You’re standing over your bike with a pair of shiny new pedals, and honestly, it looks like the easiest job in the world. It’s just a bolt, right? Lefty-loosey, righty-tighty. Except, if you follow that logic, you are about to ruin your bike.
Installing pedals on a bike is one of those deceptively simple tasks that manages to break more equipment than almost any other home repair. I’ve seen seasoned riders—people who can index a derailleur by ear—completely cross-thread a high-end carbon crankarm because they forgot one weird quirk of physics.
Bicycle pedals are unique. They don't follow the rules of your kitchen faucet or a lug nut on a car. One side is "normal," and the other is a "reverse-thread" nightmare designed to keep the pedal from unscrewing itself while you ride. If you force it the wrong way, you’re not just tightening it; you’re effectively acting as a human lathe, carving out the metal threads until there's nothing left but silver shavings and regret.
The Secret of the Left-Hand Thread
Here is the thing you have to burn into your brain before you even touch a wrench: the left pedal (the non-drive side, away from the chain) is reverse-threaded. To tighten it, you turn it counter-clockwise. To loosen it, you turn it clockwise.
Why? It’s a phenomenon called mechanical precession. Back in the late 19th century, the Wright brothers—yes, those Wright brothers, who were bicycle mechanics before they were pilots—actually helped popularize the understanding of why pedals need to be threaded this way. As the pedal spindle flexes under the weight of your foot, it creates a force that would actually "walk" a standard-threaded pedal right out of the arm.
The right side (the drive side with the chain) is totally normal. Clockwise to tighten.
Identifying Which is Which
Most manufacturers make this easy, but you have to look closely. Look for a tiny "L" or "R" stamped into the end of the spindle or etched onto the flats where the wrench goes. Sometimes, the left pedal has a series of small serrations or grooves on the nut, which is a universal "code" for left-hand threads in the mechanical world. If you don't see those marks, don't guess. Line them up next to each other. The threads will lean in opposite directions.
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Tools of the Trade (and the Ones That Will Fail You)
You don't need a massive toolbox for installing pedals on a bike, but you do need the right tool. This depends entirely on what kind of pedals you bought.
Old-school flats and many mid-range pedals require a 15mm pedal wrench. This is a thin, long-handled tool designed to slip into the narrow gap between the pedal body and the crankarm. Do not try to use a standard adjustable crescent wrench here. They are usually too thick. They’ll slip, chew up the aluminum, and leave you with a bloody knuckle.
Modern high-performance pedals, like those from Shimano, Look, or Time, often don't have wrench flats at all. Instead, they have a hexagonal hole in the back of the spindle. For these, you’ll need a 6mm or 8mm Allen key (hex wrench).
The Importance of Grease
Never, ever install a pedal "dry."
Metal-on-metal contact in a high-torque environment like a crankarm leads to "galling" or cold-welding. Over time, the two surfaces bond together. When you try to remove that pedal two years later, it won't budge. Use a dedicated bicycle grease like Park Tool PPL-1 or even a basic marine-grade anti-seize. A small dab on the threads makes the installation smoother and ensures you can actually get them off again someday.
Step-by-Step: The "No-Stress" Method
- Prep the threads. Wipe down the inside of the crankarm holes with a rag. Get the old grit out. Apply a thin layer of grease to the new pedal threads.
- The Finger-Tight Rule. This is the most important step. Start the threads by hand. You should be able to get the pedal at least 3 or 4 full rotations in without using a tool. If you feel resistance after half a turn, stop. You are likely cross-threading it. Back it out and try again.
- The Rotation Trick. Here’s a pro tip: for both sides, if you are using a wrench on the flats, you turn the wrench toward the front of the bike to tighten.
- Snug it up. You don't need to stand on the wrench. Pedals are self-tightening to an extent because of that precession we talked about. Get it "snug plus a nudge." If you’re a stickler for torque specs, most manufacturers recommend between 35 and 40 Newton-meters (Nm).
What Happens When Things Go Wrong?
If you started turning and felt a "pop," and now the pedal feels wobbly or won't tighten, you've stripped the threads. It happens to the best of us.
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Is the crankarm garbage? Not necessarily.
A bike shop can often perform a "Helicoil" repair. They use a special tap to cut a larger hole, then screw in a stainless steel thread insert. It’s actually stronger than the original aluminum. However, on cheap entry-level bikes, the cost of the repair might be more than a new crankarm. On a $500 carbon crank, the Helicoil is a lifesaver.
A Note on Washers
Some cranks, especially carbon ones from brands like SRAM or RaceFace, require a small metal washer between the pedal and the arm. Don't skip this. Without it, the hard steel of the pedal spindle can dig into the soft carbon or aluminum face of the crank, leading to cracks or annoying creaks that will drive you crazy on a long ride.
The Clipless Transition
If you are installing pedals on a bike for the first time because you’re moving to "clipless" (which, confusingly, are the ones you clip into), remember that tension matters. Most Shimano SPD pedals have a small 3mm hex screw on the back. This controls how hard it is to click out.
Pro tip: back that tension all the way off for your first few rides. You want to be able to escape those pedals the second you feel your balance wavering at a stoplight. We’ve all done the "zero-mph tip over." It's a rite of passage, but a loose pedal tension makes it less likely.
Troubleshooting the "Click"
Sometimes you finish the install, go for a ride, and hear a rhythmic click-click-click every time you push down. Nine times out of ten, it’s not your bottom bracket—it’s the pedal.
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Check three things:
- Is the pedal tight enough? A slightly loose spindle will creak under load.
- Did you grease the threads?
- Is the "dust cap" on the end of the pedal body loose?
If you’ve checked those and it still clicks, the internal bearings might be dry. High-end pedals can be serviced; cheap ones are usually "disposable," though a bit of heavy oil dripped into the seals can sometimes buy you another season.
Actionable Next Steps
Before you go out to the garage, do a quick inventory. Check the back of your current pedals to see if you need an Allen key or a 15mm wrench. Grab a clean rag and some grease. If you’re replacing pedals on an old bike that’s been sitting in a damp basement, spray the old ones with a bit of PB Blaster or WD-40 Specialist Penetrant and let it sit for twenty minutes before you try to break them loose.
When you start the actual work, remember the golden rule: Always turn toward the front of the bike to tighten. If you find yourself leaning your entire body weight onto the wrench and it’s not moving, double-check your direction. You might just be tightening the world's most stubborn bolt.
Once they're on, do a quick "parking lot test." Don't head out for a 40-mile epic without making sure your cleats line up and your feet feel natural. A slight adjustment now saves a knee injury later.
Check your pedal tightness again after about 50 miles. Components settle, and a quick "snug check" ensures that everything stays exactly where it should be.