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Discussion Starter · #1 ·
There are a lot of websites out there with wonderful calculator tools and the charts that are floating around are also very handy. This is more of an accentuation of those existing tools. I figured someone else might find it useful for planning their build.

I tested it today against my build and it was nearly spot on, but the discrepancy was a little less than 1mph at 3000RPM in 4th. Obviously, the lower the revs, the more accurate it is. lol Just need to finesse the sidewall sag adjustment number.

This will allow you to instantly see how a gear change or tire change will effect your ride in both High and Low range. As near as I can tell, no other tool will do this as easily.

The Excel workbook includes all three US JK transmissions, 4 and 5 speed auto, and 6 speed manual. Keep the tab you need, delete the others. If you want to make a "future build" tab to test changes, just copy the tab you need and rename the new one. The scripting will be attached to the new tab.

Due to Microsoft's Infinite Wisdom, I think these aren't cross compatible, so . Let me know if there are issues.
For Excel 2010+
For Pre-2010 Excel

Worst case, Google Docs, or Open Office should be able to open one of them.

Example:
 

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I always appreciate having different tools but what exactly is the value of knowing this information to the exact MPH if tires are not manufactured with the accuracy you are entering into the calculator? Just wondering.
 

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Discussion Starter · #4 ·
I always appreciate having different tools but what exactly is the value of knowing this information to the exact MPH if tires are not manufactured with the accuracy you are entering into the calculator? Just wondering.
Fair question. ;) First the tire measurement is as accurate as you want to be, because Tommy's 35x12.5 MT2 is not the same as Billy's 35x12.5 MT2. If you really wanted to be anal, you could probably determine what exact radius your tire is at 20mph on flat ground and use that as the basis of the math. Or even determine how the your vehicle will be effected with new tread and almost bald tread. Whatever makes you happy.

The color chart that is floating around is wonderful, but it is extremely generalized and relies on the user to be honest about their tires' size (my "33s" are closer to "30s" in practice). And we all know men can not be expected to be honest with measurements.

Also, the MPH side is really just a throwback to when I was using the chart to build a transmission for my Mitsubishi; and also to quickly check tire sizes on a vehicle that doesn't have programmers available. I just kept it cos I couldn't say it would never be useful.

The magic really happens on the RPM side. The idea being if one tab is setup to your stock settings, you can run the numbers on a second tab to see what effect your changes will have. If you feel that your stock Jeep performed well, but you want 37s, you can easily determine what gear change you will need to maintain that performance or how much life the 37s will suck out. That is to say, if you like cruising at 45mph at 1700rpm, you probably wouldn't want gears/tires that will have you running at 1100rpm in the same gear. This may be more useful to manuals, but with configurable shift points in autos it might not be a bad idea either.

Personally, I have found on the trails I've run that in 2/4HI, 1st gear is too revvy and 2nd gear is too logy. So I often put it in 4LO just because at the same speed I am right in the sweet spot of 3rd gear. So, my current concern is determining if a particular set of gears can put me comfortably in 2nd gear and stay in HI. But I also don't want 4LO to be so low that I am in 5th gear on the flats between the climbs.

Not that you folks aren't smart and helpful, but I want to KNOW what will happen rather than asking some guys in Missouri or Oregon to tell me how my Jeep in Arizona will behave. Especially if I am sinking a thousand bucks into the endeavor.
 

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Discussion Starter · #6 ·
You don't say...
lol Touché ;)

Unfortunately, I can't edit it, so I will have to sound like a dick forever now.
 

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lol Touché ;)

Unfortunately, I can't edit it, so I will have to sound like a dick forever now.
I'm just messing with you. :)

A lot of people don't know about that calculator. It gets spread around by word of mouth. I don't advertise. It's been around a while and many people spread the word but for all the people who know about it, I'm always surprised at how many people have never heard of it.
 
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