tires on my 1994 jeep cherokee, I'm not sure which yet, but I'm just wondering how the increased size will affect my speedometer. Will it make it inaccurate?

 

With 31's mine is off by 6-7mph above 60mph. 30's will probably be a little less. It's not enough to really worry about though.

 

IT'S ALL ABOUT YOUR RATIOS i ride 32.5 and at 50on the guage i'm running 55 but i was running 69 70 so i thought and got a ticket for 79 so the faster you go the more it throws it off. also take in to acount your tripometer will be off too. i was getting 250miles a tank stock, did some stuff to improve that then put on my lift and tires and was getting the same in all actuallity 250 on my guage is roughly 275 280 miles so keep an eye on it and good luck. and check out the maxxis at's. pretty bad a$$ and cheaper than bfg's and run just as long if not better. also they are quiet on the road.

 

30" tires shouldn't make much of a difference at all. My Cherokee with 36" tires is only off 10mph.

 

@60mph ...would be 62.3mph = 2.3 mph over odometer 235/75/15-to-30x9.50/15

 

my 93 changed 3% 60=55/30=27

 

You can get speedo gears with different amounts of teeth to correct the speedo.
Use a GPS and verify your speeds when you install bigger tires.