Bike models › Kids

Giant ARX 20: specs, upgrades and what fits

A light 20-inch kids' bike with an aluminum frame and alloy rigid fork, Shimano Altus 8-speed trigger shifting on a 12-32 cassette, V-brakes and 20x1.5in tires; this is the original US price of the 2020 model (Giant US last listed it for 2020; the 2019 version is the same bike). Best for: Kids about 120 to 140cm tall riding paths and pavement.

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My take, from the specs

A light 20-inch bike, about 8.8 kg, for kids around 120 to 140 cm who are ready for real gears. The Shimano 8-speed trigger shifter and 12-32 cassette give a wide range for hills, and the quick-release seat clamp makes height changes easy. It has rim brakes only, so on a used one check the V-brake pads, the rims and the rear derailleur hanger for bends.

Sizes: 20in: 3′11″–4′7″ (120–140 cm)

Stock specs

Upgrade limits

How far each part can go on this frame, and why. Measure your own bike to confirm the estimated ones.

Best upgrades by area

Three options that fit the Giant ARX 20 as-is in each area, from budget to best. ★ marks the one most worth the money. How we pick. Typical US prices, checked October 2026. They change often: check the price at the store.

Upgrades that fit as-is

Gearing

• Shimano CS-HG31-8 cassette 11–34, $. Cassette ↔ your Shimano HG freehub · 8-speed ↔ your 8-speed drivetrain
• SunRace CSM66 8-speed cassette 11–34 (nickel), $$. Cassette ↔ your Shimano HG freehub · 8-speed ↔ your 8-speed drivetrain
• Shimano Alivio CS-HG51-8 cassette 11–32, $$. Cassette ↔ your Shimano HG freehub · 8-speed ↔ your 8-speed drivetrain
• Shimano Acera RD-M3020-8 SGS 7/8-speed rear derailleur (40T max), $$. 8-speed ↔ your 8-speed drivetrain · Shimano cable pull ↔ your shifter

Brakes

• Kool-Stop Salmon V-brake pads, threaded post (2 pairs), $$. threaded post pads ↔ your rim brakes
• Shimano Deore cartridge V-brake pads (2 pairs), $$. threaded post pads ↔ your rim brakes
• Jagwire Mountain Pro brake cable kit (Kevlar KEB-SL housing), $$. Made for flat bars ↔ your flat bar
• Shimano Deore BR-T610 V-brakes (front + rear), $$. threaded post pads ↔ your rim brakes · Long-pull caliper ↔ your flat-bar (long-pull) levers
• Shimano S65T V-brake pads, threaded post (2 pairs), $. threaded post pads ↔ your rim brakes
• Kool-Stop threaded V-brake cartridge holders with salmon inserts (2 pairs), $$. threaded post pads ↔ your rim brakes
• Shimano Alivio BR-T4000 V-brakes (front + rear), $$. threaded post pads ↔ your rim brakes · Long-pull caliper ↔ your flat-bar (long-pull) levers

Comfort

• Ergon GP1 ergonomic grips, $$. Made for flat bars ↔ your flat bar
• Budget ergonomic lock-on grips, $. Made for flat bars ↔ your flat bar
• Suspension seatpost 27.2 mm (budget), $$. 27.2 mm post ↔ your 27.2 mm seat tube
• Redshift ShockStop suspension seatpost 27.2, $$$$. 27.2 mm post ↔ your 27.2 mm seat tube
• WTB Volt saddle, $$. Medium-width shape that suits most riders. Measure sit bones if comfort is the goal.
• Brooks C17 All Weather saddle, $$$. Vulcanized rubber top that flexes like a hammock, and this All Weather version is fully waterproof. No break-in like leather. Firm, not padded: made for long…
• Bikeroo oversized comfort saddle, $. Wide, soft and sprung for short upright rides on cruisers and hybrids. On rides over an hour wide padding can chafe; a firmer saddle that fits your sit bones…
• Ergon GA3 lock-on grips, $$. Made for flat bars ↔ your flat bar
• Selle Royal Respiro Moderate saddle, $$$. Made for a 60° "moderate" back angle (most flat-bar hybrids). Very upright cruisers suit the wider Respiro Relaxed. Standard round steel rails.
• Fizik Terra Argo X5 saddle (150 or 160 mm), $$$. Pick 150 mm for narrower sit bones, 160 mm for wider. Round 7 mm alloy rails fit every standard clamp.
• Ergon SR Allroad Core Comp saddle (men's or women's), $$$. Comes in S/M and M/L widths (measure your sit bones) and men's and women's shapes. Round CroMo rails; 120 kg rider limit.
• Ergon GP5 ergonomic grips with built-in bar ends (S or L), $$$. Made for flat bars ↔ your flat bar
• Ritchey Comp 2-Bolt alloy seatpost 27.2 mm, $$. 27.2 mm post ↔ your 27.2 mm seat tube
• Thomson Elite seatpost 27.2 x 330 mm, $$$. 27.2 mm post ↔ your 27.2 mm seat tube
• Ergon CF Allroad Pro Carbon flex seatpost 27.2 mm, $$$$. 27.2 mm post ↔ your 27.2 mm seat tube
• Cirrus Kinekt 2.1 Aluminum suspension seatpost 27.2 mm (LR or XR spring), $$$$. 27.2 mm post ↔ your 27.2 mm seat tube

