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#4563850 - 11/04/17 11:41 AM Will wider rims change off-set?
avacado11 Offline


Registered: 08/12/15
Posts: 124
Loc: Central NY/Arkansas
Put on new wheels for my Outback a few weeks ago. These cars are known to have weak wheel bearings and will get upset if the offset is off.

The factory spec wheels are 225/65/17 on 17x7 rims +55 offset. New wheels are 235/60/18 on 18x8.5 rims +55 offset. The 18s weigh about 10lbs more each.

Wheel diameter is 0.59" and Width is 0.39" bigger than stock. We're talking around 1/2" differences here. Will I need spacers or will this set up be fine in the long run? It doesn't rub at full lock and driveabity is fine. I just want to set things up to run within factory specs since don't want any future repairs due to improper modification.

The factory upgrade option is 18x7.5 with 225/60/18s with the same +55 offset.


Edited by avacado11 (11/04/17 11:50 AM)
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#4563891 - 11/04/17 12:23 PM Re: Will wider rims change off-set? [Re: avacado11]
LotI Online   sleepy


Registered: 01/01/13
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#4563896 - 11/04/17 12:35 PM Re: Will wider rims change off-set? [Re: avacado11]
Traction Offline


Registered: 06/04/13
Posts: 980
Loc: iowa
If the offset is the same, that's what you want. Both rim flanges are just 3/4 in further away from that measurement, so track width remains the same. Besides, adaptors, and spacers are never a great idea anyway.


Edited by Traction (11/04/17 12:37 PM)
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#4563900 - 11/04/17 12:37 PM Re: Will wider rims change off-set? [Re: avacado11]
SubieRubyRoo Offline


Registered: 05/14/12
Posts: 1125
Loc: Winchester, Indiana
What year is your Outback? Outbacks have had a much more robust wheel bearing design than Foresters and Imprezas for a long time now. Unless you are late 90s/early 2000s (I think the design changed around 03-04) you shouldn't have any issues.

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#4563910 - 11/04/17 12:55 PM Re: Will wider rims change off-set? [Re: SubieRubyRoo]
avacado11 Offline


Registered: 08/12/15
Posts: 124
Loc: Central NY/Arkansas
It's a 2017. I've never really messed with anything other than factory wheels for my past 3 Subarus but I've always heard about them going bad. And my 2004 Outback had one go bad, but it was a used and I had no clue what caused it.
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#4563926 - 11/04/17 01:25 PM Re: Will wider rims change off-set? [Re: avacado11]
Merkava_4 Offline


Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
Why can't people just keep the stock wheels sizes? I never could understand that. crazy

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#4563945 - 11/04/17 01:38 PM Re: Will wider rims change off-set? [Re: avacado11]
CT8 Offline


Registered: 10/09/14
Posts: 10967
Loc: Idaho
Yes, just bigger tires add load on the bearings.
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#4563970 - 11/04/17 02:08 PM Re: Will wider rims change off-set? [Re: avacado11]
A_Harman Offline


Registered: 10/01/10
Posts: 6921
Loc: Michigan
If the offset is the same, but the wheel is 1.5" wider, that means the inside rim of the wheel is 1.5" closer to the inside of the car, and that the centerplane of the wheel is .75" further from the wheel mount flange than with the original wheels. This will put more bending moment on the wheel bearing, and will decrease the effective wheel rate of the suspension. To compensate for the 1.5" wider wheel, the offset should be decreased to 36 mm to restore the original dimension between the wheel centerplane and mounting flange.
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#4563992 - 11/04/17 02:25 PM Re: Will wider rims change off-set? [Re: avacado11]
Bottom_Feeder Offline


Registered: 12/07/08
Posts: 3009
Loc: Occupied Virginia
Originally Posted By: A_Harman
If the offset is the same, but the wheel is 1.5" wider, that means the inside rim of the wheel is 1.5" closer to the inside of the car, and that the centerplane of the wheel is .75" further from the wheel mount flange than with the original wheels. This will put more bending moment on the wheel bearing, and will decrease the effective wheel rate of the suspension. To compensate for the 1.5" wider wheel, the offset should be decreased to 36 mm to restore the original dimension between the wheel centerplane and mounting flange.

That's not correct.

