Why do car tires not need a tube or liquid sealant but bicycle tires do?
In: Engineering
The main reason histrically (and still valid) is: wire spokes. Way back in the day before the days of single-piece wheels, the only realy practical/affordable way to make a tire was to have a separate hub (center part where axle goes) and the rim (outer part where the rubber/tire mounts, and they were connected by a bunch of wire spokes. Each spoke had a little hook on one end that would hook onto the hub, and the other end would have a little threaded portion and a tensioning nut that would secure to the rim. While these individual wires were not very strong in compression, when you installed them you would tighten them up verrrrrrry tight like a guitar string, so the hub and rim were under concentric tension, which made everything strong and stiff while still very lightweight. Also very easy to assemble. Problem though: it left a whole bunch of holes in the rim (outer part) where the tire isntalls. If you tried to inflate a tire, the air would just leak out the rim holes. So they used a tire to prvide structure, tread/traction and wear and tear protection, and use a thinner rubber tube inside THAT that seals the air and keeps it pressurized. This also has the benefit that if you have a puncture, you dont neccesarily need to repalce the tire, but jsut the tube (and a spare tube was small enough to carry in a pocket).
Cars rapidly went away from wire spoke wheels, though they remained popular on bicycles and motorcycles through the present day. There are a few companies like BMW that make tubeless wire wheels (instead of penetrating through the rim, the spokes interface with some flange on the interior of the rim). And also here are modifications you can do to a standard wire rim that will seal the spoke holes well enough that you can run without a tube. and most weird, there are even “mousse” options. Where instead of a pneumatic tube (i/e/ inflated with pressurized air) its basically like a big donut made of soft foam rubber. Still rpvides the cushioining effect that a pneumatic tire will, but is immune to puncture. They are msotly used on off-road motorcycles where punctures may be more common, and where top speeds are limited (a mousse tube will tend to heat up a lot faster and can be damaged by longer rides at higher speeds).
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