I read the threads on what to do to run 35s on a dana30 front / dana44 rear. It all makes sense but I was just wondering what is it about the 35s? Is it the weight increase that is too much for the Dana 30 or is there something about the increased circumference if the tires alone? I’ve seen 35s varying in weight from 60 to 75 pounds and 33s from 56 to 70. Anyone have any insight into the why? Thanks
The short is as tworley says above.
The long is you need to understand rotational mass as opposed to static mass. Rotating an object (such as a wheel and tire) is harder as the weight gets further out from the center point. Meaning 55lb 33s vs 55lb 35s aren’t equivalent (there are cases where they could be theoretically, but not in reality with tires).
What that means is it takes more force to both get rolling and to stop, adding a lot of stress on the central thing that is powering the rolling/stopping (your axle shaft and other drive train components).
All that stress adds up and can (and will) blow out a weaker axle shaft under the pressures a Jeep would see on trails. Around town/for looks you can probably get by longer without it.
If you want to nerd out: https://www.khanacademy.org/science...momentum/torque-tutorial/a/rotational-inertia
The long is you need to understand rotational mass as opposed to static mass. Rotating an object (such as a wheel and tire) is harder as the weight gets further out from the center point. Meaning 55lb 33s vs 55lb 35s aren’t equivalent (there are cases where they could be theoretically, but not in reality with tires).
What that means is it takes more force to both get rolling and to stop, adding a lot of stress on the central thing that is powering the rolling/stopping (your axle shaft and other drive train components).
All that stress adds up and can (and will) blow out a weaker axle shaft under the pressures a Jeep would see on trails. Around town/for looks you can probably get by longer without it.
If you want to nerd out: https://www.khanacademy.org/science...momentum/torque-tutorial/a/rotational-inertia
Thank you. That totally makes sense and i never thought of that part of it. I will do the nerd thing and check the link out too. I just regeared but didn’t do the chromoly shafts. I hope I didn’t double the cost to go back and do that part.
There is nothing wrong with a Dana 30 and 35'' tires UNTIL you get in a position where the wheel loses traction and suddenly grabs traction. This force can be enough to twist the shaft in two. Under a "normal" circumstance of mall crawling, FSR's, or DD it not a big deal but it is always a present danger that if the wheel loses traction it can break the shaft when it grabs.
What normally fails on the factory shafts with 35's or 33's and lockers are the non-hardened ears that hold the u-joints. They stretch or break which releases the u-joint to spin/break up. Especially if you're giving it too much gas when the steering wheel is cranked hard over which is when the stress on the ears/u-joints is maximum. Going with alloy shafts like from Revolution Gear gives you hardened ears which pretty much stops u-joint breakages.
RiverDawg24
TJ Enthusiast
What about milling stock shaft ears for full circle c-clips? In your opinion, is there any benefit to doing this?
No, that's not the issue. The material the stock shaft's ears are formed from are carbon steel and not hardened/not strong enough to keep their grip on the u-joint bearing caps. Full-circle clips are a nice addition to hardened shafts/ears.
RiverDawg24
TJ Enthusiast
So Next question...When dana 30 ears/u joints let loose do they spread out the knuckle? Destroy ball joints? spread out the inner C's?
I'm pondering if hardened shafts should be a preventative measure? or should they be a wait and see if the wheeling style, terrain type, etc will actual break a stock dana 30 shaft on 35's.
Ive seen it destroy ball joints on a trail. Wasnt a pretty sight and the guy was a good hour drive away from any sort of help short of us who just happened to come across it.
Jerry I saw that very thing happen in exactly that set of circumstances right in front of my face once, it's ugly
It's unlikely to go beyond a broken or stretched out ear.
This is what happened to one of my previous TJ's stock ears running 35" tires, it snapped.
The second time we saw him, I happened to be watching the u joint when it popped out the cap. Chances are good that he would have kept going and ripped out his ball joints like he did the year before.
What do you do when you have a stuck bolt or nut? Do you get a shorter handle or longer handle to increase or decrease the leverage? Rhetorical but we all get longer levers to put the mechanical advantage in our favor. So regardless of mass, weight, etc. the problem is the leverage is in favor of the tire, nothing else.
Nope, while that is one way to have the problem, the same issue can be had with any size tire and it is not inherent to a larger versus smaller tire. We break stuff all the time at 0 miles per hour.
Broken joints, ears, etc, do not in and of themselves tear up ball joints. What tears up ball joints is spinning the axle shaft after the yokes are not attached to each other. The yokes bypass and the spinning yoke hits the top of the stub yoke and blows the knuckle off the ball joints by forcing it down. The damage comes from the weight of the vehicle landing back on the knuckle when it is not lined up or at an axle which crashes the ball joints into the inner C and does bad things. We have had folks push the knuckle off and stop soon enough that all we did was jack it up and beat them back into the holes.