kirk35

I've been trying to decide which gears I want to go with in my car and just haven't been able to decide. This afternoon I decided to put together a spreadsheet to compare the effects of different gears and tire sizes. I got a little carried away and added automatics from the C4 to 6R80 and manuals from the SROD to MT82, 20 transmissions total.

Then I decided I wanted to compare two different set-ups side by side, the attached file is what I came up with.

Take a look and let me know what you think. I could only upload as an xml file, the excel files aren't supported on the forum. You'll have to save the file and open in excel. Excel will give you an error message saying the file appears to be in a different format, but it will open.

Duh, I discovered that all you need to do is right click and open

kirk35

Here is a screenshot of the spreadsheet.

scottmach

The 2011+ autos have proven time and time again to see zero gains with a gear change. The best option is a 3.31 but unless you're looking to squeeze every last bit out of it it's hardly worth it. Plenty of us running very low 11's N/A with stock 3.15's. Now a converter would make a huge difference.

Here's a quick example courtesy of Kris Danner using a 3.31 gear.


Consider these first gear ratios:

C4 - 2.46
4R70W - 2.84
6R80 - 4.17

Take the 4.17 and multiply it by the 3.31, you get 13.8 for an overall gear ratio in 1st. Now take that 13.8 and divide it by the first gear ratios of the other transmissions and this tells you what axle ratio would give you the equivalent with those transmissions:

C4 - 5.61
4R70W - 4.86

So, although 3.31 "sounds like" not much gear, you can see that in the end, it is quite a bit of gear with the 6R80.

We can do the same with the second gear ratios:

6R80 - 2.34
C4 - 1.46
4R70W - 1.55

That puts the 6R80/3.31 at 7.75, which is like a 4R70W with a 5.00 axle, or a C4 with a 5.31 axle.

And finally 3rd gear, where the 6R80 is 1.52*3.31=5.03, the others are 1 to 1, so 5.03 would be the equivalent axle there.


You'd all agree that an axle in the 5.00 range is a lot of gear, well, we're doing exactly the same thing with the 3.31/6R80, we just have 3 more gears to go after that.


Going the other way, a 4.10/6R80 in first gear is like having a C4 with a 6.95 gear, or a 4R70W with a 6.02 gear. You can see why hooking it is a problem.

kirk35

That's why I made the calculator, I wanted to see for myself what the best ratio would be. I thought it would be helpful to others since it is set up for many other transmissions, not just the 6L80.

A converter is planned for the future, but for now I'll probably just concentrate on shift points for optimum torque through the 1/4.