Speedo gear

[Z3v0]

Ok guys, I'm stumped. 71 dart with an LA 360 pushing a '73 727. Rear is an 8.25 geared at 2.45 and 225/60/r14's.

According to the manufacturer's spec on the tires, the math works out to a 26 tooth speedo gear. The problem is, if I calculate it manually, I get 24-25 tooth, which is insanely hard to find new. I'm attaching a pic that shows the formula I'm talking about. Thoughts?

 

[Oklacarcollecto]

Here is a used 25 tooth if it will work for you.

http://www.ebay.com/itm/MOPAR-SPEED...Parts_Accessories&hash=item2ec509ef9f&vxp=mtr

 

[fishy68]

I didn't try your formula but my chart says it needs a 26 tooth gear. That's based off of my tire size calculator showing a 225/60/14 tire is 24.6" tall. In my experience I have found I sometimes have to take into account that the tire might be slightly shorter than what the calculator shows due to inflation, tread wear, and manufacturing design differences. All tires that are 225/60/14 should be made exactly equal in size but they aren't. Close, yes. Exactly, no. With that in mind even using 24.1" as a tire ht. (1/2" is the maximum variance I've found) the 26 tooth gear is still as close as you can get. It may be off 1 or 2 mph. but on our old cars that's the closest you can get sometimes. Sometimes you luck out and nail it.