Eli5: Why do offroad bicycles have fatter tires while offroad motorcycles have skinnier tires?
In: 17
On road conditions:
Main goal for motorcycles is maximum grip.
Main goal for cyclists is minimum friction.
More tire width = more grip = more friction.
This means that for a powerful motorcycle you need a wide tyre with more grip. But for a road going bicycle you have much less power and can have a narrower tyre for less friction.
In off-road conditions:
Main goal for both motorcycles and cycles is floatation over loose surfaces, maximum grip and resistance against punctures.
More width = more surface area = more weight without sinking into sand, mud and snow.
The weight of the vehicle demands a proportional tyre width to not sink into the terrain.
More width often comes with more sidewall. This dampens impacts and makes room for knobs that allow grip.
When it comes to tyres – on any vehicle – width is a balance between speed and stability.
Wide tyres are more stable, but slower. Thin tyres are faster, but less stable.
On top of that: How heavy and powerful your vehicle is determines the minimum width the tyres need to be in order to support the vehicle. You couldn’t put motorbike tyres on, say, a truck, for obvious reasons – it isn’t going to hold.
Putting these two facts together gives us our answer:
Bicycle wheels/tyres come in broadly three categories: [thin, slick road tyres](https://contents.mediadecathlon.com/p2035470/k$51774e160b325ec55c6d57ee5147ab34/sq/26×12-folding-bead-slick-mountain-bike-tyre.jpg?format=auto&f=800×0) for stable, smooth road surfaces, [mountain bike tyres](https://encrypted-tbn2.gstatic.com/shopping?q=tbn:ANd9GcSSt_tVLGmlW9NIPzf1kI-GNusnMWyjiJLLj-obSnfqz84PRCteC7gM7Mj8Iqmexk4vWJLHbeqW1o6Ov7fC4mpNeQ7GzGSP_gT1p8WSItUSWrLiBtmxNkh4Kw&usqp=CAE) for somewhat unstable dirt and gravel, and [sand tyres](https://www.tradeinn.com/f/13894/138948534/michelin-starcross–5-sand-62m-nhs-motocross-tire.jpg) for – you guessed it – beaches and other sandy areas. Bike nerds – I know it’s more nuanced than this, but we’re five years old.
If you look at the [tyres used by offroad motorbikes](https://www.maxxis.com/uk/wp-content/uploads/sites/4/2021/02/tyre-image-MaxxEnduro-1024×1024.png), they look like a heavier version of a mountain bike tyre. A motorbike is heavier than a bicycle and generates more torque, so the tyres need to be appropriately heavier.
And there you have it.
When it comes to tyres – on any vehicle – width is a balance between speed and stability.
Wide tyres are more stable, but slower. Thin tyres are faster, but less stable.
On top of that: How heavy and powerful your vehicle is determines the minimum width the tyres need to be in order to support the vehicle. You couldn’t put motorbike tyres on, say, a truck, for obvious reasons – it isn’t going to hold.
Putting these two facts together gives us our answer:
Bicycle wheels/tyres come in broadly three categories: [thin, slick road tyres](https://contents.mediadecathlon.com/p2035470/k$51774e160b325ec55c6d57ee5147ab34/sq/26×12-folding-bead-slick-mountain-bike-tyre.jpg?format=auto&f=800×0) for stable, smooth road surfaces, [mountain bike tyres](https://encrypted-tbn2.gstatic.com/shopping?q=tbn:ANd9GcSSt_tVLGmlW9NIPzf1kI-GNusnMWyjiJLLj-obSnfqz84PRCteC7gM7Mj8Iqmexk4vWJLHbeqW1o6Ov7fC4mpNeQ7GzGSP_gT1p8WSItUSWrLiBtmxNkh4Kw&usqp=CAE) for somewhat unstable dirt and gravel, and [sand tyres](https://www.tradeinn.com/f/13894/138948534/michelin-starcross–5-sand-62m-nhs-motocross-tire.jpg) for – you guessed it – beaches and other sandy areas. Bike nerds – I know it’s more nuanced than this, but we’re five years old.
If you look at the [tyres used by offroad motorbikes](https://www.maxxis.com/uk/wp-content/uploads/sites/4/2021/02/tyre-image-MaxxEnduro-1024×1024.png), they look like a heavier version of a mountain bike tyre. A motorbike is heavier than a bicycle and generates more torque, so the tyres need to be appropriately heavier.
And there you have it.
When it comes to tyres – on any vehicle – width is a balance between speed and stability.
Wide tyres are more stable, but slower. Thin tyres are faster, but less stable.
On top of that: How heavy and powerful your vehicle is determines the minimum width the tyres need to be in order to support the vehicle. You couldn’t put motorbike tyres on, say, a truck, for obvious reasons – it isn’t going to hold.
