To 32 or not to 32?

[Ducky's Dad]

in the end upgrading the gears always comes out ahead,

Not always. Depends on what you are trying to accomplish. Two sets of gears is an expensive proposition. Too many variables in this discussion to state flatly that gears are the solution. No clear mission statement and objective from OP. Need to focus on what's important and work back from there.

 

[SilicaRich]

Gears will make a bigger difference than throwing money at 'performance' upgrades, gears will also benefit you more on the trail where gearing is needed far more than hp. The topic has been beat to death many times and in the end upgrading the gears always comes out ahead, a bit of reading and common sense goes a long way.

I know it's a topic that's been killed and revived more times than Ozzy Osborne. Trust me, I've done my research on performance upgrades for 4.0 and know that results are with any mod is minimal besides stroking, boring, and forced induction (none at which I'm interested in). It's literally a thread that's killed everyday in general discussion and tech threads on Jeep forums. This thread wasn't intended to be about the best way to squeeze power out of my motor, that was literally already done when they rolled these out of the factory. My philosophy is why not just bump down to 32" tires since I'm already geared for them and buy the necessary suspension essentials to do so instead of spending the greater cost to properly run 33" tires. I'm really just trying to consider my options to build my Jeep best fit to me and decide if I really need 33" tires or would 32" better fit my living.

 

[Korben]

I'll toss in my 2 cents with a few random thoughts.
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If the only question is 32" vs. 33" all else being equal the 33" will get better mileage, but all else often isn't equal.
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It's not really tire diameter that maters it's rolling radius, the distance from the center of the axle to the road. Most good tire manufactures will list rolling radius it however is of course effected by load and pressure.
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Tire diameters aren't exact and vary a lot between brands and models, the actual difference between two tires of different brand/model one market 32" the other marked 33" might be 0-2"
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In general when talking about drag, MPG, etc.
-All else being equal a larger tire diameter has less rolling resistance then a smaller tire diameter.
-All else being equal a larger wheel diameter is has less rolling resistance then a smaller wheel diameter.
-All else being equal a narrower tire has less rolling resistance then a wider tire.
-Of course there's also tread, pressure, etc.
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Assuming first gear is low enough a taller tire lowers RPMs, this helps mileage.
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If floatation is important then keep in mind that an increase in diameter also increases contact patch, most of all when aired down. Diameter can replace width in regards to flotation.
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A larger diameter makes every bump and obstacle smaller, the shallower angle of contact between tire and bump/obstacle is an advantage.
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So put all this together in general a narrow 33" tire on a larger diameter rim will be better. Problem is in finding the right tire, taller generally means wider, and wider defeats the purpose.
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Many people don't believe me when I say that my MPG went up when I went from a 33x12.5 to a 37x12.5. The main reason for me was that my older truck is geared too low for todays highway speeds and a 33" tire. Also though they didn't get wider and are E rated(higher pressure).

 

[4x4junkie]

I believe they offer a 32"x10.5" in a 15" rim but I'm swapping back to stock 16" rims. I currently run 28-30 psi across all 5 tires. Problem is that I'm not entirely sure how accurate that is since I've only put 300 or so miles on it in the last 5 weeks so there's chance of error there. Maybe next gas fill up I'll run it over to the air station and bump them up to 32-33 psi. 28 psi is just what's recommended for comfort and ride.

I would take them up to at least 35, maybe even 40 PSI. You'll probably see at least one full MPG increase, maybe even two, coming from 28 PSI. The tradeoff will be the ride being a little rougher over bumps/potholes/rough pavement/etc.

For slightly better mileage and certainly worse tire wear run increased tire pressure.

Just to clarify, tire wear will not be as even across the tread with increased pressure (center will wear faster than edges), however overall tread longevity should be increased, especially if they are rotated at proper intervals.

If you put on a lot of offroad miles with them aired down (especially if rock crawling), this actually can counteract some of the wear from running the higher PSI on the street (certainly it does on my big 35x12.50s that I run with 35 PSI on the street/freeway anyway. I rotate about every 6000 miles or so).

 

[SilicaRich]

I would take them up to at least 35, maybe even 40 PSI. You'll probably see at least one full MPG increase, maybe even two, coming from 28 PSI. The tradeoff will be the ride being a little rougher over bumps/potholes/rough pavement/etc.

