I have a Sears stationary exercise bike from the 1970s. I has not been used for many years but is in good shape. We were going to the gym for exercise about 5 days a week before Covid19 but won't for at least a year so I thought I would resurrect this old bike. My wife is thinking about getting a treadmill but she suggested we try this first since we have it, it takes up less space, and cost will be less. Also she has a weak knee that operates better on a bike than on a treadmill.

One of the reasons that we stopped using it is because it does not have a good motion. The resistance is felt pads and there is no flywheel so pedaling is choppy at almost any resistance.

I would like to add a flywheel effect to this bike to add momentum and overcome the choppy ride.

The front wheel is 20 inches diameter with spokes and removable plastic spoke covers. I know that adding weights near the rims will create a flywheel effect. I have not been able to find any such weights online. From search results it appears that 30 to 60 pounds is the usual flywheel weight on bikes that have them. I think 30 should be enough here.

Any suggestions?

 

I don't think there is a chance you will find something made to do what you want. You are going off road and will have to be creative. What tools and/or skills do you have?

A flywheel of any mass will have to be pretty well balanced so precision will be key. If the mass is not balanced then the bike will shake or vibrate when you're riding.

Everything I can think of relies on replacing the front wheel. Swapping out the spoked whee for a disk made of a thick plate of steel could be a great flywheel. Of course cutting a precise circle and center holes in a thick plate of steel is beyond DIY. What you would pay for the wheel could buy you a nicer exercise bike.

 

Yes, donate to local Salvation Army, then look on Craigs List for a nice, low usage, newer spinner bike. Trying to retrofit that old POC is just a waist of time!

 

Thanks guys for your input.

I have some Corian leftovers that I am going to try to use. (Specifically a double sink cutout from a counter installation in the late 1980's. Knew it would be useful eventually.) Did not rummage through the workshop until after I made the post.

So far I have cut a 15.5 inch circle and now will cut segments to match the spoke spacing and clearances to supports. I think I will also cut a smaller circle to go inside the spokes to fasten the outer segments to.

The piece I already cut is 5.5 pounds. I read that as little as 8 pounds would help. The inner segment will add to the weight.

When I took the spoke cover off I found that the rim has a standard hole for an inner tube stem. The tire is hard plastic and there is no inner tube. I may try to fill the tire with sand through that hole to add more weight.

In my opinion any time spent in the worksop is not wasted even if the project is a bust. :-)

A good Plan B. Thanks.

Will post pictures when done.

 

I would balance the wheel after you get your weights installed.

 

The project is done and I think it turned out pretty good. The steps taken and the final result (video) are shown below. The hub diameter is 1.25 inches. The 6, 10 and 4 inch circles fit snugly on the hub and are attached together with 8-32 cabinet hardware screws that self tap into the adjacent Corian layer. Those diameters were dictated by clearance between the spokes.



Six inch circle (in 2 halves) installed and 10 inch circle (4 segments) being Tetrised in.


10 inch segments being attached with 8-32 cabinet hardware screws self tapping into 6 inch circle behind.

4 inch circle halves installed. Screwed into 10 inch circle.

15.5 inch circle halves later cut into 10 segments to fit between spokes.

Segments attached to inner 10 inch circle. Some shimming required near hub to keep outer edges tight to rim (see video.)

All pieces installed. Total weight slightly over 8 pounds.

Here is a link to a video showing the motion and flywheel effect: https://youtu.be/pUqj86eAAPE

The ride is much smoother than it was before adding the weight, especially when riding with resistance.

Although you can hear some unbalance when the wheel is spinning, it is not enough to cause undue motion or thumping. The visual appears as more unbalanced than it actually is due to the non-uniform positioning of the outer edges of the larger segments. Some are further away from the centerline of the rim than others even with some shimming but not enough to interfere with the wheel supports, etc. I expect whatever unbalance there is including any side-to-side pressure will eventually wear on the bearings. This is a temporary solution to not going to the gym during the pandemic so that should not be a problem.

And there is one less scrap of Corian in the resource pile. Of course the wheel segments can always be repurposed again if necessary.

Thanks for your interest and input.