Recommended gear ratio for 32RH transmission and 33" tires?

01TJ-Blues

01TJ-Blues

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Ok, so everything listed so far has been manual or the automatic with overdrive but what about say a 32RH 3 speed auto with a 1:00 3rd gear ratio? Say for 33" tires. Just curious what the thoughts are for the best gear ratio. If you take the .12 x tire size it comes out to a 3:96 which would probably be best at a 4:10...seems too high still. Curious what say a 5:13 gear at 70mph would pull for RPM. Any input is greatly appreciated.
 
MX952 said:
Ok, so everything listed so far has been manual or the automatic with overdrive but what about say a 32RH 3 speed auto with a 1:00 3rd gear ratio? Say for 33" tires. Just curious what the thoughts are for the best gear ratio. If you take the .12 x tire size it comes out to a 3:96 which would probably be best at a 4:10...seems too high still. Curious what say a 5:13 gear at 70mph would pull for RPM. Any input is greatly appreciated.
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Actually this is a pretty simple formula I just found to calculate and eliminate the guessing.

MPH X Trans Ratio X Rear End Ratio X 336
Tire Diameter

Or MPH X Trans Ratio X Rear End Ratio X 336 divided by Tire Diameter equals RPM
 
JMT said:
And that formula yields exactly the results as the Grimm Jeeper website. Dead on. 4.88's FTW!
Click to expand...

You don’t think that 3500RPM is a bit high?

Stock 3:73= 2,658 RPM
Stock 3:07= 2,188 RPM

Not sure which this has yet, just bought it.




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MX952 said:
You don’t think that 3500RPM is a bit high?

Stock 3:73= 2,658 RPM
Stock 3:07= 2,188 RPM

Not sure which this has yet, just bought it.




Sent from my iPhone using Tapatalk
Click to expand...
It would be nice to know what you original gear ratio is. You can always plug your VIN in here and see if your Build Sheet is accessible through Jeep Customer Service. Then we can go from there for more certainty.

https://jeep.custhelp.com/app/jeep/eqlisting_detail/
 
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3:07 gears. No wonder it’s a turd. Haha.

So what is optimal rpm for 60 mph yet still have some off road capability. It will rarely see the freeway/70mph but we will be using it to get to and from the trails.


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For the 3-speed automatic, 4.0L engine, and 33" tires, you want a 4.10 ratio. The 32RH 3-speed automatic doesn't have an Overdrive gear so 4.10 is the ideal ratio for that combination. 4.56 and especially 4.88 would produce excessively high street rpms for 33" tires and your particular transmission.

The above described math technique of figuring a gear ratio to work with larger tires to generate the same engine rpms required with smaller tires doesn't work as intended. Larger tires have more leverage against the drivetrain and thus require higher rpms to maintain the same power as was available with the smaller tires. You have to regear to produce slightly higher rpms with larger tires as was required with smaller diameter and thus easier to turn tires.
 
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Jerry Bransford said:
For the 3-speed automatic, 4.0L engine, and 33" tires, you want a 4.10 ratio. The 32RH 3-speed automatic doesn't have an Overdrive gear so 4.10 is the ideal ratio for that combination. 4.56 and especially 4.88 would produce excessively high street rpms for 33" tires and your particular transmission.
Click to expand...

Much appreciated. But just for curiosity sake what is the best highway RPM range without sacrificing the off road side? I assume 2600-2900 ish?


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MX952 said:
Much appreciated. But just for curiosity sake what is the best highway RPM range without sacrificing the off road side? I assume 2600-2900 ish?
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There's no set best highway rpm, that depends on the tire size, transmission type, and engine but 2600-2900 is fine with the 3-speed. With the 3-speed automatic you have to accept higher highway rpms than you'd be able to have with a transmission with an Overdrive final drive gear ratio.

Offroad-wise, it's not a big deal since you have 4Lo that produces a big (2.71x or 4x depending on the transfer case) boost to engine rpms which overcomes most undergeared situations.
 
