why do the fastest bicycles have really thin tyres but the fastest cars have very wide tyres
In: Engineering
Funny that you ask this because the bike industry is going through some major rethinking about tire width and speed. It used to be just accepted that narrower tires were faster and people accepted this because the vibrations made them feel faster. Now people are diving into it with data and the data are showing that the standard 700×23 skinny tires are not faster. The transmission of vibration and bouncing rather than rolling smoothly is actually working against speed. We’re starting to seeing tire widths go up in the pro circuit and they’d probably go up faster if cycling didn’t have such a devotion to tradition and institutional inertia.
https://www.renehersecycles.com/12-myths-in-cycling-1-wider-tires-are-slower/
This is actually changing as road bikes move towards wider tires.
There are a number of factors to balance including:
1. Air resistance.
2. Rolling friction and contact patch size.
3. The feel of the bike and riding comfort.
Many of those issues don’t matter to the same extent with cars. For instance aerodynamics… When the car itself is 6 feet wide it matters a lot less just how thick the tires are. Similarly riding comfort is less important when the human isn’t being asked to provide the power. This more naturally biases those cars towards wider lower pressure tires, but these days road bikes moving in the same direction.
Fast cars need big tires to grab on the asphalt and go quick, fast bicycles need to be light and smooth so the effort of the cyclist moves him quick.
Well, there’s “fastest cars” for track racing, and then there’s just the worlds fastest “cars”, which DO have relatively thin tires for the size of the vehicle.
https://www.guinnessworldrecords.com/records/hall-of-fame/andy-green-fastest-car-land-speed-record
Fastest cars have narrow tires as well. See SSC Tuatara. You only need wire tires a) when cornering b) when accelerating c) while maintaining ridiculous speed due to air friction if you put the power down to the road using tires (unlike some rocket powered cars).
It´s very simple.
If you had a powerful motor on your bike, you would need wide tires.
If you Flinstone your car, y would need thin tires.
Look at a top fuel dragster. They have little front tires to save weight and reduce drag. They have big rear tires for traction because they make so much power a skinny tire would just spin.
Fast cars have massive engines. There’s not a hard upper limit on how much power you can put in a car. That means power, weight, aerodynamics ,and traction are in a constant balancing act.
You can squeeze out more power with a bigger engine, but if it makes the tires spin you don’t get that power, and it also weighs more.
For more traction, increase the weight and tire size, but increasing weight robs from power.
Aerodynamics limit the top speed, so you want to reduce drag and reduce weight to get the most speed possible out of the power your engine puts out. In order to make this work, tires get wider so they can output the force to the road on the minimal weight of the car.
Bikes literally dont have this same struggle.
Humans power the bikes, and humans weigh way more than we’d like, and only a portion of our weight is actually our leg muscles.
We’re not powerful enough to spin our tires on pavement, so we’re not limited by traction anymore.
The goals of a cyclist are to reduce weight, reduce drag, and train to add power and endurance.
Adding power adds leg muscle which is weight.
Since traction isn’t a limit, thinner tires reduce drag and reduce weight.
Reducing tire weight is a pretty big factor, because it takes a lot of energy to get something heavy spinning and change it’s speed. By lightening the tires, a biker has more power to accelerate in a burst. That’ll help them get ahead of the pack or around an opponent.
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