Next gas fill up, I'll make a stop by the air station and bump them up to 37-40 psi to see the results. I honestly don't care too much about how the Jeep rides, it's a Jeep haha. Plus the 5100s should offer some forgiveness even at that psi

So I was looking at the 235/85/R16 sizes and the more I look at the dimensions, the more I'm interested in the size. My only concern is the recommended rim width, 6.5"-7.5". To my understanding, stock Moabs on TJs were 8" in width. Is that true and would y'all be concerned about running that width with 235/85/R16 tires?

 

[Korben]

Next gas fill up, I'll make a stop by the air station and bump them up to 37-40 psi to see the results. I honestly don't care too much about how the Jeep rides, it's a Jeep haha.

I assume you take this thing off road, do you not air down? I ask cause I expect anyone that airs down for the trail would have an air compressor to fill up again for the road?

 

[jeep-N-montero]

Next gas fill up, I'll make a stop by the air station and bump them up to 37-40 psi to see the results. I honestly don't care too much about how the Jeep rides, it's a Jeep haha. Plus the 5100s should offer some forgiveness even at that psi

So I was looking at the 235/85/R16 sizes and the more I look at the dimensions, the more I'm interested in the size. My only concern is the recommended rim width, 6.5"-7.5". To my understanding, stock Moabs on TJs were 8" in width. Is that true and would y'all be concerned about running that width with 235/85/R16 tires?

You can find some stock 16x7 wheels off an XJ or ZJ for cheap in your local classifieds or check the junkyards. The 235's on my Chevy Diesel are mounted on 16x6.5 factory wheels and rides nicely.

 

[Happy Joe]

Nope, it's the good old 4.0 with 6 cylinders, but I have a Rubicon so 4.10 gearing is stock. It has the 6 speed NSG370, which from older research indicates 4.56 gearing is best with 33s, while 4.10 is best for 32s. Funny how a vehicle from factory can technically be overgeared, 31" was factory tire size on TJRs.

I hear you but your research conflicts a bit with mine.
Sounds like either you are talking to "old school" lower is best sources or 4.27 gears may not be available for at least one of your axles; its how I ended up originally over gearing to 4.56 with 33s (big mistake).
My engine is a healthy '97 4.0 and 4.56s give me very good drivability on and off road with 35 inch tires.
I shift into overdrive at 45mph and pull moderate hills in overdrive without down shifting... If you can do this it indicates that you gearing is probably OK.
I got poor highway mileage with 33s and 4.56s (the off road performance was fine).
your transmission ratios;
4.46 2.61 1.72 1.25 1.00 0.84 R4.06

my transmission ratios;
4.03 2.37 1.50 1.00 0.86 R3.76

my 3rd gear splits your 3rd and 4th gears
My transfer case is 4:1 low range (doesn't affect this discussion)

Given you lower first through 3rd gearing your setup looks pretty close already (without actually running the numbers).
As an aside; if I can score a set of 4.10s cheap for the front axle (cheap 4.27s are hard to come by any more) I have been planning on lowering the suspension, putting 32s on it and putting it back on the street...in the absence of cheap gears I will likely lower it and try to keep using it with the 35s.

Enjoy!

 

[SilicaRich]

I assume you take this thing off road, do you not air down? I ask cause I expect anyone that airs down for the trail would have an air compressor to fill up again for the road?

When I offroad, I always air down and make sure I have a way to air back up. I usually either have access to a very close public air station or another compressor from another vehicle. In all honesty though right I can't afford to offroad and take the risk of potential part failure under a college budget. Basically the Jeep is a pavement princess til December.

 

[SilicaRich]

New Issue

So I decided I would go ahead and revive this thread. New news, my rim/tire deal fell thru for the stock 16"x8" Moab rims for a TJR. I have a few people keeping an eye out for me for another set to pick up, however, these rims have turned out to be a pain to find, at least for a decent price.

