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Old 02-23-2006, 12:48 PM   #1
Portly
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Lightbulb Can we correct "The Offset Information Thread"?

The info in the offset information thread that's stickied at the top of this page is (with all apologies to Brian) just plain wrong. It's bugged me from day one, and it seems lately that more and more people are starting to realize that "ideal" offset does not change, regardless of rim width. I'm not talking about "make it fit" workaround offsets, I'm talking about "ideal". For more info, see this post: http://forums.nasioc.com/forums/showthread.php?t=942447 - dbrier's post #23, and my own post before that, present pretty decent arguments that this whole "offset varies with wheel width" idea is wrong.

We see lots of threads pop up with questions about offset, and I think a lot of them are because of the misleading info in the stickied thread. Can we agree as a forum that the info is wrong and needs to be fixed?

Not trying to cause a fuss, but I just don't like to see a stickied thread that's not correct.

Thanks

_Jeff
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Old 02-23-2006, 06:39 PM   #2
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I wouldn't say that the offset sticky is just plain wrong. It may be misleading because it lists ideal offsets based on fitting tires, instead of ideal offsets for minimizing bearing wear, or ideal offset for steering feel.

My ideal offset would fit a much wider tire, w/o severly numbing steering feel. I could accept that wheel bearings are a wear item, just like tires and brake parts. And I think the ranges posted in the sticky do that.

What do you mean by "ideal?"
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Old 02-23-2006, 11:53 PM   #3
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Well, my idea of "ideal", being an engineer, is fitting a wheel that meets the intent of the design of the vehicle.

Subaru designed the car based on an offset that works with the suspension and steering dynamics of the vehicle.

Sure, there's a tolerance range, and this appears to be about +53 to +55 for the Impreza.

I agree that sticky is fitment based, and not based on what the car should have.

If we are going with what the car was designed for anything beyond a 7.5" wheel probably isn't valid anyway.

The question is, what are people using that sticky information for?
Performance? handling? fitment?

The initial statement about wheel width being direction related to offset is certainly misleading and borderline plain wrong, depending again on what information you are looking for.
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Old 02-24-2006, 12:25 AM   #4
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uh, wow. Geez now I don't what wheels to get. Not a whole lot out there thats around 53 and affordable ie. not a custom Volk or HRE. Well I know for a fact that wack offsets will wear the krap out of your bearings and suspension parts. I know from 2 Hondas I've had before back in my ricer days. Both had wheels that deveated from the stock offset by what would be a considerable amount but I wanted that lip or "dish" look. I was even told by a local wheel and tire salon that the best bet is to get a wheel that's plus 1 at the most and has the exact same offset as stock to ensure that parts wear normally and performance is maximized. He then added that a strong light forged rim would be preferable too, one that is well designed and lighter then stock as to not add any more rotational mass or additional centrifical inertia. But nope I had to make my Honda look "dope" w/ some stunna Konigs.
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Old 02-24-2006, 01:03 AM   #5
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what ur saying is logical, but in the reality there r alot more to consider than just the "ideal" offset. according to what u've said u'd be stuck with stock Subaru wheels but nothing else.
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Old 02-24-2006, 01:37 AM   #6
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Quote:
Originally Posted by IowaRS
If we are going with what the car was designed for anything beyond a 7.5" wheel probably isn't valid anyway.
What about the STi's that come stock with 8" wheels? Aren't they designed for that? Or did Subaru make a compromise when they made that change? If they did compromise, the benefits must have been worth it for them to do it, no?
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Old 02-24-2006, 02:29 AM   #7
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sti's have different wheel bearing assemblies(05-06s atleast) that might account for change in wheel width..
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Old 02-24-2006, 10:17 AM   #8
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Quote:
Originally Posted by Scooby Freak
I wouldn't say that the offset sticky is just plain wrong. It may be misleading because it lists ideal offsets based on fitting tires, instead of ideal offsets for minimizing bearing wear, or ideal offset for steering feel.

My ideal offset would fit a much wider tire, w/o severly numbing steering feel. I could accept that wheel bearings are a wear item, just like tires and brake parts. And I think the ranges posted in the sticky do that.

What do you mean by "ideal?"
I'd have to agree. Sure Subaru designed the car with a particular wheel width and offset in mind. It is best to stick to those sizes when trying to replicate the feel of the car from the factory. However, this board is focused mainly around modifying the vehicles we have and not so much about how to modify them within the realm of what FHI engineers would consider appropriate.

For many of us that race our cars, staying with a stock offset wheel with a similar width would be a huge disadvantage. We want as much tire as we can get to the road surface to maximize grip. We can get much more tire to the road on a wheel of lower offset and higher width than we can with the stock wheels. For example, my current car is an 04 wrx. It can with 16 x6.5's et 55. I would be able to fit a max of a 225 width tire on those wheels. This may be fine for some people not interested in racing, but for me is no good. I now have 255 40 17's on 17x8's et 48. In the front I will be running 5mm spacers making the wheels et43. This will allow me to get close to -3.5* camber (also way outside factory spec). The car will handle well and will have a ton of grip over stock. Sure, I will probably have to replace my wheel bearings more often, but when you race a car you consider this part of the game. They are wear items as previously stated and easy to change with the right tools.

