Ideal Highway RPM's and Gearing For 37s

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PlayingWithTBI

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Here's a calculator where you can find your tire height and then calculate your "Optimum Rearend Ratio"
 

geeeee89

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Thank you for posting this, I’ve been searching what seems like forever for someone with a nv4500 that’s installed new gears in the axles. I was thinking 4.56 but looks like I’ll be buying 4.88.
Sure thing. Now debating between 5.13s and 5.38s for 40s when it gets a SAS but haven’t looked at a calculator yet. You will not regret 4.88s for 35s
From what I've noticed driving other people's built trucks and jeeps and now having my own gears done (4.88/37s), go as low as you can and still tolerate it on the highway. While driving around town I often think "I could have gone 5.13, that would have been nice" but on the highway I don't think I'd want to turn any more RPMs than I already am.
Exactly right and that’s why I chose the 4.88s for mine. I read a bunch of threads and looked at the calculators and decided they would fit my needs best. I commute, tow, and go off road with it and the gears are perfect for me. It had 3.73s and 35s when I first bought the truck and 5th gear was unusable
 

boy&hisdogs

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Sure thing. Now debating between 5.13s and 5.38s for 40s when it gets a SAS but haven’t looked at a calculator yet. You will not regret 4.88s for 35s

Exactly right and that’s why I chose the 4.88s for mine. I read a bunch of threads and looked at the calculators and decided they would fit my needs best. I commute, tow, and go off road with it and the gears are perfect for me. It had 3.73s and 35s when I first bought the truck and 5th gear was unusable

This is the one that I use. It has "too many" options for most people, but that's exactly why I like it. You can really play around with the settings to get exactly the specific information you need.

 

WOalmann

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Sure thing. Now debating between 5.13s and 5.38s for 40s when it gets a SAS but haven’t looked at a calculator yet. You will not regret 4.88s for 35s

Exactly right and that’s why I chose the 4.88s for mine. I read a bunch of threads and looked at the calculators and decided they would fit my needs best. I commute, tow, and go off road with it and the gears are perfect for me. It had 3.73s and 35s when I first bought the truck and 5th gear was unusable
That’s pretty much what I plan to do with mine as well. I have a 92 gmc Stepside regular cab. Before I installed the 6” suspension lift and 35’s. I dropped in a crate motor from Blueprint (5.7 350 small block with vortec heads and a mild cam). The dyno sheet they sent with it read 373 hp. I’m unsure of the stock gear ratio, the sticker in the dash is gone and I can’t find any tag on the axle itself, but it does have an NV4500. It runs through the gears decent doesn’t struggle and 5th gear is usable, but can certainly tell a difference between the 265’s and 35 inch tires. just want to be able to push some bigger tires around and not stress moving parts anymore that I have to.
 

Timmie2022

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My K1500 (5.7/4l60e) is getting lifted and geared in the near future. I plan to run 37x12.50r17 tires on NNBS stock alloys. I'm stuck trying to decide between 4.56 and 4.88.

I do probably 70/30 highway/city, only tow about once a month, and usually the towing is local. (building materials, trash to the dump, etc)

According to the Grim Jeeper calculator, and based on the claimed size of the tires I want (Toyo RT, 36.8"), my RPMs will be:
4.56 @ 70 = 2040 RPM
4.88 @ 70 = 2183 RPM

Currently I have 3.42s and 33s on steelies which sucks, since it keeps kicking in and out of 4th when the road has any incline. 4.56 would be very close to what it would have been stock with 245/75/16 and 3.73s, (2015 @ 70) which is how most of these trucks came stock.

Is ~2200 RPMs to high for sustained highway driving? Would the 4.56 get bogged down by the weight even though they "match" the stock setup numerically?

Is there a certain point in the rev range where the mileage starts to really tank?
I'm running 4.88 with 33s and it does ok. I have a manual transmission and run 2100ish at 60. Near 3k at 75. Going with 35s next set of tires. Unless I can finally get that long travel suspension and go to 37s
 

Frank Enstein

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Those were optional ratios that TCI automotive has. Their 6X trans is a 6 speed modified 4L80E with revised gear ratios and it is cool!

73 GMC 3/4 ton was supposedly equipped with the 2.75/1.57 planetary from the factory.

It was a camper special and it had shocks in the front of the bed too! No idea what those were about though!
 
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