If you want to enjoy riding together, your son or daughter needs a bike that fits (Joby Sessions)

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In cash-strapped times even cycling parents may consider economising when it comes to buying a bike for their child; after all, they’ll outgrow it in a few years.

But here’s the thing: you don’t get forever to sell cycling to your kids. They grow up fast and if you want to enjoy riding together, now and in future, your son or daughter needs a bike that fits properly and that’s light enough to manoeuvre easily.

Most children will have just one bike for everything, so with 20in and 24in wheel bikes in particular it pays to look for versatility. Will it go off-road and be suitable for riding to school or friends' houses? What about its appearance? The colour is a big deal for children of any age – much bigger, for them, than the make of brakes or gears.

As prices don’t scale down with size, you can expect to pay the same for a new kid's bike as you would for an entry-level adult bike: £300-plus (that's at full RRP – look out for bargains in sales, online and on the second-hand market).

That should get you a reasonable road bike or hardtail mountain bike that won’t weigh a ton – and that last bit is crucial. Check out the list of Related Articles on the right for some reviews of children's bikes.

The golden rule

If you do nothing else when buying a kid's bike, make sure it's the right size. It's better to progress in stages than to fit your child onto the biggest bike they can pedal; you can always hand down or sell on used bikes.

Riding a bike that you can't control because your feet don't touch the ground and your hands can't reach the brakes properly is no fun. It's also dangerous: crashing puts people off – even kids eventually.

We've grouped our bikes into four steps: Pre-school (sub-16in wheel), Ages four to six (16in wheel), Ages six to 10 (20in) and Ages nine to 12 (24in). After that, children will be on small adult bikes. But whatever the age of the child you are buying for, here are some other things you should always take account of so that your child gets the new bike that they deserve.

Weight

Weight makes a bigger difference to the fun and manoeuvrability of a child's bike than yours, because children are smaller, lighter and weaker. A kilo saved from the bike of a six-year-old weighing 30kg is like 2.5kg saved from an adult's.

Cranks

Children, like adults, need cranks that are about 20 percent their inside leg length. One-tenth of overall height is another oft-quoted rule of thumb, and though it yields a longer measurement (few of us have inside leg measurements that are half our height) it's close enough.

Unfortunately the rule of thumb for manufacturers seems to be: stick on whatever ought to be on the next size of bike up. Over-long cranks are as ungainly as they are unergonomic. And they'll ground more easily unless the manufacturer puts the bottom bracket higher, which is the last thing a child needs.

Wheels and brakes

Don't buy big wheels for small riders, they need scaling down too. While a larger wheel will roll over bumps and kerbs better, it will also be heavier (more inertia), and the steering will be less responsive. It's likely that the reach to the bars will be greater too, because the bottom bracket to front axle distance will be greater, and the bottom bracket itself will be higher. All these factors make for a slightly-too-large bike that bit more difficult to control than one that fits.

Brake levers don't necessarily need scaling down, because you can use two-finger adult levers. They must be within easy reach of the bars though (is there an adjustment screw?), and easy to operate. Check that you can operate the brakes with only the little finger of each hand.

Reach

One measurement that doesn't scale down well to children's bikes, particularly those of younger children, is reach (how far away you are from the bars). Most children are happier in a riding position that's more upright than you would adopt, so they need the bars higher and closer. BMX bars are excellent on bikes with 20in or smaller wheels for that reason.

Suspension forks

For children, air sprung forks are best. They’re lighter and can be easily adjusted to suit a growing rider’s weight. Coil forks require lighter-weight springs. Stiction is a common problem on children’s forks: kids may lack the mass to get a sticky fork moving on anything but big hits. Rigid forks are better than bad suspension forks.

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Pre-school

A child's first set of wheels usually comes in the form of a trike or push-along. These are often breakable plastic, with simple friction bearings. A decent metal trike will last longer and can be handed down. Look for: wide-set rear wheels for stability, and a durable front wheel axle. Proper ball bearings here are a bonus.

Children can learn to ride a two-wheeler at three years old, and almost always by five. It's much easier for them if they can balance and steer already. There are two ways to learn this: on a traditional two-wheeled scooter; or on a hobbyhorse. (Stabilisers give mobility to children who can't balance, but they prevent a child from learning to ride a bicycle.)

