Wheel Bolt Thread Sizes: Diameter, Pitch and Vehicle Fitment

A wheel bolt thread size such as M14x1.5 gives two measurements in millimetres. The first is the thread diameter (14 mm). The second is the thread pitch (1.5 mm between thread crests). Volkswagen, Audi and Porsche generally use M14x1.5 bolts. Most Mercedes-Benz passenger cars use M12x1.5. Older BMW models, including the BMW E46, use M12x1.5. Most newer BMW models use M14x1.25. A bolt fits only if its diameter, pitch, seat shape and length all match the hub and the wheel. The tire sidewall describes the tire and rim diameter. It never tells you the bolt thread.

What do the numbers on the tire sidewall tell you about wheel fitment?

The tire sidewall gives the tire's size and performance ratings. It contains no information about wheel bolts. A typical marking looks like 225/45 R17 91W. Each part means something different:

• 225 is the nominal section width of the tire in millimetres.
• 45 is the aspect ratio. This means the sidewall height is 45% of the section width. It is a ratio, not a length in millimetres.
• R means radial construction.
• 17 is the rim diameter in inches. It is the only value here that describes the wheel.
• 91 is the load index, a performance rating. Load index 91 corresponds to 615 kg per tire.
• W is the speed rating. W corresponds to 270 km/h.

None of these values identify the hub's bolt thread, the bolt pattern or the bolt seat shape. Those are properties of the vehicle hub and the wheel itself. Wheel markings such as 8Jx17 ET35 5x120 give rim width, offset and bolt pattern, which are closer to mounting questions. Even they do not state the thread size.

How do width, aspect ratio and rim diameter change tire size?

Sidewall height, overall diameter and circumference can be calculated from the three size numbers. Follow these steps:

1. Find the sidewall height. Multiply width by aspect ratio: 225 mm × 0.45 = 101.25 mm.
2. Convert the rim diameter to millimetres. Multiply by 25.4: 17 in × 25.4 = 431.8 mm.
3. Find the overall diameter. Add the rim diameter and two sidewalls: 431.8 + 2 × 101.25 = 634.3 mm.
4. Find the circumference. Multiply the overall diameter by π: 634.3 × 3.1416 ≈ 1,992.7 mm.

The table compares three sizes. All are commonly discussed for cars such as the BMW E46.

Tire size	Sidewall height	Overall diameter	Circumference	Difference vs 225/45 R17
205/55 R16	112.75 mm	631.9 mm	≈1,985.2 mm	≈ −0.4%
225/45 R17	101.25 mm	634.3 mm	≈1,992.7 mm	reference
225/40 R18	90.0 mm	637.2 mm	≈2,001.8 mm	≈ +0.5%

A larger rim diameter combined with a lower aspect ratio keeps the overall diameter nearly the same, while the sidewall gets shorter. A wider tire at the same aspect ratio gets a taller sidewall, because the ratio applies to a larger width.

What are the limits of these calculations?

Calculated tire geometry is nominal and does not predict actual size or vehicle fitment. Real tire dimensions vary with several factors:

• the tire's brand and model
• the width of the rim it is mounted on
• inflation pressure
• tread wear

A size with a similar calculated diameter can still rub on suspension or bodywork. This can happen if the wheel's width or offset is different. The calculation also says nothing about whether the wheel bolts fit. When you change from a 16-inch to an 18-inch wheel, the thread stays the same, because it belongs to the hub. The bolt length or seat type may still need to change for the new wheel.

What does a wheel bolt thread size mean?

A metric wheel bolt thread size is written as M, then the diameter, then the pitch, all in millimetres. In M12x1.5, M means ISO metric thread. 12 is the nominal major diameter, measured across the outside of the threads. 1.5 is the pitch, the distance from one thread crest to the next.

• Thread diameter sets the bolt's basic size. An M12 bolt will not engage an M14 hub. An M14 bolt will not enter an M12 hole.
• Thread pitch sets how far the bolt moves per turn. An M14x1.25 bolt and an M14x1.5 bolt have the same diameter, but they are not interchangeable. Forcing the wrong pitch damages the threads.
• A smaller pitch number means a finer thread. M14x1.25 has more threads per millimetre of length than M14x1.5.

Similar-looking bolts are an easy mistake. M14x1.25 and M14x1.5 can start by hand for a turn or so before binding. A bolt that resists early should never be forced in with a wrench.

Which wheel bolt thread sizes do BMW, VW, Audi, Mercedes and Porsche use?

Each of these manufacturers uses a small number of standard bolt threads. The exact size depends on model and generation. The table summarises typical factory fitment. Confirm the size for a specific vehicle using its documentation or a VIN-based parts lookup.

