I just recently got 32x11.5x15 BFG MT KM2 tires on my truck.

Previously with worn 31x10.5x15 my speedo was approximately 5 mph faster than actual speed.

When I got the 32" tires the speedo is now accurate...

Does this mean the gears are not factory? I have a 93' v6 4x4, 5sp.

 

It probably just means your speedo wasn't very acurate in the beginning. Most factory ones are off.

 

How are you measuring "actual" speed?

But, I never checked it stock, but after going from 31's to 33's, the speedo was DEAD ON to the GPS.

 

I compared my speedo with my wife's brand new stock civic when I had 31's with the "speed checking display"

You can see these from a mile away. not completely accurate but when it's 5 to 7 off you've kind passed the tolerance factor.

I used gps when I got the 32's.

 

It's not "5mph off" it may be 5 miles per hour at a certain speed but it works on a percentage scale, for instance:

5mph off at 25 miles per hour would be 10 miles per hour off at 50

I second the factory speedo being off.

I dont trust any of mine i go by gps even the stock rig is off a bit

 

When I tested the 31's it was at 70mph.

The gps was following the speedo from 0 to 75 right on.

 

Factory speedo must have been off - crazy that it could be off that far.

bottom line now I have 32's and my gps agrees with my speedo