Wheel bolts and wheel nuts

How to choose

Bolt, nut or stud

A wheel is fixed to the hub in one of two ways. Audi, BMW, Mercedes-Benz, Volkswagen and several other European makers use wheel bolts that screw straight into a thread in the hub. Most Asian and US cars have studs pressed into the hub, and the wheel is tightened on with nuts. The car decides which type you need, not the wheel, so start by checking what your car has now. You only need separate wheel studs if one of the studs on the hub is damaged.

Thread, seat and length

Three things on a wheel bolt or nut have to match both the car and the wheel. If even one of them is different, the bolt is wrong, even if it screws in.

• Thread. M12x1.5 means a 12 mm diameter and a 1.5 mm pitch. An M12x1.25 bolt has the same diameter but a different pitch: it goes in for the first few turns, then binds and damages the thread in the hub. The thread is set by the car, and you can read it off the old bolt or get it from the car manufacturer.
• Seat - the underside of the bolt head or nut that presses against the wheel. There are conical 60°, ball (radius R12, R13, R14) and flat seats. A flat seat usually has a washer, as found on some Citroën and Peugeot models, for example. The seat has to match the hole in the wheel, and a ball radius has to match exactly: an R12 bolt in an R14 hole presses on the wheel with only a narrow edge.
• Length. The bolt has to go far enough into the hub. H&R's fitting instructions give a minimum of 7.5 turns (about 11 mm) for an M14x1.5 thread and 6.5 turns (about 10 mm) for M12x1.5. A bolt that is too long can bottom out against brake or ABS parts, so after fitting, turn the unloaded wheel by hand.

Why your old bolts often do not fit new wheels

Many European cars have a ball seat on their original alloy wheels, while aftermarket wheels more often use a conical 60° seat. An alloy wheel is usually thicker at the mounting face than a steel wheel, so the bolt needs a longer thread to reach the required depth. With wheel spacers, the bolt has to be longer again by the thickness of the spacer. The wheel manufacturer specifies the correct seat and length.

Check the wrench size as well. Wheel bolts usually have a 17 or 19 mm hex, and nuts also come in 21 and 22 mm. On wheels with narrow bolt holes, such as thin-spoke designs, a standard socket may not fit into the hole or may scratch the wheel. These wheels take bolts with a small head (with "Tuner" in the name), which are turned with a special key. Keep it in the car with the jack. Chrome, black or coloured finishes make no difference to the fixing; they are a matter of taste.

Tightening and the roadworthiness test

Point 5.2.1 of Annex 1 to Cabinet Regulation No. 295 requires every wheel nut and bolt to be of the correct design and properly tightened. A wrong or loose bolt or nut is a grade 2 defect at the roadworthiness test. If more than one bolt is missing or the wheel moves against the hub, the grade is 3.

The tightening torque is set by the car manufacturer and given in the owner's manual. For aftermarket wheels, the wheel manufacturer may also state it. Tighten with a torque wrench in a crosswise pattern, and check again after the first few kilometres, because the new contact surfaces settle. McGard recommends doing this after 25 miles (about 40 km), H&R after about 100 km.