I've now considered other options by now looking at 17"x7.5" Moabs off JKs, which I've actually seemed to take a liking to especially in the grey and black. Doing this, I've opened up a whole new genre of tire sizes and classes to choose from. My ultimate decision tire wise is a tire between ~31.8"-32.5". The exact 32" and 33" is BS at this point. Specifically, I recall someone replying that 255/75/R17 are true 32" tire and indeed they are. In fact they are quite appealing, however, I'm actually very limited on selection if I choose this route. 255/75 (~$130, cheap right!) BFG KMs are my only option I would truly consider, however, I'm not too keen on investing on a MT tire for the sake of wear, mpg, longevity, etc. even though to my knowledge the KMs are fairly tame. However, playing with a calculator, and checking to make sure the sizes even exist, I've again expanded my options. These include 275/70 (32.15"x10.83" Load E), 285/70 (32.71"x11.22" Load E), 235/80 (31.8"x9.25" Load E), 265/70 (31.61"x10.43" Load C *smallest on the spectrum*), and even 305/65 (32.61"x12.01" Load E). There are a few others I'm missing but otherwise here are most. These are ALL R17 sizes so there's no confusion. Only thing right now that is still bothering me is Load E...I would prefer Load C, however, some of these sizes are tall and skinny enough to hopefully have the Load E weight not make too much of a difference versus Load C. I'm preferably looking at AT tires and would like to stick with BFG if all possible, I'm a biased buyer and I'm loyal to them, and also would prefer a tall and skinny tire. Does anyone have experience with any of these sizes and what are your thoughts?

 

[Fargo]

....Specifically, I recall someone replying that 255/75/R17 are true 32" tire and indeed they are. In fact they are quite appealing, however, I'm actually very limited on selection...

What do you mean your limited on selection? Thats a stock size tire. Going with a 255/75R17 will give you a ton of choices in a load range C. I've considered moving down form a 285/75R16 on my Moabs to that size just to get a load range C. If you want a good all terrain check out the Goodyear Duratrac or the Cooper STMAXX. Both are available in that size in a load range C. IN fact thats the only load range C I've seen in a ST MAXX. I thought they were all E until I just did a search. The brand new Cooper STT Pro is also available in that size in a load range C. I'd acturally be very shocked if the BFG AT is not available in that size. Here is a short list from tread depot.

https://www.treaddepot.com/#!tireListBySize/2557517

 

[Clutch]

Sounds like a lot of fussing just to have marginal (if any) gains.

If fuel consumption is a concern a different platform might be in order, though it is usually cheaper just to keep what you have.

 

[Dan Grec]

I ran cheap all terrain 31x10.5r15 on my TJ from Alaska to Argentina, and I never wished for more tire.

I didn't intentionally go and find the hard stuff, but I did stay off the highway and on backroads as much as humanly possible.

Remember, overlanding is not offroading, it's backroading.

-Dan

 

[SilicaRich]

I ran cheap all terrain 31x10.5r15 on my TJ from Alaska to Argentina, and I never wished for more tire.

I didn't intentionally go and find the hard stuff, but I did stay off the highway and on backroads as much as humanly possible.

Remember, overlanding is not offroading, it's backroading.

-Dan

If I could give you a high five right now I would.

What do you mean your limited on selection? Thats a stock size tire. Going with a 255/75R17 will give you a ton of choices in a load range C. I've considered moving down form a 285/75R16 on my Moabs to that size just to get a load range C. If you want a good all terrain check out the Goodyear Duratrac or the Cooper STMAXX. Both are available in that size in a load range C. IN fact thats the only load range C I've seen in a ST MAXX. I thought they were all E until I just did a search. The brand new Cooper STT Pro is also available in that size in a load range C. I'd acturally be very shocked if the BFG AT is not available in that size. Here is a short list from tread depot.

https://www.treaddepot.com/#!tireListBySize/2557517

Thanks!

I based the "limited" selection on just brief look on the shopping side of google for offroad type tires, sorry. I'm actually very disappointed that BFG doesn't have their KO, now being phased out, or their KO2 in that size. I'll definitely take a look at Duratracs, although I've always heard that Duratracs are 2 ply rather than 3 ply. How true is this statement, because I would prefer as much sidewall as I need but no less, if that makes sense. The Coopers have always interested me and seem to have really worked up a reputation over the last few years, in fact, I believe I've seen them cheaper than most other brands which is a big plus.