Torque wrench

A torque wrench measures how hard you are turning a bolt, so you can stop at the value the part's maker gives. Park Tool describes torque as the twisting force on a fastener and a useful stand-in for how tightly the joint is clamped (Park Tool torque guide).

What it's used for

Too little tension lets a bolt work loose and can cause creaks or damage, and too much can deform threads or parts (Park Tool). On an e-bike or scooter that matters for brake calipers, rotor bolts, stems, handlebars and cassette lockrings. For example, Park Tool says a cassette lockring needs at least 40 Nm or whatever the maker recommends (Park Tool cassette guide), while its Shimano brake bleed guide lists bleed screws at only a few Nm (Park Tool bleed guide).

What to look for

• A range that covers the values in your bike's manual. Small brake bolts and large drivetrain parts can need very different values, so check that your wrench covers all of them.
• Readings in Newton meters (Nm), the unit most of the bike industry uses (Park Tool). Park Tool gives conversions: Nm equals in-lb times 0.113, and Nm equals ft-lb times 1.356 (Park Tool).
• Bits that fit your bolts, including star (Torx compatible) bits if your bike needs them (Park Tool e-bike tools).

Using it safely

• Use the maker's value. Park Tool says its tables are only a reference and to contact the manufacturer for current specs (Park Tool).
• Prepare threads first. A cross-threaded bolt will not tighten properly even with a torque wrench (Park Tool).
• Some things are not set by torque, such as spoke tension and quick-release levers (Park Tool).

Guides that use it

• Replace disc brake pads
• Clean and true brake rotors
• Bleed hydraulic disc brakes
• Adjust a rear derailleur
• Fix a flat on a rear hub motor wheel

Sources

• Torque specifications and concepts, Park Tool
• Cassette removal and installation, Park Tool
• Shimano hydraulic brake service and adjustment, Park Tool
• What tools do I need for my e-bike, Park Tool