Technical Offset Question...

[West]

Ok, I'm reading my "How to make your car handle" book and I've come across something that has confused me requiring offsets. I started to question this once I thought about the offset and cornering forces effects on different offsets and effects it has on inboard and outboard wheel bearings.

The book states.

Wheels can be built so the center of the rim is outboard of the wheel mounting surface, called positive offset. Positive offset makes the track wider.

Wheels build so the center of the rim is inboard of the wheel-mounting surface, called negative offset, make the track narrower.

Track is defined as this...

Track is measured between the center of one rim or tire and the center of the other. If you change wheel offset, you are moving the center of the tire and obviously you are changing track.

Now for example. Stock wheels are 15x6 +40, lets say I put on 15x6 +35... so that's closer to negative offset from my understanding... Is that correct? If so. that's an increase in track.... doesn't that contradict the explanation above?

I have a feeling I know the answer, but Its just not clicking with me. Someone educate my ass!

[black s13]

yeah, large negative offsets increase track... spacers make less offset and wider... seems wither we both cant think straight or the book is confused.

[adey]

That looks like a misprint to me, unless I'm mistaken... negative offset should WIDEN/increase track whereas positive offset should NARROW/decrease track.
if you had a 15*6 +35, that would widen track by 10mm -- 5mm on each side. I think you and I are on the same page, but the book is not. I would say... consult BillRoberts or something. :) Just don't ask Dousan, cause this would really get his panties in a twist!

edit: what book is this? Author/title/edition might help. :d

[omen2853]

according to the book making the offset less (closer to negative or whatever you want to call it) will make the track smaller because the center of the two wheels is coming closer together. if your putting on +35's then youll be going smaller by 5mm on each side. thats what the book says anyway. but you would think that itd be the other way around because (and im poicturing this in my head so this is theory) when you put on a smaller offset wheel (take the +40 to +35 example) aside from doing other things that i dont understand, youre also pushing out the wheel toward the fender (which is why so many of you guys roll them). so youd think the track would be getting wider right? oh well im sure the person who wrote that book knows something more than me.

in any case, according to the book itd be getting smaller by 5mm on each side because the center of the wheels are moving closer together by 5mm on each side. hope that all made sense.

edit: it took me so long to write all this that they already said what i was thinking.

[[email protected]]

It seems that the book is correct in its own way. It seems to be talking about the hub face being on the outside like a stock design. So for WEST'S example the 15x6 +40 then to change it to +35 would narrow the track because you are bringing the face of the wheel closer to the car itself. Not just the hub center. So theoretically they are correct. But if im wrong let me know thanks.

[omen2853]

it sounds right either way you put it. theyre just bad writers. cause levi's post makes sense about just bringing the hub faces closer to each other.

but that seems to only work when the wheel is off the car (at least in my head). because when the face is moved in toward the car you can picture the track getting closer together, but eventually it has to be attached and then it is going to be pushed outward as lower offset wheels do. bad writing or we're retarded. makes sense both ways.

[Chernobyl]

Must be a misprint. It really can't be that complicated. Not all books are perfect, ya know.

[240Stilo]

Here's a pic of how the book explains it:

[Kain_Pabyeda]

When you use neg or pos offset, all you are doing is moving the hub face. Pos mounts the hub forward of the original 0 offset bringing the "true" center of the rim closer to the "true" center of the rim of the other.
"True"
+_ _ _ _0_ _ _ _-
+_ _x_ _ 0 _ _ _-
X= Pos. offset
0= true zero offset
I'm pretty sure that this is correct, but then again I'm stoned. I'll recheck thi tomorrow, and post again if this incorrect.

[[email protected]]

Is it not interesting to see how different yet similar our responses are just from reading that? I think it is.

[adey]

how is the way the book explains it more logical? All wheels that have their offsets stamped on a sticker that say +48 sit towards the outer edge of the wheel. The book seems to be going off its own abstract definitions of +/- offset like norms don't apply to them. :ghey:

[240Stilo]

how is the way the book explains it more logical? All wheels that have their offsets stamped on a sticker that say +48 sit towards the outer edge of the wheel. The book seems to be going off its own abstract definitions of +/- offset like norms don't apply to them. :ghey:

I just schooled myself on offsets through google and FINALLY understand it. But, I also found that people do it in two ways. The difference is in the direction they choose to call the positive and negative offset. SO...I withdraw my statement about it being more logical.

Another interesting thing I found was some issues about too much offset in either direction causing stress on lug nuts and other suspension stuff.

[West]

I just schooled myself on offsets through google and FINALLY understand it. But, I also found that people do it in two ways. The difference is in the direction they choose to call the positive and negative offset. SO...I withdraw my statement about it being more logical.

Another interesting thing I found was some issues about too much offset in either direction causing stress on lug nuts and other suspension stuff.
Care to share some links?

Also, anyone know of any other suspension related books?

This book seems to be correct. I think im with Juan when they say people explain it 2 ways... its the only thing that makes since in my mind.

[uiuc240]

Wheels can be built so the center of the rim is outboard of the wheel mounting surface, called positive offset. Positive offset makes the track wider.

Mark,

This is the exact OPPOSITE from the way everyone else refers to the terms "negative" and "positive" offset. It's the same idea, just different semantics. Normally, we would say that NEGATIVE offset pushes the center of the rim further from the mounting surface. They're just flip-flopping the + and -.

I'm not sure why...but this book is weird.

Eric

[sykikchimp]

I've read on a lot of Circle racing wheel sites where they do the offsets that way..

Negative narrowing the tract, and positive increasing.

