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Discussion Starter · #1 ·
Can any explain to me what a negative offset is? I've read it 10 xx in my 4x mags, but still don't quite get it. (I know - my IQ is smaller than my engine size!) /wwwthreads_images/icons/wink.gif/wwwthreads_images/icons/crazy.gif

Any comments (+ or -) on centerlines offroad. They're one piece alum... 15x8.5.. HT-II's

And why are beadlocks illegal in CA? just on the highway, right?

Jon-YJ94
a work in progress
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Discussion Starter · #2 ·
Offset is a pretty simple concept. Imagine looking at a wheel from the front, looking through the tire. The wheel has a certain width, for argument say it is ten inches wide. The offset refers to where the mounting face of the wheel(the flat surface that goes against the axle) is located in relationship to the center line of the wheel. So on a 10" wheel, the center line would be 5" in from the edge of the wheel. Negative offset is when the mounting surface moves closer to the inside of the wheel and positive offset is when the mounting surface moves toward the outside of the wheel. 1" of negative offset would put the mounting surface 1" toward the inside edge of the wheel from the centerline and 1" positive offset would put the mounting surface " toward the outside edge of the wheel from the centerline. Hope this helps and I explained it simple enough.

 

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instead of refering to it as negative/positive offset, i think about the amount of backspacing a wheel has.
take a look at a normal aftermarket 15 x 8" wagon wheel comparing it to a 15 x 10" one, you will see the mounting surface in relation to the inside rim edge is the same,(they hug the brake rotor/drum exactly the same) but the difference is 2" of extra wheel sticking out past your fender flares. they have the same backspacing but different offsets!
so wheels with less backspacing push the wheel out past the fender flares, and wheels with more backspacing move them in under the flares.
don't know about the centerline wheels,

ask CJDave about the beadlocks being illegal in CA, most likely the democratic/feminist/tree hugging/un-informed political decision making process in action!/wwwthreads_images/icons/smile.gif

3/4tonYJ
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Discussion Starter · #4 ·
Guess you guys should work for the 4x mags. Makes perfect sense now. Ok, what is "safe" backspacing/negative offset for YJ's?

Jon-YJ94
a work in progress
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I am thinking about getting a D60/D44 combo from a J20 (really I'd just like to find some elsewhere and fix up the J20...) Anyhow when these go on they will stick way the heck outside the Jeep and I was wondering what would be wrong about using a lot of positeve offset on a 15x10" (or maybe 15x12") wheel to pull the tires in some...?

Now if I pot a lot of negative offset on these axles what would I have?

a hummer!

 

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sorry but there ain't a simple # answer, it depends on wheel width, tire diameter & width, and leaf spring/steering component clearance.
YJ's came factory with more backspacing than most other common wheels, factory or aftermarket. (i'm not sure exactly but i think the 15 x 7" wheels have about 5" of backspacing) Now most aftermarket 15 x 8"(or 10") have 4" of backspacing, this is why you see so many YJ with aftermarket wheels/tires that stick out past the fender flares.
now you can buy(or build) wheels with custom backspacing but you must be careful, if they have to much backspacing the will contact the tierods, or hit the brake drums/rotors before the lug nuts actually seat the wheel. also when turning, the tire will rub on the leaf springs.
and also the less backspacing you have put more stress on the balljoints, wheel bearings etc..(it kind of adds some extra unwanted leverage)
so anyway i would look at some other YJ's noteing the size (tire & wheels) and asking if they rub while truning. my expereince with YJ's is a 15 x 8" rim with a 30" to 33" tire is a good size, and on a 15 x 10" rim 33" to 35" tire is good, (both 8 & 10" wheels having standard 4" of backspacing)
also i've used 15 x 7" (and have them for sale) wheels with 35" tires and i guar0wnTee they will rub when turning.

so my preferance is that the overall tire diameter needs to be decided before choosing the wheel. after the diameter is decided i get the wheel with the most backspacing possible without causing problems (touching anything). now other folks will say "wider is better" but not me.

sorry about the long post, i just got to typing/wwwthreads_images/icons/smile.gif

3/4tonYJ
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There is a lot more to the backspacing issue than just looking cool, clearances and stresses. If you
get too much offset either way, you can't get proper alignment. When I think of these types of things
I try to imagine it to extremes. Take a 10" wheel and imagine it with 2 feet of offset first positive and
then negative. See the problems? The front tires are too far away from the steering axis. Too far out
acts like negative toe in, too far in acts like positive toe in. The camber will be all wrong too. You
can wind up going down the street like that bad shopping cart at the Piggly Wiggly.


