I'll share two things I've found with my Caprice station wagon that may be helpful with your project. I know it's been a while since I've updated the wagon thread, and a lot has changed since I last posted. I'll hopefully be ready to share everything on that build in the next month or two...
In short, my wagon is now permanently a "3/4 ton station wagon." It's got a 14-bolt rear end, 4:10:1 gears, heavy duty brakes, springs, and other suspension parts, LT tires, and it will soon have an NV4500 transmission too. So, there's a lot of similarity between our two vehicles. I found that the heavy duty components didn't have too much effect on fuel economy, and it wasn't worth swapping back and forth between a lighter duty, higher geared axle (as was my original plan). I can still get close to 45 MPG under the right conditions.
However, there are two things pertaining to transmissions and tires I've discovered that may be helpful to you.
Quote:
Originally Posted by aardvarcus
Overdrive is 0.73, gears are 4.10s. RPMs are around 2100 @55, 2600 @70. With the low end torque of the diesel first/low gear on the NV4500 is useless on the street so I launch in second, unlike my old gas 350 truck.
My plan is either to stick with the NV4500 (but have it rebuilt as the 3rd gear syncro is on its way out) and convert the differentials to 3.42 (tallest stock gears) or switch the transmission to the (I’m sure very overpriced) RSG Tranzilla TR 6060 4x4 with it’s 0.5 double overdrive.
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The overdrive ratio of the 5.61:1 first gear NV4500 is actually 0.745, not 0.73. I know that's not a huge difference, but most of the information you find online about this is incorrect.
Here's what I've discovered, though: you can actually swap in a 5th gear set from an early GM (6.34 first gear) NV4500 into a later (5.61 first gear) NV4500. I haven't done this yet, but I've got all of the parts and plan to do it soon. Doing so will give you (in your 5.61 transmission)
a 0.643 overdrive! That's basically like going from a 4.10 rear end to a 3.55 rear end, in fifth gear--without losing any of your lower gearing. And, swapping the fifth gear set in a NV4500 is actually a pretty simple operation.
I think that setup would be a much less expensive and more satisfying/useful transmission in a large vehicle than a TR-6060. Even if you had a 6060 with the 2.97 first and 0.50 overdrive, that's only a 5.94:1 overall ratio spread. With the NV4500 with 5.61 first and 0.643 overdrive, the overall ratio spread is 8.71:1. I also have the feeling that the first four gears in the 6060 are so closely spaced that you'd probably end up skip shifting a lot, anyway.
Quote:
Originally Posted by aardvarcus
Swap to 235/85R16 Michelin Defender LTX from 255/85R16 Cooper Discoverer (they are more aero in addition to lower RR).
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If you are considering buying new tires, I'd highly recommend that you look into Nokian's LT offerings. Nokian makes all of their tires
very LRR, including their LT models. Since they also sell tires in Europe, you can look up their tires' European RR rating and compare them to other manufacturers. In the LT market, they tend to have much lower rolling resistance ratings than pretty much any other manufacturer. I have a feeling that a set of Nokian Rotiiva HT's would have less rolling resistance than the Michelins--and they would also be cheaper.
I have Nokian Rotiiva HT's in the 215/85R16 size on my wagon, and I'm very satisfied with them. I didn't notice a significant drop in fuel economy when switching to them from P-metric Bridgestone Ecopia (LRR) tires. They also handle well and have excellent wet traction. The tradeoff is that they will wear more quickly than the Michelins. As you probably know, when it comes to tires there is a balance between rolling resistance, wet grip, and treadwear, and only two of them can be really strong at without the third suffering. Nokian tires (including the ones--both summer and winter models--I've run on my Metro) tend to have very low rolling resistance and good wet grip, but also wear more quickly than some other tires I've used.
I don't know how much driving you expect to do with his vehicle. If you plan to do a lot, then treadwear might be more important to you. But if you don't plan to rack up the miles quickly, I have a feeling that a set of Nokian tires would probably result in better fuel economy than the Michelins.
I hope this helps!
-Funkhoss