Designing bikes for growing bodies
Who would you turn to to find out about children’s body proportions and how they grow? Perhaps a General Practitioner or a Pediatrician? We’ve been studying children’s bodies for years and have some incredible data about children’s growth patterns. To explain how this affects our bike design, we talk to Islabikes’s founder and designer Isla Rowntree.
Is a child’s bike just a scaled down version of an adult’s bike?
IR: No, because if you took an adult’s body and just scaled it down, you wouldn’t have something that looked like a child’s body. For example, a small child’s head is much bigger relative to its body than an adult’s. The more important problem for me as a bike designer is that a child’s body doesn’t grow evenly. If you look at how children grow during their childhood, the body proportions do not remain the same. That means all Islabike frame sizes, as we go up through the range, have to be designed differently.
The more important problem for me as a bike designer is that a child’s body doesn’t grow evenly.
So how do children grow?
IR: From around six or seven up to their early teens, children’s growth tends to happen more in their leg length than their torso length. Many children at this age end up with long legs and short bodies relative to their overall height. You might have a tall 11 or 12 year old child who is the same height as a small adult but is very differently proportioned.
Our bikes in that age range are designed around these proportions. A very small adult’s bike often doesn’t fit a child well because the reach is much too long, even if they are able to get the correct reach to the pedals. As children progress through their teens, their bodies start to catch up and they end up a conventionally proportioned adult.
Smaller Islabikes give their riders a more upright position, why is that?
IR: Firstly, it is easier to learn to ride in a confidence inspiring upright position than in a bent over racy one. But there is more to it than that. In young children, certain internal organs are quite large relative to the child’s overall size which is why toddlers tummies stick out – it’s crowded in there! A small child can’t bend over into a “racing crouch” comfortably as their tummy is in the way. As they grow up, their tummies gradually flatten out as the organs become a smaller size relative to the rest of them. We change their riding position as they grow through our bikes into a slightly more sporty position, sharing the weight distribution between the saddle and handlebars.
Is there any difference in the ways girls and boys grow?
IR: Until puberty, there is very little gender variation in the measurements that affect bicycle fit. At different ages, the average height for girls and boys differs slightly but the body proportions for a given size do not, so our bikes fit girls or boys just fine.
If body shape changes, do you also have to take into account changing weight distribution?
IR: Absolutely. If a rider is ten years old and sitting on one of our Beinn models, their long legs will require the saddle to be quite high to get the correct reach to the pedals, however, their short body is hardly going forward, so their weight distribution is towards the back of the bike. They need to sit further forward relative to the pedals so that when they push down the reaction to pedaling force is not pushing them off the back of the saddle. Our frame geometry seats them in the correct position for their size, resulting in better comfort and more efficient pedaling. Observation of children riding is crucial and I do lots of that and then I back this up with child data sets and use this to decide the individual measurements for a given size of bike.
What child data sets do you have access to?
IR: I use “Child Data: Data for design safety” (Dti). It is about the size of a telephone directory and it’s a handbook of child measurements and capabilities. The biggest samples are from children in the United Kingdom but for comparative purposes there is also data from studies in other countries. I used the information in Child Data when I designed the very first Islabikes and I’ve used it as my main bible ever since.
What kind of data does it have?
IR: It contains the obvious things like height, leg length and weight, and also a vast range of things you might never think of. Measurements that are relevant for designing bikes include hand strength, foot size, hand width, grip diameter etc. The results are spread out through the sample groups by gender with an average figure and 5th and 95th percentiles.
What kind of benefits does having that data provide?
IR: We use all that information to help set the individual sizes of our bikes and to help inform the gap between sizes, so the riders can grow safely from one size into another and parents can get the maximum value from a given bike. We also use it to understand a child’s capability at different ages. The data informs details such as crank lengths and reach from the saddle to the handlebar. We also used it to create our exclusive Islabikes components including saddles, pedals, brake levers, handlebars and grips. That book is heavily thumbed!
We use all that information to help set the individual sizes of our bikes and to help inform the gap between sizes, so the riders can grow safely from one size into another and parents can get the maximum value from a given bike.
Obviously an individual child will vary from the averages in the data, but if you start off by designing for the most common proportions then the adjustment our bikes offer either side of that catch those people that are further away from average.
Finally, do children really have growth spurts?
IR: Yes. It varies from child to child, but most children will grow in surges. If they are getting particularly hungry, that’s the sign that they are having a growth spurt.
At Islabikes, we know better than anybody that each child is different and has a unique relationship with their bike. It’s always important to remember that children grow and develop at their own pace. We take great pride in being able to provide them with the right bike for their size and ability. But the real excitement for all of us is seeing where their bike will take them next.