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**DONOTDELETE** 01-07-2002 05:22 PM

How do big tires stress axles?
I've been told that the weight of large tires puts more stress on an axle. Seems reasonable. Does the size of the tire (regardless of weight) add stress to the axle? I'm no physics expert but it seems to me that a wider tire would put more stress, but I'm not sure about taller.

I bought my jeep from a guy who had just finished lifting it, installing 1 piece axles/detroit locker and 35" tires. I didn't want 35" tires with the stock model 30 in front and bought it without the tires. I later put 33" tires and steel rims on the jeep. Before he sold 35" tires to someone else I had a chance to compare them to my 33" tires. The 35's were mounted on aluminum rims and my 33's were on steel rims. The 33"s were heavier than the 35's. If weight were the only issue, the 35's would be easier on the axle than my 33's. It seems to me that a wider (say 14.50") 35" tire would get more leverage on the axle (the edge of the tire is further from the axle)and would there fore put more stress on the axle. But why would a 35/12.50 tire put more stress on an axle than a 33/12.50 tire (assuming the 35" tire/rim combo is lighter)?

My jeep has 4.56 gears and an auto. As a daily driver I think I will either need an overdrive tranny, or bigger tires... The tires are cheaper if I don't have to do the axles and a bunch of other mods


82 CJ-7, dead 258, auto, 33's, 4.56 gears, detroit locker (rear) true trac (front)

surveyboy 01-07-2002 05:36 PM

Re: How do big tires stress axles?
TR would know more, but If you wheel is offset correctly, the width of the tire won't directly stress it. the rotation of the large amount of weight is what can kill it. if the tire was equal weight(35 or 33) they would both stress about the same. the heavier the weight is farther out the more rotating stress that is there.

CJ7JeepOffRoad 01-07-2002 05:39 PM

Re: How do big tires stress axles?
Think of it like this:
If you have one 10" and one 20" long ratchet, which one would twist off a 3/8 bolt faster/easyer? It's all about leverage!

Rodney C

YJAroundTheWorld 01-07-2002 05:39 PM

Re: How do big tires stress axles?
Well, Im no physics expert either, but I am going to take a guess as well.
I would have to say that just as a wider tire puts more stress on your axle, so would a taller tire. The leverage with a taller tire when say, lifted in the air would be more stress then a tire that is not as tall.
Imagine the end of the axle being point "a". Whereever point "b" is, (B being far side of width of tire, or farthest part of tire away from where point a is)is going to be the most stress-full part of the tire. whether that is width or heighth.

Then again, I could also be talking our of my @$$.
So....take it as you see it.

94 ZJ - Work Commuter.
89 FSJ - 6-inch Rustys on the way!
87 YJ - 5' of lift, Xterrains 33's. ARB Snorkel.
48 CJ2A - Lawn Sculpture.
Square-Eyed Jeeps Unite!!!!

Infernozx 01-07-2002 05:48 PM

Re: How do big tires stress axles?
I would imagine torque is the big killer.

Your trying to turn bigger (fulcrum (center of wheel)is also the energy point, and is further from the load (road)) therefore there's alot of stress on the axle shafts.

As well as having a larger diamiter ( longer distance from the pivot point to the road) you have a heavier tire to spin.
Therefore as the end of the axle shaft (part in the differential) tries to wind up and spin, the end on the wheel resists, and the metal twists and torques.

**DONOTDELETE** 01-07-2002 06:28 PM

Re: How do big tires stress axles?

All these answers seem to make sense. I wonder what the formula is for figuring this out. I've seen lots of advice on this board (and elsewhere) indicating that 35s' will break a model 30, but 33's are marginally okay. I guess the real answer is that it depends on the width and weight of the tires as well as the height. A 33/14.50 tire on steel rims might put more stress on the axle shaft than a 35/10.50 on aluminum rims. There must be a math formula for this. Does anybody have that "automath" book. Maybe it has the answer.


82 CJ-7, dead 258, auto, 33's, 4.56 gears, detroit locker (rear) true trac (front)

jeepgod 01-07-2002 06:47 PM

Re: How do big tires stress axles?
for what you are talking about.. "breaking a d30".. wider is worse.. than taller.. and a very large factor is wieght.. since it is rotating.. per say.. like you said.. you have 33x12.5 on steel rims.. vs 35x12.5 on aluminum rims.. 33's wieghing more than the 35's.. i would say the 33's would kill your axle sooner.. since you are not only spinning that wieght.. but when wheeling.. you are appling torque to said wieght.. which will multiply the torque..
this is just my thoughts.. remember.. i am a Marine.. not a physics major either.. but its how i am currently looking at things..
in the wider department.. it also has alot to do with your backspacing.. is said width out away from the axle.. or is it behind (inboard) of the mounting surface.. this also determines in the torque or leverage on the axle..
confused?... i might be.. [img]/wwwthreads_images/icons/crazy.gif[/img]

<font color=orange>If you are allergic to lead, it is best to avoid a war zone</font color=orange>

my97TJ 01-07-2002 07:08 PM

Re: How do big tires stress axles?
ALL of the factors below will effect the durablity of any axle:

regular or alloy shafts
tire diameter
tire width
tire weight
wheel weight
engine horsepower/torque
trans gearing
trans case gearing
diff gearing
how hard the driver is on their rig
the difficulty of the terrain

As you can see, there are way to many factors involved to come up with any kind of formula.

"It's a Jeep thing... and I DO understand"

Seth867 01-07-2002 08:44 PM

Re: How do big tires stress axles?
Please take note that this I have come up with this conlcusion after drinking a few beers as to remember my mechanics and dynamics courses. As far as axial load would go a wider tire would put less strain on an axle. Think about it this way. There would be less of a strain on the axle because the wider tire would not have as good of traction as the thinner. This is one factor. However I don't believe it to be a large one except for maybe in a side ways sliding motion. And even then in a side ways sliding motion a larger tire would put more torque on an axle which is a stress because there is a larger distance to the center of the shaft opposed to the smaller tire which would have a shorter distance. The only reason a wider tire would make a difference is if it changed the over all weight SIGNIFICANTLY. It makes sense to me, through centrifical force and the idea of torque mostly, that the over all tire size would make the axle a little easier to break. It still has a lot of the weight as the heavier 33 but the length to the outside of the tire is the determining factor, in my opinion.

3jeepguy 01-07-2002 10:23 PM

Re: How do big tires stress axles?
its not the size of the tire persay it is what is done with the rig bigger tires usually mean harder wheeling which leads to needing a locker wich leads to i need a bigger motor which leads to broken parts we all call it jeep fever and once ya got it you cant go back but to answer your question the more unsprung weight you have (anything not held up by the springs like tires and wheels ) the more leverage you have now if ya drive like an 80 year old woman than you could have 44 inch tires with a dana 27 but if ya drive it like ya stole it 35 inch tires could break a dana 60

jeep the first 4 wheel drive the only 4 wheel drive

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