Dumb Idea? Yay or Nay? Rollers - Indoor Training - Flywheel
 

I've got some old Minoura rollers with large diameter drums on it and had an idea. What if I filled the rear roller with sand?

Would it act as a fly wheel so I could coast?

I was looking at some of the smart roller options out there like the Tru Trainer and eMotion rollers but they are pricey.

It would improve the coasting, but Mr. Newton suggests that they'd also be slow to spin up.

Why do you want to coast on rollers?

Have you ever ridden Tru Trainers? They are fantasist. Closest thing to real road riding you can get. It's not just the coasting but it's the sprinting as well. I used my rollers with Zwift last winter and want to do the same sometimes it's nice to coast to relax for a second and also it makes it easier to ride no handed and to stand up.

I think if you brake, the 'flywheel' could pull you off the front rollers and throw you backwards?

The sand won't have much effect. The drum diameter is what?, 7"?. Not very large. To get much effect from the sand, you would need all of it right at the 7" (3 1/2" from the center of rotation) but of course, most of it is a lot closer to the center of the drum where it is doing virtually nothing to add inertia. (The grindstones that coast, the old pedal driven stones, have diameters like 2-3' (or more). The inertia for rotation is based on the square of the radius. Your roller is (say) 3 1/3". The grindstone is (say) 30". ( 30 / 3.5 ) ^2 = 15.6 That grindstone has nearly 16 times the inertia effect and it has no belt to drive, no front roller and no front wheel. (True, you have bearings for all rollers and hubs vs steel on steel for the roller axle and pedal rods but it has solid rock, not ground sand so that probably balances out.

Ben

Just fold up a towel and put it under your roller. It will add resistance.

I ride Zwift all winter on E-Motion rollers, which are about as close to road feel as I've ridden. I can do full-on sprints and whatnot. I've never felt the need to coast on mine, but to each their own.

Might work...

Another approach - make a 2nd roller frame that sits behind the rear of the rollers and mount on it a big flywheel belted also to the rear roller. (You might be able to run both belts on the same wheel or put a 2nd wheel on the other side.) With this, you could have a flywheel big enough to work and up off the floor to accommodate the big diameter. The final setup would be kinda like a tender behind the locomotive. With a belted flywheel, you also get to gear up the flywheel so it spins faster. (Inertia goes by the square of the radius/diameter but in direct proportion to the rotation speed. With the right flywheel and gearing, you could get exactly you and your bike's worth of inertia for real road speed. "Hang on ma, I'm going 40. It's going to take me a while to stop.")

If the flywheel was big enough, braking would tend to push you back and you might drop off the rollers. It might be worth considering how you would crash if that happened.

Ben

I see, that makes sense. Might be better to take an old deep dish wheel and fill that with sand and use as a dedicated trainer/rollers wheel... Hmmmm.

They really do look great. I may end up going that rout. I'm still so iffy with indoor riding in general though. But last year Zwift at least kept me entertained enough that I could stay on the bike for an hour. So it may be worth the investment.

Coast ??
Just stop pedaling. Why do you care if the wheel's turning ?

gyroscopic stabilization?

Ooops, I was thinking about a trainer, not rollers.

Use wider tires and lower pressures. That will increase resistance. The mass inertia will increase the 'coasting' a bit, too.

How about using lead shot in lieu of sand? It will need to be packed well lest imbalances occur. If you could melt lead and pour some 'donuts' to fit inside your roller that is an option. Diver's weights are a good source of lead.

Kreitler Rollers makes a flywheel for their rollers and the Killer Headwind Fan. https://www.kreitler.com/accessories I don't know that either would work for Minoura rollers since they fit to the standard Kreitler frame, but it gives you an idea what is out there. A friend who works for a fabricator or machine shop would be a great asset!

My Minoura rollers have heavy 4" drums, and carry momentum more than the previous Performance ones,

which I like. Pretty much the opposite of the suggestions for adding resistance in posts above.

I have Kreitler rollers with the flywheel. I also had an old set of Minoura rollers. It would take some fabrication to get the Kreitler flywheel to work with the Minoura rollers, but I doubt the Minoura roller end covers could sustain the load the flywheel exerts on the rear roller.

I think you are right. They are just plastic covers. But I might look into the specs on the Kreitlers adn see if one of their roller drums would fit. I'm also looking at this one, https://www.sportcrafters.com/blog/n...h-inertia-drum which might work. I need to measure everything tonight.