Novak Conversions Jeep Wrangler JK radiators

Gear Ratio for 35" tires

ObiWan

ObiWan

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Zebulon, North Carolina
So I’ve recently bought 35” tires and was wondering what the best ratio to use would be. I use it as a daily driver but also take off road a good amount. I was thinking of switching to a 3.73 or a 4.1. What brands would be best to go with and which to steer clear of. It is the 3.6 penta as well (automatic)
 
ObiWan said:
So I’ve recently bought 35” tires and was wondering what the best ratio to use would be. I use it as a daily driver but also take off road a good amount. I was thinking of switching to a 3.73 or a 4.1. What brands would be best to go with and which to steer clear of. It is the 3.6 penta as well (automatic)
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You'll want at least 4.10's if not 4.56, if your going to be doing offroading then i'd say 4.56.

Also do you have Jscan or something to recalibrate your speedometer for the tires and when you do the gears?
 
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BLACKJKU said:
You'll want at least 4.10's if not 4.56, if your going to be doing offroading then i'd say 4.56.

Also do you have Jscan or something to recalibrate your speedometer for the tires and when you do the gears?
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Not yet but I’m getting one soon. I do work at a place with a scanner I can use for now tho.
 
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Since it's a daily it will depend on how far you commute and your tolerance for engine speed.

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If you're starting with OEM 245s or 255s and 3.21 final drive you will gain 500rpm or so with 35s and a 4.56 at 70mph. Some maybe totally fine with that, some may hate it...

In my experience I would want to stay under 3000 and get as much gear as possible if I'm spending the money. I like @Snowbird Tom 's 4.88 route!
 
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Snowbird Tom said:
Minimum 4.56 in my personal experience and from recommendations from the shop that did mine. I went with 4.88 from Revolution and no regrets.

If you’re currently running 3.21s, you’ll also need a new ring carrier.
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Can’t wait to get 88s in mine.
 
Related question maybe. I am about to replace the clutch on my 2009 JK for the 4th time. First one was with stock tires etc, and after enough miles that I thought it was due.

A few years ago I put on 35's and a bit of a lift. Since then it's been a clutch a year. Tried three different shops for the repair.

Speedometer has seemed off since the new tires. Is it possible they failed to adjust the gear ratio? Would that ruin the clutch repeatedly? Something else?
 
I have 35s and run 3.73s with no issues. Of course, I'm not a rock-crawler, but even on some entertaining trails it serves its purpose just fine. I do have a Pedal Commander and the tires are BFG KO2 ATs.
Running 70 or a little more on the interstate is a breeze at 2100RPM and my mileage is pretty good, all things considered. So, while I'm driving 10k miles a year, what's the ratio of off-road miles to DD miles? Not enough to warrant a new set of gears.
 
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gcicione said:
Related question maybe. I am about to replace the clutch on my 2009 JK for the 4th time. First one was with stock tires etc, and after enough miles that I thought it was due.

A few years ago I put on 35's and a bit of a lift. Since then it's been a clutch a year. Tried three different shops for the repair.

Speedometer has seemed off since the new tires. Is it possible they failed to adjust the gear ratio? Would that ruin the clutch repeatedly? Something else?
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With a Manual trans having the speedometer off because of a tire size or gear change will have nothing to do with the clutch. Having the wrong gears will will be hard on the clutch especially if you have 3.21 gears like I do.

If your speedometer is off it'll only get you a speeding ticket.

Use a GPS to see what your speed is and see if it matches your Speedometer.
 
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BLACKJKU said:
With a Manual trans having the speedometer off because of a tire size or gear change will have nothing to do with the clutch. Having the wrong gears will will be hard on the clutch especially if you have 3.21 gears like I do.

If your speedometer is off it'll only get you a speeding ticket.

Use a GPS to see what your speed is and see if it matches your Speedometer.
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Makes sense. What's involved in changing the gear ratio? Physical replacement or just a modification to the computer to account for the tires?
 
gcicione said:
Makes sense. What's involved in changing the gear ratio? Physical replacement or just a modification to the computer to account for the tires?
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Changing the gear ratio means pulling both differentials apart and replacing the physical gears in them. If you've gone to larger tires, you probably should do this.
Modifying the computer is done to correct the speedometer and such for the new gears and wheel size. You should do this if you've changed tire size or if you've changed gears. Or both, obviously.
 
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Dirty Dog said:
Changing the gear ratio means pulling both differentials apart and replacing the physical gears in them. If you've gone to larger tires, you probably should do this.
Modifying the computer is done to correct the speedometer and such for the new gears and wheel size. You should do this if you've changed tire size or if you've changed gears. Or both, obviously.
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Very helpful. Thanks.
 
We just did 5.13 in the wifes JKU, we had 4.10, huge differnece. The place we went had a REM polish (i think its wahts its called) they ran the new gears thu a machine so we didnt have to deal w/ the break in period. This is the 4th Jeep i have had re-geard, lack of a break in period and lube change is very nice.
 
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BLACKJKU said:
With a Manual trans having the speedometer off because of a tire size or gear change will have nothing to do with the clutch. Having the wrong gears will will be hard on the clutch especially if you have 3.21 gears like I do.

If your speedometer is off it'll only get you a speeding ticket.

Use a GPS to see what your speed is and see if it matches your Speedometer.
Click to expand...
I ended up going with a heavy duty clutch kit from Extreme Terrain. Centerforce Dual Friction Organic/Carbon Clutch Kit with Flywheel; 10-Spline. Hopefully that does the trick! Next up = trying to confirm the speedo is accurate.
 
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