Shop Talk

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6061-T6

Also called 6061, T6

The aluminium alloy used for forged wheels, in its T6 heat-treated temper. It is chosen for strength and fatigue resistance rather than for cost.

B

Backspacing

Also called back spacing, BS

The distance from the wheel's mounting face to its inboard rim edge, measured in inches. It decides how far the wheel tucks into the wheelwell, which is why it — not width alone — is what settles whether a wheel clears.

Measured in inches, from the mounting face to the inboard rim edge

Say it right

Backspacing is the number these owners ask for first. Offset is the same idea expressed from the centreline instead of the back edge; quoting one when you were asked for the other is the fastest way to lose a fitment conversation.

Bolt pattern

Also called bolt circle, PCD, lug pattern

The number of studs and the diameter of the circle they sit on. These Chevrolet platforms share 5 x 4.75 in (5 x 120.65 mm), which is why one wheel design can serve several of them.

Five studs on a 4.75 in circle across these Chevrolet platforms

Barrel

The cylindrical part of the wheel that the tyre seats on, running from the outer lip to the inner rim edge.

Born with

Also called born-with

The part left the factory on that car. Useful because it says the same thing as numbers matching without over-claiming what can be proved.

C

Centre bore

Also called center bore, hub bore

The machined hole in the middle of the wheel that seats over the hub. When it matches the hub exactly the hub carries the load and the wheel runs true.

Cast

Also called gravity cast

Made by pouring molten alloy into a mould. It is the cheapest way to make a wheel and the most common; the grain structure is random rather than aligned.

Concours

Judged to the factory standard, where points come off for anything that is not as the plant built it. It is a standard of finish and correctness, not a level of expense.

D

Dog dish

Also called poverty cap, dog dish cap

The small stamped factory cap covering just the hub. Also called a poverty cap, because it was what you got when you did not tick the box for anything better.

Day 2

Also called day two, day-2

A car modified the way owners actually modified them when new — the wheels, exhaust and traction aids that went on shortly after delivery.

Say it right

The numeral, not the word. The judging body names the class Day 2 Cars, and that is the form owners use in conversation; magazines are where Day Two survives.

F

Face

The visible outer surface of the wheel — the spokes and the area between them. How far the face sits in the barrel sets the lip.

Forged

Formed from a solid billet of aluminium under extreme pressure, which compresses and aligns the grain. The result is denser and stronger for its weight than a cast wheel, and it is why a forged wheel can be lighter without giving anything up.

Flow-formed

Also called flow forming, rotary forged

A cast centre with the barrel spun and stretched under pressure. It sits between cast and forged: stronger than cast, not a forging.

H

Hub-centric vs lug-centric

Also called hubcentric, lugcentric

Hub-centric wheels are located by the centre bore sitting on the hub. Lug-centric wheels are located by the taper of the lug nuts as they pull down.

Hubcap

Also called hub cap

A cap that covers only the hub and the lug nuts, leaving the rest of the wheel showing.

Say it right

Not interchangeable with wheel cover. If it covers the valve stem, it is a wheel cover.

K

Knock-off

Also called knockoff, knock off, KO

A wheel held on by a single central nut, undone by knocking it round. Most period-look wheels on these cars are knock-off style: a centre cap over conventional studs.

L

Lip

The outer edge of the rim standing proud of the spokes. A deeper lip comes from more of the barrel sitting outboard of the wheel's face.

Load rating

The maximum weight one wheel is engineered to carry. It is a per-wheel figure, so it has to clear the heaviest corner of the car, not a quarter of the car's weight.

M

Mounting pad

Also called mounting face, hub face

The flat machined area behind the face that clamps against the hub. Every fitment measurement on a wheel is taken from this surface.

Mid-year

Also called midyear, C2

The 1963-1967 Corvette, sitting between the solid-axle cars and the 1968-on shark. The 1963 coupe is the one-year-only split-window.

N

Numbers matching

Also called matching numbers

The engine or driveline can be proved to that specific car, usually because the stamp carries the last digits of the VIN. It describes the car, never the person or the work.

