Rear axle gears

i use a simple spreadsheet calculator for this... it makes a table of engine rpm vs. mph vs. axle and tire size. calculates everything, including tire diameter, so it's perfect for what-if use. i recently upgraded it, and i pre-filled out some Ford T5 gears for you.

This looks useless at first but is really helpful in graphing all of the critical parts of shifting when and how. I've added some other math for the reverse gear because strangely, that's just as important to me.

I finally got a good look at my wheels today and they're not what I thought they were. A set of Federal Steel 2ply 215/75/R15 reads a diameter of 27.7" on this math scale and then the math gets fun:




Now I just need to highlight the appropriate shift points and compare them to 3.08 and 3.54 sets. 

The amount of time I spend in reverse has mostly to do with reverse parking(something I haven't done in a long time with this wagon), really quick trips in narrow corners and the occasional exit from a nasty offroad situation. I come from a high gear world with a Chrysler automatic that would let me punch reverse in a less than ideal parking lot situation with just enough torque to cheat the turning diameter, adding a really effective trick to heavy steering.

I've been considering axle swaps and it looks like I'm going to be doing it to both axles. The front is easiest but the rear is something I have yet to determine. I want to keep my ultra high ratio options open(2.73-3.54) for future role changes that may or may not include heavy front mounted attachments. Before all of that, it's interesting to look at all the differences going on with the AMC 20, Model 35 and Dana 44 axles. I know of one guy with a hot AMX that is using a Ford 9" but have no idea what ratios he's running and based on the insane level of control with a big  LS1 up front, it's not going to share anything close to my region of gearing, even though a hot American 285 +EFI should be more than enough power for my needs.

The stock Dana 30 is a vac/disc axle that I'll be replacing with a no-disc axle to eliminate 20+ parts and modernize kit compatibility. The stock Model 35 is a bolt in axle with a wide range of options but isn't going to handle my new engine well, especially with the stock gearing and manual swap. This leads me to believe one of these features will have to change as well but while I have options for gearing, they're all married to that front axle: 2.73 / 3.08 / 3.54

The AMC 20 axles look really big and durable but they're too scarce in the NW and I'm not ready to drop $2000+ on a G2 axle. Ford 9" is extremely common but the weight makes me worry about effective use. I could always pull a Dana 44 from a Bronco or Wagoneer but I have no idea what geometry I'll need to follow. It's actually a really difficult problem without the information tables.

I'm absolutely sick of automatics but am completely new to putting any kind of manual in a Jeep. I've been playing around on Blocklayer for a while now and while I'm unable to simulate the Ford with its wide 6.33-1.00 ratios and tall 3.73 diff ratio, the Eagle is perched tall from 4.03-0.86 and a pair of 2.72s. It's really hard to figure out what my driving style is going to be because I'm comparing all sorts of completely unworldly characteristics.

The Ford has a 2v single carb big block V8 (FE) 390ci.
The AMC has a EFI L6 285ci.
The Ford has the wide ratio T18A: 6.33, 3.09, 1.69, 1.00
The AMC will have a close ratio NWC T-5: 4.03, 2.37, 1.50, 1.00, 0.86
The Ford has a Dana 60 with a 3.73 ratio.
The AMC has a Dana 30/Model 35 combo at a 2.72 ratio.
The RPM band on the Ford idles at 1000 and physically tops at 4000.
The RPM band on the AMC idles at ??? and theoretically tops at 4250.
The preferred shift band on the Ford without 1st gear is 1700-1800.
The preferred shift band on the AMC with 1st gear is unknown.

The last time this wagon was on all fours, it had an A998 automatic bolted up. The Ford I've daily driven for two years has me desiring another manual and when my driving is relaxed(lol) I seem to shift AT 1700. If hurried, I'll shift to 2200. I have no idea what cam is in this engine and don't care. The cam I put into the AMC 6 is Crower 44243 and lives between 1500-4000. It has a low to moderate RPM window but scheduling my shifting habits with this calculator make me appear to shift anywhere from 1600-2200. The shift band is walking, which is really strange and that wouldn't be a problem except for the mild cam's design. How does a mild cam have too high of a band? It doesn't. It's a sign that I need to drop diff gears.

Is 32MPH/1000 really all that? 

Maybe it's the fact that I'm not factoring in the behavioral skip of a deep awkward unsynchronized 6.XX spur gear from the clunky T-18 that's bothering me the most about this simulation because I only use it when parking. I'm having a lot of trouble picturing myself actually using 1st gear when I move to the T-5 because I'm thinking of a really high immediate torque engagement with a really low speed ceiling. Shifting out of 1st at 15MPH(2000RPM) when doing a launch just sounds incredibly scary if not for the fact that I associate another behavior where I get stuck in that gear while trying to upshift while moving faster than 5MPH.

As I said before, the shift point on the Ford seems to stick between 1700-1800 and usually drops to 1000-1100 each time. The AMC shift points look the same if I go easy with it but I'm not planning on it. The points want to walk:
15MPH/2000
28MPH/2200
48MPH/2400
78MPH/2600
If I had a 6th gear the next point would look like 112MPH/3200. That's nuts. For what it's worth, I seem to have a 30MPH/1000 formula going on in 4th and 35MPH/1000 in 5th. But that can't be right. Can the T-5 really be comfortable pushing such tall gears? I know this is mostly going to be freeway and some city driving but wow.