Control

• External dropper post 27.2 mm, 100 mm drop + remote, $$$. 27.2 mm post ↔ your 27.2 mm seat tube
• Race Face Chester composite flat pedals, $$. Big platform with pins. Feet stay put on bumps and in rain. Install with an 8 mm hex key (no wrench flats).
• ROCKBROS aluminum flat pedals, $$. Budget metal platform with pins. A big step up from stock plastic.
• Shimano PD-M520 SPD clipless pedals (cleats included), $$. Nearly indestructible two-sided SPD pedals. You also need SPD (2-bolt) shoes, about $60–100 more. Set the release tension low and practice unclipping before…
• Crankbrothers Stamp 2 aluminum flat pedals (small or large), $$$. Sized by shoe: small for US men's 5–10, large for 10 and up. Grease the threads and tighten to about 35 Nm.
• OneUp Components Aluminum flat pedals, $$$. Bearings and bushings can be serviced with a cheap kit instead of replacing the pedal. Grease the threads and tighten to about 35 Nm.
• Shimano PD-EH500 dual-sided SPD / flat pedals (cleats included), $$$. Comes with SM-SH56 multi-release cleats, which are easier to get out of in a panic. You still need 2-bolt SPD shoes to clip in.
• Shimano Deore XT PD-M8100 SPD pedals (cleats included), $$$. Cup-and-cone bearings are fully serviceable and last for years. Shoes with a 2-bolt SPD cleat sold separately.
• KS eTen-R external dropper 27.2 mm, 100 mm drop + KS Southpaw remote, $$$. 27.2 mm post ↔ your 27.2 mm seat tube
• PNW Components Pine external dropper 27.2 mm (90 or 110 mm) + PNW Loam lever, $$$$. 27.2 mm post ↔ your 27.2 mm seat tube

Utility

• USB rechargeable front + rear light set, $$. Daytime flashing lights cut collisions. Required by law at night.
• Pletscher adjustable kickstand, $$. Handy for errands. Check it clears the rotor and chainstay.
• Lisen clamp-style handlebar phone mount, $. Cheap and tool-free for maps on paved rides. On rough gravel or trails a locking mount (Quad Lock or Peak Design, about $45–70 plus a case) is much safer.
• Topeak TopLoader top tube bag (0.75 L), $$. Keeps snacks, keys and a multi-tool within reach. Straps on, with a rain cover. Check your knees do not rub it when you stand up.
• Knog Oi Classic bell, $. Slim ring bell that wraps the bar. Large fits 23.8–31.8 mm bars; Small fits 22.2 mm kids and BMX bars. Required by law in some places.
• Wald 137 front basket, $$. Made for flat bars ↔ your flat bar
• Planet Bike Beamer 200 + Blinky Squared USB light set, $$. USB rechargeable, tool-free mounts. Use flash mode in daylight. Rear light is 30 lumens: good for town, modest on fast roads.
• Cygolite Metro Plus 800 + Hotshot Pro 150 USB light set, $$$. Nine headlight modes including a daytime flash. Aim the beam slightly down so you do not blind oncoming riders.
• Trek (Bontrager) Ion Pro RT + Flare RT light set, $$$. Daytime-running flash modes on both lights. ANT+ lets a Garmin or Wahoo show battery and switch them. Full power runs about 1.5 hours; medium lasts much longer.

Drivetrain

• KMC X8 8-speed chain with Missing Link, $. 6/7/8-speed chain ↔ your 8-speed drivetrain
• KMC Z8.3 6/7/8-speed chain (116 links), $. 6/7/8-speed chain ↔ your 8-speed drivetrain
• KMC X8 EPT 6/7/8-speed anti-rust chain with Missing Link, $$. 6/7/8-speed chain ↔ your 8-speed drivetrain

Tubes

• Schwalbe AV7 20 x 1.5–2.4 Schrader tubes (pair), $. 20" wheel size matches · Schrader valve ↔ your Schrader rims

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Buying one used? Fair prices

Worked out from the price new ($430), age and condition, not live market data. If it needs tires, a chain or brakes, take off what fixing them would cost.

See what these really sold for on eBay · Other used bike prices

Geometry (size 20in)

Compare with

• Huffy Rock It 20" · compare frames side by side
• Trek Precaliber 20 · compare frames side by side
• Specialized Hotrock 24 · compare frames side by side
• woom ORIGINAL 4 · compare frames side by side

Sources: Giant US: ARX 20 (2020) spec, geometry, rider height 120-140cm, $430 MSRP, colours · Giant AU: ARX 20 (2020) spec stating 'Shimano M315, 8sp' and 'HG-200, 12-32T, 8sp' · Giant UK: ARX 20 (2019) spec (rear hub 'R 28H NUT', RD-310, Schrader tube) · Cycle Sprog: ARX 20 review (measured 8.76kg with pedals, 8-speed 12-32, quick-release seat clamp) · SJS Cycles: Shimano CS-HG200-8 12-32 ratios 12/14/16/18/21/24/28/32