Towing Capacity

Brantley said:
It's because the charts are a load of BS, really. No chart can possibly put out a blanket statement that just because a certain ratio and tire size is used, mileage will go up. Which engine does that chart apply to? 4.0? 2.5? It can't apply to both, because they both live in completely different rpm ranges. Try running 3.73 and 33's on a 2.5, it will not get good gas mileage and it will be hell to drive.

So, you can't really rely on the chart to tell you how your Jeep will be best. Through the MANY amount of Jeep drivers that have tested 4.10, 4.56, 4.88 with all the different tire sizes, there are many of us who can say for sure that 4.56 works best with 33" tires on the 4.0 5-speed. They key is being properly geared. The engine will work much less, equating to some efficiency and much better power throughout the range. Lowering the RPM to the point of no power does NOT equate to better gas mileage.

If you don't have the 5-speed manual, that all goes out the window. That is your setup, correct?
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Man I'm real confused. I thought I had gears all figured out.

But yes, 5 Speed 4.0.

Am I right in my assessment that my current setup is more like pedaling a bicycle with big tires with a bigger gear?
Versus your and Jerry's setup is the same bicycle, but with smaller tires and a smaller gear being used?
 
Nashorn101 said:
Man I'm real confused. I thought I had gears all figured out.

But yes, 5 Speed 4.0.

Am I right in my assessment that my current setup is more like pedaling a bicycle with big tires with a bigger gear?
Therefore the engine of my TJ has to pump more gas into the throttle to get the same torque as your Jeep does, because of its better coupling of tire size to gear size?


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Yes. To maintain speed, all things being equal, you have to push the gas pedal further to hold speed on the highway compared to mine, which in turn causes the PCM to increase the fuel consumption in order to keep up. I think my cat is partially clogged but I still don't have to push my throttle that hard to maintain speed on flat ground.

33's with 4.56 is actually a little lower setup than my own which pulls 75 at 2900 instead of my 2800. So there's a tiny performance increase there as well.

Jeep geared the TJ Rubicon with 4.10 on 31" tires, and people sure loved it. I have faith if you regeared to 4.56, you wouldn't regret it at all. If you have plans to go to 35's though, 4.88 would be best.
 
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That makes sense. My Jeep came with 29" tires I believe - hence the 3.73's.

The thing though is that I reach 75mph at about 2500rpms compared to your 2700 - that's why I've always thought I had a higher fuel efficiency.

Or, in this case, I may be at 2500rpms (lower RPM's than you) but my engine has to pump a lot of gas to stay at that level?

Versus yours: you may be at higher rpms, but because of your gear ratio, your engine isn't consuming as much gas? (rpms and gas consumption are independent of each other)


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Then why are rpms important? It sounds like it's just a yield between gear ratio / rear end speed and fuel consumption to hold that speed.


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Nashorn101 said:
That makes sense. My Jeep came with 29" tires I believe - hence the 3.73's.

The thing though is that I reach 75mph at about 2500rpms compared to your 2700 - that's why I've always thought I had a higher fuel efficiency.

Or, in this case, I may be at 2500rpms (lower RPM's than you) but my engine has to pump a lot of gas to stay at that level?

Versus yours: you may be at higher rpms, but because of your gear ratio, your engine isn't consuming as much gas?


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Correct. But if your speedometer isn't calibrated, you're actually going faster than 75 when it says 75. 33 and 3.73 should give you about 2200-2300 rpm at 75. If it says 2500, you should be actually going around 80.

But your idea is correct, yes, the engine isn't working as hard. The main thing isn't so much the fuel consumption though as the mileage in Jeeps sucks overall. The main thing is the power you gain. It's like driving an entirely different Jeep.
 
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Nashorn101 said:
Then why are rpms important? It sounds like it's just a yield between gear ratio / rear end speed and fuel consumption to hold that speed.


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You can use them as a general guideline, you just don't want to only think of them for picking the gear ratio. Too many people are afraid to rev the engine up, thinking they need to keep the rpm at 2000 or below, which couldn't be more incorrect on Jeep engines.

We do use rpm and it is important, but it's not the only deciding factor to picking a gear ratio. I just don't like telling people their Jeep will rev at X rpm at a certain speed usually because then they freak out and think they'll hurt the engine or get terrible gas mileage.
 
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Brantley said:
Correct. But if your speedometer isn't calibrated, you're actually going faster than 75 when it says 75. 33 and 3.73 should give you about 2200-2300 rpm at 75. If it says 2500, you should be actually going around 80.

