Differentials and axles differences strengths

[gjptennis]

What is OD? I'm thinking contact patch, but obviously the abbrev don't match...

Outer Diamter

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[zuke]

Weight is not the issue--the larger the OD, the harder it will be to break traction and therefore the force is applied to the axle (housing and shafts) instead.

While I'll agree that OD is a big factor, Weight is just as much or more of a factor, especially in the rocks, as the inertia of the added weight will have a much bigger effect on shock loading, which is when things break. The added weight will also have a much bigger effect on the general wear and tear of suspension components like ball joints and arm bushings.

The added OD should make very little difference to the contact patch size if tire pressures are adjusted properly, and therefor little change to traction, added width might increase it, but again proper pressures will compensate...

People shouldn't disregard either factor when making tire choices.

 

[userdude]

While I'll agree that OD is a big factor, Weight is just as much or more of a factor, especially in the rocks, as the inertia of the added weight will have a much bigger effect on shock loading, which is when things break. The added weight will also have a much bigger effect on the general wear and tear of suspension components like ball joints and arm bushings.

The added OD should make very little difference to the contact patch size if tire pressures are adjusted properly, and therefor little change to traction, added width might increase it, but again proper pressures will compensate...

People shouldn't disregard either factor when making tire choices.

Do y'all think this changes any with the portal regear?

 

[Fordified1]

Thanks moderator for moving this to the correct forum. I looked but couldn’t find it.

All good info above, thanks y’all.

Reading the other thread someone linked earlier, it speculates whether the non sas front diff is up to the task running 35’s. I have to say this probably depends a LOT on how and where you wheel and how easy on parts the driver is. Anyone who has been off-roading much has that one buddy who breaks something every time they go out. A smooth driver will be way easier on parts. Most of the times I’ve broken driveline parts or seen others break, it was because of bouncing or wheel hop. Loading and unloading the driveline when it bounces is EXTREMELY hard on parts. Also applying full power when turning full lock is really hard on CV joints.
I’ve always done more with less and haven’t broken a lot of parts, but there’s always that time when peer pressure and bragging rights take over lol.
I broke the front diff on my RZR crawler last time I went out attempting to do an obstacle I knew I should have backed out of. I did make it but had to bounce up it and ring gear deflection broke the cast aluminum diff housing. A new billet housed diff is $1900.

 

[CarbonSteel]

While I'll agree that OD is a big factor, Weight is just as much or more of a factor, especially in the rocks, as the inertia of the added weight will have a much bigger effect on shock loading, which is when things break. The added weight will also have a much bigger effect on the general wear and tear of suspension components like ball joints and arm bushings.

The added OD should make very little difference to the contact patch size if tire pressures are adjusted properly, and therefor little change to traction, added width might increase it, but again proper pressures will compensate...

People shouldn't disregard either factor when making tire choices.

While I agree that weight differences between can cause additional wear LONG TERM on the suspension, the one thing that can break an axle is the larger tire is more difficult or will not spin at all and the force is transferred directly to the axle due to the traction that is gained from a larger tire.

Bouncing in rocks breaks things, when the lockers are engaged--but I have seen MANY more axle breaks due to larger tires versus heavier tires. You can move from a Load Range C to a Load Range E in the same size tire that will not have the potential to break something versus moving from a 33" Load Range E to a 37" Load Range C tire despite the weight difference being minimal or even less in the 37" versus the 33".

The twisting motion and torque that is transferred through the axle has to go somewhere and if the traction of the tire does not break, there is only one place for it to go.

 

[Tech Tim]

Do y'all think this changes any with the portal regear?

Yes, big time. Having gearing out at the wheel hubs cuts down the load the diff sees.

 

[zuke]

While I agree that weight differences between can cause additional wear LONG TERM on the suspension, the one thing that can break an axle is the larger tire is more difficult or will not spin at all and the force is transferred directly to the axle due to the traction that is gained from a larger tire.

Bouncing in rocks breaks things, when the lockers are engaged--but I have seen MANY more axle breaks due to larger tires versus heavier tires. You can move from a Load Range C to a Load Range E in the same size tire that will not have the potential to break something versus moving from a 33" Load Range E to a 37" Load Range C tire despite the weight difference being minimal or even less in the 37" versus the 33".

The twisting motion and torque that is transferred through the axle has to go somewhere and if the traction of the tire does not break, there is only one place for it to go.

We actually agree completely on what causes a break, putting a wheel in a bind or shock loading components (bouncing).

I have nothing to disprove what you're saying, I've seen a lot broken axles too, but haven't kept records of weights versus diameters.

I will however continue to believe that contact patch size, inertia and tire compound matter a lot more to breaking traction then tire diameter. Going from a 35" to a 37" is a 1" increase in a 16.5" lever/torque vector. Certainly a concern, but I don't believe it's as big a factor as you do.

 

[CarbonSteel]

We actually agree completely on what causes a break, putting a wheel in a bind or shock loading components (bouncing).

I have nothing to disprove what you're saying, I've seen a lot broken axles too, but haven't kept records of weights versus diameters.

I will however continue to believe that contact patch size, inertia and tire compound matter a lot more to breaking traction then tire diameter. Going from a 35" to a 37" is a 1" increase in a 16.5" lever/torque vector. Certainly a concern, but I don't believe it's as big a factor as you do.

I don't disagree, but there are plenty of axles broken with 37's versus 35's and not all of the 37's were heavier. BFG KO2's for example in Load Range C are typically lighter than 35's and only slightly heavier than 33's.

