Before jumping into providing a lengthy answer, it is essential to consider the motivation behind such a question.

Do you think that you can drastically cut your overall mowing time for your lawn by making the lawn mower blades spin faster?

Yes, you can make the blades spin faster. Would it be easy to do? Of course not. Can it be done with every type of mower out there? The answer is no. That is not an easy thing to accomplish.

If it is a direct drive mower, such as the standard vertical shaft, horizontal blade, walk-behind or push mower, the motor speed is directly controlling blade rotation. In simple language, blade speed is determined by engine RPM (revolutions per minute), as there are no gears or pulleys that can be changed. The blade is directly attached to the output shaft of the engine.

If you have a riding mower with blades that are belt and pully driven, changing the size of pulleys will increase the speed of rotation. ‌The smaller pulley on the blade and bigger pulley on the drive would give the desired result in that strictly achieving higher speed.

However, it would not be very beneficial. It is not only challenging to find those new pulleys, but it would also most probably involve significant modifications to be done to the mower deck.

Mower manufacturers spend countless days, months in research to optimize the shape of blades, engine power (RPM) and thus available horsepower, and many other factors to make the best possible product as retail, consumer mower. Making the blades “spin faster” would be operating the machine outside the design specifications. It may also void any warranty.

At this point, it would be wise to consider why such limitations may be there in the first place.

First, generally, the noise that comes from the operating blades is louder than the noise coming from the motor. This noise resembles the noise that comes out of a propeller on an airplane, for example. However, if you increase the speed, you increase this noise.

This additional noise may pose a safety issue when it comes to it that this noise may damage your ears if you are not wearing any safety for your ears. A faster-moving blade means higher loads on the blade, deck, and the drive mechanism.

Considering the ramifications involved in trying to increase the speed of the blades, it would help to know again why you would want to do this. The design specifications for any mower are also in such a way that the mower produces optimum cutting quality at a reasonable speed.

Faster moving blades do not necessarily speed up the total cutting time. The nature of the mowing deck has a direct impact on the quality of cutting. If the amount of grass is less than average, reasonable cuts can be achieved at lower speeds. Also, if you are operating at higher speeds, you will have to clear the cut grass frequently to avoid clogging of the deck.

Controlling emissions is also a crucial goal of designing a mower. Many regulatory bodies such as C.A.R.B (California Air Review Board) keep limits on allowed emissions. This limitation indirectly puts limits on blade speed as higher speeds mean higher emissions.

However, if your mower comes with a throttle setting, when you select a setting for a throttling level, you are a particular RPM. As the mower passes on thicker grass, the mechanism opens the throttle to keep the selected setting for the RPM.

This particular mechanism is called a “governor.” Without getting into too technical details, this mechanism involves a spring that connects the actual throttle on the carburetor. The spring tension is adjusted as the engine speed increases.

This adjustment, in turn, affects the throttle position. The blade speed of this kind of mowers can be changed either by shortening or lengthening this spring.

In conclusion, although it is possible to change the speed of the blades in that they spin faster, you would have to consider the consequences mentioned above as well as potentially voiding the warranty if you have any.