I still think Zuk made some interesting points, but I disgress too.
As for crawl ratio for a serious rock crawler, I can see how the T-case is the way to go, when crawl ratio is all someone cares about but, I've notice that most heavy duty factory 4x4s, like Unimogs, Humvees, etc, use diff and hub gearing to get the low ratios they need. With vehicle dependent expedition travel, it's usually about reliability first, and crawl ratio and capability second, since tow rigs, friends and spare parts are usually not available like with a lot of rock crawlers. So, to that end, the argument about lower diffs verses lower T-case gears, might have some real merit. If you're out in the middle of nowhere it might be worth sacraficing some overall crawl ratio, knowing that you're putting far less stress on critical components such as drivelines, U-joints, etc. And thus, going to a 5.29 gearset (or maybe 5.71) might make more sense than a duel T-case or 5-1 low gear T-case. I never looked at it that way, until I read Zuk's original article.
Oly,
Scott clearly knows what he's talking about. The only thing I'm wondering about is that I think he has an automatic, so the transmission ratios and drivability will be different than your 5 speed rig. Particularly on the highway, where his overdrive is much higher.
I believe, the 5 speed Tacos have a .83 overdrive, while the autos have a .70 overdrive. I'm going off of the older tranny specs, but I think the Taco trannys are similar. That means if the auto and the 5 speed Tacos had the same diff gears and the same tire size, the rpms on the manual trans Taco, while in overdrive would be about 15% higher. That's pretty significant. If the auto trans Taco is doing 3000 rpm, the manual trans Taco will be doing 3450 rpm, if I did the math right.
If you have 33s and I assume your current diffs are stock 4.10s, then going to 5.29s will lower your overall ratio by about 22%. Which means your rpms will be 22% higher at any given time. Where it used to be 2000 rpm at a given speed, it will now be 2500 rpm. The current 3000 rpm will now be 3700 rpm, etc. That's not necessarily a problem, but knowing where your rpms are going to be at, at speeds like 60 or 70 rpms will help you to decide what gear ratio is best for you.
The difference between your 4.10s and 5.29 s is about 5% more than the difference between your current 5th gear and your current 4th gear. But it's a close enough that if you want to have an idea of what it will be like with 5.29s on the highway, go out on the highway and drive around, but leave it in 4th gear. Then imagine that your rpms will actually be about 5% higher than even that. This will be a good test, because the only real concern with going too low is on the highway in overdrive. I can't see any disadvantage to having lower diff gears in city or trail driving. In fact, it's usually always a major advantage.
All that said, the real question is the difference between 4.88s and 5.29s, because you're going to go with one or the other. The difference in those two ratios are a little less than 8%. So, what it comes down to is that your rpms will be 8% higher if you go with 5.29s verses 4.88s. That would mean, for example, 3000 rpms with 4.88s will instead be 3250 rpm with 5.29s. Probably not the end of the world.
I'm a huge 5.29/33” set up fan. In fact, I just recently downsize from 35s back down to 33s for the addition power and I'm loving every minute of it. I think our weight will be similar, if me not heavier. But I have half the power you do, and with my truck, I need the gearing to overcome that power disadvantage. I tend to wonder if I had twice the power, if I wouldn't be better off with slightly higher gearing. Whereas I need the gearing to scream up moderate hills at near redline just to maintain highway speed, you might be better with a higher ratio.
There's one final point. I don't know the details, but I've heard that late model Tacos have an issue with running high rpms on the highway. Something about the computer, speed sensor or something like that not liking the high rpms and putting the computer into a closed loop mode or something like that, that could severely reduce fuel economy. Might be worth researching or maybe someone could shed some light on that here.
Given that you don't plan on speeds faster than 70, the advantages of running 5.29s on the trail and in the city, the excessive weight you'll be carrying, I still lean towards 5.29s if it were me, but it's a harder decision than it would be on the gutless wonder older trucks, like mine.
Sorry for the super long winded post.