Just depends on who you are talking too.

[Kreator]

Mark,

This is the exact OPPOSITE from the way everyone else refers to the terms "negative" and "positive" offset. It's the same idea, just different semantics. Normally, we would say that NEGATIVE offset pushes the center of the rim further from the mounting surface. They're just flip-flopping the + and -.

I'm not sure why...but this book is weird.

Eric

i was about to say that

The domestic ppl that i know would refer to those offsets as negative. Also most suspension books that i've looked through have it flipped as well. So basicly what we refer to as positive offset is actually negative in original terminology. I don't know why though

[240Stilo]

West- I lost the sites where I found it mentioned the two ways it is measured google might help for those. But, these two sites show how it has came to be used on the boards thus far.

http://wheeltool.com/info/offset.html
http://www.off-road.com/chevy/tech/wheel/

uiuc240- The book isn't weird it's just the way they're accustomed to. The arguement between which way is best could probably go on forever and still have no winner.

By the way...this is one of the best tech threads I've seen in a while, eventhough it's in chat. Keep'em coming.:bigok:

[uiuc240]

uiuc240- The book isn't weird it's just the way they're accustomed to. The arguement between which way is best could probably go on forever and still have no winner.

True...but the way we are accustomed to is also the way 95% of wheel manufacturers publish offsets. Fikse builds wheels with offsets ("backspacing") measured in inches instead of millimeters, but it's still a "positive" measurement for a "positive" offset.

I think the only way that this would be useful is when seen like this:

Let's say you have an OLD racing wheel. They used to have drum brakes with no caliper, so you could have a totally flat "disk" or "face" for the wheel. In this case, you would leave the "disk" or "face" in place, and simply move/reposition/reweld the rim of the wheel to change the offset. In this case, if you moved the rim OUT, relative to the "disk", you would be creating a "positive" distance from the hub, therefore a "positive" offset.

The wheel would appear to have a deep dish, and therefore we would assume it would have a "negative" offset.

Does that make sense?

Basically, the book is talking about "positive" as being relative to the rim. The hub/disk relationship doesn't change...the rim moves in and out.

I think I just made that more difficult to understand...but it makes sense to me.

Eric

[DoriftoSlut]

It seems to me that the nbook misprinted something. They clearly define their offest measurements as being taken relative to the hub mounting surface and the rim. Lowering offset will INCREASE your track (assuming the same width is kept). There is no way around that, no other way to look at it, and when talking about positive and negative offsets, EVERYONE measures it the same way.

I say you call the publishing company, or track down the copy editor of that book. Let him or his company know. And then appologize for getting him fired.

[Jsquared]

yep, the STANDARD way to measure offsets is what we're accustomed to. The book is a misprint. Also, WhoTF cares about circle track? That's like referencing ENIAC for an issue with Windows XP...


P.S. even though it's only done by domestic/Imperial-unit companies, I like Backspacing measurements as opposed to offsets. Makes things much simpler (no calculations necessary). All the offset junk revolves around two things: 1) clearing coilovers and 2) fender fitment, #1 being a lot more important than #2. All you got to do is measure the horizontal distance from the hub to the coilover where the wheel's rim will be. That's your backspacing, no english-to-metric-conversion-then-subtract-half-the-wheel-width crap. Got 5" of clearance? You need a wheel with 5" backspacing, regardless of whether it's a 7"-wide or 10"-wide wheel. Subtract 5" from the width and that tells you what to look for in the fender department. Don't have to go to http://toy4two.home.mindspring.com/offset.html to find out how a 9" +15 will fit as opposed to a 9.5" +12 or +22. You're told the main critical dimension flat out, secondary critical dimension is half-second of arithmetic in your head. [/rant :D]

[90sr]

Hey guys gota question, whoever has done a sr swap into a 90 240 can help me out, everything lines up except for the power steering column now what i need to know is if i need everything from the 91 to 94 model like the hoses the steering lines the column itself, any help at all would be great thanks.

[Equinox]

Is the book old? Like from the 70s? From what I've read, offsets used to be measured how the your book does. However at some point, people kind of flip/flopped and offset is know how we know it. Go figure...

[Frappe]

I've got that book, actually in the middle of it right now (we're around the same section, even, methinks)
and yeah, it is pretty old...published in 1980 I think? There's some great pictures of old cars with nice setups in it.

My guess is it's just a weird terminology the author used. We're all used to thinking of + and - offsets one way, he's speaking of them as swapped terms.

[BadMoJo]

Hey guys gota question, whoever has done a sr swap into a 90 240 can help me out, everything lines up except for the power steering column now what i need to know is if i need everything from the 91 to 94 model like the hoses the steering lines the column itself, any help at all would be great thanks.

:bash:


Like most of us have already said, from everything I have ever read it seems that they are saying it backwards. Correct, but backwards...

[Silverbullet]

sooo does offset affect performance, tirewear, or anything like that?

[DoriftoSlut]

sooo does offset affect performance, tirewear, or anything like that?
It affects scrub radius. Technically, an increased scrub radius will wear your tires more becasue they are "dragged" backwards or forwards when you turn, but how much does it actually wear? Hmmm nothing noticeable. Scrub radius is noticed more in steering turn-in and shit like that. Haha... think of it this way-- how long would it take for you to wear down the treads on your tires by parking your car, keeping it running, and continuously turning the wheel back and forth? Hahaha. Sounds like an event for the 240sx Special Olympics...

[Bliss]

Sounds like an event for the 240sx Special Olympics...
hahahahahaha :Ownedd: :ughd: