Pressure Measuring Device for a Wheel by SRAM

In this article, we’ll be discussing a Pressure Measuring Device for a Wheel by SRAM, US Patent 10,919,346. The publication date is Feb 16th, 2021 and the filing date is June 28th, 2017 (long time ago). This has been granted.

SRAM/Quarq have already released an iteration of their tire pressure monitor system (TPMS), but the designs in this article are different than what’s currently available. It’s important to note this is for road and mountain bikes. They even have both pictured — I just picked the mountain bike because I’m such a rad dude.

Brief Summary (tl;dr)

SRAM are introducing two different TPMS systems. The first design has the sensor/battery housed between the inner wheel bed and the spoke bed (so inside the wheel itself). They state you’ll need a wheel with a hole in it to put this thing in there. They’re solutions for the hole are rim tape, a covering plate, or a pre-designed chamber in the wheel bed. The second design places the sensor and battery on the outside of the rim, which means you don’t have to have a rim with a giant hole in it. The second design follows similar design principles as the current TPMS system, but appears to be a smaller package.

Background

A TPMS system is a device that informs a person about the tire pressure of a tire. In a modern system, they’re entirely wireless. If you have any newer car, you probably have them in all your tires.

TPMS systems aren’t new, especially in the automotive world. From what I can find, they’ve been around since the 80’s. Personally, they’re always a huge pain in the ass. They’re constantly breaking, and I’ve never needed to know my tire pressure so immediately that a TPMS sensor is necessary. They also make every tire change a little more expensive. That being said, they’re now in the bike world but you don’t ever have to actually use them. It’s a luxury item.

SRAM already have a TPMS system, from their subsidiary Quarq, with the TyreWiz. It’s a wireless tire pressure system that ‘offers a real-time tire pressure sensor for cyclists’. I can say that I have never once, in my life, thought I needed to know my tire pressure in real-time. They’re really grasping at straws here.

For posterity’s sake, the image on the left is one of the current TyreWiz patent designs. This one was filed after, and released before, the two designs in this article — so it’s possible these are DOA anyway.

Intro

SRAM have developed another iteration of their TPMS system. The current design has the entire power/pressure sensing components on the exterior of the tire, which is a pretty convenient design, but it’s not very appealing to the eye and it could get snagged on something. We all know biking is about aesthetics. Why would I be doing this if I didn’t look awesome doing it?

This new design puts the battery and pressure sensing component on the inside of the rim, between the inner wheel bed and the spoke bed. I know what you’re thinking — how the hell are they going to do that? Aren’t these wheels extruded as a single piece? Most are, but that’s for another time.

They also have another option where the battery and pressure sensing component are on the outside of the rim. This design is much smaller than the current production item.

Intended Novelty

The intended novelty here is that the power source is removable and offset from the flow path of the valve. Meaning the battery is can be replaced (probably a button cell battery), and the battery is not in line with the flow of air through the valve. Pretty concise.

Why

SRAM state:

Traditionally the pressure within bicycle tires is measured using an external pressure gauge such as may be found on a floor-based tire pump… The use of such a gauge for the identification of leaks is not ideal as many of these leaks may begin from damage incurred while the bicycle is being ridden and thus when such an external device cannot detect them.

Even more so:

The requirement of a separate or external pressure gauge, not designed to be a permanent or semi-permanent component of the bicycle, limits when a rider can make accurate pressure adjustments.

For real? Is this really a problem? I don’t believe for one second that anyone at SRAM thinks this is necessary. Even the engineers behind it are scoffing at their own designs. Even though the whole idea seems unnecessary, these designers still did a great job. I know this probably wasn’t easy. And the big dogs see a market for it; if they don’t do it, someone else will. If people are going to buy it, someone will make it — capitalism bb.

But before I get shit on, it’s possible this design is for road racing bikes, where aero is important and rim strength isn’t. In that case, it makes more sense.

What

Before we start, let’s talk about the composition of this particular sensor. Figure 13 shows 2x battery 106, circuitry 108, and sensor 58. Circuitry 108 comprises the wireless communicator. The batteries supply power to the circuit, which parses pressure data from the sensor in the sensing chamber 102. This goes back to the novelty, where the battery is removable and not in line with the flow path. Fig 8 shows a perspective cross-sectional view of the system in the wheel. Just looks like a normal valve from the outside.

Figures 4, 5, 6, and 7 show different design options based on the same idea. The big question here is — how are they going to get the protruding battery/sensor into the wheel itself?

Referring to FIG 4, SRAM say the rim will have a ‘radial access opening 66’. They don’t go into much detail as to what that means or how they’re doing that, but it looks like they just cut a hole into the rim. Then, you put the TPMS system in the wheel and you secure it with… rim tape:

…the radial access opening 66 may be covered with a flexible covering 70 that covers at least a portion of tire assembly bed 36. The flexible covering 70, such as what may be commonly known as rim tape or a rim strip, may be adhesively mounted or physically constrained by the radially outer tire-engaging portion 37 and around the circumference of the rim 20.

Referring to FIG 5, they’re proposing the same idea of putting a hole in the rim, but now they’ve got a mounting plate 72, rather than rim tape.

The mounting plate 72 may be rigid in order to provide a more stable mounting of the pressure measuring device 32. The mounting plate 72 may be used in combination with a covering such as the flexible covering 70 or in place of such a covering.

FIG 6 continues with the same idea, but they’re proposing a little chamber inside the rim. There’s no way this will make a rim more expensive.

The structure [80] may have radial walls, circumferential walls, and an axial base surface forming a compartment. The internal structure 80 may be configured to house and/or locate the pressure measuring device 32 within the rim 20.

FIG 7 shows the same configuration but with a tube (82). This system will be very similar to FIG 5, with a removable plate covering the TPMS device.

…the tire assembly 28 includes the valve stem 38 as an integral component of an inner tube 82. The inner tube 82 may be used in a clincher type configuration similar to tubeless type tire assemblies or may be used in a tubular or sew-up configuration.

FIG 17 shows a more realistic design closely related to the currently available system. SRAM state this doesn’t require any modification to a rim, meaning this can be used on any wheel.

Neither the tire assembly bed 36 nor any other part of the rim 20 needs to be configured to receive the pressure measuring device 32.

Conclusion

Man, the first design in this document is ridiculous. Could you imagine having a wheel with a big ass hole in it, only to house a little sensor that tells you information that you cannot look at every single second? I thought we were getting rid of big holes to maintain some level of rim strength? I’m fairly certain this will complicate the tire sealant process, too. I have a very hard time believing this will ever actually be produced.

Like I said, maybe this is for road bike racing, where aero is key. I’m sure a big sensor/battery isn’t great in the wind tunnel, and I’m sure wheel strength isn’t paramount on a road bike like it is on a mountain bike.

The second part is much more viable, but not that different than the current design. This one probably has a much better chance of being developed into production. Based on the filing dates of these patents, it’s possible both of the designs in this article are DOA. The current TyreWiz was filed after and is already on the market.

But, the bike world is weird. We all know it. I wouldn’t put it past tons of people with some extra coin that want to know their tire pressure in real-time, and don’t want you to know that they know they’re tire pressure in real-time.

In short, you’re going to need a special rim for the internal TPMS system. If you don’t want to do that, you could use the second example, which is similar to the current system, just a little smaller.

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