There are guys out there running 275's, 285's and higher with 9 or 9.5" wheels with offsets in the 30's. Sure that is going to cause more wear and tear, but it will also help with what they consider important.

It all comes down to what you want out of your car. If you want years of trouble free commuting you want to stick close to the stock settings. If you want performance you may end of straying from what the original engineering designed.

Tony
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Old 02-24-2006, 11:09 AM   #9
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Old 02-24-2006, 11:43 AM   #10
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Does that mean subscribe? You can click the thread tools at the top, then subscribe to this thread.
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Old 02-24-2006, 12:47 PM   #11
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Quote:
Originally Posted by Picard
What about the STi's that come stock with 8" wheels? Aren't they designed for that? Or did Subaru make a compromise when they made that change? If they did compromise, the benefits must have been worth it for them to do it, no?
Yeah, sorry, I still own a 2000 and haven't kept track of specs on the newer Subies. If I did I would end up buying one and I really don't have the $$,$$$ to do that.

Regardless, the question posed by Portly is whether we should remove and/or "correct" the sticky thread.

I would think it would be best to have a sticky that explains what we've discussed:

There is an offset that the factory intended and if you want to maintain that type of feel, performance, reliability you should try to stay within that range.

There are also ranges of widths and offsets that "fit".

Last edited by IowaRS; 02-24-2006 at 12:49 PM. Reason: corrected 2001 to 2000
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Old 02-24-2006, 11:53 PM   #12
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My head is gonna asplode. Some of the biggest diameter tires on the Legacy have 55mm offset, and so do the smallest, with 48mm offsets inbetween, all on 7" wide rims. Suspension geometry differences on Outback and Spec B perhaps? But then what about regular legacy and legacy GT? I need a beer...

16 x 7 with 48 mm offset...Outback 205/60/16
17 x 7 with 55 mm offset...Legacy (2006) 205/55/17
17 x 7 with 48 mm offset... Outback XT 215/55/17
17 x 7 with 55 mm offset... Legacy GT 215/45/17 dia:
18 x 7 with 48 mm offset...Legacy GT spec B 215/45/18

Saab sells bbs RK wheels 17x7 ET48 for Saab 92X, seems to be an official approved offset.

Last edited by Beanboy; 02-25-2006 at 12:00 AM.
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Old 02-25-2006, 12:59 AM   #13
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And does the so-called "ideal offset" change when I change my alignment from one end of the factory approved adjustment range to the other extreme? I guarantee you the loading on the bearings will be different if I have +0.25deg camber instead of -0.75deg camber. Now what do I do?

And how big an effect on wheel bearing wear (for example) is there as a result of using a +48mm wheel rather than a +53mm wheel? Is it really anything to cause a fuss about? I run +45mm wheels for auto-x and open tracking, and have been doing so for 3-1/2 years. I replaced my front wheel bearings at about 150,000 miles or so. Oh no, excessive wheel bearing wear!!!

And, if we do "correct" the sticky thread, what are we going to make it say? How about...
Quote:
7.5" - sorry, can't do it, it'll rub because everyone knows you must stay with the +53mm to +55mm offset range in order to appease the Subaru Gods
8" - sorry, can't do it, it'll rub because everyone knows using a wheel with only +45mm offset will cause your car to have the steering feel of a UPS truck and will also cause your wheel bearings to instantaneously turn to slag


Pat Olsen
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PS - I'm an engineer, too, I just also happen to be realistic about approaching things in the real world.
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Old 02-25-2006, 05:26 PM   #14
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you are missing the difference between will it work and is it ideal
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Old 02-25-2006, 06:11 PM   #15
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I think that we need to stop looking at all the different models that Subaru has. We know that different models from year to year have different offsets. What about the same year, and different model. For instance, is the suspension geometry and offset the same for the 1996 Legacy L and the Legacy GT. I know that the L has a 15in rim and the GT has a 16. Is the offset the same though? What about suspension setup? Does the diameter of the wheel make a difference. I've got a Legacy L and want to put 17" rims it, but do I have to have the stock offset since wheel diameter will change and even ride height - since I plan on lowering the car just a wee bit? Or will lowering the car cancel out the bigger wheel? These are questions that should addressed first. What happens when bigger wheels are used on one car. Don't compare one car such as a MY06 STi's offset/wheel size with a MY98 GC8. That won't get you anywhere! Get rid of as many variables as possible. Since most people on this forum seem to have WRX's (not sure which MY), maybe we should focus the discussion on this car only?!

Just my 2 cents....
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Old 02-25-2006, 06:48 PM   #16
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I understand where this post is coming from, but I completely disagree with it.

I have 17x8 +48 offset Rotas, with 225/45/17 tires, and I cant get any closer to the struts without rubbing, and I cant go out any farther without rubbing/nailing the fenders or even the chassis of the car.

Its the ideal setup on my car, from an engineering AND logical perspective.

Running a narrower tire/wheel is the conservitive thing to do, if you are worried that much about it. I'm not, nor are most people here.
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