My 1994 civic dx has an ex gage cluster and the speedometer is off by 10-15 mph how would I correct this and keep the gage cluster it says my tire size should be 175 70r13 but I have 185 60r14 which is the real problem or how can I fix this issue?

bad cluster?
BAD WIRING TO IT
LOOSE FUSE TO IT.?
is LED back lamps
or some odd, speed led that make curved virtual MPH display.
try to know we can not see your LED nor what country it is.
some cars in other countries use totally different clusters.
scan the PCm yet to see if VSS speed sensors are failing.
we always can first after all if it knows what is bad, why would you ever want to not know that?

Make sure the digital one is set to the correct units (MPH or KMH)

The clusters in these model years are know for lots of problems relating to the little DC motors (AKA stepper motor) that move the needles of the gages, you most likely need the instrument cluster rebuilt.

Do you have any codes ? Have you modified your steering/suspension in any way ? Have you changed the size of your tires ? If you can share more detail information, this would help

hi
if the noise is there and it get loud as the speed increase
then check your wheel bearing.

More info needed. Is this a hatch back, sedan, or CRX? Is the odometer mechanical [old style] or digital [LCD numbers] The vehicle speed sensor [located behind the speedometer in the instrument cluster] drives both the speedometer and the odometer [mileage meter]. It sounds like an electric problem in the instrument cluster. Remove the instrument cluster and take it to your local speedometer repair shop. Look in the yellow pages for them. Or simply buy and install a used instrument cluster from a junk yard.

you need a new speed sensor. it bolts onto the the back of the transmission(towards the firewall) it is plastic and has one bolt succering it in place.

most likely

You have a speed sensor on the transmission casing. Look in the front part of the engine bay down on top of the casing. It should be a little to the left between the radiator and the engine and has a wire plugged into it. It's pretty small and is very easy to replace.

Yes, that is correct. What probably happened is the bulb for the check engine light burned out. The way to fix it is to pull the gauge cluster out and replace the bulb. It's not very hard to do either. If i remember right, for that year civic there are two screws holding the cluster trim in on the top inside by the cluster case. Then the dash peice connected to that that goes around the steering wheel just pops out and u just unplug the electrical switches and pull that whole peice out. Once that's out there should be 3 screws holding the cluster in, take those out and the cluster will pull right out. Carefully unplug the harness and speedometer cable and locate the check engine light bulb and twist a quarter turn and pull straight out. Then just replace with new bulb and reinstall the parts. If u can do it yourself you'll save a lot of money. A dealer would probably charge u an hour of labor which is somewhere around $115 depending on the dealer and location. Then the price of the bulb, probably a few bucks. Hope this helps, good luck!