Manufacturer	Typical wheel bolt thread size	Typical factory seat type	Typical bolt pattern
BMW (older models, e.g. E46, E39, E90)	M12x1.5	60° conical	5x120
BMW (most newer G-series models)	M14x1.25	60° conical	5x112 on many G-series models
Volkswagen	M14x1.5 on most modern models; M12x1.5 on some older models	Radius (ball)	5x112 on most modern models; 5x100 or 4x100 on some older or smaller models
Audi	M14x1.5 on most modern models; M12x1.5 on some older models	Radius (ball)	5x112 on most modern models
Mercedes-Benz	M12x1.5 on most passenger cars; M14x1.5 on some larger SUVs and other models	Radius (ball)	5x112
Porsche	M14x1.5 (some high-performance models use centre-lock hubs instead)	Radius (ball)	5x130 on most models; 5x112 on the Macan

The bolt pattern (PCD) is a separate measurement from the thread size. Two cars with the same pattern can use different threads. Two cars with the same thread can have different patterns.

BMW wheel bolt thread size

Most BMW models built before the G-series generation use M12x1.5 wheel bolts with a 60° conical seat. Most newer models use M14x1.25. This includes most G-series cars and some earlier large SUVs. BMW uses wheel bolts screwed into the hub, not studs and nuts. The thread therefore belongs to the hub. When moving wheels between BMW generations, check the bolt pattern and the thread, because both may have changed.

E46 wheel bolt thread size

The BMW E46 3 Series uses M12x1.5 wheel bolts with a 60° conical seat, on a 5x120 bolt pattern. This applies across the E46 range on standard hubs. Bolt length depends on the wheel. OEM alloy wheels, steel wheels, aftermarket wheels and any spacers can each need a different shank length. The thread size still stays M12x1.5.

VW wheel bolt thread size

Most modern Volkswagen models use M14x1.5 wheel bolts with a radius (ball) seat. Some older and smaller VW models use M12x1.5. Factory VW alloy wheels use a radius seat. Many aftermarket wheels are made for 60° conical bolts instead. The wheel, not the car, decides which seat the bolt needs.

Audi wheel bolt thread size

Most modern Audi models use M14x1.5 wheel bolts with a radius (ball) seat. This matches Volkswagen Group practice. Some older Audi models used M12x1.5. Because VW and Audi share many hubs, bolts are often interchangeable between them. Still check the thread, seat and length for the specific car and wheel.

Mercedes wheel bolt thread size

Most Mercedes-Benz passenger cars use M12x1.5 wheel bolts with a radius (ball) seat. Some larger SUVs and other models use M14x1.5. Mercedes and VW/Audi both commonly use the 5x112 bolt pattern and radius seats. Even so, their bolts are not automatically interchangeable. The thread diameter can differ, and the seat radius is commonly specified differently: about 14 mm for Mercedes and 13 mm for VW/Audi. A wrong radius gives poor contact between the bolt and the wheel.

Porsche wheel bolt thread size

Porsche road cars on five-bolt hubs generally use M14x1.5 wheel bolts with a radius (ball) seat. Most models use the 5x130 pattern, and the Macan uses 5x112. Certain high-performance versions use a centre-lock hub with a single central nut instead of five bolts. Five-bolt wheel bolts do not apply to these cars.

Why is thread size alone not enough for wheel bolt fitment?

A wheel bolt fits safely only when four things match: diameter, pitch, seat type and length. The thread must match the hub. The seat and length must match the wheel.

• Seat type is the shape under the bolt head that contacts the wheel. Common types are 60° conical, radius (ball) with a specific radius, and flat seat with a washer. A mismatched seat touches the wheel on a small area. The bolt can then loosen.
• Shank length sets how much thread engages in the hub. If the bolt is too short, too few threads engage. If it is too long, it can bottom out before clamping the wheel, or hit parts behind the hub. Thicker alloy wheels and spacers usually need longer bolts than steel wheels.
• Torque specification is set by the vehicle manufacturer for each model. Take it from the vehicle documentation, not from the thread size alone.

How do you identify the wheel bolt thread size on your car?

The most reliable way is the vehicle's documentation or a VIN-based parts lookup. You can confirm it by measuring an existing bolt.

1. Check the documentation. Look in the owner's manual or service data, or run a parts lookup with the VIN, for the exact bolt part and thread size.
2. Remove one bolt. Do this with the car safely supported and the other bolts in place.
3. Measure the diameter. Use a caliper across the outside of the threads. A reading slightly under 12 mm or 14 mm indicates M12 or M14.
4. Measure the pitch. Use a thread pitch gauge. As an alternative, count thread crests over a known length. Ten pitches spanning 15 mm means 1.5 mm pitch. Ten pitches spanning 12.5 mm means 1.25 mm pitch.
5. Identify the seat. Check whether the seat is a straight 60° cone or a curved radius. Then check that it matches the seat machined into the wheel.
6. Measure the shank length. For conical and radius seats, measure from where the seat contacts the wheel to the end of the bolt. Compare this with the length needed for the wheel and any spacer.

If any value does not match after you change wheels, change the bolts, not the hub. If you are unsure about the seat or length, compare against the wheel manufacturer's specification before fitting.