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[Kolohegirl]

The data is in, and I'm blown away.

Same speed on cruise control. Same stretch of road. Very similar conditions (winds 9-12 mph, left quarter headwind). Both data points appropriately programmed to correct tire size by Tazer. Same Jeep loadout. Here's what I've got:

35s:

37s:

The two pictures are taken from video clips of a run between the same two signs on a stretch of highway going in the same direction. 35s returned a range of 14 - 16 mpg. 37s returned a range of 19 - 22 mpg. This was by no means done in a controlled environment, but it's about as good as I could get. Science is undefeated.

I will say that I'm...very surprised by this. And sure, there may be 1-2 mpg of error, but 6 mpg gain? Wow. Even if real-world ultimately translates to just 1 or 2 mpg of gain, I'd still be ecstatic about that.

At 11 pounds lighter per tire, I can feel the reduced stress on the driveline. Takeoffs and braking are smoother. The Jeep starts rolling with less effort. Shifts feel more leisurely. With the same driving habits I continuously found myself driving several mph faster than usual at identical points on my commute across a couple of days. Also, notice the roughly 200 rpm reduction while holding the same speed on 37s (I know this is a result of tire size and not weight, just pointing it out). Finally, the ride is MUCH more plush. I ran 32 psi on 35s, and have 30 psi in the 37s. My only regret is that I didn't make this change sooner.

While I likely will regear in the future when budget allows, I can confidently say that the Jeep drives better now than it did before. We'll see how it is after I run a few tanks of fuel through it. Can't wait to get it off road to test out that side of things.

Pictures/comparison coming soon!

I am soooo happy to find this post! I've been considering the same thing. I have a new stock mojave with the 33 Falken and want to go up in tire size and 2 inch spacer. I have a smart cap and it just really needs the height. I don't want to do a ton of work to the jeep so thought about sticking to 35s since you don't have to do much with that size. But then after reading through so many posts and how much lighter the KO2s are I started thinking about this exact scenario. If I put on a 2 inch spacer with the 37 KO2 and eventually regear should I do anything else? Did you actually swap out gears or just do the tazer gearing? Any updates?

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[TheHops]

I am soooo happy to find this post! I've been considering the same thing. I have a new stock mojave with the 33 Falken and want to go up in tire size and 2 inch spacer. I have a smart cap and it just really needs the height. I don't want to do a ton of work to the jeep so thought about sticking to 35s since you don't have to do much with that size. But then after reading through so many posts and how much lighter the KO2s are I started thinking about this exact scenario. If I put on a 2 inch spacer with the 37 KO2 and eventually regear should I do anything else? Did you actually swap out gears or just do the tazer gearing? Any updates?

I'm glad the info helped!

I have a 2.5 inch lift with a Tazer reprogram--that's it. No further tinkering or regearing (yet). When the budget allows, I'd like to regear, because the drop in RPMs is a bit more exaggerated with my manual transmission vs. the automatics. I think some good 5.13s or 5.38s would beef things up a bit, and allow me to actually use 5th, maybe 6th gear regularly. Since putting on 35s, I never really go over 4th gear. I'm a slow driver and usually cruise at 65-68, tops.

Overall, I'm very haply with the change. I think it balanced out the look a bit, and the performance is excellent. I never thought I'd go over 35s, but I have no regrets!

 

[TheHops]

Regear has been scheduled! I'm moving up to (all Dana Spicer) 5.13s, with chromoly rear axle shafts. I don't think I *need* the rear shafts, but the labor is free since they have to pull the axles anyway, so I figured I may as well make the upgrade.

I'm looking forward to getting 5th and 6th gear back. I've basically been living in 4th gear since I put on 35s at 900 miles. I'm sitting at just under 41,000 miles as of today, now on 37s. I'll be sure to post impressions!

 

[TheHops]

Regear complete! I performed the break-in as recommended, and just did my 500 mile fluid change with very few metal shavings. The oil looked great. I went to Offroad Synthetics over in the Buffalo/Niagara, NY area. Brian was exceptional throughout the process, and I can't recommend him enough. I found him over on the Wrangler forum in an old post.

It drives like an entirely new vehicle. I haven't been able to use 5th or 6th gear since I swapped to 35s at around 900 miles. Now, at ~43,000 miles, I can comfortably cruise--uphill, even--in 6th gear at 70 mph. Fuel economy is notably up as well. On a road trip from NY to OH and back, with tires/gear calibrated in the Tazer, I was getting just shy of 18 mpg. Typically, I'll see 14.5-16 mpg.

One thing to note is that it did cause an auto stop/start code to be thrown each time I drove after a mile or two. I'm not sure if that is typical. This was a simple fix, however, by doing a battery disconnect reset: Headlights on, and disconnect the main negative terminal then the main positive terminal to drain residual power. I lost a couple of uconnect and Tazer settings, but kept my odometer/trip meter. Your process may vary on this if you still have the auto stop/start battery--I have the Genesis dual-battery system.

All in all, highly recommended. I put off this regear for far too long.

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