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Jerry Bransford said:
There's no set best highway rpm, that depends on the tire size, transmission type, and engine but 2600-2900 is fine with the 3-speed. With the 3-speed automatic you have to accept higher highway rpms than you'd be able to have with a transmission with an Overdrive final drive gear ratio.

Offroad-wise, it's not a big deal since you have 4Lo that produces a big (2.71x or 4x depending on the transfer case) boost to engine rpms which overcomes most undergeared situations.
Click to expand...
Thanks for the insight!


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Sorry @MX952, I deleted a few posts because the information was inaccurate. I was using 4.10 as a base gear ratio and trying to match those rpms. Looks like Jerry got everything straightened out. And at least I got you your VIN Build Sheet!
 
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JMT said:
Sorry @MX952, I deleted a few posts because the information was inaccurate. I was using 4.10 as a base gear ratio and trying to match those rpms. Looks like Jerry got everything straightened out. And at least I got you your VIN Build Sheet!
Click to expand...
Super helpful on both parts! Now to get the axles built...slightly disappointing that the rear ended up being a Dana 35 but I'll be running 33s so it should be fine.
 
MX952 said:
Super helpful on both parts! Now to get the axles built...slightly disappointing that the rear ended up being a Dana 35 but I'll be running 33s so it should be fine.
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It should be so long as there's no locker installed into it and you take it easy and don't let the rear-end start bouncing on a tough trail climb or obstacle. :)
 
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Jerry
So I'm slightly confused. I have done a little research and the Dana 35 built (Super?) should be able to handle most anything wth 33s on a normal trail minus hardcore rockcrawling? I see the Superior Axle used to make a Super 35 Kit (?). Woudl this basically be the same as upgrading the carrier, axles, ring and pinion as well as a locker and with that would it still not survive as well as say a stock Dana 44? Or is their indeed a special "Super 35 Kit" that I should be looking at?
 
Jerry Bransford said:
For the 3-speed automatic, 4.0L engine, and 33" tires, you want a 4.10 ratio. The 32RH 3-speed automatic doesn't have an Overdrive gear so 4.10 is the ideal ratio for that combination. 4.56 and especially 4.88 would produce excessively high street rpms for 33" tires and your particular transmission.

The above described math technique of figuring a gear ratio to work with larger tires to generate the same engine rpms required with smaller tires doesn't work as intended. Larger tires have more leverage against the drivetrain and thus require higher rpms to maintain the same power as was available with the smaller tires. You have to regear to produce slightly higher rpms with larger tires as was required with smaller diameter and thus easier to turn tires.
Click to expand...
What number speedometer gear would you need to run 4.10s on 33's with the 32RH 3-spd auto with the 4.0L engine?
 
Trendsetter75 said:
What number speedometer gear would you need to run 4.10s on 33's with the 32RH 3-spd auto with the 4.0L engine?
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A 36 tooth speedometer gear has been GPS verified to give an accurate speedometer indication with 33's. Here's a good website on the process together with a known-accurate speedometer gear chart.

http://www.4x4xplor.com/speedo.html
 
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I regeared to 4.10 earlier this year with the 32RH and 33’s and can confirm that’s where you want to be.

I went with a 35 tooth speedo gear which consistently reads about 2mph faster than actual GPS speed and radar detected speed. I kind of prefer it to read faster so that when the gauge says 70mph I’m actually running 68mph.
 
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MX952 said:
Ok, so everything listed so far has been manual or the automatic with overdrive but what about say a 32RH 3 speed auto with a 1:00 3rd gear ratio? Say for 33" tires. Just curious what the thoughts are for the best gear ratio. If you take the .12 x tire size it comes out to a 3:96 which would probably be best at a 4:10...seems too high still. Curious what say a 5:13 gear at 70mph would pull for RPM. Any input is greatly appreciated.
Click to expand...
I have the 32rh with a 4.0 engine, running 32's with stock 3.73 gears. I tach 2500 at 60mph and my speedo is dead on with this setup. I agree you should go to the 4.10 gears to go up to the 33's, but for the added height and width of the 33's over the 32's the cost of a re-gear, extra lift, speedo gear change, and all of the other needed changes was just not worth it to me.
 
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