For example (I owned these tires and weighed them so I know exactly what they weigh):

61.3 Pounds = Falken Wildpeak 285/70/17 LRC
65.4 Pounds = Kanati Trail Hogs 315/70/17 LRE
64.7 Pounds = BFG KO2 37x12.5x17 LRC

Unless you are moving from a 33" LRC to a 37" LRE, the weight difference is not enough to matter. The lever despite how small it seems that you are referring to is exactly the issue when the tire cannot rotate and torque continues to be applied. Jam a 37" tire in the rocks versus a 33" tire and I will bet you a steak dinner the 33 will turn before the 37 will.

 

[swooshdave]

Jam a 37" tire in the rocks versus a 33" tire and I will bet you a steak dinner the 33 will turn before the 37 will.

Another way to look at it is to use the above scenario and then pretend the axle is made out of a chopstick.

I agree the 37 will break the stick first.

But I also suspect that the person who can break an axle with 37s will also break an axle with 33s.

 

[zuke]

I don't disagree, but there are plenty of axles broken with 37's versus 35's and not all of the 37's were heavier. BFG KO2's for example in Load Range C are typically lighter than 35's and only slightly heavier than 33's.

For example (I owned these tires and weighed them so I know exactly what they weigh):

61.3 Pounds = Falken Wildpeak 285/70/17 LRC
65.4 Pounds = Kanati Trail Hogs 315/70/17 LRE
64.7 Pounds = BFG KO2 37x12.5x17 LRC

Unless you are moving from a 33" LRC to a 37" LRE, the weight difference is not enough to matter. The lever despite how small it seems that you are referring to is exactly the issue when the tire cannot rotate and torque continues to be applied. Jam a 37" tire in the rocks versus a 33" tire and I will bet you a steak dinner the 33 will turn before the 37 will.

I'll take that bet! If we could make everything else equal, Tire Weight, Contact Patch, Tire Compound, and angle of bind, The 37" will break traction first, because of the longer lever action....

And if everything else is equal, as above, I agree that if the traction is too much to overcome, the 37" WILL break something first.

I Also believe that if two 33" tires with a 20 pound difference bounce on a locked axle, the heavier tire will break the axle first.

I don't think we disagree on anything, I just think you're over estimating the effect of OD on traction, and underestimating the effect of weight on shock loads. It's the amount of friction that matters, and many factors go into that beyond the OD...

 

[CarbonSteel]

I'll take that bet! If we could make everything else equal, Tire Weight, Contact Patch, Tire Compound, and angle of bind, The 37" will break traction first, because of the longer lever action....

And if everything else is equal, as above, I agree that if the traction is too much to overcome, the 37" WILL break something first.

I Also believe that if two 33" tires with a 20 pound difference bounce on a locked axle, the heavier tire will break the axle first.

I don't think we disagree on anything, I just think you're over estimating the effect of OD on traction, and underestimating the effect of weight on shock loads. It's the amount of friction that matters, and many factors go into that beyond the OD...

You are looking at the lever from the wrong direction. It is the inverse from the axle perspective since it turns the tire and the tire does not turn it.

Think about how larger rotors stop a vehicle better than smaller--it's because it's harder for the axle to turn. The same situation applies to larger tires.

 

[zuke]

You are looking at the lever from the wrong direction. It is the inverse from the axle perspective since it turns the tire and the tire does not turn it.

Ummm.... Are you trying to prove my point for me? Yes the lever is a line from the hub to the contact patch with the Hub trying to move the contact patch, There for the mechanical advantage of the lever is given to the hub, and it has a better chance of breaking traction with a 17.5" lever than a 16.5" lever...

I think we're dragging this thread way off track though, maybe we should start a new thread for this subject if you think we ever have a chance of agreeing?

 

[CarbonSteel]

Ummm.... Are you trying to prove my point for me? Yes the lever is a line from the hub to the contact patch with the Hub trying to move the contact patch, There for the mechanical advantage of the lever is given to the hub, and it has a better chance of breaking traction with a 17.5" lever than a 16.5" lever...

I think we're dragging this thread way off track though, maybe we should start a new thread for this subject if you think we ever have a chance of agreeing?

No, I'm definitely not proving your point. Not sure how to explain it any better. The lever is reversed for the axle. If you turn the tire, then yes, a 37 turns the axle easier than a 33, but that is not what happens.

It is harder to break traction on a 37" tire than a 33". If what you are saying is true, you would never have to regear when increasing tire size and it would be easier to smoke 37" tires on dry pavement versus a 33".

We both know that is not the case.

 

[Fordified1]

Ummm.... Are you trying to prove my point for me? Yes the lever is a line from the hub to the contact patch with the Hub trying to move the contact patch, There for the mechanical advantage of the lever is given to the hub, and it has a better chance of breaking traction with a 17.5" lever than a 16.5" lever...

I think we're dragging this thread way off track though, maybe we should start a new thread for this subject if you think we ever have a chance of agreeing?

You have it backwards sorry. Swing a bat from the very end then choke up on it. Which is easier?

 

[zuke]

No, I'm definitely not proving your point. Not sure how to explain it any better. The lever is reversed for the axle. If you turn the tire, then yes, a 37 turns the axle easier than a 33, but that is not what happens.

It is harder to break traction on a 37" tire than a 33". If what you are saying is true, you would never have to regear when increasing tire size and it would be easier to smoke 37" tires on dry pavement versus a 33".

We both know that is not the case.

You have it backwards sorry. Swing a bat from the very end then choke up on it. Which is easier?

Hmmm, yup, you guys are both right, I got that point backwards. I owe @CarbonSteel a steak dinner...

However I'm not sure how we arrived at this point. Where we started was with @CarbonSteel saying the OD was the only factor that matters, and me saying, no, other things matter as much or more, and I still stand by that.

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