I also think the contact patch tends to affect how the sealant disperses during slower riding & spin up/down. Every tubeless tire I’ve ever used has shown parallel sealant build up at the sides of the contact patch, inside the tire. Which is shown in the videos but not emphasized as much as I believe it would be with the tire in contact with the ground.
Didn’t realize i-bob was private. Text and links quoted below:
Reviving this thread with some fun empiricism…
I made a “see-through tire” so the movement of sealant can be visualized. The “tire” is actually a tube made of TPU (Revoloop brand). It’s a semi-transparent and relatively rigid when inflated to low pressures. To simulate “sealant”, I used water mixed with red food coloring to make it easier to see.
Videos of the setup in action are on Flickr and Instagram. Please check these out! I think they are cool.
Some takeaways:
Physics suggests that at steady-state somewhere above 4 mph, the sealant should cease tumbling and form a continuous ribbon under the tire tread. The experiments show a ribbon develops at around 4-5 mph, but sealant continues to tumble back into a distinct pool until the rotation exceeds about 8 mph. Beyond that speed, the sealant is flung against the wall like that carnival ride of yore.
As the speed increases from 2 to 8 mph, the sealant pool moves further aft and begins to climb up the back of the tire. It is continually replenished by sealant that flows and tumbles off the rising back side of the tire.
At about 10 mph and above, the tube deforms and develops a high spot, where the sealant tends to accumulate. This is likely an artifact of the use of a squishy tube, rather than a more rigid tire.
As the wheel slows down, the ribbon breaks up and tumbles as the speed drops below 4-5 mph.
Some caveats. This visualization uses water, which has a somewhat lower viscosity than sealant and probably a higher surface tension. The TPU tube is smoother than a typical tire. Together, these differences probably result in higher speeds required to reach the transition point between the tumbling and ribbon states. With real sealant in a real tire, the overall behavior is probably similar, but with somewhat lower transition speeds.
For a fatbike, where speeds are often less than 5 mph, sealant is sloshing and tumbling much of the time. There is energy loss associated with that fluid movement.
These experiments don’t quantify the energy loss, but they are useful for visualizing the process and developing a conceptual model. An interesting next step would be to time the spin-down from some steady speed to zero, with and without the added fluid. That would give some indication of the energy loss related to fluid movement. Unfortunately, the Hope hub and XD driver have enough drag that the wheel stops relatively quickly, too quickly to get a repeatable reliable time difference. Might need to switch to a front wheel for that experiment…
Eric “too cold to ride, so let’s do science instead” in NH
I also kinda wonder about the encapsulation of knowledge in formats that are getting increasingly archaic, like email lists and ah, forums.
Like do the young people on relevant bike Discords know that there are these older communities, or does their cultural memory of the bike internet start with r slash bicycling?
Chains don’t stretch they wear out. Tire beads stretch but it usually doesn’t mean it’s bad or unusable except for maybe cough compass cough a few special brands
A thing that AFAIK is under examined and also real is micro fractures (?) in carbon frames. You could probably take that all the way to GCN tech article.
So the old BS from the steel days that a frame goes “soft” with use is actually true to certain extent in carbon. Since I’m not a materials engineer I won’t do the topic justice but basically higher modulus fibres in highly stressed areas breaking locally under load without disrupting the greater structure of the composite. Changes the stiffness of the structure.
This was discovered because a certain sprinter, who is well known to be a bit of whiner, would complain about his frames going soft over the course of the season. An engineer decided to humor him and test his used frame vs. a new sample. There was a measurable difference so the frame was cut up and sent out for testing.
Coming in hot on the heels of the Reserve Filmore, a new high-flow tubeless valve stem. Looks like this is now a legit category, and I’m looking forward to trying these as I build new wheelsets and replace old stems.
I just cram a spoke or something in there to get all the gunk out every time I take the core out. The cores are replaceable so if they get all cocked up I am not too worried about that either.
Schrader might be the least proprietary valve in the world tho. not gonna work on all rims and won’t work with some bike inflation accessories. but that’s not schraeders fault
