can't figure out offset - Subaru WRX Forum
 
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post #1 of 9 Old 03-20-2008, 10:43 PM Thread Starter
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can't figure out offset

so im looking into getting some wheels so i have been doing my research. my biggest problem is i keep finding conflicting discussions, both on this sight and nasioc. For one example, I read a thread about a guy with a wide body kit and he wanted to get rims that sit farther out, people were saying get a rim with a +30mm offset to have the wheels sit out farther. i thought this was totally wrong.. hypothetically speaking, if you get a 6.5" wide wheel with say an offset of +40, does that sit in closer to fender or closer to struts than oem +53 offset? And please guys no smart ass answers, my problem is i've looked at too many threads on the subject and im getting conflicting answers.
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post #2 of 9 Old 03-20-2008, 11:46 PM
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What exact tire/wheel combo are you looking at? Or what specific rim option (i.e size(17x8))?

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post #3 of 9 Old 03-21-2008, 12:04 AM Thread Starter
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i am looking at some 18 by 7.5 rims, offset of 43. i could put a small 8 mm spacer (i know they arent good, but under 10mm ive heard is acceptable) to push the offset to 51... i havent chosen an appropriate tire yet.
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post #4 of 9 Old 03-21-2008, 12:07 AM
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Wheel / Tire FAQ
Quote:
Originally Posted by mosc
Q: The rim I want has a different offset than stock. How far from stock can I be? Why does it matter?

The stock offset is 53 mm. This means your rim is mounted to the hub about two inches further out than center. The suspension expects the center of the rim to be there accordingly. Changing the offset more than a few mm is unwise. You can seriously hinder the stock suspension's capabilities. Try to stay within 5 mm of stock so, basically, no less than 48 mm. Is 47 so bad? No, but <40 sure is. It's a gradual thing. 5mm is just a rule of thumb. Balance the decrease in performance due to offset issues against what you'll be gaining in tire though.

The reason for all the offset concern is people wanting rims that are not designed for a WRX. Other cars out there mount closer to center which means they have smaller offsets. Wheel companies want to sell their rims to lots of different cars but few have the high offset of a WRX. Since lower offset rims will indeed fit (they'll just stick out more and move the center line further towards the hub), lots of companies will be more than happy to sell you them despite the reduction in handling.

Offset because of this also limits how wide a rim/tire you can use. Even at 48mm offset (already about as far as you should go), putting fatter than about a 225 tire on there can cause rubbing, especially when lowered. This corresponds to about an 8" wide rim.


It's the position of the CENTER of the rim, it has absolutely nothing to do with the width of the rim. The inside or outside position can only be determined with the offset AND some width number (usually tire width, but rim too it's just less relevant).

A 305mm wide tire and a 205mm wide tire with the same offset have the same center position. The difference is 50mm on either side of center so it'd be 50mm closer in and stick out 50mm more.

If you want to move offset and add more width but also want to keep the tire as far away from the inner fender as it used to be, you can move both. Lets say you're 205mm +53 and you want to go to 265mm but maintain that same distance. Well, that's 60mm more tire which is 30mm on either side of center so you'd shift offset 30mm and go to +23 offset.

This is all abstract though as cars are not designed to have radically different offset than stock. I recommend in that thread that you stay within 5mm of stock. Other ppl will say up to 10mm from stock. Either way, you have very little room to play with which effectively limits your wheel/tire width.

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post #5 of 9 Old 03-21-2008, 12:43 AM
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Quote:
Originally Posted by beaterwrx View Post
i am looking at some 18 by 7.5 rims, offset of 43. i could put a small 8 mm spacer (i know they arent good, but under 10mm ive heard is acceptable) to push the offset to 51... i havent chosen an appropriate tire yet.
spacers are illegal and dangerous and they only work to reduce offset, not increase it so they only make your problem worse. Buy a rim that actually fits well on your car. You'll have much better results.

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post #6 of 9 Old 03-21-2008, 03:43 AM
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Dang Mosc, thanks for that explaination. Me and a friend where just discussing this and really werent positive how it worked. Thanks for the info.

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post #7 of 9 Old 03-21-2008, 06:34 PM Thread Starter
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thanks mosc, the spacer thing is mostly what was confusing me.... i thought if you got a spacer it pushed the centerline out causing a higher positive offset. but than id read some threads about spacers reducing offset and thats what was confusing me a lot. thanks again
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post #8 of 9 Old 05-07-2008, 08:53 PM
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Ummm?... Dang!

dang...now i gotta go downstairs and measure the new rims i picked up (used) AZA i think ...might have mentioned a 48 mm offset, 17" Just bought new Goodyear F1 Asymetricals from Tire rack (being shipped to me) to put on the little beast.

Now where'd I put that tape measure....:eek:
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post #9 of 9 Old 05-08-2008, 11:56 AM
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measuring it yourself is really really hard because the center line of the rim is not easy to identify.

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