Have you tried using google? I just did, and here's what I found out. That motor, is designed for offroad use.
However, I figure a 4wd buggy is probably in the ballpark for an on road tc. (at least its the closest match weight and driveline wise). Now castles website, which you can find in google, actually lists a bunch of example cars with their spur and the pinion range to use as a guide. I picked the first one a B44. So again I turned to google. This gave me the internal ratio of a b44, which turns out to be 2.5. Now castle list 16-18 as the pinion range, so i picked 17, and went to the trusty windows calculator (didnt need to google that one I knew where it was). And long story short, its an fdr of 12.7.
Now another translation, just to check it out novaks gearing chart (guess how i found that?) says for a 4wd off road buggy and fdr of 11-12 would be about about a 5.5t to 4.5t motor, sounds about right for 5700kv. The same motors in a touring car would be 8.5-9.5. So, I googled how to work out an fdr (I didnt really just wanted to say google, I know how to do this though because i googled and found a friendly forum that had all the answers i needed, and for the questions it didnt i aksed nicely... and didnt use caps, or a
).
For you to produce an fdr of 9ish you need a... drum roll please... a 19t pinion. Which will be 9.16. But you'll need to keep a close eye on temps, and go lower in the pinion (or up in the spur) if it gets too hot. You can find temp guides on castles website, google it up and have a look.
If you dont have a temp gun you can probably find a bunch of places that sell them if you just jump on google...
Why tell you all this? I wanted to prove how long it took me not only to work it out, but to research it, I started right after I last posted, and proofed this before i submitted.
Of course, all this goes out the window if your on a 3s and not a 2s.. want to know what that is? GOOGLE IT