35 Inch Tires And Drivability

[Gadabout]

So I bought a new to me 2008 two door JK with quite a few mods already on it. They seemed to be well chosen and the installs seemed good as well.

First impression of the 35 inch tires around town was that they worked surprisingly well. When I took the Jeep on the highway to go up north in Michigan, it was a whole other story. First of all, the conditions for my first road trip were horrible. There was a constant 20-25 mph headwind. This plus trying to keep up with traffic - I was trying to cruise at 65 to 70, made the trip very annoying. Due to the fact that the PO didn't change the axle ratios, the jeep just couldn't buck the headwind in high gear (automatic trans). It would constantly downshift and was extremely unresponsive to throttle in high (rpm was only 1500 at 65 mph). So as I drive along and get into high, it starts to slow down and as I give it more throttle, it downshifts, speeds back up to cruising speed and shifts back into high. Now that doesn't sound so bad, except that it was constant for 150 miles. I'd say each cycle of downshifting took about 15 seconds. The only good news is that I still got 15 mpg. Pretty amazing considering the wind and the constant downshifting.

So, what have I learned? 35's are not great highway tires unless you change your gearing. Fortunately, I plan to use this jeep mostly on the trails, and for that the tires are great. But this does bring me to a question for all you experienced off roaders out there (I have a fair amount of experience off road, but it's all been in a dune buggy, dirt bike, or quad). I don't have bead locks, but I want to air the tires down for traction and to absorb some of the bumps. I'm running in very sandy soil. How far down can I go without doing damage?

I also have a front sway bar that can be detached with locking pins. I'm assuming that would also be a good idea? Any other good hints to make my off-roading more enjoyable?

BTW - one more question. The PO also sold the rear seat to make room for his dog and I'd like to take friends along. I thought I could just pick one up for cheap on Craig's or Amazon, but they seem rare as hen's teeth. Any suggestions, or does anyone have one for sale? OK I lied, here is another question? Why does the shopping menu take you to Amazon? Isn't there a classified section in the forum?

Happy Trails,
Gadabout

 

[Danarch]

Sorry about the trip. There are a couple of things, one if it is an automatic the tire size may need to be inputted into the computer so the shift points are correct. Two as you pointed out the gear ratio may need to be changed. I believe the three stock gears are 3:21, 3:73, and 4:10. The 3:21 would not pair well with 35’s on the freeway.

 

[DirtDauber]

4.56 or 4.88s would make you much happier on road and off with 35s. I have an '11 3.8, 6 speed manual with 4.56s and its a daily driver. I would go even lower with the gears if it was a trail only Jeep. I air down my non beadlock wheels to 14-16 lbs when off road, but my wheeling consists running over rocks and other pointy things. I'd say you could go to 10 psi in the sand with no issues. Hope this helps.

 

[BLACKJKU]

Yes we have a Classifieds Section near the bottom of the page. I remember seeing a rear seat for sale somewhere down in my area in N Indiana, I could look to see if I can find it again if interested in the drive.

Like to 2 others have said check to see what gears you have and if your Speedometer is calibrated. My guess you have 3.21 gears and if so that is your problem.

You can check your stock gears here to see what you have.

FCA RAM

fcacommunity.force.com

 

[Anybodyhome]

As others have said before me, just throwing a set of 35s on the vehicle without making the necessary adjustments will make your off- and on-road life miserable.
1. Either go to a tire shop or, if you have an OBD dongle, chip or JScan, check to ensure the tire size was updated to reflect the 35s.
2. If you're running the 3.21 rear end, it won't matter if there's a headwind, hill, cross wind or flat road, your engine and tranny is going to suffer trying to keep up with the 35s and that gear ratio- just not a good combo.

If the tire size is correct, then you need to make a choice, and both will cost you comparably- either go back to a stock tire/wheel size until you get a new set of gears (4.56 if you're going to off-road is my opinion); or just get the new gears installed and be happy with the change in performance. In my opinion, if you go up to a 4.88, I'd probably look at upgrading to a Dana 44.

 

[JeepJeezy]

Definitely check to see if the tire size was inputted 1st. It's free. Set your speed on the Jeep, say 50mph and check your speed through the GPS on your phone. If they match, then tire size was inputted. If they're off then you'll need to tell your Jeep the correct tire size. The physical size and not the "35 size". This is very important for your transmission to shift properly.

 

[SteveF]

I was running 35's with 3.21 gears and it sucked. It couldn't get out of its own way. I re-geared to 4.56 and love it. No more down shifting on the highway. At the same time I got rid of the stock open differential and put in a Yukon Limited Slip differentials in both axles. I don't go off-road enough to justify the expense of having lockers put in so I figured going to limited slip differentials was the way to go. Enjoy your ride. Remember Jeep stands for Just Empty Every Pocket.

 

[Speartip]

What they ^^^^^^^ all said

 

[Gadabout]

Thanks for all the inputs - makes a lot of sense. The computer has been updated so that the speedo reads correctly. At least the PO did that much. I'll have to save up my nickels for a new set of gears in the future. Anyone know what that should cost?

 

[SteveF]

Thanks for all the inputs - makes a lot of sense. The computer has been updated so that the speedo reads correctly. At least the PO did that much. I'll have to save up my nickels for a new set of gears in the future. Anyone know what that should cost?

Just because it says 35 inch on the tire you need to measure the distance from the top of the tire to the ground. I set a level across the top of the tire and when the bubble was in the middle I took the measurements. All my tires were 33.75 inches so that is what I put in Jscan for tire size. I read that is has to be accurate within 1/4 inch to be accurate. My build sheet said I had 3:73 gears when I actually had 3:21 gears, 4:56 is the way to go and get rid of the open differential if you have one. Change it all while you're in there.

 

[14JKGRINDER]

I am having similar issues. I have a 2014 Unlimited Rubicon, which came factory with 4:10 and e-lockers. PO installed a 4inch lift with 35's. I changed the shocks and springs for a different style. If I am driving anything over 70 it seems the motor and transmission are tapped out with RPM between 2800 to 3000. At times it feels like it is rolling over itself on the power train sometimes going up an incline or down an incline it loses momentum and then check engine light and traction control light come on with a 50% power loss. I researched that to vibration pickup in the cam sensors. I have talked with several people and even got a chart on gear ratio's vs. RPM and been told to change to 4.56. I am thinking I need to go to 3.73, mainly because I do a lot of highway driving. I have a bad e-locker on the front so I am planning on doing an entire rebuild on the differentials with new axles, gears, bearings and arb air lockers. My question is should I go with 4.56 or 3.73 and still be able to be on or of road comfortably.

 

[SteveF]

I am having similar issues. I have a 2014 Unlimited Rubicon, which came factory with 4:10 and e-lockers. PO installed a 4inch lift with 35's. I changed the shocks and springs for a different style. If I am driving anything over 70 it seems the motor and transmission are tapped out with RPM between 2800 to 3000. At times it feels like it is rolling over itself on the power train sometimes going up an incline or down an incline it loses momentum and then check engine light and traction control light come on with a 50% power loss. I researched that to vibration pickup in the cam sensors. I have talked with several people and even got a chart on gear ratio's vs. RPM and been told to change to 4.56. I am thinking I need to go to 3.73, mainly because I do a lot of highway driving. I have a bad e-locker on the front so I am planning on doing an entire rebuild on the differentials with new axles, gears, bearings and arb air lockers. My question is should I go with 4.56 or 3.73 and still be able to be on or of road comfortably.

After I put the 4:56 gears my highway rpm's at 65mph is about 2600. I am a right lane driver when in the jeep. 70 mph is usually my max speed.