aluminum vs. steel

which is harder on bearings (front and rear) steel wheels with stock backspacing and 32" swampers or 3.25 " backspaced aluminum rims and the same tires. i have some rubbing and would like to get rid of it but not at the expense of trashing my bearings .( with too much backspacing) plus i wonder if tires would hit right where i trimmed fenders. d-30 and d-35. i have wheeled these stock axles for 5 years and have had no problems so far, lockers, lift, etc., etc. on an XJ. any experiance would appreciated. (i believe stock b.s. is 5.25)

Thinking about a response, I am wondering does the backspacing really affect bearing life? I can see an argument for spacers beucase it moves the wheel mounting surface farther away, but does the backspacing really change the forces on the wheel bearing? My thought is it doesn't. I would think the heavier tire/wheel combo will put the most stress on the bearings regardless of the backspacing.

Eric@OA said:

I would think the heavier tire/wheel combo will put the most stress on the bearings regardless of the backspacing.

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I have to agree with Eric@OA but then it also depends on which type of steel and aluminum the rims were made of. If it were me i would go with the steel.

Spacers do significantly increase the loads on the bearings due to the longer lever arm. Now, that being said, Bearings are not all that prone to failure as long as lubrication is maintained. the highest point of stress would normally be when the axle is tipped to the point where all the oil is down on the bearing. The failure point would be the axle, not the bearing. In my years of wheeling, I have never seen an axle failure that I could attribute to a spacer unless the axle was seriously compromised before. Now if you are talking a spacer well over an inch in thickness, I might start to think about it, but the normal spacers around an inch in thickness don't seem to cause too many problems. The key is to keep them tight. Loctite on the holding lugs and keep the wheels tight.

A one inch spacer puts no more load on the bearings and axle than a rim with a 1" difference in back spacing and people have run those for decades.

i don't know much about backspacing, but your question provoked some thought and this is what i decided:
aluminum and steel = no difference. what makes the difference is where the weight of the vehicle puts pressure on the bearings vs the pressure of the ground in relation to the wheels.
i guess an example of this would be to get a broom stick and hang a weight from it. when the weight is close to your hands it seems light. move the weight to the end of the stick and it will seem heavier. now try to swing the stick in both positions (weight close to you and weight away from you).
in theory the increased pressure in your wrists is similar to the increased forces on the bearings from spacing. friends tell me that on a vehicle its not so simple, and bearing wear isn't noticeable, but IMHO thats (spacing) extra wear even if small amounts... but for bigger wheels is seems like a trade off alot of guys are willing to accept.
above:longer lever arm...thats what i mean by the broomstcik weight scenario.

first of it your going to be wheeling hard i would def think about steel it can be bent back to shape and hold air after much abuse because it is more flexible than aluminum, aluminum does not flex much making it more prone to cracking and letting the air leak out. i know of a few people that regret getting those nice looking alum wheels because they can't handle abuse.

that being said the best for the bearing is to have the wheel mounting surface (WMS) in the middle of the tire putting all the load up an down on the bearing not trying to bend it like a lever. everyone warned me about getting less backspacing on my wheels (less backspacing=more the tire sticks out) but when i look at my stock wheels and my new wheels with 3.75" BS it seems like the 3.75" BS ones have the WMS more tward the center of the rim actually making it better for the bearing.

Aluminum or steel will make no difference on the load in the bearings if the backspacing is the same because its unsprung weight. Factory backspacing trys to keep the center of the tire centered on the the steering knuckle pivot axis as it makes steering easier and produced less force and hence less wear on the steering components. Also having more backspacing has a greater effect on the life of your ball joints because they are what directly resist the forces applied when the backspacing places the center of the tire away from the pivot axis of the axle steering knuckle.

thanks for the input guys. i was just wondering about the extra leverage from the wheel being further out from the end of the axles, have heard less backspacing(numerically) can cause extra strain? i kind of figured any less weight would be good .(in general) since tires are at the end of the drivetrain it would also be easier on power needs with less weight.