Need help with 700R4 Speedometer Gears

I am installing a 700R4 transmission into a 1941 Chevy. My rear tire is a 27.7" tall P215/70R15. Rear end is a 3.73 ratio Explorer unit.

When I put these numbers into Bowtie Overdrive's calculator, it recommends a 19T/34T combination.

Put the same information in the TCI calculator, and it generates a very different 15T/41T combination.

The difference is that the Bowtie Overdrives calculator factors the overdrive ratio into the final drive ratio whereas the TCI calculator does not.

Which is correct?



Here are links to the two calculators:

http://700r4.com/speedoCalc/speedocalc.shtml
http://www.tciauto.com/tc/speedometer-gear-calculator


Thanks,
Ed

 

Transmissioncenter.net (PATC0) has a calculator that shows a drive gear of 15 teeth and a driven gear of 40 teeth. They also have all the gears for sale.

 

TCI would be better IMO. The gears are on the output of the trans
so the o/d ratio would not be a factor.

 

3.73 rear gears you'll need around 3 to one ratio on the trans gears...the Bowtie calculator is out to lunch?

 

Thanks guys! That's what I needed to know.

 

Most of what Bowtie Overdrive has is out to lunch!

You want a "gray" 15 tooth drive gear and a "yellow" 41 tooth driven gear.