Speedo gear and rear gear

With no other changes 2.94/3.23=91%= 9 percent..
From a 24.5" tire to a 27" you can have another error of up to 10% (27/24.5= 1.102)
Technically speaking it could be out anywhere from zero to 19%, depending on the actual tooth count.
The best and fastest way to figure out the error of the speedO versus real roadspeed, is to figure it in percent, and to change the pinion by the same percent.
To find real roadspeed; you can use GPS, or mileage markers on a hiway set up for that, or you can use mile-markers and a stopwatch. One mile should take 60 seconds, keep changing your speed until it does, then calculate the difference from what the speedO is displaying to 60mph.
Or record the actual seconds and compare it to 60.
Example 1;
the speedO displays 54 mph at a true 60 mph. Your speedo is displaying 54/60=.90= 90%. You need to increase it 10%.
Example 2;
You drive 5 miles in 270seconds which is 54 seconds per mile. 54/60=.9 or 90%, and you need to increase it 10%
So
you pull out the pinion gear and count the teeth, and find 33teeth. to increase the reading you need to spin the cable faster so you need fewer teeth, subtracting 10% from 33 you get 30.
Your numbers may be different but the percent rule is never wrong.

Or you can do what probably most of us do, which is drive thru a radar zone and determine our % error and after that,just do the mental computations for the various speed zones we encounter on a day to day basis. Ten percent is easy math lol.