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Random Dude
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3,014 Posts
Great insight on gear ratios in this thread. MY 2011 JK standard 6 speed transmission with 3:21 gears ratio and I have (265[30"] 70 17) AT tires on right now and just added a 2.5 inch lift.

From what I gather if I wanted to go up to a 35" tire I should regear to at least 4.10.

MY 30" tires run about 2000 rpm at 70 mph, a 35" tire as the chart reads that my rpm would drop to 1800 rpm or maybe lower?

I don't do much highway driving so it may be okay? but would gas mileage go down?

I'm around 16 mpg avg. right now.

So as I hear a 33" from a tire store, may be the tallest I should go with to keep mpg the same and rpm's the same and not have to regear? Although I see here in the Forum 35" to 37" are the go to tire size.

Hopefully I can get some feedback from longtime members here or merchants.

Thank you in advance.

Regarding fuel economy changes:
33s will cost you fuel economy - not as much as 35s or 37s, but there's no magic threshold.
Any increase in tire diameter and/or weight will likely reduce fuel economy.
You may already see ~0.5 MPG reduction from your lift (increased wind resistance).
Performance gains will cost you at the pump.
- I think that's in the Bible (First Octanes; 87-91 or something :laughing: ).​



Regarding tire sizes:
What limitations have you encountered with your current tire size?
What offroading do you do now - snow, mud, sand, rocks, potholes in mall parking lot?
What do you wish to gain by changing tire size?

I'd throw 35s on that 2.5" lift and regear to 4.88 - but you might hate that setup.
My Jeep on 37s with 4.88s is great for my wheeling needs, but sucks as a "car".

Beware the slippery slope: bigger tires will wear stuff out quicker, and they're far more likely to bend or break shit than 30" tires are. Along with the 35s and regearing, I'd gusset the front C's, sleeve or truss the front axle, seriously consider chromoly axle shafts, and be open to the idea of hydro assist steering. You can blow through 2-3 grand like <snaps fingers> that. And that $2-3K is if you DIY - if you're paying for labor, God help you :laughing:


My 2 door 6MT Rubicon did great stock on the factory 32s with factory 4.10 gearing :rockon:
Lifting it 2.5" and running those 32s / factory rims on 1.5" Spidertrax spacers was good.
Ran 35s for years with the 4.10s and it was good, but 4.88s really put it back to "sporty".
Stepping up to 37s with the 4.88s wasn't a huge performance hit, but I'd love some 5.13s or 5.38s :devil:
NOTE: all of those^ modifications cost me fuel economy, and made it a shittier road trip vehicle.

If it's a daily driver, don't go over 35s without a damned good reason (performance, not looks).
If you want fuel economy & don't wheel it, get the smallest tire you think "looks badass" :thefinger:

So . . . the answers to your questions rely entirely on what you're trying to accomplish :dunno:

 

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Random Dude
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3,014 Posts
This thread is 7 years old.

Sent from my LM-V405 using Tapatalk
No shit - the topic is twice as old (not counting Pentastar recalculation - I don't :thefinger: ).

Sure, they could'a searched :homersimpson: but IMHO bumping an existing thread is far better than starting the 500th "gears for 35s" thread.

Meh, I tried to help. Now it's up to sprkeng to provide details so we can argue what's best :laughing:
 

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2011 Jeep JK Sport 2 Door 6 Speed Manual
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52 Posts
Hey thanks guys for the information,

My intentions for my JK are to make it look better, at times I get compliments on my Jeep as is now. I think the 265s look too small with the lift.

I'm ready for new tires the ones I have All Seasons are in need of replacement. I want something a little aggressive AT for going off road, but still be a semi-daily driver, my other car is a 1985 Porsche 911 summer only driver. I use my JK for fishing, grouse hunting and camping plus winter driving snow/rain. I go off road primarily on fire trails and dirt/mud trails. My old tires were ok for trails, but many times I wished I had a little more aggressive tires. I'm sold on the BFG KO.

I've talked to a few 4x4 shops and it's why I bought a 2.5 inch lift from 4WheelsParts, but they all said start with the lift. So it's lifted and leveled that I have started with. I've always wanted it leveled and the old suspension needed to replaced. So far my mpg is at 16.8 dropped a little.

