Standard PPV Wheels: Exact Specs?

Discussion on wheel & tire issues
SBRMD
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Standard PPV Wheels: Exact Specs?

Post by SBRMD »

Hey Guys,

Just looking to ascertain the exact numbers on the standard steel wheels, while entertaining other nicer-looking options.

We know they're 18 x 8, but what is the:

Bolt pattern (I think 120mm, but I don't know if I'm measuring right)
Backspacing (I think 6.25 inches but again, not exactly sure)
Stud/lug size (1/2"?)

And...anybody (CP are you listening?) know what the diameter of a Holden wheel center medallion is?

Thanks to all in advance,
Steve in Mpls.
Steve Robin
Minneapolis, MN
'11 PPV 9C3 Phantom Black Metallic
Navy Lifer
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Re: Standard PPV Wheels: Exact Specs?

Post by Navy Lifer »

bolt circle: 120mm

stud size: 14mm

offset: +38mm - backspacing can be useful, and aftermarket tends to speak in terms of backspace instead of offset...although OEM's typically deal in OFFSET dimensions. With offset known, the backspace dimension can be calculated fairly closely, as long as the advertised rim width (bead to bead) is known, and overall width of the wheel, lip-to-lip, is known.

A +38mm offset means the mating flange surface of the wheel is 38mm toward the outboard side of the centerline of the wheel. If you were to take a wheel, measure it's width, whether bead to bead or lip to lip, and divide that in half, that dimension is "zero" when it comes to establishing the reference plane for measuring how far off of zero the wheel mating surface is. Now, if I've confused anyone....these were the top 4 in a search that goes on & on:

https://www.rsracing.com/tech-wheel.html

http://www.1010tires.com/Tools/Wheel-Offset-Calculator

http://www.ehow.com/how_5021837_calcula ... ffset.html

https://www.google.com/search?q=calcula ... 97&bih=545
SBRMD
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Re: Standard PPV Wheels: Exact Specs?

Post by SBRMD »

Just what I needed, thanks Bill!

Do you think the 14mm studs are the same as typical GM (eg Buick LaCrosse, etc) or might they be bigger? They look oversized to me....1/2" would be equivalent to a shade less than 13mm.

Best regards,
Steve.
Steve Robin
Minneapolis, MN
'11 PPV 9C3 Phantom Black Metallic
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Re: Standard PPV Wheels: Exact Specs?

Post by Navy Lifer »

Before the Metric "revolution, most GM automobile wheel studs were 7/16". When the 1980 Chevy Citation (X-car) came to market, it was one of the first GM cars to use 12mm - specifically M12x1.5 - wheel studs. I'm not sure about the earlier Chevette, but few if any US/NA GM cars were metric prior to Citation. With exception of cars that were already in production (B-body) most everything else from GM went Metric over the next decade.

B-body (full size) and other variants, depending on application and "heavy duty" use specs, continued to be either 7/16" or 1/2" (station wagon, cop car, Fleetwood limo) from 1977 to 1990. Anything that was 4.75" bolt circle was 7/16" until that model went Metric, then became 12mm (Camaro, Malibu). All FWD cars starting with Citation were M12. When the B-body went 5x5 bolt circle on all applications, in 1991, the wheel studs reverted to 12mm, where previous 5x5 applications had been 1/2-20 thread.

Trucks were largely 1/2", using a 5x5 pattern, until the late 80's Silverado came along and the wheel studs were increased to 14mm, but initially remained in a 5x5 pattern. Later light truck stud pattern size was increased to 5.5" x 6 studs, still using 14mm studs. Astro van used 1/2" studs all the way to early 2000's, then went M14, and from 5x5 to 6x5.5 pattern.

To my knowledge, the Pontiac G8 was the first GMNA car to utilize 14mm (M14x1.5) wheel studs, and the Camaro, being of the same family, followed suit, as well as PPV.

Current GM (Chevy) fleet stud sizes:

Cruze/Sonic - 12mm - 4 & 5 studs
Malibu - 12mm - 5 studs
Impala - 12mm (2013) - 5 studs
Impala - 12mm (2014) - 5 studs
Camaro - 14mm - 5 studs
Caprice - 14mm - 5 studs
Corvette (2013) - 12mm - 5 studs
SS sedan (2014) - 14mm - 5 studs

I am curious to find out whether the re-engineered 2014 Corvette will remain on M12 studs, or move up to M14--I am guessing it will continue with 12's as a matter controlling mass/un-sprung weight--a BIG deal with Corvette.

Just what precipitated the change to 14mm on the Zeta chassis isn't known (at this level), but I'm OK with it!

Silverado - 14mm - 6 studs
SUV's - sorry, don't know, don't much care!
SBRMD
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Re: Standard PPV Wheels: Exact Specs?

Post by SBRMD »

Bill, that's great info, many thanks!

I assume from that discussion that a LaCrosse has M12. The reason I ask all this is I've run across a very nice set of 18 x 8 wheels from a 2012 LaCrosse that I could potentially use on my PPV. It seems that the bolt circle was moved up from 115mm to 120mm for LaCrosses with this style wheel, and apparently the back spacing/offset is workable too (I have to double check that tho). The only thing left to know is the stud size, as they come with a set of lugs that match the wheels. If they're M12, I'd obviously have to use some others.

And....I've had to change the center medallions...

The guys that changed my rubber for winter observed the rotors and studs and said, "this thing is built out of pickup truck parts!"
Steve Robin
Minneapolis, MN
'11 PPV 9C3 Phantom Black Metallic
gregc
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Re: Standard PPV Wheels: Exact Specs?

