Although a somewhat common feature on cars these days, tire pressure sensors (TPS) are also useful on bicycles. The SKS Airspy range of TPS products is one such example, which enables remote monitoring of the air pressure either to a special smartphone app (SKS MYBIKE) or to a Garmin device. Of course, proprietary solutions like this require reverse-engineering to liberate the hardware from nasty proprietary firmware limitations, which is exactly what [bitmeal] did with a custom firmware project.
Rather than the proprietary and closed communication protocol, the goal was to use the open ANT+ sensor instead, specifically the (non-certified) TPS profile which is supported by a range of cycling computers. Before this could happen the Airspy TPS hardware had to be first reverse-engineered so that new firmware could be developed and flashed. These devices use the nRF52832 IC, meaning that development tools are freely available. Flashing the custom firmware requires gaining access to the SWD interface, which will very likely void the warranty on a $160 – 240 device.
The SWD programmer is then attached to the 1.27 mm spaced SWD holes per the instructions on the GitHub page. After flashing the provided .hex file you can then connect to the TPS as an ANT+ device, but instructions are also provided for developing your own firmware.
I like that very much.
Full drama at https://github.com/bitmeal/sks_airspy_ant_community_fw/blob/master/doc/HARDWARE_PROTO.md
That looks like it has way too much wind drag for a road bike and it looks too fragile for a mountain bike.
huh, a cycling gadget i wasn’t aware existed. moderately rare, given how much i love my bikes. oh well.
one doesn’t normally bother to balance one’s bicycle tires, but with a box that large bolted to my valvestems i think i’d definitely want to. i’d honestly worry a little bit about it being there in a fast descent, but i may be paranoid.
Why would you put a 160 -240 dollar device on your tires when you can take a ten dollar pump with you?
Oh, you still have to take the pump with you. But at least in Europe they are way cheaper; 70€ new and as low as 30€ second hand a pair.
Quite handy on tour to get the tire back to the exact pressure you want without guessing and hopping on and off the bike for multiple attempts to get it right.
Even if you wanted pressure monitoring I can’t help but wonder if there’s a cheap mechanical way to do it. Something like a green/red indicator that flips at 20% under your desired pressure.
occasionally squeezing it by hand has worked fine for me so far
If you pay attention to the amount of squeaking that happens when you turn on smooth pavement, that is also a very handy giveaway for what kind of pressure is in your tires.
i’ve tried that too, but it turns out my thumb is horribly poorly calibrated. fortunately, a battery-powered pressure gauge runs forever on a coin cell and really doesn’t cost that much. (i’ve had bad luck with mechanical ones, they haven’t lasted very well for me. also they don’t have nearly the read-out range of an electric one.)
Those definitely exist;
https://www.amazon.com/Pressure-Monitor-Universal-Sensor-Indicator/dp/B0BSF11Q3Q
There’s also, although I can’t remember the name, some people who made tiny pressure relief valves that keep your tires from going over a certain pressure when they heat up – so just add a little extra and let it come out the first time they warm up, then you’re good for awhile. More applicable to cars, there. These first ones could be your thing, i dunno.
Great jailbreak hack for a poorly conceived device:
Too big, too bulky, flying stick or rock go…PPPPFFFFHHHHHttttttt t t….
I use the most sophisticated technology to check the tire pressure of the bikecycle : my thumb.
Whoever dies with the most gadgets wins.
Apart from those silly Presta bicycle-valves, if you have tyres with standard Schrader automobile valves, TPMS sensors for screwing on with BLE can be had for pretty small money on AliExpress or similar platforms. They also come in a 433/866 MHz variant if you want that, but it’s more work making a receiver for these.
SRAM markets their tyrewiz (a similar product) in conjunction with the shockwiz, a system that uses air pressure to figure out position, then uses that and derivatives (shock velocity and acceleration) to tell you how to adjust. Since your tire “springiness” is related to pressure you can better tune shocks (in theory) with the suspension.
There are light applications in aero estimation (pitot tube stuff) that is improved by knowing tire pressure as heating can affect things from rolling resistance to tire diameter enough to affect all the guess work in those aero drag guessing machines.
Does the measurement device look odd to anyone? It looks very tall and although I see it being supported by a spoke, I can’t help but think a few accidental kicks will probably damage the valve because of the massive lever action
My Garmin Edge already has a datafield that shows the AirSpy tire pressure.
I also use a Rpi0 with ANT dongle to read the AirSpy tire pressure, tire temperature and rev count. I used the draft TPMS description to help decode the transmitted data. So why do I need to reflash the sensors?
Your project sounds very interesting, is it published anywhere? I would be interested!
Regarding your question: You most likely shouldn’t!
From my current understanding, Garmin does not natively support the (draft) TPMS profile. AIRSPYs, as well as the TyreWizz, require a connect IQ data field – effectively a third party app. Other cycle computers – e.g. Wahoo – do support it, but the AIRSPY does not pair with these devices; likely because they do not implement the device profile, or use a different ANT network key, or else. Last firmware I checked was from mid/end 2024. And there is a negative response from SKS to the question whether they would every implement the TPMS profile around the interwebs.
If they are compatible with the TPMS profile with a recent firmware upgrade, this firmware project is purely academic and for personal education.