Why do bicycle tires loose air faster than car tires?
I can literally go years without needing to put air in my car and truck tires but it seems I need to ‘top off’ the tires in my 3 bicycles every couple of weeks. I even bought new tubes.
Logic would seem to dictate that a tube would be a more airtight enclosure than a hard rubber tire up against a steel rim.
Where’s the breakdown?
tirewall-width? … my guess …
car tires are about 5mm in thickness, bike tires possibly below 1mm…
and bike tires have become extremely thin, compared to 30 years ago (weight? less material?)
also, bike tires may have way higher pressures (esp. road-bikes can go up to 120psi (vs. 30ish of cars))
I would recon it mostly has to do with air pressure. Typical car tire is at, what, around 35 PSI? Bicycle tires for a road bike should be around 100 PSI, a hybrid type bike maybe around 60 PSI, and a mtn bike maybe around 40 PSI or less. The valves for inflating/deflating bike tires are probably not the greatest, with an eye on cost and weight, so that is where the air loss is occurring, assuming no other issues like punctures. I check my road bike tire pressure before each ride, several times/week. Mtn bike maybe every other week.
And bike inner tubes are much thinner which allows air to permeate through the material.
This was my thought too, so I examined both valves and, honestly, the bike valves seem sturdier.
Car valves are about 50 cents each.
another relevant variable:
stored air volume … bikes and cars share (mostly) the same valves … those are dirt cheap an surely leak over time … but there is a difference between losing 1L of air in a bike (very noticable) vs. 1L of air in a car tire (not noticable)
(ignoring the fact that air compresses)
when I did 4x4 ing … those 12v compressors would inflate a bike-tire in 10 sec. … but took forever for a say 265/16 tire … (easy north of 3-4 min) … just a frame of reference, that works the same inverted (losing air)
Much thinner than the car tire? Sure, but I would think the failure point on car tires is the seal between the tire and the rim - there is no corresponding seal on bike tires.
Also, I have cruiser bikes so only 40 pounds pressure.
Fully agree. To illustrate this concept, the OP should take a normal floor bike pump and add 5 PSI to the already full tire. Then go to his car tire and pump it up 1 PSI. There will be a huge difference in the amount of time it takes to push those two amounts of air into each of those tires.
Check the tube material. Butyl leaks much less than latex.
Not stored volume per-se, but the ratio of surface area and rim length to volume.
Put another way, say a car tire has 100x the volume of a bike tire. But the surface area might only be 20x. So if it leaks slowly through the rubber, the effective leak rate will only be 20%.
And the rim length might not change much at all (or might even be higher on the bike tire). If it’s slowly leaking through that, the effective rate might only be 1%.
Good to know, thank you!
The modern automotive radial tire is probably the most highly engineered unified mechanism product on the planet, with the materials, design, and construction built on literally tens of millions of years of engineering experience and real world testing. (Technically there are several distinct components to a tire, but once it is manufactured they are, save for the valve stem, essentially a single body that cannot be serviced or have parts replaced without substantial remanufacture.) Even the cheapest tires are designed to operate for thousands of miles without inspection, and with a typical service life exceeding 30k miles or more. Diffusion through a pristine radial tire sidewall and tread is essentially negligible and leaks on most tires are generally through a badly installed valve stem or puncture, although after enough service or exposure, sunlight, and caustic chemicals cracks will form as the sidewall breaks down and old tires will experience slow leaks. (Of course, this also results in a product that is nearly impossible to refurbish, recycle, or even reduce to minimum volume without substantial effort.)
By contrast, tube tires on bicycles—which are pretty much still 1920s technology—will last only a few hundred miles, and often require multiple tube patches or replacements even before the tread wears down. Because the tube is a separate part, it is made as thin as possible to keep the weight down, and is constantly flexing within the tire body. Both the abrasion and flexing contribute to breakdown of the tube, and as noted both butyl and latex are moderately porous to diatomic nitrogen and oxygen even in their just-out-of-box state. Tubeless bike tires are theoretically less prone to leakage through the sidewall or tread but leakage due to problems with installation are common. Of course, nowhere near the same engineering effort has been done to bike tires (tube or tubeless) because there just isn’t a market for it, and the potential product liability of a defective tire on a bike is far less than on an automobile.
Stranger
Also consider that many bicyclists, myself included, look for the lightest possible tires. My current tires have sidewalls so thin that when I put in the tubeless sealant, I can see patches where the sealant foams through the sidewall fabric.
Say what? A few hundred miles? That’s ridiculous. A few thousand miles at a minimum, even for lightweight racing tires, and for the heavier commuter tires several thousand would not be unexpected. The chief cause of tire failure for bicycle tires is punctures cause by foreign objects. Automotive tires are less susceptible to this by dint of being much thicker and heavier, not because they’re more highly engineered.
Also, bicycle tires might not have as much engineering spent directly on them, but they’re made by the same companies that make automotive tires, and presumably Continental doesn’t forget everything it learned about tire manufacture when it goes to design the successor to the GP5000.
Bicycle tires don’t hold pressure as long as car tires because they’re much more lightly built, and that’s just about the entire extent of it.
+1
a couple of thousand miles is quite normal … most problems are snakebites or foreign objects puncturing - here tire-patches are your friend …
I’ve regularly gotten 5-6K on the two handcycles I’ve had.
I feel like when you ride a lot, the rubber does not have time to degrade due to aging and you can usually then get thousands of km on bicycle tubes, compared to something that has been sitting around for a decade. Make sure you keep your tires in good shape and not bald or cracking. I like the French valves, though not sure it makes a huge difference.
Lately I seem to have had a rash of bad luck encountering sharp bits of broken glass all over the place, so I broke down and got a couple of sealant-filled tubes, which I do not normally do.
If you use a pressure gauge you’ll find that in most climates you need to pump your car tires at least every fall and spring.
Car tires are losing air slowly like any other tire.
With bicycle tires it is more pronounced because bicycles run at a higher pressure, are constructed much lighter and have a much smaller volume vs. surface. Pressure and volume (and the type of bicycle tires) will decide how often you need to “top up” your air.
Some random data points:
I am now using latex inner tubes in 32mm tires on my road bike, I need to pump 2x a week.
With 25mm tires and latex I’m pumping every other day.
With butyl inners and 37mm tires I’m pumping once every two weeks.
On my box bike with 47mm and butyl inners I’m pumping every 2 months.
My daughter (half my weight) pumps (tells me to;))
her tires 3x a year (47mm/butyl)
I’m finding different valves (presta/schraeder?/dunlop) do not matter in air retention.
I pump my bike somewhere around every half year. If it get flat faster I mend the puncture or change tube and tire. Butyl tube and Schwalbe puncture resistant tire.
I’m amazed that your car and truck tires can go years without needing air. Are you checking them or just eyeballing the tire?