After restoring my 64 dodge I replaced the 14 inch wheels to 15. Now the speedometer reads 5 mph more at 60 mph. So do I need to go to a gear with more or less teeth to correct the speedometer reading? I forgot to mention that I went from a 2.76 to a 2.94 post. I could not find a chart in the service manual to figure the new gear tooth. Now what do I need to do? thanks

Is the gear ratio the same? Going to larger wheels means you travel farther for one revolution of the wheel. So in theory your car should be faster than what the speedometer says. If you actually slower than the speedometer I would assume your axle ratio changed too.

Anyway you want to slow the speedometer down, so a larger gear would do that. One revolution of the output shaft would turn the speedometer cable less, with a larger gear.

There are charts in the service manual that would give you correct gear size base on tire and axle ratio.

Pull your current speedo gear, count the teeth, multiply by 1.0833 to find the tooth count you need now, obviously you'll round off to the nearest whole number. Last time I checked (long ago, it could be a curve, I was looking in a fairly narrow range, I assumed it was linear) the worst you could be off was 1.8%, so each tooth represents ~ 3.6% difference. So probably 2 or 3 more teeth. 2¢

http://www.brewersperformance.com/products.php?cat=60

these are the ones that are available.

If you figure out what you need, send me a PM I have several used OEM's

Here is the formula I used: CTC X (SI/SA) = pinion tooth count needed to correct speedo

Where CTC = current pinion tooth count
SI = speedometer indicated
SA = Speedometer actual (determined by GPS, stopwatch etc)

example : 33X (60 mph/54mph) = 33 /1.11 = 36.7 tooth Use a 36 or 37 tooth gear.

mine had a 33 tooth in the trans and my speedometer registered 60 , GPS indicated 54. I used a 36 tooth and now speedometer reads 61 mph at 60

You already know your gear ratio so just measure your tire diameter and head here.

http://www.moparts.org/Tech/tech/pages/speedo.html

Totally disregard the above link if you still have the 62 - 65 trans. it probably needs the small speedo gear instead of the ones in these charts.
Measure the tires and call Brewer.

https://tiresize.com/calculator/

put in the sizes here and it will tell you the diff

the 62-65 speedo pinion gears are totally different than 66 and up. the early speedo pinions are in one tooth increments and that figures to about a 5% change per gear and there were only 6 different pinions made; 16-21 tooth. if a 66 or later trans was installed then there are charts to help navigate the process.