Post by gregc »

SBRMD wrote:Bill, that's great info, many thanks!

I assume from that discussion that a LaCrosse has M12. The reason I ask all this is I've run across a very nice set of 18 x 8 wheels from a 2012 LaCrosse that I could potentially use on my PPV. It seems that the bolt circle was moved up from 115mm to 120mm for LaCrosses with this style wheel, and apparently the back spacing/offset is workable too (I have to double check that tho). The only thing left to know is the stud size, as they come with a set of lugs that match the wheels. If they're M12, I'd obviously have to use some others.

And....I've had to change the center medallions...

The guys that changed my rubber for winter observed the rotors and studs and said, "this thing is built out of pickup truck parts!"

I was just looking at LaCrosse 18x8 wheels on ebay because they look almost like the 5 spoke G8 wheel. I've read that these fit the G8. I also looked at the Buick center caps and they look like they have the same backing as the Camaro SS wheels. That means that Holden caps won't fit. You'll have to use Camaro SS caps. I have ME Caprice SS caps made by holden that I was going to put on the Camaro SS wheels, but they won't fit. The flange is slightly larger than than Camaro SS bow tie caps and I didn't want to force them in. If I were to clone a Chinese Park Avenue, I would use these wheels.
SBRMD
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Re: Standard PPV Wheels: Exact Specs?

Post by SBRMD »

Greg: Great minds....
Steve Robin
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'11 PPV 9C3 Phantom Black Metallic
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Re: Standard PPV Wheels: Exact Specs?

Post by gregc »

Here's the Camaro caps and the Holden ME Caprice SS Caps. As you can see the Camaro caps should fit the Lacrosse wheels, but the Holden caps won't. This limits my choices to G8 5 Spokes or the Replicast Wheels. The picture on the bottom has the holden caps on the left and the Camaro caps on the right. For you, the Camaro caps would be perfect.
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storm9c1
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Re: Standard PPV Wheels: Exact Specs?

Post by storm9c1 »

Really good post regarding the history of the bolt patterns on GM cars. I used to have an '81 Citation (I was young and beat the living daylights out of it and I couldn't break it). I remember the funky metric bolt pattern (funky at the time, apparently standard now). As ugly as that car was, it sure set the stage for GMs FWD platform. The Citation was a tank, but it was dang scary above 80 MPH and never handled worth crap in any conditions, but it was a decent winter car as long as you drove slowly, unlike the Pontiac 6000 I had for a short time after, which always got stuck in the snow...everywhere. This is what convinced me that RWD was where I wanted to be, and I've driven nothing but B-Bodies as a DD since. Ironic because FWD cars are "supposed" to be better in the snow. Hogwash. My B-Bodies are great in the snow as long as I have good snow tires and 50 pounds of sand in the trunk.

I remember when mechanics would work on my B-Body Caprice, they also mentioned that it looked like it was made out of truck parts. So it sounds like the Caprice PPV isn't far off.

Back on topic, a friend of mine has a LaCrosse. If he ever has it in my shop, we can play with the wheels off of his car and I'll post back.
Tom (AKA: Storm)
2011 Caprice 9C3: L77, 8K miles, first-owner, purchased July 2011.
1995 Caprice 9C1: LT1, 178K miles, summer car.
1995 Impala SS: LT1, 21K miles.
1995 Caprice Wagon: LT1, 62K miles.
1995 Caprice Wagon: LT1, 128K miles. Rust In Pieces
1994 Caprice 9C1: LT1, beater winter car.
1969 Chevy C30: 383ci stroker, 4L80E, rollback car hauler.
1972 Chrysler Newport: 400ci big block, survivor 27K miles, 2-door hardtop.
1969 Dodge Charger: 383ci big block.
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Re: Standard PPV Wheels: Exact Specs?

Post by Navy Lifer »

Stud patterns and hub register diameters (center bore) are the other moving targets in all of this.

4.75" (120.65mm) was the standard for GM cars for a very long time--both with 7/16" & 12mm . Hub register diameter was in the 70.3mm to 70.5mm range (up to 2.776" nominal)

5.00" (127mm) was always for HD & truck applications with 5 lugs--typically with 1/2-20 studs, until B-body change to 12mm in 1991. Hub register diameter was 77.8mm for B-body (3.063")

That Citation was 100mm, with 5 studs - no idea what hub register was, but it's small!

Later FWD cars - mid-80's as the "full size" cars transitioned to front drive - a 115mm pattern was introduced, with the same hub register/center bore as 4.75 pattern. Still using 12mm studs.

What has really created confusion on top of all this is the Gen 5 Camaro & now PPV have introduced a new pattern, ALMOST identical to the old 4.75" pattern, but using a smaller hub register diameter--and the previously discussed 14mm wheel studs.

I'm going to guess without researching that Cadillac CTS also uses 14mm wheel studs--and some will recall that the original CTS-V had 6-lug wheels (as does Viper), but (and again I'm guessing here) the move back to 5 studs on the 2nd generation CTS-V also included upsizing the wheel studs, at least for the V.

Interesting tidbit--the 98-02 Camaro and most recent FWD Impala (2000-2013) actually share a front rotor--and that's with the 2 cars having different wheel stud patterns. The rotor center bore (hub register) is the same for both, and both vehicles use 12mm studs--so what GM did was make the 5 holes in the rotor (these are slip-on design) large enough to clear both patterns!
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