OK kids, get out your calculators!!

I'm gettin ready to drop a sammi case in my Tracker. Just want to figure out how far off my speedo's gonna be.

Here's the numbers:

1st gear - 3.65
5th gear - 86
Diff - 5.12
Hi range in the sammi case - 1.409
31x11.50R 15 LTB's.

OK, so how much is my speedo gonna be off at say 65? I know it'll be reading WAY fast (like 45mph will show like 60 or something), but by how much?

I predict that at 65MPH, your speedo will read 80.4 mph.

Why do I say this?

Because with 5.83:1 diffs, and 31 x 10.50'S and a 1:1 transfer case, my speedo is dead on.

My "after tranny gear ratio" is 5.83:1
Your "after tranny gear ratio" will be 7.21:1

So 65 / 5.83 * 7.21 = 80.4

I predict that at 65MPH, your speedo will read 80.4 mph.

Why do I say this?

Because with 5.83:1 diffs, and 31 x 10.50'S and a 1:1 transfer case, my speedo is dead on.

My "after tranny gear ratio" is 5.83:1
Your "after tranny gear ratio" will be 7.21:1

So 65 / 5.83 * 7.21 = 80.4

This was pretty much what ours said when we did this modification.  ('cept we went back to 5.12 gears in the diffs)

65 actual = ~72 indicated.

~Nate

Drive it on down to Central Florida and lets throw a moving radar in the truck and check it out.  That way you will have a dead on accurrate readout and will know for sure!

Then we can go out to the Bull Creek or 3 Lakes Wildlife Management Areas and hit some trails and see how the gears really work!

Or you could just go find a nice friendly local Police Officer in your area and ask him to do the radar thing for you.  But then you wont have the fun of wheelin in Central Florida!

If you are concerened about your speedo reading then I guess you will be using it on the road. Have you thought about what it will drive like, how many rpm to do 55mph for instance. It could get very tiring on a drive of any distance. Dave Jones had a similar set up, fitted 35s to get the gearing better for road use and then went down to 31s with a stock Sammi case.

Your best bet, is to just drive it with a GPS on board.  The GPS is easily as accurate as any radar.

If you are concerened about your speedo reading then I guess you will be using it on the road. Have you thought about what it will drive like, how many rpm to do 55mph for instance. It could get very tiring on a drive of any distance. Dave Jones had a similar set up, fitted 35s to get the gearing better for road use and then went down to 31s with a stock Sammi case.

Earplugs.  

Yea, it'll be driven on road some. My DD is a Tacoma, so I won't be driving on the road THAT much, and never very far, like MAYBE 30 mi at the most 1 way.

Your best bet, is to just drive it with a GPS on board.  The GPS is easily as accurate as any radar.

That is the best solution I could come up with also. Saving money for the swap tho, so can't drop the coin on a GPS unit. Dunno who has one either I could borrow.  :-/

O, and thx Bob!