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Old 12-10-2003, 12:36 AM   #101
aspera
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"The degree of deviation from a specification is proportional to some negative result."

Well put. The problem is that some negative results, like wheel bearing failure, require a threshold to be met over time. It is unclear right now how long that time is, or how much offset it takes to really shorten the bearing life.
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Old 12-10-2003, 12:39 PM   #102
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Quote:
Originally posted by EHobron
Kean: I can appreciate your question. That is how I learned. No, I don't think 3mm will cause "drastic" problems in any specific area. The degree of deviation from a specification is proportional to some negative result. In other words, a wheel offset difference of 12mm might cause greater problems than one differing by only 3mm. Keep in mind that a wheel sticking out and added 1/2 inch has greater leverage and will change handling characteristics and increase wear.
I understand the detrimental affects a lower/higher offset could have on a vehicles components and overall handling characteristics. However, your first post lead me to believe that you were implying anything over a 3mm difference would have a drastic affect on the bearings, etc. I'm sure most folks understand the basic physics that are at work here and how the affects can be compounded as you lower/raise the offset.

Quote:
Originally posted by EHobron
The offset calculation formula originally came from Weld Wheel Industries' website, a couple of years ago. It is however the standard. It was provided as a guide and for those who needed to find offset for their wheels.
....there's no dispute from me on this. .....but I've always used the method of finding the center-line of the wheel and measuring from that point to the mounting surface (guess I like doing things the hard way).

Quote:
Originally posted by EHobron
As far as my assesment of wear, I've driven dozens of cars and trucks over the years and have noticed differences in driving feel and parts wear with offset differences of only 5mm.
Every vehicle is going to react differently and some will be more tolerant to changes in the offset than others. About 13 years ago I owned a Mazda B2200 as a daily driver and overall "off-road fun" car. I bought a set of wheels that had a dramatic difference in offset (it was at least a 1" variance from stock). In the 4 years I owned the vehicle I never once had an issue with component failure or excessive/unusual wear. I'm not sure what vehicle you experienced parts wear with only a 1/4" (5mm) offset variance, but I'd be very surprised if the WRX would be adversely affected by this. Personally, I think we would be seeing many more posts regarding things like "wheel bearing failure" from the community if this were the case for our cars. There are a lot of folks out there running ~+45mm offsets.

Quote:
Originally posted by EHobron
As somone mentioned in an earlier response, a major difference in offset might cause a dealer to refuse warranty coverage of wheel bearing repairs.
I agree. Some dealers are more "mod friendly" than others.

Quote:
Originally posted by EHobron
The bottom line is, wheel offset should remain as close to OEM design spec as possible for best results. Differing wheel widths and back spacing can change since those aspects really only effect clearance of some parts.
I agree. The ideal offset is the factory spec. Unless there are clearance issues, I believe it's in the owner's best interest not to deviate from that recommendation.

Thanks Eric,
- Kean
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Old 12-10-2003, 09:31 PM   #103
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I think we're all on the same page. Hind sight shows my use of the word "dramatically" in my original post was probably too strong. Hopefully the "Newbie" title affords me some lattitude..?

By the way, the wear I experienced (ball joints mostly) was on a couple of DSM products and even one Toyota over about 20k miles in one year. My vehciles are used hard in rally and heavy off-road applications. Several $80 adjustments at the alignment shop and use of proper wheels corrected the problems.

There is no doubt there are many very knowledgeable people contributing here. There were a few questions about offset though and I offered the formula as help for those who need it. Using the formula with measurements from a wheel you can see (and know is correct) might help understanding of what happens as offset and back spacing change. Hopefully this helps those who need it for aftermarket wheel selection.

I enjoyed the exchange and look forward to future threads on this cool site!

Keep the shiny side up and enjoy the snow.

Regards,
Eric
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Old 12-11-2003, 11:29 AM   #104
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The info is appreciated Eric.

Thanks,
Kean
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Old 12-12-2003, 10:40 PM   #105
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Actually, the Legacy and Forester are the same in regards to offset requirements,
Just another data point. My 04' Forester with stock 16 X 6.5" rims have a +48 offset which is not the same as the Impreza with the same width rim. Now to figure out what offset will work for me with a 7" rim, I'm so confused now

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Old 12-12-2003, 11:37 PM   #106
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Peaty:

The simple answer is that the offset should never change despite wheel width. Even a 10" wide wheel will have a +48 offset on your vehicle. It would never fit the car but suspension geometry would be correct if you could bolt it on. I'll explain geometry in a minute. That's where it gets a little more complicated.

Offset is relative to backspacing and wheel width. That's why it's so confusing.

For example, with both wheels having +48mm offsets, the back spacing on a 6.5" wheel is about 5 5/8" while the back spacing on a 7" rim is about 5 7/8". Additionally, a 7.0" wheel with a +42mm offset would have backspacing of about 5 5/8". Note the similarities and remember this for the last paragraph.

Offset is the distance between the centerline of the wheel and the mounting surface of the wheel. Positive offset occurs when the mounting surface is outward of the centerline of the wheel.

