Oring/O-ring Boring. What governs stretch?
 

I have several sensors mounting with Orings and they break over time. When going to a Hardware store I am seeing a lot of variability in oring elasticity/stretch, which is a big deal in sensor mounting.
Does anyone have a resource for targeting stretchy orings , rather than the thicker Buna rubber ones more directed towards sealing?
I really need robust rubber bands, not seals. more a bike mount band kit
Either a discussion of this or a source . Onesies and twosies are more expensive and hard to reproduce results.

Most of mine came with sensors from China and OEM is not a good source.

Sources state:
"To provide an effective seal, the O-ring's inside diameter (I.D.) must be smaller than the piston groove diameter, so that the O-ring is slightly stretched, fitting snugly in the groove.
This stretch should be between 1%-5% with 2% as the ideal in most applications. A stretch greater than 5% is not recommended."
"With the O-ring calculator, engineers can specify the groove dimensions for a specific O-ring or a specific groove.
The O-ring calculator calculates the most relevant size O-ring for any given groove and includes O-ring inner diameter stretch and the desired Polymer Group or Seal Hardness. ."
Examples: Garmin Bike mount band kit (replacement) 6 for $15.77,CatEye CA5447010 Rapid X Spare Bands- 2 for 8.95,Ascher Bike Silicone Mount Band, Cycling Bicycle Rubber Straps, Pack of 4 $6.99
All seeming less than ideal

Do you have any inner tubes that you had a blow out that you can't patch? If you do, there is your rubber source.

If you do not have any tubes that you want to use a scissors on, next time you are in a bike shop, ask a mechanic if you can have a blown out tube out of their garbage bin. If they look at you with an odd look, just tell them size does not matter, you want to use it to make some rubber bands, and tell them the thicker the better.

Most of my sensors are attached with zip ties, not with a stretchy band.

+1, would read again.

Are you confusing the specs for o-rings used to seal things from fluid and/or gas leakage with specs for using as rubber bands? Even so, there are many different specs for O-rings that operate in different environments. IE, space shuttle booster vs air chuck on floor pump.

Didn't see anything about UV resistance in your specs. Maybe that's an issue for those companies using O-rings that were only intended to seal.

As suggested, cut up an old inner tube o use nylon wire ties (tie wraps).

Yes.

As Iride01 pointed out, these are two very different purposes with different engineering.

​(​​​​​I wouldn't use rubber bands either.)

You guys aren't using ceramic o-rings?

Seriously, I haven't had issues with any garmin or cateye bands.

Just the OP apparently is having issues. I still have my garmin quarter turn mount for my edge 500 using the same two o-rings I put on it 10 years ago. And Garmin gave me a a lot of extras too that I still am waiting to use. Most sensors and crank magnets I have nylon wire ties holding them on.

+1. I bought spares probably 10 years ago when Garmin came out with the quarter mount and have never broken one

The O-rings I've got from Garmin and Cateye do look an awful lot like the polynitrile (?) O-rings I buy at my Local Hardware Store (LHS) to fix plumbing problems. (Great, now we can debate LHS vs. Home Depot web orders...)

My biggest worry is that when one of the Garmin O-rings break, I'll have forgotten where I put the extras.

Thanks for the help.
My most vulnerable Orings are ones that get nicked when being swapped between rides, or are holding pedal cadence sensors in place where a shoe can bump them.

I imagine stable settings that don't get moved are not an issue and pretty durable.

The ones I get from bike vendors at $4 (!) ea are ~2mm and
the HDW store ones closer to 3mm butyl and pretty stiff.
I swap them out at the first hint of a nick.
I have plenty of skinny tires so will try the inner tube route.
I put a tape wrap on almost everything to protect them, if they are exposed to blows, as a $200 Varia light is not something I want to trust to any oring.
and that is inelegant. I may switch to safety wires as carrying tools to cut cable ties also gets elaborate

o-rings for sealing might not work for mounting. That is, something designed for one purpose might not work for the other.

The Garmin o-rings are designed for the purpose you are interested in.

Garmin gives you multiple mounts with most of their devices and a slew of o-rings to fasten them on. Why are you swapping mounts? If you don't have the right mount for all your bikes, then get multiple mounts so you aren't constantly stretching and relaxing the o-rings and subjecting them to wear, abrasion and nicks.

Most everything Garmin on a bicycle uses a 1/4 turn mount. Garmin makes all sorts of variations of that mount to fit bars, stays, seat post or where ever you want to put them. And many third party vendors have their own version of the Garmin 1/4 turn mount that is even more inexpensive or more costly depending on what you want.

Don't be switching mounts from bike to bike.

Thanks @Irideo1.
For the ones I ride regularly, good mounts rock. Still, I have to constantly reconfigure, and the Orings become a consumable.
I have a roadie, a "touring" setup for trailering utility, several foldies, and a trainer.
Plus occasional MTB and new builds. Champagne problem, right? At least I make them work for their living.

Temporary mountings with the orings are useful, but they are vulnerable, needing trustworthy Orings, and tape/tethers.
I use permanent mounts where I can and they are indeed hard to move around, and nice ones pricey.

Permanent mounts and separate sensors for each bike would be a spiraling complexity.
inexpensive mounts for low stress installs , like the trainer, compete with the price for OEM Orings (!), but is pretty reasonable for the head unit.
Another problem with permanent mounts is the limited real estate on the seat tube, for bags, lights and trailer hitch, complicating flexible configuration.

The head unit wants a stout mount, and heavily loads the Garmin mount , which was designed for watch size units.

The biggest challenge is for cadence sensors and hub mount speed sensors, which don't have separate mounts,
and the rear facing Varia which needs differing positioning for each bike ,
has a funky mount, and doesn't have flexible mounting well thought out by Garmin.

I'm not trying to belabor it, but having a 10cent consumable selling for $4 chafes when needed in bulk,
and losing lights and sensors likewise.

Wanting to keep it fun and safe

Ask yourself this - which is less expensive? Multiple mounts on your multiple bikes, so you can move sensors from one to the other, or replacing a lost sensor because you didn't want to spend $4 on a $0.10 item?

Just because they have the same basic shape doesn't mean the $0.10 thing is the same as the $4 thing.

Why are you constantly reconfiguring? I put the cheap'o plastic 1/4 turn Garmin mount on my Paramout and it's been there with the same Garmin bands (o-rings) since 2017. My Raleigh would be older, but I disassembled that bike in 2020 and took the original Garmin mount and bands off of it that was put on in 2010.

Lights? Does Garmin make lights for bikes other than Varia radar? That comes with both a cheapo plastic mount and bands or a better clamp on mount with adapters for tube size.

Still I can't see changing mounts between bikes, which you sort of said you don't do, but then you said you are always re-configuring. So I'm still at loss to understand why you have to move the mount so much. The device, yes, the mount no.

And if the lights and other things you are moving or reconfiguring the mounts for aren't Garmin, then I guess I've no idea how good their bands (o-rings) might be. Maybe they just used the cheapest they could find that have no UV resistance or are otherwise intended to remain stretched. A o-ring intended to be a seal wouldn't need UV resistance or would it remain stretched after it's installed.

Iride01 I build and collect. Short of being like DCRainmaker, but still have to configure cadence sensors lights and head unit s between Foldies , commuter, roady, mtb, ebike and trike for different settings, plus the new builds, and different setups for different rides.
I go though a fair number of bands and like to standardize as much as possible.
It'll be easier when I get the chip put in my neck or a PAN like universal module.

I don't know if this is still timely for Bike^3, but have you tried shopping for rings at the McMaster-Carr site? Often they list objects based on real technical specs, which may be more useful.