If you've spent any time looking at your bike lately, you've probably realized that swapping out the stock honda msx swing arm is one of the coolest ways to change both the look and the actual handling of the machine. The Honda MSX125, or the Grom as most of us call it, is arguably the most customizable mini-bike ever made. While most people start with an exhaust or some tidy tail kits, the swing arm is where you really start getting into the "big bike" modifications that make a world of difference.
The factory swing arm is well, it's fine. It's a basic, square-section steel unit that Honda put on there because it's cheap to manufacture and sturdy enough for a 125cc engine. But let's be honest, it looks a bit unfinished. It's heavy, the chain adjustment mechanism is a bit of a pain to use, and it doesn't exactly scream "performance." Moving to an aftermarket honda msx swing arm isn't just about vanity, though the aesthetics are a huge part of it. It's about shedding weight and getting a more stable platform for your rear suspension.
Why Even Bother Replacing the Stock Arm?
When you first start looking at aftermarket parts, you might wonder if spending a few hundred bucks on a chunk of aluminum is worth it. The biggest thing you'll notice immediately is the weight difference. Most aftermarket arms are made from high-grade 7075 or 6061 aluminum. When you hold the stock steel arm in one hand and a CNC-machined aluminum one in the other, it's shocking how much lighter the custom one is.
In the world of motorcycles, we talk a lot about "unsprung weight." This is basically any part of the bike that isn't supported by the suspension—like the wheels, tires, brakes, and, you guessed it, the swing arm. The lighter these parts are, the easier it is for your rear shock to do its job. A lighter honda msx swing arm allows the rear wheel to react faster to bumps in the road, which keeps your tire in contact with the ground more consistently. You'll feel this immediately when you're taking a corner on a road that isn't perfectly smooth.
Then there's the adjustment factor. If you've ever struggled with those little plates and nuts on the back of the stock MSX to get your chain tension right, you'll love the integrated adjusters on high-end swing arms. Most of them use a much more precise "clicker" or screw-type system that makes aligning your rear wheel a five-minute job instead of a twenty-minute headache.
Understanding Length and Stretch
One of the first decisions you'll have to make when picking out a new honda msx swing arm is whether you want to stick with the standard length or go for a "stretch." This is a big point of contention in the Grom community, and it really depends on what you plan to do with the bike.
A standard length aftermarket arm keeps the nimble, flickable nature of the MSX intact. If you love weaving through traffic or hitting tight, technical go-kart tracks, stay with the stock length. You get all the benefits of the weight savings and better looks without changing the geometry of the bike.
On the other hand, an extended or stretched swing arm (usually +2, +4, or +6 inches) changes the vibe completely. Stretched Groms are huge in the custom scene. Longer wheelbases make the bike feel much more stable at high speeds, which is great if you've bored out your engine to a 186cc or added a turbo. It also keeps the front wheel on the ground, which is helpful if you've built a little torque monster that wants to loop out every time you touch the throttle. Just keep in mind that a longer swing arm means you'll need a longer chain and potentially longer brake lines.
Materials and Construction Styles
When you start browsing for a honda msx swing arm, you'll see a few different styles. The most common is the triple-square aluminum tube. This mimics the shape of the original but uses much better materials. It's a classic look that fits the bike's proportions perfectly.
If you want something that looks more industrial or high-tech, you might look into over-braced or under-braced arms. These have an extra tubular support welded to either the top or bottom of the main arm. While these are technically designed to add rigidity for racing, on an MSX, they're mostly there for the "wow" factor. They make the bike look like a miniature superbike, and honestly, they look incredible when they're anodized in bright colors or polished to a mirror finish.
Speaking of finishes, you aren't stuck with boring silver. Because most of these are aluminum, they come in a rainbow of anodized colors—gold, red, blue, black, or even neon green. It's an easy way to tie your bike's color scheme together. Just a pro-tip: if you go with a cheap anodized finish, it might fade over time if your bike sits out in the sun a lot. It's worth spending a little more for a high-quality finish that won't turn pink after three months.
Installation Realities
I won't lie to you—swapping a honda msx swing arm isn't a five-minute job, but it's definitely something you can do in your garage on a Saturday afternoon. You'll need a way to support the back of the bike without using a traditional swing arm stand (since, you know, you're taking the swing arm off). Most people use a jack under the engine or hang the rear of the frame from a sturdy rafter in the garage.
The pivot bolt is usually the trickiest part. Over time, these can get a little stuck, so having some penetrating oil on hand is a smart move. You'll also need to transfer over your rear brake caliper, the rear wheel, and the shock mount. If you're buying a quality arm, the fitment should be "plug and play," but always double-check your spacers.
One thing people often forget is the swing arm bushings or bearings. Some aftermarket arms come with high-quality needle bearings already installed, while others might require you to reuse your old ones or buy new ones separately. I always recommend going with needle bearings if you have the choice. They provide much smoother movement than the rubber bushings found in the stock setup, which translates to a more "connected" feeling when you're riding.
Maintaining Your Aftermarket Setup
Once you've got your shiny new honda msx swing arm installed, you can't just forget about it. Aluminum is great because it doesn't rust like steel, but it can still corrode or get pitted if you live near the ocean or ride on salted winter roads. A quick wipe down with a mild cleaner every time you wash the bike will keep it looking new.
You should also periodically check the torque on your pivot bolt and the rear axle. Since you've moved away from the factory setup, it's just good practice to make sure everything is staying tight. Also, keep an eye on the chain slider. The slider is that plastic piece that protects the swing arm from the chain rubbing against it. Aftermarket arms usually come with their own, and you want to make sure it isn't wearing through. If the chain eats through the slider, it'll start chewing into your expensive aluminum arm, and that's a very bad day.
Final Thoughts on the Upgrade
Is a new honda msx swing arm a "necessary" mod? Probably not if you're just using the bike for a three-minute commute to the grocery store. But if you're someone who takes pride in the build and wants to extract every bit of performance and style out of the MSX, it's one of the best upgrades you can do.
It's one of those rare parts that hits the trifecta: it looks better, it reduces weight, and it improves functionality. Whether you're going for a long-and-low drag style look or a nimble, track-ready corner carver, the swing arm is the backbone of that transformation. Just take your time picking the right length and style for your riding needs, and you'll find that it completely changes your relationship with the bike every time you hop in the saddle.