Eli5: Why do offroad bicycles have fatter tires while offroad motorcycles have skinnier tires?
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Off-road bicycle: i want to keep the tire pressure as low as possible to gain grip on surfaces. This provides also a smoother ride which increases the visibility: high frequency vibrations are absorbed/prevented by the tires. The higher the tire pressure the more your eyes shake on off-road. If you reduce tire pressure, you need to increase the contact surface to compensate. This is true for downhill riding. It really feels better and grip better. As soon as you are not propelled by gravity, you want to get higher pressures and smaller tires, like on gravel bikes. More pressure, smaller tire= less friction and more speed for the same muscle power. And this is why road bikes have very small tires.
Motorbikes off road: I’m not using one since a long time… small tires makes tight cornering easier. They are still twice as wide as bicycle ones. I’m not sure they are trying to make them any smaller. You can see a pattern between size and power. Due to tire wear, the more power you have the more tire you need.
Road big tires allow you to carry more tire, which means it takes more to wear it down, which allows to use softer rubber that grips more. Conversely to offroad tires, this wide tires handle like a drunk pig at tight corners and low speeds. But that extra stability comes handy as soon as you step up the game and ride at 100-300 speeds. Again there’s a gain into carrying enough tire for the power. A lot of power on a small tire will inevitably wear it too quickly.
In all cases too much is too much. All of these are trade offs. There has been a time someone tried to make things way bigger or smaller and failed. There’s a compromise between all the effects of a bigger or smaller tire.
Off-road bicycles, road and off-road bikes: don’t need anything bigger than what they use.
And road bicycles don’t need tires smaller than what they use.
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