Can someone explain this?
In: Physics
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Bike tires need to be as aerodynamic and low resistance as possible. Otherwise you’d slow down really quickly.
Cars are trying to maximize the power transfer from the engine to the pavement.
Turns. Bicycles are low power, and need low wind resistance during forward movement, and have multiple means of dealing with turns (riders can lean, for example, and turns tend to be fairly mild in physics terms). Cars (other than drag cars on a straight line) typically are raced around courses where they need to keep turning — and that means they need enough friction to hold the turn at high speed, which in turn means they need enough width on the pavement, because the friction is proportional to the contact area.
A person would be lucky to make 1 horsepower. A $60,000 Corvette has 500. A bike with rider might weigh about 200 lbs while a Corvette weighs 3,500.
So a bike tire needs to be small, light, and aerodynamic so that a human can spin it as fast as possible while it only holds up a few pounds. A Corvette tire has to be wide enough to reasonably transfer 500 horsepower to the ground. The levels of grip needed to allow a car to accelerate and corner necessitate more rubber.
Drag racers (top fuel) have wide tires in the back and skinny tires in front
It’s about maximizing power to the wheels. (And then some safety figures like normal cars)
With the weight of the car and engine you need a bit more grip so you don’t just spin the wheels
Bicycles have a lot different torque ratios and stuff that they can use skinny tires on both drive wheel and free wheel
for cycling, skinnier tires are not necessarily faster. the ideal fastest tire will vary in width depending on the rider and the riding surface. there are plenty of circumstances in which a wider tire run at a lower pressure will outperform a skinny high pressure tire.
the reason you still see a lot of skinny tires on high-end peloton bikes is because of – i’m guessing here – tradition, and the general *perception* of being faster. but that has already begun to change and will continue to do so.
as for cars, that’s not really my area of expertise but i do know that their engines are so powerful that a big problem becomes keeping the car on the ground and not just lifting off. you definitely don’t get anywhere fast if you’re floating in the air, so traction becomes important. the fastest cars have wide tires with very sticky smooth surfaces to maximize the area of contact with the ground so they can actually grip the tarmac and propel the car forward.
Very, very fast cars do have thin tyres. Check out any of the land speed record cars. The Bloodhound LSR has 150mm (6″) wide wheels. I couldn’t find information on the current record holder the Thrust SSC, but the look about the same width.
It’s all compromises. General road tires on a car (and a normal bike) are a compromise of minimal resistance, compound, weight, and reliability.
On a car, the more you want to get power down, the wider the tire gets (and more slick the tread), as it’s very easy to overcome the amount of power to downforce you have, and spin the tires. Conversely the steering wheels are a compromise between the amount of grip you want, while not making slow speed driving a process of grinding away large portions of tire on the ground, but not having the tires so wide that you have more grip than you really need. Most cars this means the same or almost the same width tires on front and back (assuming rear wheel drive). You also tend to have body panels covering most of the tire, so the thickness having an impact on aerodynamics is *less* of an issue.
On a bike, the more grip you want the wider the tire gets, so you get into BMX and mountain bikes, and being more capable in more weather conditions on the road. On the other side the faster you go the thinner you make the tires, to reduce the impact of that road drag, because you generally aren’t going to have enough power to weight, to spin the tires. This is also going to reduce your grip, meaning you’re more likely to slide off in bad road conditions, and less able to turn using purely the handle bars, but this is less of an issue on a bike since a large portion of your steering is done by leaning. This is also going to reduce weight, reduce aerodynamic drag (being thinner), but also reduce braking power (more likely to skid even in perfect conditions).
The ultimate TL;DR is that the power:weight(/downforce) on a bike will very rarely be enough to spin the tires, where on a car that is a very common issue with even mid and some lower performance cars.
Cars can be what we call “traction limited.” The amount of power is so much that it just makes the tires spin. This does not happen on bicycles because the amount of power a human makes is not enough to overcome the traction of a bicycle tire.
To put the power from an engine that needs to be transferred to the ground through the tires into perspective for this example, a good recreational cyclist makes 250-300watts of power average and maybe can do 1000watts in an all out start from a stop for a couple seconds if they are a big guy. Tadej Pogacar is very dominant in the pro races and can do 470watts but keep in mind he is a fairly light guy and raw power isn’t the biggest factor in pro races. Big muscle pro sprinters can do 1500-2000watts in a sprint for tens of seconds.
A 2025 Toyota Camry has 232hp between its engine and hybrid. That is 173,000 watts! That power is not nothing and can get you up to highway speeds on an on ramp nicely but no one is saying the Camry is a fast car. A new Ferrari GTB 296 makes 819hp combined which is 610,000 watts! A top fuel dragster makes 11,000hp or 8,202,000 watts! All that power needs to go to the ground through the tires in order for the car to move forward. More rubber equals more grip. Bikes just don’t need it and smaller aerodynamic and low resistance tires are better for the application.
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