After switching from 225, 70, 14 in tires in the back to 275, 60, 15 in tires which speedo gear do I need.

There is currently a 45 tooth one in there... online calculator said 19 with a 3.23 gear ratio... but this one won't fit.

Thanks in advance!

 

It would help to know what transmission you have. Are 3.23s the gears currently in the rear?

In any case, the speedo gear is directly related to tire diameter. 225/70-14s are 26.40", 275/60-15s are 27.99". The larger tires make fewer revolutions per mile, so the speedo DRIVEN gear (the one that comes out of the trans with the speedo gear adapter) needs to be smaller to speed up the speedo cable at a given output shaft RPM. The difference is 27.99/26.40 = 1.060245.

 

Thanks. The trans is TH400

 

Well there are still NINE possible drive gears that could be on the output shaft of that trans, and again, is 3.23 your current rear axle ratio?

ASSUMING 3.23, if your trans has an 8-tooth drive gear, you need a 19 tooth driven gear. If your trans has a 15 tooth drive gear, you need a 35 tooth driven gear. Etc, etc. If your speedo was accurate with the old tires, tell use how many teeth are on the driven gear, or what color it is.