Honda Grom upgrades
No bike in the US gets modified at a higher rate per dollar than the Grom — it is the platform where riders learn to wrench, race minimoto grids, and try everything because parts cost pocket money next to big-bike prices. Nothing about a Grom stays stock, and Honda leaned into it with quick-release panels on the current bike.
Spec plate & generations
Claimed figures and the generation map. The year splits decide whether a part fits.
- Engine124 cc air-cooled single
- Power~9.7 hp (claimed)
- Wet weight223 lb (claimed, 2022+)
- Seat height30.0 in
- Gearbox4-speed (2014–2020) · 5-speed (2022+)
Generation map
- JC61 (gen 1)2014–2016
US launch of the global MSX125. Air-cooled 125 single, 4-speed box. The frame code (JC61) matters — Japanese kit makers list fitment by it.
- JC75 (gen 2)2017–2020
Restyle with LED headlight and sharper panels. Same 4-speed engine family as gen 1 — engine parts largely cross, bodywork does not. No 2021 US model year.
- JC92 (gen 3)2022–present
New 5-speed engine, higher compression, flatter seat, quick-release body panels made for swapping. Engine and exhaust parts do not cross from the 4-speed bikes. SP editions add color, not fitment changes.
Street path & track path
Two ordered sequences for the same machine. The order is the advice: spend where the next problem is, not where the catalog is loudest.
Street path
Clean up the tail
Fender eliminator with an integrated tail light — TST Industries is the Grom lighting standard, with gen-specific kits.
Cage it or slide it
Frame sliders or a full crash cage (T-Rex Racing is the Grom staple). Groms live hard lives; protection first is the community rule here too.
Exhaust plus fueling
On a Grom the 'slip-on' is usually a full system with header — Yoshimura, Two Brothers, Hindle, Tyga. Pair it with fuel management (EJK piggyback at minimum); the tiny single runs lean with an open pipe.
Gearing for grins
A rear sprocket change on the 420 chain transforms around-town punch for the price of dinner. The cheapest personality change in motorcycling.
Suspension that keeps up
The stock shock and fork are built to a price: a YSS shock is the budget classic, Öhlins the serious pick, with fork springs or cartridge internals from minimoto specialists.
Seat and contact points
Aftermarket seats fix the stock plank on long rides; grips and levers finish the fit. Gen 3's flatter stock seat already helps.
Track path
Race rubber on 12s
12-inch race tires — PMT slicks and Mitas race compounds are the minimoto grid standards. Street IRC stockers are the single biggest lap-time limiter.
Suspension for your weight
Adult riders overwhelm the stock setup instantly: shock upgrade plus fork springs or internals, set for rider weight. This is the first real money a race Grom needs.
Controls that fit a crouch
Rearsets from the minimoto specialists solve peg-folding lean angles; shorty levers and grippy pegs finish it.
Make it crash-able
Case covers or a cage, plus race bodywork — gen 3's quick-release panels make glass swaps trivially fast between sessions.
Engine — where classes allow
Big-bore kits (Takegawa and Kitaco are the trusted Japanese names) with an aRacer standalone ECU are half the fun of Grom racing — but check your class displacement rules first, and never bore it without fueling.
Gearing per track
Minimoto tracks are tight; carry two or three rear sprockets and match the 420 gearing per layout. Racers change these like tire warmers.
Parts notes for the Grom
What fits and what the community runs, category by category. Typical street prices sit at the other end of the links.
Exhaust
Yoshimura, Two Brothers, Hindle and Tyga all make Grom systems — almost all are full systems, and every one is generation-specific (4-speed vs 5-speed headers differ). Loud is easy on 9.7 hp; pair any pipe with fueling to actually run right.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Tune
EJK piggyback controllers handle bolt-on fueling; the aRacer standalone ECU is the built-Grom standard, with autotune and support for big-bore setups. Stock ECU plus big bore equals lean — budget fuel management into any engine build.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Suspension
YSS shocks are the budget classic, Öhlins the premium pick, and minimoto specialists carry fork springs and internals. An adult at speed is far outside the stock suspension's design brief — this matters more than engine work.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Tires & Wheels
Street: stock-size sport rubber is limited but adequate for 9.7 hp. Race: PMT slicks and Mitas race compounds in 12-inch sizes are the grid standards — sourced from minimoto specialty shops rather than big retailers.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Levers
Shorty levers fit the Grom's small controls well; the usual ASV/CRG quality argument applies at Grom prices — budget pairs are common and the risk is lower at these speeds.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Rearsets
Aftermarket flat and comfort seats address the stock plank; gen 3's flatter seat reduced the need. Stunt and race seats change mounting by generation.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Crash Protection
T-Rex Racing cages and sliders are the Grom staples, with case protection for race grids. Gen-specific — a JC75 cage does not bolt to a JC92.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Tail Tidy & Billet
TST Industries owns the Grom lighting niche: fender eliminators, integrated tails, flush signals, all gen-specific and plug-and-play.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Drivetrain
420 chain and cheap sprockets make gearing experiments nearly free. Street riders typically add rear teeth for punch; racers carry multiple sprockets per track. The most-changed part on any Grom.
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between platforms — the sheet shows a typical figure.
Gotchas & fitment traps
The year splits and part quirks that eat money on this platform.
Cross-model interchange
Community-reported. Paddock folk knowledge, not manufacturer fitment data. Verify part numbers for your exact year and market before spending.
- Community-reported: the Honda Monkey 125 shares the Grom's engine generation-for-generation (4-speed through 2021, 5-speed from 2022) — many engine and drivetrain parts cross between them.
- Global-market MSX125 parts fit the matching-generation US Grom (community-reported) — the bikes are the same machine under different names, which widens the used-parts pool considerably.
Honda Grom FAQ
Will 2014–2020 Grom parts fit a 2022+ Grom?
Bodywork, cages and lighting: no — and engine parts absolutely not. The 2022+ bike has a new 5-speed engine that shares no big-bore kits, headers or clutch parts with the older 4-speed. Check the frame code (JC61/JC75/JC92) on every listing.
Do I need a tune after an exhaust on a Grom?
You should plan fueling with any full system — which is what most Grom exhausts are. An EJK piggyback covers bolt-ons; an aRacer ECU is the standard once a big bore enters the picture. The lean-running stock map is not kind to open pipes.
How much faster can you make a Grom?
Meaningfully, by Grom standards: gearing and a pipe change how it feels, and big-bore kits with proper fueling change what it is. No dyno claims here — but the minimoto race grids prove the platform takes serious building.
Can you race a Grom?
Yes — Groms fill minimoto and mini-roadracing grids across the US, including youth and adult classes. Race prep is cheap relative to big bikes: tires, suspension for your weight, protection, and gearing get you on grid.
Read before you spend
Chapters from the manual that apply to the Grom.
Builds on the Grom
Reference sheets assembled by the shop — every part at typical street prices. Open one and steal the order.
Prices are typical US street prices at publish time and drift with sales and supply — verify at the retailer. Fitment is advisory: always confirm the exact part number for your year, generation and market before buying.