Suspension geometry in basic terms is determined by drawing a straight line from the center of the upper ball joint, through the center of the lower ball joint and down to the center of the contact patch of the tire. Since that line is rarely perfectly plumb, the wheel is OFFSET to make the contact patch of the tire sit in the correct position. The offset is determined by some crazy smart engineer with way too much education.

Since offset is calculated using the centerline of the rim, offset will remain the same regardless of wheel width.

One of the reasons problems occur when choosing wheels that are too wide is that backspacing is changing. In the case of high positive offset wheels as are used on most sport compacts, the backspacing increase is noticed more at the inward portion of the wheel. This is evidenced by rubbing on inner fender skirts, the sub-frame, or even on suspension parts in high negative camber applications.

Take some measurments. As long a you have at least 1/4" clearance from the innermost edge of your wheel/tire, you can choose a 7.0" wheel with a +48 offset. The 1/2" added wheel width will be divided equally to the inner and outer edges of the wheel. 1/4" on each side when compared to the stock wheel.

On the other hand, changing to a +42 offset would move the wheel outward 1/4" so the entire 1/2" width change would be noticed only on the outermost edge of the wheel. The result would probably be no clearance issues inside but parts wear "might" be increased.

Bottomline, I recommend you stay with +48mm offset on the 7.0" wheel.

I hope this helps reduce some of the confusion.

Good luck,
Eric

Last edited by EHobron; 12-13-2003 at 03:07 PM.
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Old 12-16-2003, 11:13 PM   #107
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OMGHi2U Oh my God!

This has got to be the longest thread. A friend of mine happens to be a parts man at my dealer and he told me that the WRX wheel bearings are junk.

Rich
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Old 12-17-2003, 05:53 PM   #108
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Junk?
If that turns out to be true, then there are going to be lots of WRX wheel bearings sold in the future. Many, many WRX owners get aftermarket wheels.

But how many Impreza/Legacy wheel bearings fail? Surely the same parts that are used in the WRX have been widely used for over a decade worldwide. Yet there are only a few stories on NASIOC about failures...
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Old 12-17-2003, 07:01 PM   #109
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There was a TSB on the bearings not too long ago, I think it's all sorted out now. Much of the problem was repeat failure due to bad installs messing up the hub that held the bearing.

Rear Wheel Bearing TSB 03-50-02 link
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Old 12-19-2003, 11:43 PM   #110
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so im guessing RO_JA GT Drift 18x7...with offset of +42mm...wont work or will it???...please help...
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Old 12-20-2003, 11:20 PM   #111
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phat50,

I'm not a Subaru expert but the answer depends on stock offset. I think a +48 offset is fairly standard/common on Subaru vehicles. You could measure your stock wheel and calculate offset using the formula mentioned earlier in this thread.

That said, a +42 offset should "work" on the car. You will notice though that the wheel sticks out slightly (1/4") more than stock. You may also notice more sensitive steering feel. Bearing wear may be an issue but many of the Subaru specialists feel wear would be insignificant or non-existent.

Hope this helps,
Eric
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Old 12-21-2003, 09:20 AM   #112
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EHobronm, thanks for answering my question, it was a good detailed one at that.
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Old 12-22-2003, 02:37 PM   #113
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Quote:
Originally posted by Peaty
EHobronm, thanks for answering my question, it was a good detailed one at that.
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Old 12-25-2003, 03:48 AM   #114
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with a 22b widebody kit on a gc. what size wheels and what offset would u guys recommend? i think the wheel wells are about 2.5" wider, not exactly sure. i want maybe a 9-10" wide wheel but i dont want to get something too small or too big. is there a way i can measure the wheel well and measure the offset...if anyone has any info for me, please post...thanks
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Old 01-29-2004, 05:15 AM   #115
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I hope someone can clear this for me.

I have a GC, which is lowered ~1.75" all around, and now I want to get a set of 17" rims with +45mm offset. Am I going to have rubber problem?

Andy
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Old 01-31-2004, 08:37 PM   #116
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Another question...i found a rim that is pretty cool...sorta of a Subzero knockoff...it is an Enkei RSV...18x7.5, 5x100, with a +45 offset...never seen this offset before....would this work for an 02 wrx?
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Old 02-04-2004, 02:05 AM   #117
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Yes, the offset should work. The beginning of the post showed the "ideal" offsets, and you should try and stick as close to them as possible, + or - a few. Just like the Volk LE22Ns. I have heard of problems with them, except in a +44 offset. Just stick close to the recommended offset, it doesn't have to be exact.

I would try to find someone with those particular wheels to be completely sure, still. Different rims tend to be a little different, like I said with the Volks above.

Enjoy!
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Old 03-07-2004, 08:43 PM   #118
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I'd like to put the STi Potenza RE070 tires on my WRX.

I'd be going with 17x7.5s, just like the STi rim. However, I can't figure out what offset I should be looking for.

Does anyone know about putting 17x7.5s on a WRX?
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Old 03-08-2004, 02:17 AM   #119
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The USDM STi (BBS) wheels are 17" X 7.5" ET53 and will fit your WRX just fine. In fact there are some nice pictures in this forum if you do a search.

