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My son is 6 years old, weighs about 20kg himself. The bike we have for him is this Merida Matts J20 which weighs about 13kg.

His riding skills are fine but I get the feeling he's not comfortable on the bike. He often raises himself from the seat and rarely rides in a straight line, which frequently leads to minor accidents.

We're not going fast - about 10km/h average - but it seems he still needs a lot of effort to keep going. The bicycle just doesn't seem to have nearly as much inertia as everyone else. This results in him standing up to deliver more power to the pedals and the aforementioned swerving when going too slow.

And sure, the mass and its distribution is definitely a factor here; as well as him being easily distracted and not paying full attention to the road, but... feels like it should still be better than it is.

I've tried spinning the wheels but they seem to be moving freely (although the rear wheel does slow down a bit faster than I would expect, but perhaps that's normal). The tire pressure also seems normal, but I'll check tomorrow with a meter.

I'm wondering if perhaps tires could be a significant factor? They have a large protector like for off-road usage and we're riding almost exclusively on paved sidewalks:

Tire

Would the bike handle better with smoother tires? Are there any other tips you might share that could help? Or is this just par for the course with 6 year olds?


Update

I increased the tire pressure to 3.5 bar (was below 2) and raised the seat by a few cm. This seems to have made a significant difference and he is riding better now. I also checked with a LBS that the rear wheel was turning normally. He still likes to raise himself from the seat but is now riding with less swerving and seems to require less effort. Here's a picture, maybe there's something else that can be gleaned:

Full picture

  • Have you tried just pumping them up to the top of their rated range? – Affe Jul 3 at 23:38
  • @Affe - Will try tomorrow. I know that when he rides the bike, the tires don't seem deformed at all. For my own bike the tires had become quite visibly flattened when I sat on the bike before I noticed. – Vilx- Jul 3 at 23:46
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    It might be helpful to install smoother tires -- they would roll easier. And, as suggested, make sure the tires are reasonably well inflated -- 40 psi or better. – Daniel R Hicks Jul 4 at 2:43
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    While better tires (smoother and lighter) would probably help, don;t expect too much. Sounds like a lot of 6yo's. Bike is possibly too big for him, and how would your riding look is your bike weight as much comparatively (around 50kg presuming you a pretty average 80kg )? – mattnz Jul 4 at 3:36
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    @Vilx- Here's an off-the-wall idea, try riding your son's bike yourself. Not far, not on the road, just "around" and see how it feels. Mind out for toe-overlap and knees hitting the handlebars. This shouldn't damage the bike, unless you're particularly large. If pedalling doesn't work for you, try your right foot on the left pedal and "scooter" it around. See what you feel/find. – Criggie Jul 5 at 1:45
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Not a helpful answer, but I would definitely find a lighter bike. In the UK, Frog and Isla are popular makes for light bikes. I would say a 20" wheel is OK for a 5-6 year old.

A single-speed Frog 52 (20" wheels, 10" frame) weighs under 8kg. Make sure the saddle is high enough, and raise it if he looks uncomfortable.

Both my children had Frog bikes and did fine. We bought ours second hand. They are very expensive, but maintain their value, and we sold both of ours for a profit when both children had outgrown them.

I doubt tyres will make any difference.

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    The weight is... kinda a mixed blessing. On one hand, a lighter bike means he can accelerate faster and with less strength. On the other hand, it also means less inertia once he's picked up speed. Oh, yeah, I forgot to say - we also shifted a gear down (he doesn't shift them on his own yet) and he says that it made riding easier. I guess there's nothing to do now except wait until he's older and bigger. – Vilx- Jul 6 at 12:10
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    Unless you are riding on particularly rough ground inertia is rarely very useful. – Andy P Jul 6 at 12:21
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    Kids out grow bikes fast and Isla bikes are very expensive, not sure they are worth it for most families. – Rider_X Jul 6 at 15:13
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I see in the specs that this bike has 20 inch tyres. That's a very big bike for a kid who is only 6 years old.

I'm guessing you have the saddle right down to help him get on it? That could be another indication of a bike too big for the rider.

As a start, I'd suggest getting him to test-ride another bike. Someone else's would be ideal and there's no cost. Perhaps ask another parent at school or someone else you know ?

You can always put the bigger bike away for a few years until he grows into it.

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    No, the bike is definitely not too big. We had a smaller one (16" wheels) and that was so small he could barely sit on it anymore. The saddle on the current bike is also at a medium height, not even close to minimum. But I do agree about the weight. The bike is quite heavy compared to the kid. Unfortunately lighter bikes at this size cost a fortune. And anyway - shouldn't a larger mass result in more inertia? It might take more energy to get up to speed, but after he's there he could just keep on rolling. – Vilx- Jul 4 at 11:07
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    Could it be that the axles are not running smooth which would require more effort to keep going? – Carel Jul 4 at 11:21
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    I think 20" wheels would be fine for a 5-7 year old child. More likely the weight of the bike is the problem. – Mark Williams Jul 5 at 19:57
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    Yeah. Although it is stil pretty heavy compared to the kid. Not sure if it's good or bad. A lighter bike would make accelerating easier, but it would also have even less inertia after he's picked up speed. That's the main difference I notice between him and the rest of us - he requires nearly constant pedaling, while we just pedal a bit and then coast, pedal a bit and then coast... – Vilx- Jul 6 at 12:16
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    Inertia doesn't really work that way. If you want to get an idea about what the bike feels like to the kid, try strapping stuff to your bike until it weighs more than half of your weight and try how it handles. Those tires aren't really helping, though. – ojs Jul 6 at 16:50
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From your update it looks like you did all the right things. In the photo, and after your tweaks, the bike looks to be correctly sized, he has a nice upright position and his elbows are slightly bent which is ideal. The saddle height looks good as well. Good job!!

As he gets more comfortable riding you might be able to raise the saddle ever so slightly to get a little more power, but that is more of an adult/advanced saddle position and it is better to be a tad too low than a tad too high as the latter can stress connective tissue more. The rule of thumb is that you rotate the pedal away from you (the crank should follow the angle of the seat tube), and raise the saddle until your knee locks out (I.e., fully extended leg) when your heel is on the pedal. This gives you a slight bend in the knee when the ball of the foot is on the pedal. Children often ride on the middle of their foot so this rule of thumb may not always work as intended.

Beyond that I would not consider a new bike (as suggested elsewhere). The bike looks fine, just ride what you have and have fun.

Raising out of the saddle can be an indicator of a number of things:

  1. terrain may just require it;
  2. Gearing choice too hard for the terrain or starting (my children are constantly doing this despite my best suggestion/guidance);
  3. Lack of strength; and
  4. Incorrect fit

None of these are mutually exclusive so it could be a combination. I would be careful not to over interpret this as an issue as it has been my experience that some of this is just growing pains associated with learning to ride a bike and when to do what. Getting the hang of gear selection can be a big one, my eldest (9 years) still refuses to ride in any gear but the hardest, even up hills. So she struggles with her stubbornness.

In general pedaling out of the saddle is more powerful but more fatiguing. It can be useful to take a closer look why the child is looking for more power.

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