Nerd Alert: tubeless and pressures

Regarding the sealant discussion, Josh had his revalation when he realized the wheel is a centrifuge. While that is true when testing in the lab, as Josh has said about wheel aerodynamics, while riding wheel speed is zero at the point of contact and double road speed at the top.
How does this affect the sealant distribution while in motion? Does it surge? Does it “spray” similar rainwater off the outside of a tire? Can we put a video camera inside tire to see?

Also, IIRC when Mavic patented the original UST designs they made to available free of charge to tire (and maybe rim) manufacturers. If they wanted to use the UST logo and name the tire needed to be tested by Mavic (for a fee) and pass their safety and performance standards. Then they could license the name and logo.

Disclaimer - I suck at physics and anything STEM related, soooooooo…remember that. :stuck_out_tongue_winking_eye:

I believe those points re: wheel speed are in relation to the road, not what is actually happening within the wheel. The wheel is still rotating so the associated forces are still present throughout the entire rotation.

Smarter people can correct me if I am wrong…:sunglasses:

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That is the question. Josh related it to how they were doing the lab testing

I haven’t listened to the podcast yet so I have no idea if this is exactly what he said or in what context it was said but this is absolutely not correct.

Well Mr. Knowitall (you generally seem to think you do on these forums) it absolutely is correct in the context of the wheel/tyre speed relative to the road.

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Well Mr. Knowsnothingatall… it’s actually not correct and certainly not “absolutely” correct, in fact it’s physically impossible for two opposing points in a fixed ring to be traveling at different speeds.

Again, not sure what the context is that it was used in and if it was just a bad way to convey some otherwise valid point he was trying to make but the statement as written is absolutely not correct.

The speed of each point on the wheel comes from two components. All points have the same translational and rotational speeds. However, they cancel out at the bottom, causing the bottom-most point of the wheel to be stationary relative to the ground.

However, only the rotational speed affects the centrifugal force that distributes the sealant. There should actually be a greater force on the sealant on the bottom because gravity is also pulling it down, although this will be small compared to the centrifugal force at speed.

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OK, whatever you say. :rofl:

Well put.

Translational speed is the motion of the system, the wheel as a whole from one point to another

Rotational speed is the motion of a fixed point moving around an axis

Neither of these “cancel out” and cease to move at any point short of you stopping.

Best I can assume without hearing the statement is that he was referring to the instant center of a wheel absent slippage… in which case the contact point has zero velocity in relation to the road surface. That said, the top of the wheel would still not be going double the “road speed”… the top of the wheel would be moving at twice the velocity of the axis of rotation, in this case the center of the hub.

So… still not sure what Josh was trying to say but the statement as written above is still absolutely incorrect.

You obviously failed physics, it’s all about frame of reference. Yes, all points of the wheel rotate and the same speed relative to the wheel/bike. In the plane of reference of the road (or outside observer), the bottom of the wheel has 0 velocity as it is rotating backwards at the same speed the bike is moving forwards and the top has 2x the forward velocity of the bike. If the bottom of the wheel wasn’t at 0 velocity then the wheel is skidding…

That was great, thanks for the laughs

From the frame of reference of my eyes while riding the bike, the ground is moving backwards and the wheel is rotating just fine.

At the contact patch the they are moving in the same direction and at the same velocity if none are slipping, sure. That has absolutely nothing to do with what is happening inside the tire with, eg. the sealant.

Think of a tire spinning in a lab; if I to the side of it, totally unrelated, move a body forward at the same velocity in the opposite direction as the tangential velocity of the wheel at the bottom, making the relative velocity between the two zero, did the wheel stop spinning? Did the sealant suddenly decide to do whatever?

When talking about aerodynamics, though, the fact it’s spinning does need to be properly accounted for in testing.

Looking for a video from inside the tire with sealant in it you say?

Behold…

Park Tool Company, at your service.

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That’s so cool. Thanks for finding this.

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Park Tool did an interesting video on this - they put a camera inside a tyre with sealant ( albeit a fat bike wheel /tyre afaik) but gives a good idea of the action of sealant when riding : A Look Inside Your Tire | Tech Tuesday #184 - YouTube

As per my last post… :stuck_out_tongue_winking_eye:

Welcome to the forum!

thanks and sorry! - I must have had a stale tab left open

No worries, great minds and all that :wink: