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Discussion Starter #1
A bit of a physics question?
A 35 inch Toyo Mt weight about 80LBS each
A 37 inch Cooper STT Pro weigh about 82 LBS each

I wanted to run some 37 inch tires but am worried about the wear and tear and increased chance of bending my D44 front axle. Also worried about DD qualities. Is there a big difference in running a 35 as a daily driver vs 37? AND is it the weight of the tires that causes the issue or the height.

Any thoughts.

Thanks
 

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Weight and rotational mass and rotational inertia.
More weight on a longer fulcrum takes more energy to accelerate and stop.
So a lighter 37 might still need more energy to speed up or slow down because the lever (distance to center or fulcrum) is longer.
Wish I paid more attention to archemdies in skool, but that's as deep as I go.
As for bending axles...I dunno.
 

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Discussion Starter #3
Thank you I appreciate it. That is what I am finding. I think the static weight has more to do with bending the housing. I think I am going to stick with my 35s.

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Thank you I appreciate it. That is what I am finding. I think the static weight has more to do with bending the housing. I think I am going to stick with my 35s.

Thanks
Wait a minute. Axles don't just up and bend because you go from a 35 to a 37 inch tire. You are reading too many forums and too many posts by people who are repeating what they read somewhere.

Wheeling 37s on stock D44 housings is VERY doable. I have been doing it for 8 years now, on hard ass trails in CO and Moab. Rock crawling does not bend axles. But that myth is alive and well on the internet.

What bends D44 housings, especially the front housing is high speeds on trails and then hitting a dip or gulley. If the front end gets airborne or the springs get compressed to the bump stops, that is when you can bend the tubes. (Have never actually seen a bent C. Someone once asked for anyone to post up a picture of a bent C - no one did.) If you keep your speeds at a moderate level, you can run 37s on stock D44s for years and years.

Several years ago, I got into a food fight on this topic on another forum. Dynatrac, of all people, jumped in and agreed with me. I think the Dynatrac guy said it best. (I am paraphrasing.) "You can run 37s on stock D44 axles as long as you have reasonable expectations." Reasonable expectations. Can you get hung up in the rocks and use full throttle massive wheel spin as a "technique"? Not hardly. Can you pull pre-runner speeds thru whoops and washes with 37s and stock axles. Not gonna be a good day. Can you wheel hard trails without failures using good lines and knowing where the limits are - all damn day.

So stop believing all that BS about 37 inch tires bending D44 axles just by driving past the Discount Tire store!! If you want to run 37s, then run 37s. Just wheel appropriately. Stop believing shit people just post because they can type. I think too many people have fallen into the "37s require trusses, sleeves, gussets" because they believed it and spent the money on that stuff.

Now, I am not saying that trusses and sleeves are not necessary in all cases. That too is not true. They have there place and usefulness. Its just a lot further up the degree of abuse than most people are reading into it.

Flame away........................

PS I think a lot of people think they bent their Cs because they wheeled their jeep and then took it in for an alignment. They found out one side or even both where out of spec for camber. Well I have news for you. Both of my JKs where out of spec before ever setting a tire off pavement. My current one was out of spec with 200 miles on the odometer and completely stock, no dirt. They come from the damn factory out of spec!!! So its not bent Cs causing camber issues - its piss poor quality control at Fiat (or whoever welds the damn axle housings together).
 

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As said before, I bent my front 44 with 37's. I dropped off a 3 foot ledge harder than intended. Def not an alignment issue. Nothing to do with the tire size. Nucleophile is right about the housings.
 

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Nucleophile speaks truth. I don't have the history that he does, but I have about 30,000 miles on 37s on stock axles (other than a regear) and have had no catastrophic failures. What I have had is a completely worn out steering system (other than the box itself) -- tie rod, drag link, ball joints, track bar, and frame side track bar bracket. I've also slightly bent a rear axle shaft flange, and I know where it happened; it was on Fordyce Creek trail during Sierra Trek 2014. Wasn't bad, just about .025" runout, but that was enough to get a telltale squeak, squeak, squeak from the rear brakes.

So, to your question about 35s vs. 37s, let's think practically as well as mathematically. (Disclaimer: for all you engineers out there, I'm going to oversimplify this for the sake of illustration, rather than pulling out the formulas for precise calculations, so don't jump all over me and tell me how wrong my calculations are.) A 37 will create a 1" longer lever arm than a 35. (37-35=2; 2/2=1). For purposes of illustration, say your 80 lb. 35 has all its weight concentrated at the end of that lever. You can figure the torque on the axle shaft like this: 80 lbs. * 17.5" = 1400 in.-lbs, or 116 2/3 ft.-lbs. of torque. By the same token, your 82 lb. 37 will exert: 82 lbs. * 18.5" = 1517 in.-lbs., or about 126.5 ft.-lbs. of torque. So what's 10 ft.-lbs. of torque among friends, or axle shafts, right? But understand that as the torque of actually driving the beast ramps up, and is multiplied through your low range gears, and lower-than-stock differential gears, you can begin to see those figures ramp up proportionally.

