Recently the school I volunteer at had an old bike donated that they wanted to use as a stationary bike for the kids to let off some energy. Looking online, the only options I saw for converting a normal bike into a stationary bike were designed for adults and were generally pretty lightweight. I needed something much more sturdy, so I modified this design to stand up to heavy use from preschool-aged children. I did this project with two boys, aged six and seven, who were able to do most of the work themselves using hand tools, with the exception of one step for which I used a miter saw. In addition to schools, I think many families could benefit from having one of these, especially when kids are cooped up inside during long winter months.
What you'll need:
20" children's bicycle (Another size could work with modifications.)
bike axle pegs
2 8-foot 2x4s
3 feet of 2x8
2 feet of 2x6 (or wider depending on size of bike)
saw (I used a compound miter saw for the tricky cuts and hand saws for the rest).
drill with hole saw bit to match the diameter of your pegs
screwdriver or drill to drive screws
hammer and nails (optional)
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Step 1: Measure Your Bike
Children's bikes generally come in four sizes, depending on the wheel diameter (12", 16", 20", and 24"). We had a 20" bike, which works well for most of our school-aged children. I will include the dimensions of the stand we made as I go, but a stand for a smaller or larger bike would require some adjustments. I aimed for 1½" of clearance between the wheel and the bottom board to make sure it wouldn't rub, but it's good to keep the back end as low as possible, so that it's not too much higher than the front. You'll also want to check that there's plenty of clearance between the pedals and your frame so that the kids don't hit their heels on it. If you want to double check that your 20" bike is the same size as mine, I measured roughly 3 feet from axle to axle, 15" from the rear axle to the crankshaft where the pedals connect to the bike, and 5" crank arms for each of the pedals.
One measurement that's important to get right is the width of the bike frame near the rear axle, since you'll want a tight fit between the supports and the frame here. The thing to measure is not the frame at the axle itself, but the widest part of the frame within a few inches of the axle (i.e. the tubular part rather than the flat part). I measured this distance at 5½", which is happily the width of a 2x6.
The other thing that you need to know precisely is the diameter of the pegs you are using, but I imagine that they are pretty much always going to be 1½" in diameter.
Step 2: Build the Frame
This first step was actually started remotely by my brother and my dad. They had heard we needed a bike stand, but they did not have the bike dimensions, so they simply built a frame out of 24"-long 2x4's. They also included a few boards which we did not use, but the 24" frame ended up working well for our 20" bike. The boys and I added a 2x6 down the middle to keep our vertical supports the right distance apart.
To make the frame, simply cut an 8' 2x4 into 4 24" lengths and screw them together in a rotationally symmetrical pattern to form a 25½" by 25½" square. Then cut a 24" 2x6, lay it flat and center it within the box, and then screw it in. We used two screws per joint.
note: I neglected to take pictures of the process as we were building this, so most of my pictures for the next few steps are going to be simply screenshots from the sketchup model I made of this.
Step 3: Make the Vertical Supports
Since the goal is to make this bike stand very sturdy, you want the bike pegs to rest snugly in their supports and not lift out if the bike was being rocked back and forth by an inexperienced rider. To make the bike easily removable for transportation and storage, however, I aimed for slots from which the bike could be lifted out with the pegs still attached, but only with some effort.
For a 20" bike with 1½" pegs, drill a 1½" diameter hole in the middle of a 2x8, with the center of the hole 13" from one end of the board. For any other size of bike, just add 3 inches to the tire radius.
Next, cut the board straight across near the top of the hole, where the end of the board you measured from is the bottom. using a hand saw and a rasp, cut down into the hole from the cut you just made such that the hole becomes a kind of horseshoe shape, with the upper part being only slightly skinnier than the original hole, and flared back out at the top to receive the peg. You may have to play with this a little bit and see how much work it is to get the peg in and out.
Repeat this step to make a second support.
Step 4: Cut the Cross Braces
This is the one step for which I think power tools are required.
Using a compound miter saw, cut a 2x4 at an angle which is 45° across the shorter dimension and 37.1° across the larger one. Measure 12 and 7/16" and make another cut parallel to this one. Continue until you have cut 4 boards.
On two of these boards, make a mark 2 and 15/16" back from the farthest corner on one end and cut at an angle of 74.3° along the larger dimension. This cut is straight up and down along the shorter dimension, since the two cross braces on each side are coplanar. If you care about your bike stand being bi-laterally symmetrical, then make sure to cut these boards such that they are mirror images of each other.
note: The measurements for these cross pieces assume a 24" base. They only extend about 9" up the vertical supports, so they would probably work for a 16" bike, but not a 12" without modifications. Taller cross braces would likely require a bigger base, since most miter saws do not cut angles more acute than 45°.
Step 5: Put It All Together
At this point, it's worth putting all of the pieces together with the frame and the bike to make sure everything fits together the way you want it to. If the angles for the cross braces aren't quite right, for example, you may want to adjust them before screwing everything together. You could also check the clearance between the bike pedals and the frame, though that is not as easy to adjust. With the frame flat on the ground, all the other pieces and the bike should hold their positions simply with gravity, so you can get a feel for what it will look like, and could even try out riding it as long as you don't lean too much to one side or the other.
While the bike is in position, make a mark on the vertical supports where they are met by the top of the cross braces.
Once you're satisfied with your cuts, it's time to assemble:
Start by joining the top ends of the two cross braces on each side with a single screw from the cut face of the longer piece into where you cut the corner off of the other. Make sure that all relevant faces on the two boards are flush. Then screw the top of the cross-brace assembly onto the vertical supports just below where they lined up in your dry run. This slight adjustment squeezes the bike frame in between the vertical supports for extra stability. You can put a couple screws in from both sides, or just 2 or 3 from the inside if you want them hidden.
Next, screw the vertical supports onto the 2x6 running down the center of your frame. Position them in the middle of the 2x6, with the bottom of each support flush with or slightly above the bottom of the 2x6 so that the stand will sit stably on the frame.
Finally, attach the bottom of the cross braces to the frame. If you did all the previous steps correctly, these should already be basically in position, but again, you want them flush with or slightly back from the bottom of the frame. We flipped the stand up sideways and used nails for this step because it didn't need to be held in place so precisely and the boys wanted some practice hammering. The nail heads are also on the bottom of the stand, so any hammering mistakes here are basically invisible. Of course, screws would work just as well if you prefer.
Step 6: Let 'em Ride!
Once the stand is assembled, simply press the bike pegs down into their notches and make sure they are sitting all the way at the bottom. Depending on your fit, you may need to do this one side at a time and really stomp on the pegs to get them down in there. The one we made requires a little effort to the get the pegs in and out, but once they are in the whole thing can be moved simply by picking up the bike, which is handy, in addition to the added stability for riding. You may also want to remove the kickstand from your bike, as it is no longer necessary and in our case was kind of in the way.
And then you're off! Or, rather, you stay on, and stay in place while letting off bundles of energy. You even still have full control of the handlebars, and could adjust the rear brakes to provide a little resistance to your ride (or use ankle weights). And of course when summer comes, you can simply pop the bike out and ride it around like normal while stowing the stand away for the next time you need a stationary children's bike!
I hope this was helpful and easy to follow. Feel free to let me know how it goes, if there's any edits or modifications you would make, and how it works for you and your kids.