What is the difference between a 5W40 and a 10W30 oil?

We can see several types of references on oil cans, including 5W40 which is the most widespread but also among others the 10W30? what does it mean this letter and the two figures? what type of motor do they refer to?

The first number is the winter viscosity index. This is the cold viscosity; closer to 0 is the index, more fluidic it is. The second number is the hot viscosity; higher is the index, the better is the protection at high temperature.

The 5W40 engine oil is suitable for the following situations: a dynamic driving, a sports car, a recent sedan engine. It is a synthetic oil.

The 10W30 oil is a semi-synthetic oil, it is designed especially for so-called high efficiency diesel engines that have an anti-friction treatment. This oil is made for motorcycles and sports motorcycles.

Best 5W40 oil:

The Castrol EDGE Turbo Diesel engine oil 5W-40 5L, is the best oil to fight deposits, it protects the engine in the long run. The oil film has a reinforced strength. It meets the most the demands of the engine. Its synthesis technology reaches the highest standards of performance.

Best 10W30 oil:

The Motul word 10 W30 4T 1L oil is one of the highest quality lubricants. It is made for the highest demands of the market. There is no need for a funnel with this can because it has its own spout. In addition to road bikes, it is perfect for trail, off-road, enduro, trial, 4-stroke engines.