There is an issues with some rear end gears. Namely the stock 10 bolt (think 98-02 Camaro/Firebirds) when you start getting 4.10 and up. Biggest issues are low end torque, sticky tires and trying to launch from a dead stop.

Here in the off-road world, I don't see anyone doing that. You shouldn't have an issue. If you do, always find better parts or upgrade your axles (like most 10 bolt guys run a 12 bolt or 9").

Just my $0.02

 

Did you consider the size of teeth?

 

The smaller the pinion gear diameter, the less contact surface it has on the ring gear. Fewer pinion teeth will be engaged at any given moment.

 

There are some axles where the higher numbered gear sets are stronger if you are just going by tooth counts.

I don't remember which ones but on say a Dana 44 you have 45/11 teeth for 4.10 and 44/9 teeth for a 4.88, so in theory there is a weakening of the teeth for the 4.88 because there's less teeth.

There are other axles where the opposite could be true. Like on a Dana 60 a 3.54 gear has 39/11 and a 3.73 is 41/11. So on that axle the higher ratio is stronger going by the conventional logic the OP mentions.

I don't think tooth count is always the measure of strength. More teeth equals smaller teeth, right? I also would like to know if there's any science here. Seems like all we have is random anecdotes of some guy broke this gear set on this obstacle. We don't know the quality of the set up, steel quality, heat treat, or driving style. So it's really hard to go by forum reports.

 

^^^ This

 

With the JK D30 and D44 the higher the numerical number of the gear ratio the fewer teeth on the pinion gear. With fewer teeth they is less contact surface area between the ring and pinion.

So you have more lbs per square inch being applied between the gears at the same instance. Gear reduction is also a force/ torque multiplier which is felt my the axle housing. This causes the housing to flex more under load. The flexing/distortion of the housing will affect the mess of the gears.

When setting up gears the mess is the contract between the ring and the pinion. An improper gear mess will have the same negative affect as the housing distorting under load does. It will decrease the surface area of the gears c contacting each other with means that the psi on was is touching is greater.

There are so many variables that come into play when gears break; some gears have a higher quality metal, some are heat or cryo treated for more strength, how much traction where the tires getting, was a tire bound up, was there a shock load, some gears have tighter tolerances allowing for a better gear mess.

But yes with everything being 100% the same a lower gear will me more likely to break in a D30 and D44. But things are never identical so the difference in strength can't be easily quantitated.

My D30 with 4.88s is stronger than it was stock. The Detroit locker I have in place of the stock carrier is much stronger. My gears have been cryo treated for more strength. The person who installed my gears made sure the mess was better than OEM acceptable tolerance. The stamped steel diff cover was replaced with one that added more rigidity to the housing..... But now I have taller and wider tires with more aggressive tread pattern and compound. So my weak link is back to my axle shafts again.

I would rather run chomoly shafts instead of 300m because I would rather replace a shaft for a couple hundred then than to replace gears, locker, and bearings. If a shaft breaks a can pull out and still drove home without causing more damage.

 

Story time. I once had a friend who refused to regear because 3.21 is the strongest. He also refused to air down his 37" Toyo OC's so that he didnt break his ring and pinion. It sure was fun watching him burn up his clutch and hit every obstacle with tons of speed because that was the only way he was going anywhere. He eventually moved on to a 4.10 rubicon on 40's. The thing did like 70 in 4th.

Meanwhile, everyone with 5.13's just crawls over everything. I am not going to break anything when the jeep goes over most stuff with a little tap of the throttle.

Numerically lower gears may be stronger, but what does that matter when you break everything else?

 

Meanwhile, everyone with 5.13's just crawls over everything. I am not going to break anything when the jeep goes over most stuff with a little tap of the throttle.

Numerically lower gears may be stronger, but what does that matter when you break everything else?

I don't know, with a 4:1 transfer case and 3.73 on 35's, my Jeep crawls perfectly for me. Changing the gears would be nice on the street, but mostly just annoying on the trail because the max 4lo speed would go down. My crawl ratio is 85% higher than the Jeep you describe (assuming that was a sport due to 3.21) so I can imagine that person having a very bad time.

I'm not necessarily going to not re-gear due to a strength loss, but I am quite curious how the numbers work out on strength changes.

 

In short, less teeth do weaken the ring and pinion so a higher set will break first with the same torque load on each, but you don't need that much torque because there is more gear reduction. Numerically higher gears do the same work as lower gears, but with less torque required. It just takes more input turns to do the same amount of work

 

For sure it's way weaker for the same pinion torque, but you're right that's fine because you need less pinion torque to do the same thing. But I'm interested in the relative strength for the same ring gear torque (that is, the vehicle doing the exact same thing).