There’s an undeniable appeal to the Honda Grom and other little bikes like it – the Kawasaki Z125, Kymco K-Pipe 125, SSR Razkull, and Benelli TnT135 come to mind. All of these little tikes offer silly amounts of fun for a relatively small ding to your wallet. Of course, gearheads being gearheads, we can’t leave well enough alone, and it was only a matter of time before the aftermarket had gone crazy modifying these things. It’s madness to see this little 125cc, two-valve Single, meant for simple mass transit especially in the Asian market, get transformed to fire-breathing racers with five-speed transmissions and carbon fiber wheels costing more than the bike itself! We’ve even seen some making double their stock 10-ish horsepower! Imagine taking your bike and bolting on twice the power.
If you’re one of those serious about making your Grom better than the rest, we’ve gathered 10 must-have items to give your Grom the edge.
While sprockets don’t add any power to your bike, having the ability to tailor the power application more to your liking via gearing changes can really transform any bike. This is especially true when you have as many fingers as you do horsepower. Changing the gearing via larger or smaller sprockets can either help you reach a higher top speed or help you accelerate quicker. Many times, aftermarket sprockets are made from lightweight aluminum rather than the heavy steel of the stockers, significantly reducing both unsprung and rotating mass. If you don’t know what that means or why it’s important, just know it’ll help your bike in most all performance applications. Vortex makes a wide variety of sprockets to fit the Grom.
Once you start getting serious with Grom performance – especially if you plan on going to racetracks – you’ll soon discover the stock pegs will drag on the floor very quickly. Luckily, there’s a solution to that: aftermarket rearsets. As the name implies, these pegs place your feet slightly higher and a little more rear set. The result is less chance of dragging pegs or boots on the ground at lean. If you’re really racy, some offer the ability to reverse the shift pattern, so first gear is up and the rest are down – just like the MotoGP guys. Lastly, rearsets also have a side benefit of looking cool, too. Several different companies make rearsets for the Grom. This is just one example.
Lots of people focus on going fast and forget about other crucial aspects of performance… like stopping. In the case of the Grom, the stock rubber lines are fine for a trip down to the coffee shop, but they start to feel real spongy when you’re riding hard. Steel braided lines solve that problem by not expanding (like a rubber line) when the brakes are applied. The end result is a much firmer feel at the lever. Like the rearsets, steel braided brake lines are widely available from a large number of retailers and companies.
Of course, there’s more to stopping a motorcycle than brake lines. A more aggressive pair of brake pads, particularly those of the sintered variety, will go a long way in transforming the braking characteristics of your Grom. Sintered pads will have metal particles embedded within the pad material for more bite when you pull the lever. The tradeoff to the stronger bite is quicker pad wear, but replacement pads are cheap and easy to swap out, so there’s really no reason not to upgrade your pads. EBC is a trusted name, if you’re looking for a specific example.
If you really want to get serious about scrubbing speed on your Grom, then the above mentioned lines and pads should get paired up with a larger rotor. The stock 220mm disc is actually fairly adequate for most people and most situations, but if “good enough” won’t do, this EBC rotor kit delivers a 240mm disc and an adapter bracket to relocate the brake caliper accordingly. The result, we’re told, is insane stopping ability likely beyond what any Honda engineer ever imagined for this little bike.
If there’s one area severely lacking on the Grom, it’s suspension. Sure, the stock stuff is fine for a leisurely stroll around town, but if you’re silly enough to take one of these to the track like we are, you need a little more damping at both ends. Thankfully, there are enough other crazy people like us out there to warrant suspension companies to make fork kits and shocks to massively upgrade the Grom’s handling. Contacting the companies directly is the best way to go, as they can assess the kind of riding you do and develop a kit specific to your needs and your weight. It’s surprising how much better these little bikes handle and feel with proper suspension.
You might have noticed the first bits and pieces we recommend for the Grom have little to do with increasing power. That’s because we think those areas are of more immediate concern than boosting power. Of course, once you get your Grom handling correctly and stopping on a dime, then it’s time to go nuts adding power. The first stop is taking care of the basics, like adding an exhaust to help the Grom breathe. It’s no secret the standard setup chokes the little Grom. Aftermarket exhausts not only allow it to breathe easier – which boosts power a little – but they also sound better and shave a little weight compared to the stock components. There are several exhausts available for the Grom. This is just one example.
Following the “breathe easier” train of thought, the Chimera air intake for the Grom is a very popular upgrade. Like the exhaust, the stock air intake is restrictive. With the Chimera intake, airflow has a much clearer path to follow. As a bonus, the kit itself is easy to install and the gains are significant when you combine it with an exhaust. We’ve seen over 10% gains in power over stock in our own testing – that’s huge!
Anyone who knows a little bit about adding power to an internal combustion engine knows you don’t simply throw an intake and exhaust at it – you have to make sure the air/fuel ratio is correct. That’s where a Dynojet Power Commander V comes in. While the capabilities of the PCV are far greater than the capabilities of the Grom, you might be impressed by the fact the PCV is able to map each individual cylinder in each gear on a multi-cylinder motorcycles. It also allows the user to adjust timing +/- 20 degrees, no longer needs a 9-volt adapter, and has a built-in, two-position map switching function. Like we said, it’s far more capable than the Grom, but can also awaken the little Single, too.
If your pockets run deep and you’re absolutely serious about getting the most out of your Grom, the black hole of performance upgrades is huge. Big bore kits and even entire engine swaps are not out of the realm of possibility, but here we present the modest end of extravagance as far as engine mods go. With the Koso 4-valve cylinder head kit, you can swap out the stock two-valve head and double the amount of valves. In the process, you also up the compression ratio quite a bit and get a new camshaft. While we haven’t tested one of these ourselves, anecdotal evidence says the massive improvement in airflow results in equally substantial gains in power. We believe it!
We are committed to finding, researching, and recommending the best products. We earn commissions from purchases you make using the retail links in our product reviews and other articles. Learn more about how this works.