Gears For 37s?

[Chrisn162001]

Do you have 48RFE or aisin? I forgot about 4.30s. Also I'm debating on 38s depending on prices when I need tires within next year.

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I got a 68RFE.

I’ve been debating going 38s since that would probably make the 4.56 perfect.


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[scs210]

Here's a link to a couplecharts I made to compare the 4.10 gears with 35" vs 37" tires and asecond one comparing 4.56 gears with 35" vs 37" tires.

Each color linerepresents each gear (1st - 6th) and you can see the corresponding speed vsRPM.

I've been running my DRD enhanced truck with 4.10s and 37x12.5 for about 40,000 miles.

I drove the truck with 37 and stock 3.42s for about a month and it drove me crazy.

Didn't shift to 6th gear until 65 mph and was just sluggish.

With the 4.10s it was like driving with stock tires again.

Shift points went back to normal, towed well and the mpg didn't suck.





https://www.igotacummins.com/threads...398#post185398

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[ricky_bobby]

^So, based on your charts and driving experience, would 3.73’s be adequate for 35’s?

My chart would show it going about 120ish rpm higher now in 6th gear and restoring stock gearing plus some.

As you have found, I think 4.10s are perfect for 37’s if you are trying to restore stock gearing

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[scs210]

I updated a few things since I played with the spreadsheet.

Here are 3.73s and 35.

35x3.73 chart.jpg

35x3.73 graph.png

While we are at it.

Here are the 4.10s and 37s again cleaned up.

4.10x37 chart.jpg

4.10x37 graph.png

I believe 3.73s and 35s would be a great setup.

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