A hypothetical...

The consensus for appropriate backspacing on aftermarket wheels, on here, is 4.5". Stock is 6.25", IIRC. Do we automatically assume the preferred 4.5" backspacing is for a 9" wide wheel or are you guys keen to the same backspacing on anything from 8" wide to 10" wide? The reason why I ask is... well... below, beware of the thought process:

When looking at the wheel itself, you want it to be as balanced as possible. Perfect measurable balance occurs when the backspace equals one-half of the overall wheel width. So, for a 8.5" wide wheel (I am intentionally not choosing a 9" wide wheel for the sake of this hypothesis)... the median backspace would be 4.25". Given that more material (the face of the wheel, where the hub mounts) would be at the front of the wheel... a 4.25" backspace on a 8.5" wheel would place extra weight (not necessarily nominal given the weight of the typical wheel) on the front of the wheel. This, of course, would transfer to the hub... and then axle. Wouldn't you want to offset this by cheating to the backside of the wheel, i.e. On an 8.5" wide wheel, choosing a 4" backspace or maybe a 3.75" backspace. This theory is personified when you consider a 4.5" backspace on a 10" wide wheel... as the load (extra weight) shifts to the backside of the wheel.

I am not entirely retarded and understand the elements involved, I also understand the premise of wheel balancing and weights. I'm just thinking about how to mitigate the use of weights and how to place as little extra weight/load on the hub/axle. In the end, it really seems marginal and not really worth the energy I have put into thinking about this (and typing this thread), but, needless to say, I'm flexing my brain this morning. :brain flare:

I'd draw a picture to help explain this, but I suck at drawing. My forte is words... so hopefully I explained this hypothesis thoroughly (enough). So, if I missed something in my drivel, above, ask away.

Best,

JB

 

There may be merit to your thinking on pavement but offroad you don't know where the load is going to be applied across the tread of the tire. In fact, it will probably wander across the tread as the terrain changes.

The main criteria for choosing backspacing is to make it so the tire doesn't rub the vehicle. The components are designed to handle the load offsets. Otherwise, the designers would have followed your suggestion when closing the back spacing on the factory wheels. They could have easily centered the hub and made up the distance in axle length.

 

...there are a lot of assumptions in my crazy-ass theory, so yes you are right. On a flat, hard surface the hypothesis makes sense. Truth is, though, our vehicles spend more time on a flat, hard surface... so wouldn't you want to consider that when making a wheel purchase? I'm taking an overly simplistic view here.

As for eliminating rubbing and, also, the associated aesthetics, I grasp that. Again, just thinking out loud and waxing poetic.

 

Perfectly centered wheels will, of course, rub if much wider than stock. So you have to have them project beyond the end of the axel to avoid this. I am curious about how the Jeep axle and bearings handle this additional stress (torque). Does the Jeep have unit bearings (I hear they wear out quickly if wheel is not centered), or the old-fashioned (and maybe more rugged) hub bearings?

 

Not suspension rubbing, but I would open up potential stock fender/bumper rub. The stock wheel (I'm using my vehicle as an example) is 17" x 7.5", supposedly the backspacing on the stock wheel is 6.25". If I go to a 17" x 8.5" wheel and go with a 4.25" backspacing ("perfectly centered" as 8.5" / 2 = 4.25") I am actually creating 3" of movement away from mounting point on the hub -- 2" less back space plus 1" of additional wheel width. Obviously, if you are going to a wider wheel and a taller tire, you want to pay attention to potential rubbing... I'm just specifying my hypothesis to weight distribution at the mounting point on the hub.

With the potential additional weight of the wheel and a larger tire, considering weight distribution on the hub/axle has an advantage. I imagine, again, that it's minimal, but I still want to talk it out.

 

Awesome, good to know!

 

In all of my searching on various topics on this forum, I've grown to love it when you respond. Your comments include a level of detail and analysis that makes my pants tight.

I know I am over-thinking it, my contention was more an exercise of theory and less about an actual application. That being said, my intended setup is 315-70/17 on 4.25" backspaced 17" x 8.5" and I am not particularly worried about the setup or my hypothesis/theory in the original post. It's Friday and I felt like exercising the old noggin.

Thanks.