The same basic steel 5 spoke wheel was used on all
years of second generation Z28s. Chevy sells it
under part #3983045. From 1970 to 1975 Chevy used
a Bowtie center cap on it. The number for the
Bowtie cap is #3989479. From 1977-1981 a Z28
cap was used. The part number for it is #469688.
The GM trim ring for these wheels is #3984524.
HINT: A good source for used trim rings is a mid-'80s S10 4x4 with steel wheels. Two different
trim rings were used on the S10, one is correct
for the Z28 wheel.
The early wheels with the Bowtie caps were painted with a special gray paint with a flattening agent and a pebble finish agent added to get a finish that simulates the rough surface of a "mag" wheel. This paint was available from Ditzler as DDL-32961, but Ditzler dealers are phasing out lacquer paints so it is no longer available. Ditzler has a different paint to replace this. The later wheels with the Z28 caps were painted body color.
GM codes all of its wheels, and the code for this wheel is AU. This
code is stamped near the valve stem hole along with a date code.
The date code looks like this: K12 This translates as:
K=Kelsey Hayes (they manufactured wheels for Chevy)
1=wheel plant (Romulus, MI)
2=year of manufacture
Also, on the surface of the wheel where the tire is mounted, is another date code like 14D, which is day and month of manufacture. (14th day,April)
Early wheels had oval holes where the valve stem protrudes through the central portion of the wheel. Hole on 1970 wheels measure 1x5/8", 1972 wheels measure 1"x13/16". On these wheels, the 5 spoke portion of the wheel protrudes approximately 1/8" beyond the outside lip of the wheel, so when the trim ring is mounted, only the flat portion facing the outside of the wheel is visible.
By contrast, the later wheels have round holes for the valve stems. The 77-78 ones are 7/8", while 79-81 are 1". On these, the 5 spoke portion of the wheel is set approximately 1/4 INWARD of the wheel lip, so that when the trim ring is in place, about 3/8" of the horizontal part of the trim ring is visible along with the entire vertical portion.
The Chevy part number never changed to reflect these minor differences.
In '78 and early '79 the Z28 could also get an
optional 15"x7" finned aluminum wheel which was available
in silver, black, and gold. These wheels should be stamped "Chevrolet" and the size.
The 15"x7" five-spoke aluminum wheel that replaced it in mid-'79 was available for the rest of the second generation. This wheel was available in silver (part #14022118), black, and gold metallic. On this wheel each spoke is numbered one to five, one spoke is stamped "Made in USA", another "Western Wheel Div.", and a third "15 x 7". 1980 wheels are stamped SBxxx on the inside of wheel behind the valve stem; 1981 are SLxxx (xxx=undecoded numerical code).
Both styles were also available on other Camaro models in 14"x7" and
14"x6" flavors as RPO N90.