Wheel Offset Question

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Bama_Kiwi

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My smooth-surfaced monkey brain can't make sense of the dark art of calculating wheel offset. So I come, hat in hand, to you for guidance and clarification.

I'll paint the picture:

I currently have OEM 18" alloy wheels with a +46 offset. In conjunction, I have installed 30mm (~1.2") wheel spacers - this sets the outside edge of my tires right on the edge of the fenders and looks great, IMO.

However...

These wheel spacers are technically illegal here in NZ - anything greater than 20mm must be recertified by an engineer in order to pass Warrant of Fitness vehicle inspections. To have recertification done is big money and potentially opens you up to a rabbit hole of "fix this, fix that". Currently, I have to remove the spacers prior to taking my car in for inspection then put them back on afterwards. This is a pain.

However...

Wheels with an offset that achieve the same result of the wheel spacers are not subject to the same recertification requirement. ¯\_(ツ)_/¯

So, my question is: What offset wheel will I need to achieve the same result that my current wheel spacers provide?

Thanks.
 

Advocate II

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Should be +16 I believe. A more positive number will bring the wheel in closer under the body, negative offsets would get you further out. If add your 30mm wheel spacer to the offset of your wheel ( by subtracting it from the positive number ... I know it's a weird way to do things) than you should get your needed number.
I prefer looking at backspacing myself but sometimes it can be just as complicated.
Zero offset would make the wheel mounting surface exactly centered in the wheel.
 
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Advocate II

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Also keep in mind the wheel width. Because that isn't measured in offset, if you have a 7" wide wheel and move to a 9" you will have 1" more outside of where you were before even with the same offset.
 

Bama_Kiwi

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I worked for 8 years selling offroad aftermarket products for Jeeps lol. It can be tricky stuff.
It's especially tricky for me because I already have perfectly fine tires - I am not interested in getting an entire full new set of wheels AND tires. If I suddenly find myself flush with disposable income, sure, but as for now...oof. And if I were to do that, I'd go down to 16" and then the world is my oyster.

I think I'll just get a nice floor jack and get really good at swapping on and off the spacers.
 
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It's especially tricky for me because I already have perfectly fine tires - I am not interested in getting an entire full new set of wheels AND tires. If I suddenly find myself flush with disposable income, sure, but as for now...oof. And if I were to do that, I'd go down to 16" and then the world is my oyster.

I think I'll just get a nice floor jack and get really good at swapping on and off the spacers.
I have 1.5" spacers on my TJ and 1" spacers on my compass. I just took 8mm spacers off because they aren't legal here either. They are .ore lenient with "adapters" that have a wheel stud built in which is what I use on both. 20210410_124603.jpgIMG_20210130_220712_300.jpg
 
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Billiebob

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This is as simple as it gets,,,, 46 - 30 = 16.

The other part is a bit more complex, 20 is the max and yet you deliberately break that law.......
Reminds me of a guy who said "The best 3 years of my life were Grade 8"
 
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Bama_Kiwi

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The other part is a bit more complex, 20 is the max and yet you deliberately break that law.......
Reminds me of a guy who said "The best 3 years of my life were Grade 8"
Hey Billibob,

Thanks for the input. Very helpful. I hope you and your family remain blessed. <3
 

TahoePPV

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Ronny Dahl did a video last year where he explained this and other things about wheels. It was pretty straightforward once you see it explained with a wheel, ruler and straight edge.
 

smritte

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Offset and back spacing can be confusing. I have to teach it in my suspension class. Most of the students walk away knowing, the rest have their head explode. I have them use their vehicle spec, lower the vehicle or raise it (on paper) and calculate wider tires and rims without rubbing. I make them do it in inch and mm.

Here's the reason I make them learn both ways. If the rim is made in America, its mostly Back Space and inch's. Everywhere else its mostly Offset and mm. Know both and never have to guess.

I went to order some rims once. The catalog said 9.5 wide with 4.5 offset/back space. I know the rims were going to be centered and the list was obviously back space but I needed to ask. The guy I spoke with said there both the same measurement. I tried to explain what the rim would look like with a 4.5 inch offset but his only reply was he's been building rims forever and he knows what he's doing. I bought my rims elsewhere.
 

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Website has handy tools for wheel offsets and getting a general idea where a new set of tires and wheels will end up

 

Bama_Kiwi

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Website has handy tools for wheel offsets and getting a general idea where a new set of tires and wheels will end up

This is brilliant. Thank you.

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MidOH

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+16.

+one half of the extra width of the new wheels. Which in your case might be 15-20mm.

So that's a +20 to +30 wheel. You should contact other Pajero owners and see what issues they've had. This is a good point to see if you should space the tire in more for body clearance (+20), or swing it out more for suspensions clearance and paint removal (0 to +10).

Avoid negative at all cost. Those are brodozers almost always. And yes, spacers are the debil. I won't service anything with them.