Depends on the tyre and the rider weight (and ability) the same as for any adult rider actually.
1\. Does the tyre deform slightly and create a wider contact patch when the rider is sat and stood on the bike?
2\. Can the rider angulate the bike without the tyre collapsing?
Job done.
As a coach there are several common issues I see with kid's bikes (and women's bikes too) which are:
1\. Tyre pressures are way to high (25-30 psi is fine for the bike path commute to and from school),
2\. Bars are too wide (cut em down, some other small kid is going to be riding that bike when you are done with it).
3\. Pedals are as grippy as an ice cube (as Andrew has stated Radars might be expensive but far less so than an injury from a slipped pedal or a developing dislike in mountain biking because trying to pedal or ride obstacles is a constant source of frustration).
4\. A chain guide; kids are generally on hard tails and have less leg length to absorb trail obstacles so their chain is getting a total shake down. Add to that missed shifts, back pedalling mid shift, and crashing and it is a miracle (aided by NW tech) that a chain stays on a kid's bike at all. Please be a good parent and help them as much as your finances allow you too.
5\. Good brakes, that old set of two pot XT brakes with reach adjust levers is way more valuable on your kid's bike than it is dollar terms as a local sale. When they know that they can safely stop they will try almost anything.
Happy trails.
May 10, 2021, 5:35 p.m. - AndrewR
Depends on the tyre and the rider weight (and ability) the same as for any adult rider actually. 1\. Does the tyre deform slightly and create a wider contact patch when the rider is sat and stood on the bike? 2\. Can the rider angulate the bike without the tyre collapsing? Job done. As a coach there are several common issues I see with kid's bikes (and women's bikes too) which are: 1\. Tyre pressures are way to high (25-30 psi is fine for the bike path commute to and from school), 2\. Bars are too wide (cut em down, some other small kid is going to be riding that bike when you are done with it). 3\. Pedals are as grippy as an ice cube (as Andrew has stated Radars might be expensive but far less so than an injury from a slipped pedal or a developing dislike in mountain biking because trying to pedal or ride obstacles is a constant source of frustration). 4\. A chain guide; kids are generally on hard tails and have less leg length to absorb trail obstacles so their chain is getting a total shake down. Add to that missed shifts, back pedalling mid shift, and crashing and it is a miracle (aided by NW tech) that a chain stays on a kid's bike at all. Please be a good parent and help them as much as your finances allow you too. 5\. Good brakes, that old set of two pot XT brakes with reach adjust levers is way more valuable on your kid's bike than it is dollar terms as a local sale. When they know that they can safely stop they will try almost anything. Happy trails.