Auto parts have no single freight class — the same group runs from class 50 for a pallet of transmissions to class 300 for a boxed truck hard top, and density decides most of it. Since the July 19, 2025 NMFC overhaul, general automobile parts rate on the standardized 13-tier density scale: drained driveline parts sit at the dense end (35–55 lb/ft³, class 55–50), a palletized iron V8 runs 12–19 lb/ft³ (class 85–70 under NMFC item 120790), and boxed sheet metal is mostly air at 1–4 lb/ft³ (class 250–150). The famous exception is tires, which still behave like a commodity item and rate around class 70 no matter what the density math says. Here's the part-by-part map, the worked engine example, and the core-return trap.
What freight class are auto parts?
Think in shipped density — the part plus its box, crate and pallet — and the chaos collapses into bands. Here's where common auto parts land as tendered, per broker-published listings and the density chart:
| Auto parts, as tendered | Typical shipped density | Typical class |
|---|---|---|
| Transmissions, transfer cases, differentials (drained, palletized) | 35–55 lb/ft³ | 55–50 |
| Bare blocks, heads, crankshafts, rotors (boxed on pallet) | 22.5–35 lb/ft³ | 65–60 |
| Complete engines, palletized or crated (NMFC 120790) | 12–22.5 lb/ft³ | 85–70 |
| Axles, struts, springs, manifolds (boxed, palletized) | 8–15 lb/ft³ | 100–85 |
| Tires, palletized (commodity-style item — see below) | 4–15 lb/ft³ as stacked | 85–60 |
| Fenders, hoods, doors, body panels (boxed or crated) | 1–4 lb/ft³ | 250–150 |
| Plastic fascias, spoilers, trim (boxed) | 1–3 lb/ft³ | 300–250 |
The pattern is metal-to-air ratio, same as any commodity: a transmission is a solid lump of iron and aluminum, a fender is a painted shell around nothing. A standard automatic transmission weighs 150–250 lb in 4–6 cubic feet — 35–55 lb/ft³, the cheapest tiers on the chart — while the fender math below barely clears 2 lb/ft³. Your exact class comes from the four-step density calculation: measure the packed handling unit at its extremes, cube it, divide the weight, read the chart.
What freight class is a car engine?
Engines ship under NMFC item 120790, and broker listings break it down by packaging: standard palletized engines — strapped and shrink-wrapped — at class 85, crated engines denser than 18 lb/ft³ at class 70, and heavy iron and diesel blocks over about 31 lb/ft³ cited as low as class 60. Typical weights run 250 lb for an aluminum 4-cylinder, 500 lb for an iron-block V8 and 1,000 lb for a heavy-duty diesel. Here's one 500-lb V8, tendered three ways:
| Configuration | Dims (in) | Weight | Cube | Density | Class |
|---|---|---|---|---|---|
| Strapped to bare 48×40 pallet, wrapped | 48 × 40 × 38 | 540 lb | 42.2 ft³ | 12.8 lb/ft³ | 85 |
| Snug crate, integrated skid | 44 × 34 × 36 | 585 lb | 31.2 ft³ | 18.8 lb/ft³ | 70 |
| Crated with the transmission riding along | 44 × 36 × 38 | 810 lb | 34.8 ft³ | 23.3 lb/ft³ | 65 |
Row one: 48 × 40 × 38 = 72,960 in³ ÷ 1,728 = 42.2 ft³; 540 ÷ 42.2 = 12.8 lb/ft³ — the "12 but less than 15" tier, class 85. Row two shrinks the rectangle: a crate sized to the engine instead of the pallet cuts the cube by a quarter, density jumps to 18.8, and the shipment crosses the break at 15 into class 70. Row three adds the 200-lb transmission to the same crate — 810 lb in 34.8 ft³ is 23.3 lb/ft³, past the 22.5 break into class 65. Same engine, three classes, and the cheapest version is the one that ships more. Broker-published 2026 examples price a 250-lb engine cross-country at $200–$275, a 500-lb V8 at $250–$340 and a 1,000-lb diesel at $350–$480. Drain oil and coolant completely first — carriers can refuse a dripping unit, and residual fluid means cleanup fees.
Why don't tires follow the density math?
Run the numbers on eight loose-stacked passenger tires: 48 × 40 × 60 inches is 66.7 ft³, and at roughly 256 lb with the pallet that's 3.8 lb/ft³ — class 250 on the density chart. Yet nobody pays class 250 to ship tires. Tire items have long carried commodity-style classes: class 70 is the traditional anchor, and current broker listings range from 60 for tightly laced pallets to 85 (one lists NMFC 16956 at class 85 around 14.6 lb/ft³ laced and nested). Tires stack, interlock, survive handling and hurt nothing they ride with — the handling and stowability factors that an NMFC item encodes beyond raw density all favor them, so their class does too.
The general lesson from the 2025 changes: density is now the default, not the whole rulebook. Items with genuine handling, stowability or liability quirks kept condition-based classes — automotive sheet metal with irregular edges is cited at class 150 where voids kill stowability, and tires went the other direction, rating far better than their density. Never guess which regime your part is in. Lace tires in interlocked columns, band them to the pallet, and confirm the applied item and class with your carrier before the BOL is printed.
Body panels and sheet metal: you're paying for air
Commodity-style listings for auto body parts read like a punishment schedule: boxed doors and tailgates at class 150, primed fenders at 200, engine hoods and body sections at 250, hard tops at 300. The density math explains it — a 58 × 30 × 22 box with two fenders and packing runs about 50 lb in 22.2 ft³, or 2.3 lb/ft³, which is class 250 territory all by itself. A big light box is also exactly what terminal dimensioners flag, so an optimistic class rarely survives the reweigh. The plays that actually cut the bill: nest several panels in one crate with foam between them, size the box to the part rather than the pallet, and consolidate — five panels in one 120-lb crate beats five 30-lb boxes on both cube and minimums. Broker-published LTL figures for auto body parts run about $300 to $1,500+ per shipment depending on size, distance and packaging.
Core returns: same class, $9 of coverage
Cores — the used engines, transmissions and alternators heading back for remanufacturing credit — ship at exactly the class the density math produces, because the NMFC doesn't care about age. Carrier liability does: standard tariffs commonly cap "articles other than new" at $0.10 per pound, versus roughly $0.50–$25 per pound for new goods. A 90-lb transmission core recovers about $9; a 500-lb used engine, about $50; a pallet of eight cores worth $2,000 in credits, perhaps $65. That's not insurance, it's a rounding error — real coverage on valuable used parts has to come from declared-value cargo insurance, which typically prices from a few dollars per $1,000 declared. The rest of the core playbook is fluid discipline: drain everything, cap or plug every port, bag the unit before it's banded to the pallet, and describe it honestly on the BOL as used parts — a leaking core can be refused at pickup and billed for cleanup after it.