Part 7: Building a Kids 20inch Full Suspension MTB
Rear Suspension
The rear suspension on these bikes is a spring coil. The coil is rated at 550lbs/in so is quite strong, especially for kids that don’t weight much. With me sitting on the bike I can make the rear bounce quite easily but then I weight a lot more than a 7 year old. Also the coil weighs in at 350g so is not light:
Air Rear Suspension
I found the smallest air suspension unit on ebay as it needed to be 100mm free length. It was called KS A5-RE but came in other names from different suppliers.
This unit weighed 150g so over half the weight of the coil. I installed it on my daughters bike and it looked pretty cool:
I used a suspension pump to the correct psi for my daughters weight, but I could not get the unit to actually do anything. I think the travel length is so small it is not at all noticable.
Change Coil Spring
So the next thought was to change the actually coil spring to a lower lbs/in. Online there are ones for higher rating at 750 and 1500lbs/in, but I need something nearer to 300 or 350lbs/in so I tried to find something online:
However they didn’t fit, the internal diameter was just too small, I needed:
- External Diameter: 57mm
- Internal Diameter: 45mm
- Coil Thickness: 6mm
So back to the search, at least rear coil spring are back in fashion…..
