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A average mower engine runs somewhere around 3000 RPM. Other then a push mower I don't known what the spindle speed would be. The question is what would cut grass better a 30in blade or two 15 in blades. It just seems by the time you get to the end of the blade the 30 in blade would be traveling a lot faster then the 15 in blades.

It seems that way, but if all the ratios are the same from the engine to the spindle, the speeds will be the same. It dosen't matter if the blade length is 2" or 200". Adding blade length will only require more power from the engine to sustain the same engine speed due to air drag.

I don't think I have seen a direct engine mount blade over 24 inch blade...
You are right if there is a 30 inch direct mount blade. That tip speed would be Fast.
A 30 inch blade at 3000 RPM would be:
30 x 3.1412= 94.236 inches divided by 12 = 7.853 feet, so
7.853 for each turn x 3000RPM = 23,559 FPM.... that is Too Fast.

I think most spindle mount blades are kept around 18000 FPM... :smile:KennyV

While I'm sure there are some diminishing returns, generally speaking, the faster the blade turns, the better it can cut most grasses and produce a good, clean cut.

The speed of the TIP of the blade (in feet per second, or MPH, etc.) is regulated by the Federal Government's Consumer Product Safety Commission. Standards, as I recall, vary a bit from walk-behinds to belt-driven riding equipment. The bottom line is, most mowers are designed so when the engine is at full throttle, the blade tips speed is at or below the maximum allowed by law.

FYI, in Europe, blades are often odd-shaped, with large "ears" at the tips to reduce noise. They too, have tip-speed regulations, but also noise levels that must not be exceeded.

Caveat: I work for Honda, but the preceding was my opinion alone.

KennyV said:

I don't think I have seen a direct engine mount blade over 24 inch blade...
You are right if there is a 30 inch direct mount blade. That tip speed would be Fast.
A 30 inch blade at 3000 RPM would be:
30 x 3.1412= 94.236 inches divided by 12 = 7.853 feet, so
7.853 for each turn x 3000RPM = 23,559 FPM.... that is Too Fast.

I think most spindle mount blades are kept around 18000 FPM... :smile:KennyV

Click to expand...

You confuse me yet again Kenny... Congratulations.

Hello,I sold Snapper rear engine riders years ago with 28',30" and 33" single blades and they worked well.The rear bagger had wing lifts that bolted to the blade and they were one of the best bagging riders of their time.

The max tip speed of a mower blade of almost any kind including bushhogs is set at 19,000 fps. The reasoning behind it is that at speeds above that the steel used in the blade will create excessive harmonics causing stress cracks to develop leading to blade failure. The blade can crack and break causing serious injuries or death.