Where I'm at right now is divided by two sides of opinions, some say 35's won't affect the gears on my rig, but it maybe sluggish, 2.5 lift is plenty of room, the other side says to me don't go past 33" it's a perfect size for stock gears and they look good on a 2.5 lift.

I've seen many JKs around town with 35s seems to be the go to size and they look good.
But my deal breaker could be to regear, It's not cost it's more like, do I open a can of worms..

I value your opinions or arguments. 😊

(I'm trying Photobucket Below)

<a href="http://s1243.photobucket.com/user/sprkeng56/media/Mobile%20Uploads/C360_2017-04-16-09-00-46-985-01_zpsxuppwqlo.jpeg.html" target="_blank"><img src="http://i1243.photobucket.com/albums/gg554/sprkeng56/Mobile%20Uploads/C360_2017-04-16-09-00-46-985-01_zpsxuppwqlo.jpeg" border="0" alt=" photo C360_2017-04-16-09-00-46-985-01_zpsxuppwqlo.jpeg"></a>
 

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Random Dude
Joined
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3,014 Posts
Hey thanks guys for the information,

My intentions for my JK are to make it look better, at times I get compliments on my Jeep as is now. I think the 265s look too small with the lift.

I'm ready for new tires the ones I have All Seasons are in need of replacement. I want something a little aggressive AT for going off road, but still be a semi-daily driver, my other car is a 1985 Porsche 911 summer only driver. I use my JK for fishing, grouse hunting and camping plus winter driving snow/rain. I go off road primarily on fire trails and dirt/mud trails. My old tires were ok for trails, but many times I wished I had a little more aggressive tires. I'm sold on the BFG KO.

I've talked to a few 4x4 shops and it's why I bought a 2.5 inch lift from 4WheelsParts, but they all said start with the lift. So it's lifted and leveled that I have started with. I've always wanted it leveled and the old suspension needed to replaced. So far my mpg is at 16.8 dropped a little.

Where I'm at right now is divided by two sides of opinions, some say 35's won't affect the gears on my rig, but it maybe sluggish, 2.5 lift is plenty of room, the other side says to me don't go past 33" it's a perfect size for stock gears and they look good on a 2.5 lift.

I've seen many JKs around town with 35s seems to be the go to size and they look good.
But my deal breaker could be to regear, It's not cost it's more like, do I open a can of worms..

I value your opinions or arguments. 😊

(I'm trying Photobucket Below)

<a href="http://s1243.photobucket.com/user/sprkeng56/media/Mobile%20Uploads/C360_2017-04-16-09-00-46-985-01_zpsxuppwqlo.jpeg.html" target="_blank"><img src="http://i1243.photobucket.com/albums/gg554/sprkeng56/Mobile%20Uploads/C360_2017-04-16-09-00-46-985-01_zpsxuppwqlo.jpeg" border="0" alt=" photo C360_2017-04-16-09-00-46-985-01_zpsxuppwqlo.jpeg"></a>
Pic check:



I made the "http" into "https" and dropped it into image tags^.


Your 2011 is a 3.8L, yes? If so, 33s on 3.21s may be a bit of a struggle - you'll have 90% of current RPM at any given speed / gear. 6th gear will be for downhill on the freeway above 60 MPH.

Here's the time-honored quick reference table:



Learn it, live it, love it :laughing:

Sounds like 32s or 33s would accomplish what you say you need.
If you don't want to regear, take 35s off the table for now. 3.8L + 3.21s + 35s would bring the suck.
Maybe rock new "sensible shoes" for now, and plan to build up and regear for 35s next time around?
 

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Registered
2011 Jeep JK Sport 2 Door 6 Speed Manual
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52 Posts
Thanks ExWrench on your feedback it's valuable information I can use. I'll more than go with the BFG KO2 285 or 33" actual size 32.8". If go with a new wheel with -12 set back it will extend the tire out about 1" outside the fender. Might look good.
Thanks again.
 

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Super Moderator
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6,284 Posts
Thanks ExWrench on your feedback it's valuable information I can use. I'll more than go with the BFG KO2 285 or 33" actual size 32.8". If go with a new wheel with -12 set back it will extend the tire out about 1" outside the fender. Might look good.
Thanks again.


