Ideal Highway RPM's and Gearing For 37s

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WOalmann

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I have 4.88s with 35s and an nv4500. 5th gear at 70 mph is right at 2500rpm. Won't hurt a thing. Consistently get 12-13 mpg with this setup. Plenty of power for towing, great for running around town, and not bad at all on the highway. I can actually use 5th gear going uphill or against a headwind now. I definitely wouldn't want any higher gear than 4.88s for 37s
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.
 

boy&hisdogs

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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.

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.
 

Nad_Yvalhosert

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Dont fear the gear.
Go big or go home.

Opt for the lower gear (higher numerically). You'll want it due the increased weight of the lift, and heavy tires.
 

Supercharged111

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What! nobody posted a chart! I'm no expert but heres the awnser....

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This chart kinda sucks because we all have OD and different speed limits. It also fails to account for the fact that a big block gets about 10mpg no matter the circumstances.
 

Supercharged111

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is there a better one? iv been referencing that for years and your the first person to say that.... BUT who knows, maybe its irrelevant data. is it?

Not totally irrelevant, but it does ignore the subjectiveness of gearing too IMO. Consider how different the 4L60 and 80 are geared when you present that chart. It's fairly relative od or not as it's not but 200 RPM difference between the 2 in OD. I personally created an excel chart that allows you to plug in tire sizes, trans ratios, and diff ratios to compare different setups.
 

boy&hisdogs

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is there a better one? iv been referencing that for years and your the first person to say that.... BUT who knows, maybe its irrelevant data. is it?

It assumes your top gear is 1:1, so think an old school, non-overdrive 3 spd auto or 4 spd manual. This chart doesn't work for modern vehicles since they all have OD transmissions. Plus different cars have different ideal RPM ranges. A big American V8 can comfortably cruise at 1800 RPMs all day long, but try doing that in a little import car, especially something that makes all it's power high in the RPM range like a turbo 4 cylinder, and 1800 is lugging the engine. Conversely, that same little turbo 4 cylinder import car might comfortably cruise the highway at 3500 rpms where a diesel pickup would be bouncing off the rev limiter.

The chart recommends turning 2700-2800 rpms at 65. In our trucks, something like that would get single digit gas mileage and would only be good as a tow rig or maybe a plow truck. I don't know what vehicle or engine they are basing those numbers on but it's defiantly not accurate for a full-size V8 truck.
 

boy&hisdogs

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now I need to find an accurate chart to know whats what.

burb has 3.73 and 30" tires. I know they are 3.9% larger/faster than stock.

Sierra has 3.43 and 28" tires...

I thought these set ups had me just slightly in the fuel economy side but now I have no idea.

Those are good all-around ratios for daily drivers. My truck originally had 3.42s with 32" tires, and 4x4, which adds rolling resistance as well as air resistance since the 4x4 rides a few inches taller than a 2wd. Even then it was fine 99% of the time just driving around.

What mpg are you getting from the pickup? if it's 15+ I'd say that's pretty good for these trucks.
 
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