But your idea is correct, yes, the engine isn't working as hard. The main thing isn't so much the fuel consumption though as the mileage in Jeeps sucks overall. The main thing is the power you gain. It's like driving an entirely different Jeep.
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Good point. Yes I still have my stock speedo gear.

And torque in relationship to power is a whole 'nother ball game - I've tried to understand it.

Is it that torque is the actual force required to overcome the opposing force of your wheels trying to stop turning (I.e. starting off from a red light, or going up a hill, or just accelerating for that matter)

And power is ... I don't understand what horsepower is.


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Your best mileage will come when the engine is running at optimal efficiency. Burying your foot in the right pedal to keep at XX mph will kill your mileage as opposed to being light on the gas because your gearing keeps the engine spinning at an efficient RPM.

The charts I have seen are bunk. Take your advice from people that have real world experience, not some chart based on calculations.
 
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3.73 is appropriate for 30" tires and 5-speed with the 4.0 engine. That's why it's a factory ratio for 30" tires.

3.73 is not even close to being enough gear for 33" tires which is why you struggled to tow your trailer

No, 3.73 is not helping to maximize your mpg, it's likely harming it since your engine isn't operating in its most efficient power band with your 33" tires. In most situations your engine is lugging. 4.56 is the appropriate ratio for your particular combination which would most likely also improve your mpg.

Your memory failed you that Chris posted a chart saying 3.73 is appropriate for 33's on a TJ. It's not even close to being appropriate for 33's for any engine or transmission combination.

And starting out in your above post replying to my post by saying BS, followed by including how your TJ struggled to tow an even lighter trailer isn't going to convince many, especially me, that you were just being sarcastic.

It's no wonder you notice you sometimes offend people by how you post. Perhaps not calling BS on people you don't know so easily or quickly might help reduce how often you offend people.
 
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Brantley said:
You can use them as a general guideline, you just don't want to only think of them for picking the gear ratio. Too many people are afraid to rev the engine up, thinking they need to keep the rpm at 2000 or below, which couldn't be more incorrect on Jeep engines.

We do use rpm and it is important, but it's not the only deciding factor to picking a gear ratio. I just don't like telling people their Jeep will rev at X rpm at a certain speed usually because then they freak out and think they'll hurt the engine or get terrible gas mileage.
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Understood! Thank you. This makes more sense now.

@Jerry, read my post and respond damnit. So that I know I didn't bring offense upon thou. ;)
 
We can conclude this by saying that 3.73 is definitely not appropriate for 33" tires :p

That's a horrible, horrible combination.
 
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martin said:
Completely of topic!!! to Jerry Bransford:
What is the name/make of your trailer?
It looks like the one I have been trying to find for myself
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It is a Fleetwood Taos Martin, they're out there for sale all the time. Google's a good way to find them for sale. It has really been a good one, I've been happy with it since buying it new.
 
I tow a 5x10 Cargo trailer about 9000miles a year for work, barely know it is there. Right now, full of tools, it weighs 1900#. Been doing this for 7 years now. Best part about 5' wide is the stock mirrors see right past the trailer.
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billiebob said:
I tow a 5x10 Cargo trailer about 9000miles a year for work, barely know it is there. Right now, full of tools, it weighs 1900#. Been doing this for 7 years now. Best part about 5' wide is the stock mirrors see right past the trailer.
View attachment 16317
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Altho this ^^^^^ is a Rubi with 4.10s and 33s... I also towed it with a YJ and 33s and 3.07s.... I NEVER felt short of power, I just dropped another gear. Anyone telling you 3.73 is a bad choice is speaking from an off road, extreme use only. 3.73 is one of the best, most versatile ratios around. The biggest factor, reason to go lower is not related to power at speed. It is starting from a stop and finding not enough lift. Like when a tire is tight to a rock, or curb, or log.


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billiebob said:
Anyone telling you 3.73 is a bad ratio is not much of a driver.
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A bit of a strong assumption there. 3.07 and 33's sucks, plain and simple. All 5 gears are out of their range, 5th is 100% useless, 4th still has no power doing about 2200 rpm at 70-75 and 3rd is a bit too low that you don't want to drive in it all day long. Not to mention driving around the city with 1st and 2nd isn't ideal at all because you have to slip the clutch so much to get it rolling and neither of those two gears really have any power with such tall gears.

I would much rather have better gears where I can hold nearly everything in 5th, still get the same gas mileage as those guys with horrible gears, and then only on the very steepest of grades, I downshift to 4th. Not to mention 1-3 gears are way more fun with the lower gears.

3.73 with 33's still leaves a whole lot to be desired, with or without towing.
 
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