What about side loading? Here the weight of your tire/wheel combo becomes irrelevant. For ease of calculation, let's say your rig weighs 6,000 lbs. Now let's say that you have it on a 22.5* side camber. And for grins, let's say that all four points of contact with the ground are equally loaded. In practice, they won't be, but again, we're just illustrating here. This side loading will still generate torque (a moment of inertia), but instead of revolving around the axis of the shaft, this is going to create a bending moment around the last point of contact between the housing and the shaft (the bearing), and is going to manifest itself in a bent flange. So here goes: 6000 lbs. / 4 [proportioned for the slope] = 1500 lbs of side loading. 1500 lbs. / 4 tires equally side loaded = 375 lbs. side loading per wheel/tire. 375 lbs. * 17.5" [the lever arm for your 35] = 6462.5 in.-lbs., or almost 587 ft.-lbs of torque trying to bend that flange, and 375 lbs. * 18.5" [the lever arm for your 37] = 6937.5 in.-lbs., or a little over 578 ft.-lbs of bending moment. Again, doesn't seem like much difference, but remember that as you increase that side loading with things like unbalanced loading, dynamic loading, steering input, higher CG, etc., the worst-case scenario can dramatically increase those figures.

Now having said all that, I'm going to go back to what Nucleophile suggested: that the longevity of your equipment has far more to do with how you treat it, than the difference between 35s and 37s -- just like the risk of rollover in a stock, pre-1986 CJ7, had far more to do with how idiots drove them than it did with any supposedly inherent design flaws (those of you old enough will remember. This is why we got those goofy looking "wide track" CJs). I have not babied my JKU, but I have been reasonably cautious in choosing lines while running some very challenging trails, and I don't take the approach that the skinny pedal is the solution to every problem. I would anticipate that if you take a similar approach, you should realize similar results. There is no doubt that 35s will be easier on your equipment. The question is whether that difference is significant. In my opinion, the answer is no, if you approach your wheeling like I do. Others may disagree.
 

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I'm not going to get mathematical or scientific, but I have some basic real world observations.

I went from 35" Fierce radials to 37" BFG muds and could barely tell a difference, mileage or performance wise. Maybe 1/2mpg and the shift points were a little different(I did change tire size with my procal).

Then I went to 37" Trepador bias plies...

I don't have exact weights but they are clearly MUCH heavier and have a lot more drag. They are a good bit taller than the BFGs also...

I have lost about 1 1/2 to 2 mpg and feel like I am pulling a trailer now. So I can imagine that has an effect on durability as well. Not really complaining because these tires are pretty indestructible and I go a lotta remote places, sometimes alone.

I should add that I beat my Jeep at high speeds with the 35"s out here in the desert with no adverse effects. I did truss and brace it with the 37"s because I felt lucky to still have relatively straight axles after all the abuse up to that point.
 

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I have to chime in on this subject as well and all set to have smoke coming off my fingers typing as fast as I could until Nucleophile said it perfectly. My 2007 Rubi has the same experience with 37s and Dana 44 axles on my daily driver and weekend trail runs.

When I decided to move up from 35s I too almost got caught up in the 'forum fears' thinking I needed trusses, dana 60s, and RCV axles. This is really not true. I might eventually beef up my Dana 44 housing because I do at rare times like to baja but that will come after everything else is said and done. I had to take a step back and say to each potential mod, "Is this worth it?". Some guys will harass me for going with a Spicer 1310 u-joint. To me I like a fuse in the system. I can easily change a u-joint on the trail...ring and pinion (will be your weak link of you put in unbreakable axles) are not easily changed.

One of my friends said it best "$500 to repair it, $2000 to prevent it."

I did however, move up to a 1-ton style steering because of the added stress and wearing out two sets of stock tie rods and drag links with 35s and only 40k miles. This was a great mod and now I drive straight down the freeway and bash rocks yet still steering with only a light touch.
 

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Running 37's as a daily driver is dumb but lots of people do it. Only common sense will tell you it may create more problems with maintenance and cost you fuel economy. And yes both weight and size are harder on your jeep.
 

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. . . 37" Trepador bias plies...