Say it right

It modifies a component or a car - a numbers-matching 402ci V8. Nobody calls themselves a numbers-matching restorer, and there is no such thing as a numbers-matching restoration. Attaching it to a person reads as someone who learned the term from auction listings.

Numbers correct

Also called date correct, date-code correct

The right casting number and date code for the model and build date, but with no way to tie the part to that particular VIN. Also called date-correct.

Say it right

This is the distinction insiders police. Matching is provable to the car; correct is right for the model. Most drivetrains can only ever be correct.

O

Offset (ET)

Also called ET, wheel offset

The distance from the wheel's mounting face to its centreline, in millimetres. Positive offset pulls the wheel inboard, negative pushes it out. ET is short for the German Einpresstiefe.

Measured in millimetres, from the centreline to the mounting face

One-piece, two-piece, three-piece

Also called monoblock, multi-piece

How many parts the wheel is built from. One-piece (monoblock) is machined from a single forging; multi-piece wheels bolt a separate barrel or barrels to the centre, which allows more width and offset combinations.

P

Poke and tuck

Also called poke, tuck, flush

How the wheel sits relative to the fender line. Poke stands proud of it, tuck sits inside it. On these cars the factory line is the reference everyone is judging against.

Pro-touring

Also called pro touring, protouring

A muscle-era car built to be driven hard on real roads and at track days. The line between this and a restomod is what the car is built to do, not which parts are on it.

R

Rolling diameter

Also called overall diameter

The overall height of the mounted tyre. Changing it changes your speedometer reading and how the gearing feels, which is why a taller wheel usually wants a shorter sidewall.

Rubbing

Also called rub, tub rub

The tyre touching the fender lip, frame or suspension — often only at full lock or over a bump, which is why it can pass a driveway test and fail on a road.

Restomod

Also called resto-mod, resto mod

A period car rebuilt with modern running gear, brakes, and suspension while keeping the original body and proportions.

Say it right

One word. The closed spelling is what the forums where owners argue about it use; Resto-Mod survives mainly in older thread titles.

RPO code

Also called RPO, regular production option

Regular Production Option — GM's code for a factory-fitted option. On Chevelles especially, the RPO codes are the currency in which owners describe a car.

S

Section width

Also called tyre width, tire width

The widest point of a mounted tyre, sidewall to sidewall — the first number in a size like 235/60R15. It is not the tread width, and it changes with the rim it is mounted on.

Staggered fitment

Also called stagger

Running a wider wheel and tyre at the rear than the front. Common on restomod and pro-touring builds, rarely correct on a car being judged to its option sheet.

Spinner

Also called spinners, spinner cap

The finned centre piece that gives a knock-off or wheel cover its blades. On the Impala SS the whole piece is a wheel cover, and owners just call them the spinners.

Survivor

An unrestored car carrying its original finishes and components. The word does real work, so it is worth reserving for cars that have genuinely never been apart.

Solid axle

Also called solid-axle, SA, C1

The 1953-1962 Corvette, named for the live rear axle it used before independent rear suspension arrived in 1963.

T

Tribute and clone

Also called clone, recreation

A car built to look like a higher-spec model it did not leave the factory as. Tribute is the courteous word, clone the blunt one; both are honest, and neither is a fake.

Tri-Five

Also called tri five, trifive

The 1955, 1956 and 1957 Chevrolets, taken as a set. The name is used as a single word by the people who own them.

U

Under-tired

Also called under tired

Left the factory on tyres too small for the car's weight and power — a defining trait of the era rather than a fault of any one car. Owners use it about the plant's decision, not the owner's.

W

Wheel cover

Also called full wheel cover, spinner wheel cover

A full-face piece that covers the whole wheel, including the valve stem. The 1962-64 Impala SS spinner piece is a wheel cover.

Say it right

This is the vocabulary this audience polices hardest. A wheel cover covers the wheel; a hubcap covers only the hub and lug nuts. Owners correct each other on it in public, politely and immediately.