I was thinking about kids bikes this week. There were some discussions of 26″ hardtail design and another on building a kid bike. It sent me off. It’s a good mind experiment. How to design a bike that has no reference?
Imagine trying to ride a bike like this?
Sadly, that’s what most kids have to ride as mountain bikes. A bike designed to be ridden in a driveway. That’s what most of them are. Worse than this, when most folks go about building a bike for a kid, this is what they model after. It’s pretty sad. Parents can be cruel, just by being ignorant.
I’ve built frames for and worked with kids and small people bikes in the past and it’s shameful how bad the bikes they ride can be. Not many can you call “usable”. They certainly never fit and they weigh a brick ton. I find it amazing how many adult cyclist can look at a kid on one of these bikes and think that it’s fine.
Here’s the 2011 PVD Micro-DH – PodRacerOne. It was pretty cool back then.
I took a fresh look at the problem, here in 2018. I’d apply some of my more modern way of looking at bikes and geometry and see what I would build now. New ways of solving old problems.
Both bikes here use a 26″ fork. A shame that the one I have is a 1st gen tapered steerer fork that will only go down to a 100mm headtube. In a perfect world, on both the 24″ and 26″, I’d be using a 75mm tube. This would allow for greater travel which would be good.
Generally, a child isn’t able to make much use of suspension as they don’t weigh much, don’t ride hard, and what’s available in that scale is generally terrible and brick. A problem more than a help.
Both bikes need to be put together with special attention to the drivetrain as 345mm and 380mm chainstay lengths are functionally too short to work with a standard configuration system. Going down to a wide-range 7 speed system is sensible.
Crank length here goes down to 155mm or 160mm. Great versions of these are available from Canfield Brothers. SRAM now has an NX 94mm BCD crankset available in 155mm (00.6118.416.000), a very cool thing for budget minded shredders. The minimum ring size of 30t (OEM) or 28t (aftermarket) may be an issue though.
I approximated saddle heights as these are not for a specific child. These were just quick sketches and not fully sorted designs.
Below is a 24″ wheeled version:
This is the 26″ version. The chainstay is far too long for a good fit but squeezing into the 26″ wheel has huge benefits on the trail.
One cool thing I was just turned on to is the Sugino Mighty Mignon – 901D Cranks. They are square taper which is kinda lame but that does mean that a very narrow system can be made. Arm lengths are 140 / 145 / 150 / 155mm. Very cool and 10 speed parts.
Otherwise, the Canfield cranks are the obvious choice.
Better than these two bikes I show above is a more modern approach to bike design where the bike is full rigid but uses a plus tire up front, skipping the suspension for a larger wheel diameter. This makes much more of a difference to the kid using it. I’ve tested this exact platform extensively for myself and it works very well.
This bike is not drawn to an actual fit. I would ensure that the front center is maximized like most any modern bike. This brings a ton of weight from the bike and makes it faster.