Need some Diff./Gearing Help
 

Hey all, I just found a RX7 speed calculator site and did a little bit of number crunching to decide on what final drive ratio I wanted after I switched to my Miata Gears and 17 inch rims. I am kinda thinking that the site might have been a little bit off though. The first thing was that it said my new 17 inch tires would have a smaller diameter than the 14's that are on it now. the 14's were at 25.1 inches and the 17's were at 24.4 inches. The tires that are on my car now (I am NOT the one that had these put on) are 235/60R14 on my phone dials. My new tires would be 235/40R17. I will post all the combos that I put in and maybe someone out there could tell me if they look right.

Possible Gearing
Tires

NOW - 235/60R14 25.1 inches
PLAN - 235/40R17 24.4 inches

Trans Raitos
1 2 3 4 5
S4 N/T - 3.475 2.002 1.366 1 0.711
Miata - 3.136 1.888 1.330 1 0.814

Max Speed 4.10 w/ 235/60R14 at 7500 RPM
1 2 3 4 5
S4 N/T - 39 68 100 137 192
Miata - 44 72 103 137 168

Max Speed 4.33 w/ 235/60R14 at 7500 RPM
1 2 3 4 5
S4 N/T - 37 65 95 129 182
Miata - 41 69 97 129 159

Max Speed 4.10 w/ 235/40R17 at 7500 RPM
1 2 3 4 5
S4 N/T - 38 66 97 133 187
Miata - 42 70 100 133 163

Max Speed 4.33 w/ 235/40R17 at 7500 RPM
1 2 3 4 5
S4 N/T - 36 63 92 126 177
Miata - 40 671 95 126 154

Max Speed 4.44 w/ 235/40R17 at 7500 RPM
1 2 3 4 5
S4 N/T - 35 61 90 123 172
Miata - 39 65 92 123 151

How the hell did you they fit 235's on the phone dials. The 215's I have on mine are bubbling out a lot. :eek:

I don't know, the only thing that I do know is the the previous owner of my car was a friggin idiot.

bump

how bout another bump to the top

Dammmnnn, maybe I forgot how the gears on a tranny are, but either you put the decimals in the wrong place or I am confused in the way you wrote that. Because a 3.475 to 1 gear ratio in first gear is impossible!!! 5th gear in a car isn't even a 1 to 1 gear ratio. But if you have a tranny like that and a motor to pull it, you will be going much faster then the 180 MPH that you figured with the miata diffy and 17's.

I know that the tranny ratios are right. And yes 5th is an over drive gear, only drag racing trannies have a 1 to 1 5th gear, usually 4th is 1 to 1

An S4 NT tranny's 5th gear has a gear ratio of .697. So how do you see that it is over a 1 to 1?

No offense cory but you should go read about transmissions and stuff on the internet cuz you have no idea what ur talking about. You should check out http://auto.howstuffworks.com/transmission1.htm then you'll understand. And yes the 5th gear is an overdrive gear that means that the drive shaft will turn more than the crank will, in the other gears (except 4th cuz its 1:1) the drive shaft will turn more than the crank will.
And by the way how is your exhaust holding up?

I know how tranny's work it is just that you have the gear ratio wrong for an S4 NA, or at least the 5th gear becasue I don't remember the rest of them. :D And I had the ratio bass acwards, so I was thinking it was high in first and low in 5th, I don't know what I was thinking.


And the exhaust is doing great, and holding up awsome. But I need to find a digital camera and sound recorder so that I can see the flames and let people hear the exhuast.