 

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I never really thought that backspacing has anything to do with alignment. now when your turning(with alot of backspacing) the tires will "scrub" putting alot of extra forces on the steering components. just like bigger tires do.
but i don't see how it can affect toe in/out, camber, or caster(the shopping cart thing) at all? (now more backspacing would exagerate problems due to worn bearings/balljoints/tierods that could show up like a camber or toe problem)

3/4tonYJ
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Discussion Starter · #9 ·
OK 3/4 -
I agree that the offsets don't affect the camber or toe settings but one thing it does affect is scrub radius. How does one determine what the optimal contact point is for a given axle assembly? Is this charted somewhere? How do you determine what the backspacing is for a given wheel/tire assembly to not hit the leaf springs? I seems to me that one thing required here is to know the location of the outside edge/corner of the tire is in relationship to the centerline of the wheel when aired up. Where can this information be acquired? Are all steering axis inclination angles the same? (It doesn't make sense that they would but then I'm asking here - not telling.) Also, are steering axis inclination and king pin angle the same? Next question: what determines ackerman?
I'm not asking any of this to be rhetorical but am deep in the planning stages of my new this fall front axle assembly and I have to know all of this and more. For instance, if I use a seriously backspaced wheel for reducing stress on bearings and avoiding cutting a housing and and axle and adding wide flares, what is that going to do to my brake options? (A 4400 pound Jeep with a 2000 pound trailer is in need of all the brakes it can get coming down off of some of those passes in Colorado and elsewhere at 80-85 MPH.) What will happen to my steering arms? If I cut/drill/ream them to fit, will this affect ackerman? I know it will affect steering ratio, but what else? And what does the backspacing do to affect the 'contact patch'? .....ad infinitum.......
Inquiring minds want to know!
I need some serious help from this BBS as I am low on the learning curve. (I don't even know enough to be dangerous yet!)
I was going to wait a few weeks to ask my questions and maybe should have anyway and thus formulated them better but the earlier questions and answers have opened what to me is a Pandora's box and now is the time, I guess.
sln

 
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Discussion Starter · #10 ·
First of all, I don't know where anyone learned that different offsets change your alignment angles. There is no way this is possible. As for SAI(steering axis inclination), ALL vehicles ARE different!!! Tire scrubbing does change with different wheel combinations, camber changes can greatly improve tire life, when going to a wider tire. ANY reputable shop that does alignments SHOULD be able to explain all of this in detail. If there is a GOODYEAR in your area, go there. I KNOW they send their people to school for alignments, as they sent me! As for the braking question, a corvette brake swap will greatly improve braking, due to the 4 piston set up used since the early 70's. Hope this helps
Mark

66 CJ-5
225"Dauntless"V-6
33" Goodyear Wrangler MT's
2.5" Susp. & 1.5" shackle lifts
 

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SAY WHAT? That's not what I said at all, I think you need to re-read. I said you won't have proper
alignment with too much offset. I didn't say the offset changed the angles, but rather the angles weren't
right for where the center of the tire is.

The shopping cart I used still had plenty of caster, the bent wheel introduced a camber or offset that
fought the caster. Either the wheel rode on one edge (camber) or the center of the wheel was not
directly behind the caster pivot with the wheel straight (offset) or a combination of both.


 

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Hmmm, (i seem to be just sitting here thinking) i can't really answer many of those questions but i'll give my 2 cents about steering stuff.(now i'm writing with a trial Jeep in mind also)
Ya, putting more backspacing (than it's designed for) on a front axle will interfere with steering components. unless you put 16.5" wheels on a knuckle designed for a 15" wheel, but thats a bad idea because you want all the leverage you can get by a tie-rod being mounted as far away from axle as possible. (if you use big tires, turn while stopped and have much scrub radius)
Ackerman, is not something that can be adjusted if your going to use a one piece tierod, besides obtaining the "best" ackerman angle is more important at higher speed while cornering to reduce "scrubbing", like NASCAR, it's different for every track (even every corner)
Steering axis inclination is different from design to design slightly but more important is your "Caster & Camber" which is something we have control over,it very much so changes how tight your Jeep turns. Caster/Camber can allow your jeep to turn tighter with a lesser axle shaft U-joint angle/wwwthreads_images/icons/smile.gif,
(I just re-read your post, if your going to drive @80 mph you don't want this degree of caster) Hmmm, maybe YOU are more concerned with ackerman(tire wear)?
this is alot to talk about, i've sat around with my "race car buddies" and talked for hours

Lets keep this post going
later,

3/4tonYJ
My Jeep Page
 
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Discussion Starter · #13 ·
changing you offset will not change "static" toe, caster, or camber. but it will change the values while the vehicle is in operation due to changing the wheel centerline in relationship the the steering knuckle. there are a lot of imaginary lines that are not talked about at the alignment shop that are based off of the wheel centerline. now toe and caster are affected in operation due to increased leverage and drag of big tires and deep offsets. wheel bearings also see a different load center and thereby changing the wear characteristics. tj and xj jeeps are even more prone to problems due too the tie rod and panhard bar design. ever heard of the "Death Wobble"? this is due to lifting and changing of wheel offsets. ifs vehicles are worse yet, they have way more angles to worry about. your best answers to these questions is to go pick up a road racing chassis tuning guides. most good ones will have an entire chapter on wheel offset and what it does to a chassis. the rules they use also apply to use on the street.

dan

/wwwthreads_images/icons/smile.giflet it snow/wwwthreads_images/icons/smile.gif
 
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