The one rule: avoid the BSO
BSO = Bicycle-Shaped Object. The category of bikes sold in department stores and on Amazon for €120–€250, badged with names like "MTB-X", "Cyclmax", "FabricFrame", weighing 18+ kg, with steel frames, plastic-shelled suspension that doesn't actually move, and brakes that bend the lever before they slow the bike.
A BSO will be heavier than your child. It will not survive a single drop off a kerb. It will turn them off the sport. Spend €0 on a BSO. If the budget is €200, buy a second-hand mid-range bike one year too big and grow into it instead.
What "proper" means
A bike from a real cycle brand, sold through a real bike shop, with the following minimums:
- Frame: aluminium (not steel or "hi-ten"). Branded geometry, not a generic frame.
- Fork: a real suspension fork with an air spring or a coil with proper damping — SR Suntour XCM/XCR/Raidon level minimum, RockShox/Fox if budget allows. Lockout is useful, not essential.
- Brakes: hydraulic disc brakes. Cable disc is a step down. Rim brakes on a kid's MTB are a no.
- Gears: 1× drivetrain (single chainring) preferred — easier for a kid to learn, less to break. 10 or 11 speed is plenty. Shimano Deore or SRAM SX/NX level is fine.
- Wheels: sealed bearings, double-walled rim, tubeless-ready a bonus.
- Tyres: at least 2.25" wide with real MTB tread.
- Weight: under 13 kg for a 24"–26" hardtail, under 14 kg for 27.5". Heavier than that and a kid won't enjoy lifting the bike.
Frame size by height
Forget age. Size by inside-leg and standover height — kids vary wildly. As a starting point:
| Rider height | Wheel size | Frame |
|---|---|---|
| 115–130 cm | 24" | XS / kids 24" |
| 130–145 cm | 26" (or 27.5" XS) | S kids / adult XS |
| 145–160 cm | 27.5" | XS / S |
| 160+ cm | 27.5" or 29" | S / M |
Standover gap (frame-to-crotch with both feet flat on the ground) should be at least 3 cm. More is fine for off-road — a kid needs room to bail.
Hardtail vs full-suspension
For 99% of 8–14 year olds, the answer is hardtail. Reasons:
- Lighter — usually 2–3 kg less than a comparably priced full-sus.
- Cheaper — a €700 hardtail rides better than a €700 full-sus, every time.
- Simpler — fewer bearings to seize, no rear shock to service.
- Builds skill — you can't hide behind suspension. Kids who learn on a hardtail descend better as adults.
Full-sus for a kid only makes sense if (a) the kid is riding bike park 20+ days a year, (b) the bike is sized correctly (most are too big), and (c) the budget is €1,200+ for a credible spec. Otherwise, hardtail.
Wheel size
24" is for under-12s usually. 26" is now a kids-bike-only size (adult bikes have moved on to 27.5" and 29"), which is fine — second-hand 26" frames are everywhere and cheap. 27.5" suits a 13-year-old approaching adult height. 29" only for the tall kids (~165 cm+).
Brake type
Hydraulic disc. End of debate. Cable disc is acceptable on the absolute entry-level if hydraulic genuinely isn't in budget, but adult brake fluid is cheap and a bleed every 18 months is a 30-minute job at any shop. Kid hands have less force than adult hands — hydraulic gives them the modulation they need.
Gearing
1× drivetrain (single front chainring, 10- or 11-speed cassette) is now standard and is the right choice for kids: one shifter to think about, no chain-drop issues, lighter. A 28- or 30-tooth chainring with an 11–46 or 11–51 cassette covers everything a kid will pedal.
What to spend
€300–€800 — entry-level, hardtail only
What you actually get: aluminium frame, basic air or coil fork (SR Suntour XCM/XCT), 1× 9-speed Shimano Altus or SRAM SX, hydraulic brakes if you push to the top of the range, mid-tier tyres. Bikes in this band:
- Vitus Nucleus (UK / IE — Chain Reaction) — best value in this band, regularly £450–£550.
- Calibre Two Cubed / Two.Two (UK — Go Outdoors) — good kids' hardtail, often under £400.
- Frog MTB 62 / 69 / 72 / 78 (UK / IE) — lightweight, properly sized for kids, expensive for spec but holds value.
- Cube Acid 200 / 240 / 260 — Cube's kids' line, well sorted, around €450–€700.
- Specialized Riprock 24 / 26 — bombproof, slightly heavy, around €600.
€800–€1,500 — mid-range, where the magic happens
Real RockShox Judy or Recon air fork, Shimano Deore 1×11 or 1×12, four-piston brakes, dropper post on some, tubeless-ready wheels. Bikes that will last 3+ years if sized with a bit of room:
- Vitus Sentier / Mythique 27 — strong all-round trail hardtails, regularly £900–£1,200.
- Cube Aim Pro / Reaction Pro — solid mid-range, easily found in IE/UK shops.
- Trek Roscoe 6 / 7 — Trek's trail hardtail, geometry that works for a tall kid or small adult.
- Specialized Rockhopper Comp / Expert — wide size range from XXS up, good geometry, easy to service.
- Cannondale Trail SE 3 / SE 4 — similar pitch, available through IE dealers.
Second-hand in this band is the sweet spot — last-year's £1,200 bike often goes for £600 with 200 hours on the clock. Check Done Deal (IE) and Pinkbike BuySell (UK/EU) and ask the seller for a recent service receipt.
What to spend the rest on
If €800 is the bike budget, leave another €150–€250 for the kit that keeps the rider riding: a real MIPS helmet, knee pads, gloves, and flat shoes that aren't trainers. The cheapest way to ruin a new bike is one bad fall that knocks the rider off the sport for six months.
What to ignore
- Carbon frames at this age — overpriced, fragile to crashes, not worth it for a growing kid.
- Electronic shifting — overkill.
- Anything labelled "mountain bike" in Argos / Lidl / Aldi / Decathlon's bottom shelf. Decathlon's mid-range Rockrider is OK for a beginner; the entry-level is borderline BSO.
- "Comes with free helmet" — the helmet is the cheapest part of the package and almost always one you'd throw away.