You can turn a starter bike into a hobbyhorse by removing the pedals and lowering the seat so your child can put both feet flat on the floor. Find a gentle slope and let them coast down it towards you. When they've got the idea, refit the pedals and get them to ride towards you.

First bikes will have 12in or 14in wheels. The bike should have: a low stand-over height; ball bearings in hubs, bottom bracket and headset; 90-100mm cranks; pneumatic tyres; at least one working brake.

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Ages four to six

Bikes with 16in wheels still sometimes come with stabilisers: if so, bin them. All 16in wheel bikes come with a singlespeed gear. The chainstays are too short for derailleur gears, and they'd only confuse anyway. A three-speed hub gear would be nice, but they're pricey so you won't see them. As children of this age won't be riding far, a single gear is okay.

Low overall weight will give a more easily manoeuvred bike. Avoid suspension and fat steel frames; thin steel tubes are fine. A lowish bottom bracket will enable your child to get a foot down from the saddle – which, as they can now ride properly, you'll be gradually raising. Cranks should be 100-120mm; the shorter the better. A chainguard of some sort will keep clothing or inquisitive fingers out of the drivetrain.

By this age, children can hurtle along so easily operable brakes are a must. A light action V-brake or sidepull is fine up front, but less effective at the rear: the longer cable run means more friction so the lever is harder for the child to pull. A back-pedal coaster brake is a good solution.

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Ages six to 10

Gears are the obvious extra with 20in wheel bikes. A three-speed hub gear would be ideal: it's easy to understand and hard to break. Again, it's more expensive to fit, so five- and six-speed derailleurs are what you'll usually find. For knocking around on the street, don't discount singlespeeds: they're lighter, simpler and rarely develop problems.

Some 20in wheel bikes come with suspension forks. They'll be basic, unadjustable springs that nevertheless score credibility points with children. There are two disadvantages: extra weight and less money to go round elsewhere. If the bike costs £120 or more, front suspension may be adequate. Rear suspension is poor unless you spend a lot more.

If the bike has a rear derailleur, get a derailleur guard for when the bike is dropped on its side. A kickstand is useful, as kids this age aren't good at propping their bikes up. Look for easy-to-use shifters. Cranks will again be too long. You want 120-130mm; 140mm may do.

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Ages nine to 12

Spend in the region of £200 and you'll get a light(ish) weight aluminium mini-mountain bike that can be passed on to siblings. We'd like to see a 24in wheel bike with a single chainring and a decent, wide-range eight-speed cassette hub (ie. 11-30T). But you'll get a seven-speed, screw-on freewheel hub and most likely a triple chainset up front. If it's a double, look for a smaller inner ring (22 or 24) rather than a larger (42) outer.

Bike spec should compare to an adult's bike at the same price. So expect a micro-adjust alloy seatpost, a cartridge bottom bracket, an alloy flat or riser bar, a threadless stem, brand name V-brakes and a decent set of a wheels. They'll have off-road tyres – kids like these, but a set of semi-slicks would be better for all-round use.

'Less is more' applies: instead of disc brakes, look for disc mounts for later upgrading. And look for a good suspension fork (adjustable preload and damping), not full suspension. The cranks will again be too long: you want 140mm, 150mm at a push. You may get 160mm.

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Big kids' bikes

Children aged 12 or 13 – and some lanky younger ones – are ready for a small-framed adult bike. Most manufacturers make frames down to 14in or 15in, and some do 13in. Urban freeriders and serious off-road riders may want the smallest frame for the extra clearance over the top tube, but most teenagers can go straight to 15in.

Don't be tempted to put your nine- or 10-year-old on a 13in adult frame just because they happen to be able to reach the pedals. They'll be much better off on a 24in-wheel bike with a 12in or 13in frame. A 24in-wheel bike may be lighter and it will be easier to control. Imagine what your bike would feel like with 28in wheels instead of 26in. The smaller bike should also have more kid-friendly cranks, etc.

Teenagers are acutely aware of peer pressure and will want a bike that's considered cool. Currently this seems to mean simple paint jobs (such as black, white, matt grey/brown or camo green, silver, or maybe red) and a vaguely dirt-jump style frame.

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