Look here: http://forums.nasioc.com/forums/show...hreadid=475744

For most aftermarket wheels, ET48 is the common Subaru offset. There are many 17" X 7.5" ET48 wheels available for your car.

Check the Tire Rack and subydude for some nice choices.

Last edited by EHobron; 03-08-2004 at 02:42 AM.
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Old 03-12-2004, 08:31 PM   #120
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Smile I know you guys are tired of answering this question

I know you guys are tired of asking this question


As much as I hate to ask it cuz I know many of you have answered similar questions, but for my benefit I need to know. I am ordering 18X7.5 enkei RPM2's with a 50 mm offset on my 2003 wrx...is this ok? Also, my car has a eibach pro kit on it and the tires I'm getting are 225/40/18 do any of you think I might have rubbing problems? Any help would be greatly appreciated.


Travis



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Old 03-21-2004, 12:41 PM   #121
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i dunno about 18" wheels but it's funny that this thread's first post says 7.5" wide wheels should have an offset less than what the optional BBS 17" wheels are - the sti wheels. is the sti offset different from the wrx offset?


the offset this thread says for 7.5" is 47 to 50mm whereas the multispoke silver/gold 17"x7.5" has an offset of 53mm.

what gives?
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Old 03-23-2004, 03:35 PM   #122
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Lightbulb

*** Post edited to remove bad advice. The numbers were mathematically correct, the mindset was bad. ***

< Blues_Brothers_mode >
&nbsp;&nbsp;"I see the light!!"
&nbsp;&nbsp;"Do you see the light?!"
&nbsp;&nbsp;"Yes!! I
SEE the light!!!"
< /Blues_Brothers_mode >

Stick as close to 48-53 mm offset as possible. Regardless of the width. Remember that for each inch of width you add to the wheel, it is getting a half-inch closer to your struts and a half-inch closer to your fenders.

The width applies to tires also. If your car comes with 205s stock, a 225 will be almost an inch wider. 235s will be over an inch wider. And over a half inch closer to your struts/fenders...



Some definitions to help others with their learning curve:

Offset This is, as said previously here, the distance of the hub-mounting surface from the centerline of the wheel.

Backspace The distance from the back edge of the wheel to the hub-mounting surface

Scrub Radius the distance between the center of the tire's contact patch and the Dave Point TM It is also where all the talk of stress on the bearings comes from -- the further the center of the contact patch from the Dave Point TM, the more stress on the bearings.

mm Millimeters. 25.4 of them per inch. It's the UOM (unit of measure) used to measure the backspacing, and to define the tire width (the 205 in 205/55R16) -- albeit very loosely; but it is what the Miata Tire Size Calculator uses to make its calculations).

&nbsp;&nbsp;- Eric
&nbsp;&nbsp;&nbsp;&nbsp;Lil' Red '98 2.5 GT Wagon - Pics

Last edited by Radio Flyer; 03-25-2004 at 11:34 AM.
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Old 03-23-2004, 07:17 PM   #123
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Wrong.
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Old 03-24-2004, 01:53 PM   #124
Radio Flyer
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< Jedi_mind_trick > There is nothing informative here. Read the next entry. Move along. < /Jedi_mind_trick >

Thank you, Mr. Helpful!!

Care to explain? If I'm way out of line, tell me how, and I'll delete my entry...


This reply was to the above response to my previous post that has now been completely changed, and would now, hopefully, no longer qualify for the simple response of "wrong" above.

I believe that these two entries can be completely removed...

&nbsp;&nbsp;- Eric
&nbsp;&nbsp;&nbsp;&nbsp;Lil' Red '98 2.5 GT Wagon - Pics

Last edited by Radio Flyer; 03-25-2004 at 11:39 AM.
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Old 03-24-2004, 07:55 PM   #125
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Well, if you really read the umpteen posts in this thread, you would certainly know why "wrong" was my only answer.

In all fairness, much of your explanation is OK. The problem is that your final numbers are way off.

The simple (best) answer for offset is; the offset....is the offset....is the offset...period. If the suspension was designed for a +53 then all wheels regardless of width will be +53.

Now that is of course the source for all the debate. I and many others are comfortable with a +/- 5mm difference in offset. Some go way out to 10mm but that again is up for debate.

Offset is a caulclation involving backspacing and the centerline of the rim. In order to distribute forces properly, the offset should remain as close to stock (or as recommended by a suspension mfg.) as possible.

The result of all this is that some wheels just will not fit some cars. Changing offset to deal with larger calipers or to fit extra wide wheels is simply wrong. If a wheel in the proper offset does not clear something, then it is the wrong wheel.

All that said, +48mm offset is generally considered the "Subaru offset." It's close enough to stock and requires mfgs. to machine fewer variations of each of the millions of wheels available currently.

Personally, I have a set of 18X8.5" ET48 SSR Comps on my STi and that is the limit (width and offset) for that car. Even that 5mm difference is noticeable to me in steering feel...but I deal with it cause they look kooool.

Eric
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