I've become pretty aware of the bfg ko2
as-well-as the 3.8l in various tranny configs & gearing's ; Ex have sound advice on 35" tires really pushing the max of what 3.21 r&p will be able to be driven without noticable struggles .
285-70r17C is going to not be much larger than the stock tires.

with the KO2 you get some extremely wide ranging differences w/ weights. The "E" rateds versus D or C plys can add weight that - frankly -;unless towing or using on a dually truck , you may not need. A "D" rated
34x10.50R17/D weighs under 55lbs. That's not a stretch for 3.21s rolling resistance wise. They are also almost 34" (33.4" or something?) so just be mindful of the carcass weight when you shop & often you can get a size larger if offered in a less beefy tire. Oh , with the CoreGuard sidewall tech, you get more sidewall resilience than you requirefor a DD out of a DRated. a C rated ko2 will be lighter , likely ride better and you can run a little bigger . Samedize in an "e" carcass will add 10+ lbs to it ( 10lbs X five = 50 additional rolling weight pounds ...)


 

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Registered
2011 Jeep JK Sport 2 Door 6 Speed Manual
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52 Posts
Thank you. That was very informative. I didn't know the KO2 came in a C rating. That's all I need, I never had to deflate to get through a forest trail I have traveled. Thank again.
 

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2011 Jeep JK Sport 2 Door 6 Speed Manual
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52 Posts
I'm sure now that I have made up my mind on the size tire for my '11 JK Sport 3.21 gear

Depending on price difference I'll buy either the 285/70/17 or the 305/70/17 they're both around the 33" range. I need 5 of them.

 

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I'm sure now that I have made up my mind on the size tire for my '11 JK Sport 3.21 gear

Depending on price difference I'll buy either the 285/70/17 or the 305/70/17 they're both around the 33" range. I need 5 of them.

Just remember BFGoodrich tires are not known to measure even close to true. My 34s from them don't measure even close to 33 inches with an inflation around 30 psi and mounted on the vehicle.
 

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2011 Jeep JK Sport 2 Door 6 Speed Manual
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Well I should lean more to the 305 and hopefully a C rated is available in that size it's a lighter weight tire.

I plan on waiting until after the holidays and my ear out for deals.
 

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2011 Jeep JK Sport 2 Door 6 Speed Manual
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I've read that the BFG KO2 makes the ride stiff even with a C rating.

Any truth to that?
 

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I've read that the BFG KO2 makes the ride stiff even with a C rating.

Any truth to that?
Not that I'm aware of. The BFG KO2 34x10.5x17 are D rated and I didn't notice much of a difference from the factory BFG KMs. I would expect that it would depend on your tire pressure you use though.
 

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I've read that the BFG KO2 makes the ride stiff even with a C rating.

Any truth to that?




I have run 3 sets of the KO2s, 1 of those presently on my wife's truck / my tow rig.
I have had D rated 37" and both "E" and "C" rated metric 35" sizes.
They all were the best riding AT tire I've ever experienced on street.
Whomever is telling you that or wherever you're pulling that feedback from likely doesn't understand how PSIs affect a tire & ride.

I will tell you this on the subject , since I learned it quickly; the KO2 CAN ride "stiff" if not at the absolute proper air inflation for that specific vehicles GVW . I found for my just under 5,000lb Wrangler Unlimited, the KO2 in 37" 'D' , that 24.4 PSI on rears & 24.8 PSI fronts was the sweet spot on asphalt. That was the original compound , too. Notice the 10ths . Yes, that made a difference.
The 34" "E" rated set on my much heavier, towing RAM truck requires 28.2 PSI all the way around. fwiw, they are the slightly less "sticky" , more durable compound for trucks and dually or towing .

you'll need a higher quality , digital air guage & some trial & error to time them for your particular rig and desired ride.

I can see how just relying upon a tire store / service place to set all of that for you could result in someone declaring they are stiff or rough riding but if time is spent , you can find that magic pressure & they almost ride like an all season tire,heh.


they are the most sensitive to either too much or too-little air in them tire I've ever come across, to be sure .

everything is always in the details ...

 
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