Math for offset

[blooie]

Hi, got a math question. I have a 2022 Gt thinking of doing widebody/fenders 1.5 inch wider.
if I am currently running
255/40/19, with offset 42.5, how much more offset do I need to flush with the new fenders? Same tire thickness, same 19 inch.
Thanks

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[robvas]

However many more milliliters you want to bring the wheel out. Subtracted from your current offset

If you want 1.5" more you need 38.1 (1.5 * 2.54) less offset, so +3.4

 

[blooie]

Awesome. Thanks!!!

 

[Farkel]

However many more milliliters you want to bring the wheel out. Subtracted from your current offset

If you want 1.5" more you need 38.1 (1.5 * 2.54) less offset, so +3.4

I was told there would be no math, but that being said I have to question your result. 42.5 - 38.1 = 4.4. A +4.4 offset sounds like an invitation for wheel bearing trouble, and I think you'd have to have the wheels custom made.
Ben, I think you should consider wider wheels and tires if you want to move the outer edge of the tires out 1 1/2 inches. How wide are your current wheels; I'm guessing 8.5 or 9 inches. One inch spacers would get you most of the way there, but I'm not a fan of spacers. Let us know how it works out if you do the widebody thing.

 

[blooie]

I was thinking wider wheels and tires but don’t know sizes I should get to fit that 1.5 inch, hence asking the question (probably looked at it incorrectly)
what would the best wheel/tire width I should get? Want to make sure I know the wheel width before budgeting for wide body 🫡🫡

 

[Farkel]

I was thinking wider wheels and tires but don’t know sizes I should get to fit that 1.5 inch, hence asking the question (probably looked at it incorrectly)
what would the best wheel/tire width I should get? Want to make sure I know the wheel width before budgeting for wide body 🫡🫡

You might get some ideas from the wheels & tires section of the forum, but I don't remember seeing anything on the widebody fenders. Your safest bet would be to get advice from one or more of the wheel sponsors, ex: @Apex Wheels.

 

[robvas]

I was told there would be no math, but that being said I have to question your result. 42.5 - 38.1 = 4.4. A +4.4 offset sounds like an invitation for wheel bearing trouble, and I think you'd have to have the wheels custom made.
Ben, I think you should consider wider wheels and tires if you want to move the outer edge of the tires out 1 1/2 inches. How wide are your current wheels; I'm guessing 8.5 or 9 inches. One inch spacers would get you most of the way there, but I'm not a fan of spacers. Let us know how it works out if you do the widebody thing.

Why would that be a cause for wheel bearing trouble?

 

[stannypack]

Why would that be a cause for wheel bearing trouble?

Doesn't lower offset mean more stress on the bearings since it's more lateral/angular load? Just what I've heard

 

[robvas]

Doesn't lower offset mean more stress on the bearings since it's more lateral/angular load? Just what I've heard

it would shift the load from one side of the bearing to the other...but unless you're running some crazy offset it shouldn't be enough to matter.

imagine if everyone with non-factory wheel setups was coming in here asking why they are replacing wheel bearings every year....but that basically doesn't happen

 

[Farkel]

Why would that be a cause for wheel bearing trouble?

Pretty good explanation here:
https://forums.nasioc.com/forums/showthread.php?t=870349

 

[robvas]

Pretty good explanation here:
https://forums.nasioc.com/forums/showthread.php?t=870349

Again, it doesn't actually affect anything and you're talking about a tiny difference.

 

[Farkel]

it would shift the load from one side of the bearing to the other...but unless you're running some crazy offset it shouldn't be enough to matter.

imagine if everyone with non-factory wheel setups was coming in here asking why they are replacing wheel bearings every year....but that basically doesn't happen

My reply was based on the OP's idea of keeping the OEM 255/40 tires, which wouldn't fit on wide wheels. Moving a narrow wheel 1 1/2 inches out is a more drastic change in offset than with wider wheels which counter the offset with more wheel inboard.

 

[Apex Wheels]

It sounds like you're referencing fitment with the stock wheels/tires, which is pretty weak on stock fenders if we're being honest. They can come out at least 1/2" all around and still tuck inside the OE fender.

"Offset" on its own is a bit irrelevant because it's dependent on wheel width. If the fenders you're looking at offer a full 1.5" increase in coverage front and rear, you should also take the opportunity to run a wider wheel and tire. These cars can swallow 305/315s under the stock bodywork.

Have a feeling this is more for looks than performance, so I would look for something at least 10" wide front and rear with a 285 width tire, which would mean you'd need an effective offset of around -10mm for a 10" wide wheel to bring it "flush". I doubt you'll find anything off the shelf in that spec, so it's either a custom wheel, likely multipiece due to low offset, or a more standard wheel with spacers. Don't buy a cheap custom wheel, you're asking for trouble.

 

[blooie]

It sounds like you're referencing fitment with the stock wheels/tires, which is pretty weak on stock fenders if we're being honest. They can come out at least 1/2" all around and still tuck inside the OE fender.

"Offset" on its own is a bit irrelevant because it's dependent on wheel width. If the fenders you're looking at offer a full 1.5" increase in coverage front and rear, you should also take the opportunity to run a wider wheel and tire. These cars can swallow 305/315s under the stock bodywork.

Have a feeling this is more for looks than performance, so I would look for something at least 10" wide front and rear with a 285 width tire, which would mean you'd need an effective offset of around -10mm for a 10" wide wheel to bring it "flush". I doubt you'll find anything off the shelf in that spec, so it's either a custom wheel, likely multipiece due to low offset, or a more standard wheel with spacers. Don't buy a cheap custom wheel, you're asking for trouble.

I don’t mind buying new wheels/tires but which sizes I should get along with the wider fenders. I will follow up with u when I am closer to it then. Seems like no custom, find best ones already available

 

[Apex Wheels]

I don’t mind buying new wheels/tires but which sizes I should get along with the wider fenders. I will follow up with u when I am closer to it then. Seems like no custom, find best ones already available

If you want a 19x10", we keep it simple and it's only offered in 19x10" +40mm, so you'd need 2" bolt on spacers which would be fine to use from a good company like Motorsport-Tech.com

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