At what point will axles needed to be upgraded with tire size increase?

[George C Lone]

When it comes to stock Jeep suspension components, at what point of tire increase do you need to upgrade axle and major parts like?

 

[smritte]

That's going to depend on your vehicle and foot. I had my life lessons on axles when rock crawl was evolving. No one made good upgrades so we carried extra's. That made me paranoid. I now upgrade my axles almost right off the bat. I also periodically pull them and check for twisting and cracks.
Here some spline/axle sizes.

Dana 30, 27 spline
Dana 44, 30 spline
Dana 60, 30-35 spline

Assuming you have a newer Jeep Rubicon. You should have a 32 spline rear and 30 spline front. The higher the spline count, the bigger the axle. 32 splines is very strong but Jeep has a reputation of skimping on quality of the metal.
I believe the standard wrangler is 30 rear and 27 front.

Weight and gear ratio also plays into this. The lower the ratio, the more torque on the axle. These numbers are my experience with Jeeps and rocks. Bigger/heavier is harder on axles. I'm also throwing ring and pinion sizes. This is assuming you buy quality gears.

The (loosely based) general rule of factory axles is
30 spline limit is, 35's all day long with a heavy foot and 4.88. 37" and 5.13 gears is the limit but can break with a heavy foot.
35 spline is good to 40's Gear ratio 5.38 all day and 6.17 depending on weight.

I will always recommend at least upgrading the front axles. If you can, go RCV. You will not break them and their not much more then the cost of good chromo axles.
Their design is similar to a front wheel drive car axle. The weak point of the front axle is the U-joint and the yoke. Straight driving isn't the issue, its turning. This is where the RCV shines.

 

[smritte]

Forgot to add.
I have wheeled with 35's, a 27 spline front and lok rite diffs. This is fine as long as you keep your foot out of it. Also I would be careful with 4.88 in that axle size. In the early days this was a common combo. This is also why we carried complete axle sets in our rigs.

The record on one of my trips was three broken axles on one vehicle. He broke a front, then a rear while backing into a flat spot. We found the other rear cracked when we tore it down. These axles didn't break from a heavy foot, they fatigued and cracked over time. The driver did not commonly have a heavy foot.

As I said, my experience has made me paranoid when it comes to axles.

I've also seen street Jeeps not break axles with 40's and 27 spline axles.

 

[Ryan Frost Outdoors]

I was told anything over 38" you really need to start thinking about upgrading your steering and axles.