265/75r16 and gearing

E2 · **Posted:** Sat Mar 13, 2010 9:47 pm

So I just had a 265/75r16 (31.9") fitted on my driver front with the 4" lift.

Goo think is that it fit with a few spots a finger clearance. But the issue I am wonder about is gearing.......

DirtyKK · **Posted:** Sat Mar 13, 2010 10:32 pm

i used an online calculator and if you go from stock size tires to 32" the 4.10 gears will be like stock. the speedo wont be off and your only loss is from the weight gain going to larger, heavier tires.

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

Actually the speedo isn't affected by gears. You will still need to get it adjusted with the 32's. Also, it will be more sluggish than stock even with the 4.10's because of the greatly increased weight of the tires compared to stock. They will help alot though.

E2 · **Posted:** Sun Mar 14, 2010 12:02 am

DirtyKK wrote:

i used an online calculator and if you go from stock size tires to 32" the 4.10 gears will be like stock. the speedo wont be off and your only loss is from the weight gain going to larger, heavier tires.

Weight gain?
Tire diameter?

I BFG is heavier then a Yoko by like 9# each tire in the 265 width the 235 are lighter. I thought the 32" dia made the biggest difference.??

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

Both diameter and weight make a difference. Tire compound and rolling resistance make a difference too. With heavy 265/75R16's, definitely get the 4.10's to help with the power loss. You'll still have a power loss and mpg loss, but they shouldn't be nearly as bad as if you stick with the 3.73's. You need to get the speedo corrected with a diameter change. For 32's with 4.10's to be like 29's with 3.73's, they would have to weigh the same amount and have the same rolling resistance.

dieselenthusiast · **Posted:** Sun Mar 14, 2010 12:51 am

I agree with everything KY Liberty said……… the only thing I would add is to consider installing your locker(s) at the same time you do your gears to save on labor cost. :pepper:

DirtyKK · **Posted:** Sun Mar 14, 2010 1:00 am

How would regearing with taller tires not correct the speedo? Think stock.. put taller tires on and your speedo will tell you you're going slower then actual. It would be opposite if you did the gears. Put em together and with the right calculation you can figure what gears for the difference. When I figured it out it came out within .02 or .03 of 4.10 iirc. That is why I've purchased 4.10s... if I'm thinking wrong please explain to me.

E2 · **Posted:** Sun Mar 14, 2010 2:27 am

DirtyKK what 4.10s did you get and how much?

Diggerfreek · **Posted:** Sun Mar 14, 2010 4:15 am

Dirty, since the KK reads the speed (revolutions per mile) at the wheel and not at the diff like the KJ's, gearing will not correct the speedo............. Even then, one still has to so a "pinion reset" or change the rpm of the tire in the computer...

daspes · **Posted:** Sun Mar 14, 2010 9:18 am

To piggyback of Diggers comment.

Considering the KJ's (not sure about the KK's) came from the factory with the Speedo off by so much. On 31.9" tires my speedo is finally displaying the correct speed. So you may not need to have the PCM reflashed for tire gear changes at all.

tommudd · **Posted:** Sun Mar 14, 2010 3:39 pm

Right now mines shows 63 on the speedo and 70 by way of the GPS so mine went way off, when I switched to 245-70s it was spot on, 265-70s about 3 to 4 off
70 MPH By GPS and 1900/1950 RPM
Gotta take time for the 4,10s soon! :banghead:

dieselenthusiast · **Posted:** Sun Mar 14, 2010 4:00 pm

tommudd wrote:

Gotta take time for the 4,10s soon! :banghead:

What's the holdup? Are you waiting for lockers?

Fulltimer · **Posted:** Sun Mar 14, 2010 4:23 pm

I have full 32" tires, not 31.9". I also have the 4.10 gears. My speedo is off 5pmh @ 50mph. I did NOT gain back my lost power. Some of the power came back and the speedo is closer than it was before I changed gears. The dealer said he couldn't get the speedo back down again. I think he is wrong but....

Terry

dieselenthusiast · **Posted:** Sun Mar 14, 2010 4:47 pm

Fulltimer wrote:

I have full 32" tires, not 31.9". I also have the 4.10 gears. My speedo is off 5pmh @ 50mph. I did NOT gain back my lost power. Some of the power came back and the speedo is closer than it was before I changed gears. The dealer said he couldn't get the speedo back down again. I think he is wrong but....

Terry

Yeah, I do too much mountain driving to enjoy a tire that's taller than 31". I'll probably stay between 30.0"-30.5" with 4:10's and call it good.

DirtyKK · **Posted:** Sun Mar 14, 2010 5:36 pm

oh thanks for clarifying guys. ill know for future reference now i guess. E2, i have oem 4.10s from a jk for the front and motive for the rears... i kinda want 4.56 though... im still up in the air, just dont want to spend the money on installation and not be happy with 4.10. i dont want 4.56 to save on highway mileage cause i go on a 2.5-3k mile road trip every year.

Diggerfreek · **Posted:** Sun Mar 14, 2010 6:48 pm

DirtyKK wrote:

oh thanks for clarifying guys. ill know for future reference now i guess. E2, i have oem 4.10s from a jk for the front and motive for the rears... i kinda want 4.56 though... im still up in the air, just dont want to spend the money on installation and not be happy with 4.10. i dont want 4.56 to save on highway mileage cause i go on a 2.5-3k mile road trip every year.

Dirty, did I send you the RPM/Tire size chart I have?

DirtyKK · **Posted:** Sun Mar 14, 2010 6:56 pm

Diggerfreek wrote:

DirtyKK wrote:

oh thanks for clarifying guys. ill know for future reference now i guess. E2, i have oem 4.10s from a jk for the front and motive for the rears... i kinda want 4.56 though... im still up in the air, just dont want to spend the money on installation and not be happy with 4.10. i dont want 4.56 to save on highway mileage cause i go on a 2.5-3k mile road trip every year.

Dirty, did I send you the RPM/Tire size chart I have?

no...

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

DirtyKK wrote:

oh thanks for clarifying guys. ill know for future reference now i guess. E2, i have oem 4.10s from a jk for the front and motive for the rears... i kinda want 4.56 though... im still up in the air, just dont want to spend the money on installation and not be happy with 4.10. i dont want 4.56 to save on highway mileage cause i go on a 2.5-3k mile road trip every year.

I don't know about the KK, but the 4.10's from a non Dana 30A don't fit the front of a KJ.

Diggerfreek · **Posted:** Sun Mar 14, 2010 9:58 pm

KK's use a D30M that is modeled off of a JK D30

tjkj2002 · **Posted:** Sun Mar 14, 2010 10:32 pm

Diggerfreek wrote:

KK's use a D30M that is modeled off of a JK D30

Fixed it for you.

265/75r16 and gearing

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