Introduction: Bike Trainer Rocker
This is a super simple way to make riding on a bike trainer much more fun. It let's you really balance the bike without having a giant set of rollers around and it feels better than the expensive spring-based trainers that lean. It uses your own weight to give you something to push against.
The thing to build is a platform that sits on the floor under your trainer and gives it a curved foot profile so it can rock side to side as you pedal.
The "special sauce" involves using a progressively contoured curve on a foot under the existing basic bike trainer. The curve is smaller radius in the center and increasing radius toward the outsides. Using a curvature that matches the height of your center of gravity (CG) off the floor would mean that you would have no return force at center as you leaned over. You would fall once you started leaning. If you decrease the radius, you get lower as you lean so you have nothing to push against as you lean and you also fall every time. If you increase the radius, you actually lift your body as you lean so your weight helps you return to center. That's what you want to happen, but not too much or it becomes too easy. The extreme case is when the radius of curvature is infinite (i.e. flat) and you are back on a flat-based trainer.
After much experimentation and falling over, I found a set of curvature values that work well (for someone of my height). Center radius 1.5m, progressing to 2.0m with a few inches of flat on the outer ends of the foot so that if you get that far over you still have a chance to "bottom out" and recover.
I've provided a printable outline of that shape you can cut out to make your own. If you modify the profile I suggest you start using the rockers near some furniture you can use to catch yourself and don't clip in your pedals!
Step 1: Building Instructions
- Plywood, 1/2 or 3/4"
- Sander or sanding block
- glue or screws
1) Make a rectangular or square piece of plywood that is 18" wide and slightly longer than your trainer's footprint front to back.
2) Cut 2 thin strips of the plywood to make a seat for the front set of trainer feet. They can be glued or screwed on to the top of the main plate to keep the trainer from sliding forward or back. I made some angled cuts off a 2x4 for this purpose but that was really not necessary.
3) Print 2 copies of the template .pdf file from this instructable on 11x17 paper (or use the .dxf to modify and make your own version). Spray mount that pattern onto a piece of plywood and cut it out. Be careful to make a very smooth curved edge and follow the contour exactly to avoid flat spots. Take some time to get this right.
4) Attach your nicely sanded rockers to the base, one at the front and one at the back using screws or some serious wood glue.
Step 2: Ride
Put the rocker under your trainer and try to get the left/right position dialed in. It turns out that some trainers are really asymmetric and have to be moved to the side to balance the bike over the center of the rocker. Now mark that spot. You'll need it every time.
When you get on the bike, it will feel pretty unbalanced. You will get used to riding on the rockers over a few minutes. Also remember that as you stand up, your CG moves up and you will not get as much resistance from the rocker as when sitting down. This makes standing a bit of a challenge, requiring some good balance and smooth pedaling. (I think this is an excellent way to not be bored while watching old Giro videos and waiting for the snow to melt.)
Happy riding and please feel to add suggestions or other versions. I set this geometry up for someone on a 52cm frame bike. I can imagine that someone on a taller bike will want a slightly larger radius to find the best combination of tip and stability.
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