Offset help please

Discussion on wheel & tire issues
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pinebluffhand
Posts: 5
Joined: Wed May 16, 2018 1:08 am

Offset help please

Post by pinebluffhand » Mon May 21, 2018 3:09 pm

I'm looking at some wheels and I need help with the offset. Will they fit? And please explain what it will be compared to factory.

18X8.5 56mm offset
18X10.5 56mm offset

CrashTestDummy
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Re: Offset help please

Post by CrashTestDummy » Mon May 21, 2018 8:50 pm

This might be a good read:

viewtopic.php?f=19&t=2316
Gene Beaird,
Pearland, Texas
2012 Caprice 9C1
1992 B4C 1LE Camaro
2010 Tahoe PPV (her car)
1995 DGGM Impala SS
1996 BBB Impala SS (11-second DD)
1985 Firebird - 310 LS1 C Prepared autocross car.
And some others
Do YOU have my SPID?

Navy Lifer
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Location: Canton GA

Re: Offset help please

Post by Navy Lifer » Mon May 21, 2018 8:52 pm

Some perspective - Chevy SS sedan wheel offsets, which we KNOW will fit a PPV:

Front - 8.5" +48mm (stock tire 245/40-19)
Rear - 9.0" +57mm (stock tire 275/35-19)

Your front 8.5" +56 will be too far inward - the tire will probably rub against the strut - an appropriate size would be 245/45-18 or 255/45-18

The rear 10.5" +56 will be "close" but may work, although there may be contact between outer edge of tire and body opening

A 10.5" wheel will require a tire of at least 275/40 section width/aspect ratio for proper sidewall fitment

https://www.willtheyfit.com/" onclick="window.open(this.href);return false;
Calculations: other sizes can be plugged in to the calculator to check fitment

Front: compares 245/40-19 & 245/45-18
- https://www.willtheyfit.com/index.php?w ... offset2=56" onclick="window.open(this.href);return false;

Rear: notice how sidewall stretch changes with the wider wheel - compares 275/35-19 & 275/40-18, and 295/35-18 (may be too short)
- https://www.willtheyfit.com/index.php?w ... offset2=56" onclick="window.open(this.href);return false;
- https://www.willtheyfit.com/index.php?w ... offset2=56" onclick="window.open(this.href);return false;

pinebluffhand
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Joined: Wed May 16, 2018 1:08 am

Re: Offset help please

Post by pinebluffhand » Tue May 22, 2018 4:20 am

Thanks Bill, that link helped understand better.

Navy Lifer
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Re: Offset help please

Post by Navy Lifer » Tue May 22, 2018 12:01 pm

I'm guessing that wheels with those offsets are most likely from Corvette, which are 120.65mm, or 4.75" bolt circle, with a larger wheel center bore (70.3mm vs 67.1mm) than used on Zeta/PPV.

If that is the case, just be aware that the wheel stud pattern is not the same on PPV (120mm, or 4.72" bolt circle), and you'll want to run a hub-centric ring setup to properly support them, and either have the wheels machined to correct the lug nut seat alignment, or use floating-seat lug nuts (yes they do exist) to avoid side-loading of wheel studs and provide full-contact support of the wheels at the lug seat tapers.

This is a contentious issue that many choose to ignore and disagree with - I'm only stating this to provide full understanding of the difference. There's no doubt that many run wheels that don't match the OE specs and report no problems.

pinebluffhand
Posts: 5
Joined: Wed May 16, 2018 1:08 am

Re: Offset help please

Post by pinebluffhand » Sat May 26, 2018 6:18 pm

Thanks Bill, I think the back wheel will be pushing it. What do you think about using the front wheels all the way around?

Navy Lifer
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Re: Offset help please

Post by Navy Lifer » Sun May 27, 2018 12:04 am

Unless a spacer is used to push the wheel out to a position that ensures no tire/wheel contact with the strut, the problem will be that the +56 offset on an 8.5" wheel will give the car a sunken look--the wheels will appear to be deep(er) into the wheel openings, than even stock wheels.

Put another way - imagine the SS sedan rear wheel (+57mm) with another 1/4" to 1/2" of rim width removed (from 9" to 8.5") from the outboard side of the wheel. Same in front--SS wheel is 8.5 +48mm, and you put that +56 wheel in it's place, it's now 8mm further inboard, and would end up looking "lost" in stock wheel openings--and, as mentioned above, may not clear the strut.

Capeasy
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Joined: Thu Aug 08, 2019 2:16 am
Location: Downey, CA.

Re: Offset help please

Post by Capeasy » Fri Apr 17, 2020 6:32 am

Hey Bill, I know that was two years ago but I'm in the middle of attempting to widen my rear steelies to about 10" or from what you mentioned about a 10-1/2" but may not be doable with our OEM offset. But just to check my math, if he's using a 10-1/2" wide wheel at positive 56 offset does that leave about 7.455 backspace as in my sketch?
BTW what is our OEM offset?
Thanks
Walt
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