What size mountain bike does my child actually need?
Getting Trail Ready · Part 1 of 3
Buying a bike for a child sounds simple — until you're standing in a shop surrounded by wheel sizes, frame sizes and acronyms nobody explained. Here's a straightforward guide to getting it right first time.
Why age is the wrong starting point
Almost every "kids' bike guide" on the internet starts with age. It's a tempting shortcut, but it's not actually that useful. Children of the same age can vary enormously in height, reach and leg length — and on a bike, those differences really matter. A child who's too stretched out to steer comfortably, or who can't put a foot down confidently, isn't going to enjoy riding. Start with height, not age.
Understanding wheel sizes
Kids' mountain bikes come in a few common wheel sizes, and choosing the right one is the foundation of a good fit.
20-inch wheels suit most riders roughly between 110–130cm tall. The bike is light, nimble and easy to control — great for learning trail skills and building confidence. 24-inch wheels are the next step up, typically suited to riders around 125–150cm. The bigger wheel rolls over rough ground more easily and starts to feel like a "proper" trail bike. 26-inch and 27.5-inch wheels appear on larger junior bikes for riders approaching adult height — usually 145cm and above. At this point, some children can move onto an adult XS frame depending on their proportions.
There's often overlap between sizes, which is why standover height matters. When your child straddles the bike flat-footed, there should be a few centimetres of clearance between them and the top tube. Squeeze test done.
Buy to fit now, not to grow into
It's tempting to size up so the bike lasts longer. Resist it. A bike that's too big is harder to control, less fun to ride, and can knock confidence early on. Fit now, upgrade later — and remember that kids' bikes hold their value well second-hand.
What else to look for
Beyond wheel size, look for hydraulic disc brakes (easier for small hands to modulate than cable brakes), a lightweight frame (children feel extra weight more than adults do), and wide flat bars for stability. Most kids' trail bikes come with suspension forks as standard — and that's a good thing. Even on mellower trails, a bit of front suspension takes the sting out of roots and rocks and makes for a more comfortable, confidence-inspiring ride.
A word on gears
Fewer is often better at first. A single-chainring setup (1x drivetrain) removes the front derailleur, simplifies shifting and reduces weight. Most modern kids' trail bikes come set up this way — it's one less thing to think about when they're learning.
Liv bikes to explore
STP 20 FS LivThe STP 20 is a lightweight, confidence-building bike for riders discovering off-road fun. Its stable geometry, low stand-over height, and youth-specific components make it ideal for developing skills on pump tracks, dirt jumps, or local trails.
STP 24 LivFor young riders ready to level up their skills, the STP 24 delivers the perfect mix of stability, control, and fun. With youth-tuned suspension, balanced geometry, and components built for smaller riders, it helps them flow through corners, jump higher, and push their limits with confidence—on trails, pump tracks, and everything in between.
STP 26 LivThe STP 26 is made for riders who live for dirt jumps, pump tracks, and big sessions with friends. With its tough aluminum frame, dialed geometry, and smooth suspension, it’s built to boost confidence, nail landings, and keep the fun going from first drop to last light.
Quick sizing guide
110–125cm → 20" wheel · 125–145cm → 24" wheel · 145cm+ → 26" or 27.5" wheel. When in doubt, visit a local bike shop and get your child on the bike. Five minutes of test-sitting is worth more than any chart.
Getting the fit right from the start means more confidence on the trail, faster progression, and — most importantly — a child who actually wants to go riding again.
This post was created in partnership with Liv Cycling, proud sponsors of Limitlass: Next Gen 2025.