Wheel nuts, like ketchup bottles, always seem to be either too tight or too loose. When it comes to wheel nuts,
too loose and you might make a mess or lose a wheel; too tight, and you might need pliers to waste time or you could break something. Unfortunately, it seems that most DIYers tend to err on the side of “tighter is better,” leading to frustration, broken bolts/threads, and even damage.
For convenience, repeatability, consistency, and safety, engineers specify the necessary compression for each cap (yes, there is a torque specification for the ketchup bottle cap), screw, bolt, nut, sensor, and spark plug. Every DIYer should learn to use a torque wrench and have at least one or two in the toolbox.
What is a Torque Wrench?
When it comes to opening ketchup bottles and tightening wheel nuts, torque is an important measurement to understand. Torque is an indirect measure of the compression exerted by the bottle cap or wheel nut on the bottle or hub, wheel, and brake rotor. We say “indirect” because there is no practical way to measure the compression or stretching of the bolt, but what is “torque” anyway?
Torque is a measure of twisting force, usually expressed in lb·ft, lb·in, or N·m (pound-foot, pound-inch, newton-meter), i.e., force times distance. To visualize this, imagine removing wheel nuts with a 2-foot breaker bar. With the socket fixed on the wheel nut, applying 50 lb of force at the end of the breaker bar results in 100 lb-ft of torque on the wheel nut, i.e., 50 pounds of force multiplied by 2 feet of leverage. With a 3-foot breaker bar, you only need to apply 33.3 lb of force to achieve 100 lb-ft of torque, while a 1-foot ratchet would require 100 lb of force.
Since human beings weren’t made with calibrated dynamometers in their hands, there’s no way to consistently measure the force you apply to a wrench and the torque you put into a nut or bolt. A calibrated torque wrench is exactly what you need to ensure proper tightening of everything from oxygen sensors and spark plugs to valve cover gasket bolts, wheel nuts, and cylinder head bolts.
Types of Torque Wrenches
Depending on the application, several types of torque wrenches are available, but three of them are the most common in the automotive field, including beam, click, and electronic torque wrenches. Each type works slightly differently to accurately measure the twisting force you apply to a given fastener.
Beam: Invented about a century ago, beam torque wrenches are the simplest and easiest to use. The main beam features a handle that you use to apply force to the socket. The indicator beam is attached to the socket head and does not move when tightening a fastener. The gauge on the main beam measures the distance it is deflected, giving you a torque reading.
Click: Click-type torque wrenches resemble standard ratchets more closely, although they have special internal mechanisms to measure torque. The most common is the micrometer adjustment, which compresses a spring inside. The spring presses against a ball or cube, which rests in a detent in the head. When the specified torque is reached, the ball or cube pops out of the detent, making a click. The tighter the spring, the harder it is to push the ball out of the detent.
Electronic: Using a piezoelectric sensor, which changes resistance based on its strain, electronic torque wrenches have no moving parts. Electronically, they detect the twisting force applied to the socket, providing a reading on a digital display. To set a specified torque, the display can usually be set to flash, vibrate, or beep when reached. Electronic types may also include a torque angle function.
Beam torque wrenches do not ratchet and can be used for tightening or loosening. Most click-type torque wrenches ratchet and can be used for tightening or loosening, although some only allow you to apply tightening torque. Beam and click torque wrenches can be used for loosening, but exceeding the specified maximum torque can damage the wrench. Split-beam torque wrenches should only be used for tightening, as loosening can damage the wrench.
Torque Wrench Sizing
To use a torque wrench correctly, the first thing you need is a torque specification. Torque specifications are found in the repair manual, but usually not in the owner’s manual. The torque wrench you choose will depend on the torque specifications: you wouldn’t use a small pound-inch torque wrench on a wheel nut, and you wouldn’t use a large pound-foot torque wrench on valve cover bolts.
Small torque wrenches, ranging from 10 to 250 inch-pounds, are useful for valve covers, throttle bodies, transmission valve bodies, some intake manifolds, and interior fasteners.
Medium torque wrenches, ranging from 5 to 100 lb-ft, are useful for engine accessories, suspension components, brake components, interior components, and some wheel nuts.
Large torque wrenches, ranging from 20 to 250 lb-ft, are useful for cylinder head bolts, major components, wheel nuts, and wheel bearing hubs.
Using a Torque Wrench Correctly
Any torque wrench requires a firm and steady hand. If there is a torque sequence, for example, for tightening wheel nuts, cylinder head bolts, and some internal engine and transmission parts, follow the steps carefully to avoid damage and ensure proper operation. Some fasteners, such as torque-to-yield cylinder head bolts, require an additional measurement beyond twisting force. After setting the bolt to a specified torque, an additional angle will be specified, turning the bolt further, regardless of torque. You can sometimes use paint marks, but torque angle gauges and electronic gauges are more accurate.
To use a beam torque wrench, watch the gauge carefully until it reaches the required torque, then stop applying force to the handle. To use a click-type torque wrench, whether spring or split-beam, adjust the dial and lock it to the required torque specification, then gradually tighten the fastener. When the torque limit is reached, you will feel and hear a “click” in the handle, at which point you stop applying force. Electronic torque wrenches are used similarly to click types, except that the setting and notification are electronic. When the torque is reached, indicated by a beep, vibration, or flashing light, stop applying force to avoid over-tightening the fastener.
Split-beam and beam torque wrenches do not require special care when storing, but micrometer-adjustment torque wrenches should be set to zero. This will prevent the spring from “setting” and distorting future torque readings. Torque wrenches should be stored in their protective cases and never dropped. About once a year, you should have your torque wrench calibrated to keep it within tolerances.
The Ketchup Bottle
By the way, a plastic ketchup bottle with a 28mm plastic cap seals best at about 14 lb·in of torque – tighter isn’t necessarily better!