I don't have exact weights but they are clearly MUCH heavier and have a lot more drag. They are a good bit taller than the BFGs also...
When radial tires first came out, that was one of their major selling points: lower rolling resistance than an equivalent bias ply, and thus better MPG, which was a pretty huge selling point during the Arab Oil Embargo.

The Treps probably are significantly heavier, and together with the larger diameter that will create a greater "flywheel effect," or in other words, greater inertia. That makes starting from a dead stop much more like driving in sand, or as you said, towing a trailer. Add in the increased rolling resistance of a bias ply, aggressive tread, and I'm not surprised you've noticed the differences you have. No real way to prove it, but I'd be willing to bet that if you'd gone to a 35" bias ply Trep it would have felt more sluggish and offered lower MPGs than your 37" BFG (radial) MTs.
 

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Running 37's as a daily driver is dumb but lots of people do it. Only common sense will tell you it may create more problems with maintenance and cost you fuel economy. And yes both weight and size are harder on your jeep.
Please explain your theory.

My personal fact: Fuel mileage is still within 1 mpg vs 35" tires. Simple re-program with my AEV and shift points were back to normal.
 

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Please explain your theory.

My personal fact: Fuel mileage is still within 1 mpg vs 35" tires. Simple re-program with my AEV and shift points were back to normal.
He does not need to explain the facts as they are well-stated in prior posts in this thread. And, nothing in your personal 'fact' changes this information.
 

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Discussion Starter #13
I appreciate all the feedback. I really like this forum! Nucleophile you make some great points and so to the other posts. There are folks I look to specifically for answers on this forum and I find it is always good to check my thinking on items. I think for the over-landing type wheeling we do here in Florida 35 is more than enough. I would much rather put money towards other items.

Appreciate it!
 

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He does not need to explain the facts as they are well-stated in prior posts in this thread. And, nothing in your personal 'fact' changes this information.
I'm sorry, who asked you?

I took this thread as an update the age old question and get a modern perspective. Don't like the fact many of us run 37s very successfully; don't care. Opinions are like....

The beauty about Jeeps is each to their own.
 

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Bigger tires do cost more to run. Rotational momentum/inertia is a fact, it takes more energy to change if there is more weight or leverage. (Ya...high school physics and watching Bill Nye don't make me an expert, feel free to correct)
Bigger dia. tires often have wider tread in contact with the ground ergo more friction to overcome. Also consider the flex in the tread pattern. Usually big tread flexes more = more energy to change overcome inertia. Gear ratio and shift points are not germain to the subject, all factors considered.
If you think your mileage is close to the same, cool. 9% more is still 9% more. In any case, was the op concerned about fuel? Or was it more wear and tear?
 

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Please explain your theory.

My personal fact: Fuel mileage is still within 1 mpg vs 35" tires. Simple re-program with my AEV and shift points were back to normal.
37's cost more, reduce mileage, increase vehicle drag (not that the jk is aerodynamic) , increase wear and tear on ball joints, unit bearings, steering linkages, and the steering pump. 37's require more to stop and can overheat the stock braking system if you do lots of stop and go's or drive up and down steep grades. Without proper gearing 37's will increase the strain on the entire drivetrain from the motor to the transmission to the driveshafts. For a daily driver the only gains is a bit more of a contact patch on the road and they look cool.

If you want to run 37's by all means do so, it your jeep but if comparing pro's and cons of long term use of them on a daily driver they make no sense at all.
 

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37's cost more, reduce mileage, increase vehicle drag (not that the jk is aerodynamic) , increase wear and tear on ball joints, unit bearings, steering linkages, and the steering pump. 37's require more to stop and can overheat the stock braking system if you do lots of stop and go's or drive up and down steep grades. Without proper gearing 37's will increase the strain on the entire drivetrain from the motor to the transmission to the driveshafts. For a daily driver the only gains is a bit more of a contact patch on the road and they look cool.

If you want to run 37's by all means do so, it your jeep but if comparing pro's and cons of long term use of them on a daily driver they make no sense at all.
And all good points. I like to hear other thoughts.

I also forgot to mention I upgraded the brake system and what a huge different that makes. This is extremely important.

I run 37s because I choose to, as you mentioned. It has also cost me A LOT more in suspension, gears, driveshafts, brakes, and steering.

Also like to be just a little bit different than the other 100s JKU's in Idaho.
 

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Well that went better than expected. Usually people will defend to the Nth degree their absolute insistence that a truss / sleeves / gussets / axle shafts are mandatory to run 37s. I have seen those statements even attributed to situations where the person asking does not take their jeep off road! Huh???

This forum is soooo much better than the shit-for-brains forums.
 
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