Offset is the difference between the center of the wheel and the actual mounting surface. It is not affected by wheel width. His new wheels have identical offset from the stock ones, and since they are 1.5" wider then that difference is going to be split evenly between the inside and outside, .75" each.

The only thing detrimental to his wheel bearings in this case will be added tire/wheel weight and any increased cornering loads a 'better' tire may allow the car to generate. The tire/wheel centers will be the same.

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#4563999 - 11/04/17 02:36 PM Re: Will wider rims change off-set? [Re: Bottom_Feeder]
A_Harman Offline


Registered: 10/01/10
Posts: 6921
Loc: Michigan
Originally Posted By: Bottom_Feeder
Originally Posted By: A_Harman
If the offset is the same, but the wheel is 1.5" wider, that means the inside rim of the wheel is 1.5" closer to the inside of the car, and that the centerplane of the wheel is .75" further from the wheel mount flange than with the original wheels. This will put more bending moment on the wheel bearing, and will decrease the effective wheel rate of the suspension. To compensate for the 1.5" wider wheel, the offset should be decreased to 36 mm to restore the original dimension between the wheel centerplane and mounting flange.

That's not correct.

Offset is the difference between the center of the wheel and the actual mounting surface. It is not affected by wheel width. His new wheels have identical offset from the stock ones, and since they are 1.5" wider then that difference is going to be split evenly between the inside and outside, .75" each.

The only thing detrimental to his wheel bearings in this case will be added tire/wheel weight and any increased cornering loads a 'better' tire may allow the car to generate. The tire/wheel centers will be the same.


Oops, you're right. I forgot the definition of offset while I was typing the note.
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#4564535 - 11/05/17 07:00 AM Re: Will wider rims change off-set? [Re: avacado11]
CapriRacer Offline


Registered: 02/22/03
Posts: 3369
Loc: Somewhere in the US
If I remember correctly, when you go to a wider wheel, they tend to try to keep the distances the same on the inside - so the offset increases (or decreases if you started off positive) by half the amount of the width change.

Note: I may have the sign wrong on the offset. But both Discount Tire and Tire Rack can set you up with proper fitting wheels - and that's what I would recommend doing.
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#4564844 - 11/05/17 12:32 PM Re: Will wider rims change off-set? [Re: Merkava_4]
dlundblad Offline


Registered: 09/30/13
Posts: 10028
Loc: Indiana
Originally Posted By: Merkava_4
Why can't people just keep the stock wheels sizes? I never could understand that. crazy


What?

I thought you said the first thing you did to your Buick was upgrade to those spinny bro wheels?
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#4564861 - 11/05/17 12:50 PM Re: Will wider rims change off-set? [Re: Merkava_4]
4WD Offline


Registered: 09/21/10
Posts: 6369
Loc: Texas
Well when I ran 265s on my Canyon it was pretty limited then I tried 285s:


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#4578771 - 11/19/17 09:39 AM Re: Will wider rims change off-set? [Re: Merkava_4]
avacado11 Offline


Registered: 08/12/15
Posts: 124
Loc: Central NY/Arkansas
Originally Posted By: Merkava_4
Why can't people just keep the stock wheels sizes? I never could understand that. crazy


With the width of the rim I couldn't run the factory 225. Even if I ran a stretched tire the rim would still be wider then OE. I could have done a 18x7.5 rim except they were all aftermarket trash lol(didn't like the 18" upgrade wheels). These 18x8.5s came off a STI
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#4578786 - 11/19/17 09:49 AM Re: Will wider rims change off-set? [Re: CapriRacer]
avacado11 Offline


Registered: 08/12/15
Posts: 124
Loc: Central NY/Arkansas
Originally Posted By: CapriRacer
If I remember correctly, when you go to a wider wheel, they tend to try to keep the distances the same on the inside - so the offset increases (or decreases if you started off positive) by half the amount of the width change.

Note: I may have the sign wrong on the offset. But both Discount Tire and Tire Rack can set you up with proper fitting wheels - and that's what I would recommend doing.


I did a quick search on tire rack with a 18X8.5 rim set up on my car and it's showing 45mm-50mm depending on what rim I buy frown

I'm gonna hope Subaru updated the bearing design(bolt patterns 5x114 and not 5x100 like they used to be). Otherwise I'll throw my factory wheels back on and run the wheels as a winter set up.
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