Putting these two facts together gives us our answer:
Bicycle wheels/tyres come in broadly three categories: [thin, slick road tyres](https://contents.mediadecathlon.com/p2035470/k$51774e160b325ec55c6d57ee5147ab34/sq/26×12-folding-bead-slick-mountain-bike-tyre.jpg?format=auto&f=800×0) for stable, smooth road surfaces, [mountain bike tyres](https://encrypted-tbn2.gstatic.com/shopping?q=tbn:ANd9GcSSt_tVLGmlW9NIPzf1kI-GNusnMWyjiJLLj-obSnfqz84PRCteC7gM7Mj8Iqmexk4vWJLHbeqW1o6Ov7fC4mpNeQ7GzGSP_gT1p8WSItUSWrLiBtmxNkh4Kw&usqp=CAE) for somewhat unstable dirt and gravel, and [sand tyres](https://www.tradeinn.com/f/13894/138948534/michelin-starcross–5-sand-62m-nhs-motocross-tire.jpg) for – you guessed it – beaches and other sandy areas. Bike nerds – I know it’s more nuanced than this, but we’re five years old.
If you look at the [tyres used by offroad motorbikes](https://www.maxxis.com/uk/wp-content/uploads/sites/4/2021/02/tyre-image-MaxxEnduro-1024×1024.png), they look like a heavier version of a mountain bike tyre. A motorbike is heavier than a bicycle and generates more torque, so the tyres need to be appropriately heavier.
And there you have it.
Bicycle:
Road tyres are thin to reduce rolling resistance so the rider can go faster for longer. Traction is not a big problem with about 1bhp peak to handle.
Off-road: Tyres are bigger to absorb bumps and to spread the load of the rider and bike so they don’t sink into the soft stuff.
Motorcycle:
Road tyres are sized according to the power and weight of the bike. A 125 which weighs 100kg and has 15bhp can happily apply power through a turn without losing grip. A 1000cc with 200kg and 180bhp needs a lot more tyre area to do the same. A large bike could corner on the smaller tyres but applying the power becomes problematic.
Off-road. Tyres need to be large enough to spread the weight and small enough to dig into the ground and to steer. It’s a trade off between digging holes and going nowhere or acting like a sled, spinning and going nowhere. Traction is always an issue but it’s not one that a larger tyre can solve.
Bicycle:
Road tyres are thin to reduce rolling resistance so the rider can go faster for longer. Traction is not a big problem with about 1bhp peak to handle.
Off-road: Tyres are bigger to absorb bumps and to spread the load of the rider and bike so they don’t sink into the soft stuff.
Motorcycle:
Road tyres are sized according to the power and weight of the bike. A 125 which weighs 100kg and has 15bhp can happily apply power through a turn without losing grip. A 1000cc with 200kg and 180bhp needs a lot more tyre area to do the same. A large bike could corner on the smaller tyres but applying the power becomes problematic.
Off-road. Tyres need to be large enough to spread the weight and small enough to dig into the ground and to steer. It’s a trade off between digging holes and going nowhere or acting like a sled, spinning and going nowhere. Traction is always an issue but it’s not one that a larger tyre can solve.
Bicycle:
Road tyres are thin to reduce rolling resistance so the rider can go faster for longer. Traction is not a big problem with about 1bhp peak to handle.
Off-road: Tyres are bigger to absorb bumps and to spread the load of the rider and bike so they don’t sink into the soft stuff.
Motorcycle:
Road tyres are sized according to the power and weight of the bike. A 125 which weighs 100kg and has 15bhp can happily apply power through a turn without losing grip. A 1000cc with 200kg and 180bhp needs a lot more tyre area to do the same. A large bike could corner on the smaller tyres but applying the power becomes problematic.
Off-road. Tyres need to be large enough to spread the weight and small enough to dig into the ground and to steer. It’s a trade off between digging holes and going nowhere or acting like a sled, spinning and going nowhere. Traction is always an issue but it’s not one that a larger tyre can solve.
One thing to remember is that even the “skinny” off road motorcycle tires are wider than either of the two types of bicycle tires.
I think the main question is why motorcycle road tires are so big. That’s because they can put down more power, at the expense of a little efficiency loss.
Road bicycles don’t need such wide tires because human riders can’t make enough torque to overload the grip of even skinny tires, and do burnouts. There’s no point in going wider for more grip, if you don’t make enough torque to overpower the grip you’ve already got. Motorcycle engines can do that, so having wider tires let’s them put down more power/torque.
One thing to remember is that even the “skinny” off road motorcycle tires are wider than either of the two types of bicycle tires.
I think the main question is why motorcycle road tires are so big. That’s because they can put down more power, at the expense of a little efficiency loss.
Road bicycles don’t need such wide tires because human riders can’t make enough torque to overload the grip of even skinny tires, and do burnouts. There’s no point in going wider for more grip, if you don’t make enough torque to overpower the grip you’ve already got. Motorcycle engines can do that, so having wider tires let’s them put down more power/torque.
One thing to remember is that even the “skinny” off road motorcycle tires are wider than either of the two types of bicycle tires.
I think the main question is why motorcycle road tires are so big. That’s because they can put down more power, at the expense of a little efficiency loss.
Road bicycles don’t need such wide tires because human riders can’t make enough torque to overload the grip of even skinny tires, and do burnouts. There’s no point in going wider for more grip, if you don’t make enough torque to overpower the grip you’ve already got. Motorcycle engines can do that, so having wider tires let’s them put down more power/torque.
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