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Old 03-18-2008, 09:55 PM   #1 (permalink)
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Increasing gear ratios

What's the easiest (read cheapest) way to increasse my gears ratios? I've got a ton of torque and fairly low gears, so I think it would help my mpg. The problem is I have a 4x4, otherwise, I'd be looking at a rear axle swap or differential regearing. If I did that, I'd have to also regear the transfer case and just the thought of that seems prohibitive. I wouldn't be opposed to putting bigger wheels on it, but it's got 15" rims with fairly tall tires already (265/70R15s, I think; I know, horrible mileage killer right there!), so I think I'd have to go to a bigger rim and I really don't want to $4k for a 10% higher ratio. Any other ideas, suggestions?

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Old 03-18-2008, 10:05 PM   #2 (permalink)
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You can go pretty big on a 15" rim. Something to the order of a 37" tire. With gearing the wording is kinda funky by increasing your gear ratio I'm assuming you want go down numerically? E.G. a 3.73 set to a 3.07 ? On a truck easiest way is to upsize your tires. You are running a 30x10.5x15 tire right now. If you can fit it, might want to consider a 32x9.5x15 is you could find one. That would numerically decrease your gear ratio and also cut down on your rubber width.
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Old 03-18-2008, 10:13 PM   #3 (permalink)
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hmmm. I thought I was running fat tires at 235/75R15 (biggest stock) but I didn't know you were running that wide!

Oh, first, which... vehicle are we talking about here? the Frontier? the WJ? the CM400E?

I'd say, go with thinner tires, but stay at the tall-ness that you have. Or go taller. Problem is this will raise the vehicle, but In my understanding you do mostly city driving, so that won't matter much. But this is probably highway we're talking here.

Hmmm. What RPM range do you run at 70? If you run near 2K, then you're probably doing fine. around or over 3k? we gotta work on that.

Aero on highway will help you if your driving a brick. If you can't do that, then we'll have to think of creative ways to get some approval.
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Old 03-18-2008, 10:15 PM   #4 (permalink)
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Quote:
37"
Or maybe if your lucky, TALLER!!!
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Old 03-18-2008, 10:22 PM   #5 (permalink)
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extragoode -

Have you researched your car's tranny into the ground? I was lucky because I was able to swap a 5th gear from an "economy Saturn tranny" into my "sport Saturn tranny". I'll publish the details later tonight on a new thread.

If you trace the lineage of your transmission, there may be a 5th gear "out there somewhere" that will fit right in. I would only worry about the 5th gear because that is where you will spend most of your time.

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Old 03-18-2008, 10:32 PM   #6 (permalink)
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you could find a ZJ... DANG IT!!! I still don't know which vehicle we're talking about!!!

Plus your WJ has a 4.8L V8 right? different tranny than the I6 i think. ah well.
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Old 03-19-2008, 09:53 AM   #7 (permalink)
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There are 85s out there... I'm not sure how much heavier they are, but they are load range E and have sidewall maxes of 80 psi or so...

215/85R16 is 30.4" tall
235/85R16 is 31.7" tall

These are made for full size pickups... see Michelin LTX A/S
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Old 03-19-2008, 02:13 PM   #8 (permalink)
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I wasn't expecting this much of a response, wow! First of all, I'm talking about the Frontier and it runs somewhere around 3200rpm @ 70mph, but I'm not sure, it's been a while since I've had at that speed. I usually shift into 5th around 25mph at which it settles somewhere around 1000rpm, but I only have hash marks for every 500rpm, so I'm not sure exactly on that either.

Whoever it was that was talking about a 5th gear swap, no I haven't done much research on the transmission at all. How hard was it to replace that gear? I want it to be worth while if I'm going to go the trouble of doing transmission work.

DPOV - yes, these tires are HUGE! They were put on by the previous owner because they looked cool, who cares about mileage, they were awesome in the snow though! The stocks were 235/75R15s, I think. Yes, getting bigger tires would raise the total heigth of the vehicle, but it's already something crazy like 9 inches off the ground, so I figured I'd already be going with a belly pan instead of building a freaking huge airdam.

Like I said, I'm mainly asking about the Frontier, but if it works out well, I might go these on the Jeep as well.
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Old 03-19-2008, 02:18 PM   #9 (permalink)
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Gas HOGS or working class trucks? You decide.

Extragoode,

If you must change gearing, then do both diffs ($300x2) with the tallest ratio you can find and save low range for hauling heavy stuff & in the rough. If you do only rear diff, you will screw up your 4x4 system & make truck unsafe. Tall tires ($350-$500), complete tuneup w/synthetics ($100-$200) & weight reduction (FREE!) are the least expensive fuel savers besides driving slower & less often.

I have an '06 Ranger with the 3.0L, 5-spd auto & 4.10's. I need low gears for towing & 4x4 for the farm. Ranger now has Continental SUV tires 235/70R16 @40psi yielding 23mpg w/o topper or trailer. I plan to install 235/85R16 D or E highway tread tires when needed as I mostly haul BIG loads over long distances.

For the cost of a set of truck tires, I bought a Metro for $450 that gets twice the mileage as my $20K truck and use it for daily commutes. This works best for me and saves the most fuel for the money when I'm not hauling a load. See pic.

Good Luck,
Cowspots
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Old 03-19-2008, 02:22 PM   #10 (permalink)
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FYI: When I ran Dean 235/75R15 Bias 6-Ply Mud & Snow tires, my mileage dropped to 20mpg. Ciao!

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