Blade Tip Speed

Discussion in 'Lawn Mowing' started by Qdriver, Jan 16, 2004.

  1. Qdriver

    Qdriver LawnSite Member
    Messages: 186

    O.K. I saw this mentioned in another thread and it got me to thinking. I did a a search & browsed through the first Ten or so but did not find the info I wanted. I did not want to get off-topic in that thread so I started a new one.

    SO! Having said that....

    I understand the concept. Also, it would seem that engine size and BTS would be in direct correlation. (all things being equal- same size rider to rider or WB to WB .)

    :p just gota funny picture in my head of a ZTR w/a top fuel engine :p

    Anyway, is BTS REALLY that large of a factor in choosing a unit, or is it just one of the small things in the overall package.

  2. John Gamba

    John Gamba LawnSite Fanatic
    from ct
    Messages: 10,812

    High Blade Speed, Deep Deck & High HP Is What Cuts It Here In Connecticut.

    This is a 52"Ultracut, 23 Kohler Turf Tracer.

  3. sildoc

    sildoc LawnSite Silver Member
    Messages: 2,925




    It is not a factor! It is one of many.
    You have many things to factor in. Deck, BTS, Dealer service, Functionality of controls for yourself, Availibility, and personal preferance. If you like a mower and see that it has a nice cut and have a good dealer then BTS is a minor technacality that can be dealt with at a later time with tinkering with the pullys.
    Technically the engine hp does not even count in the initial bts. It is all calculated via the pullys and length of blade. Now when you mow if you dont have a big enough engine for the deck size it does not mater what the bts is if the engine can't power it under load.
  4. Qdriver

    Qdriver LawnSite Member
    Messages: 186


    Glad to hear from you again. :) What is that attached to the rear....a slider?


    I was hoping you would recognize the topic. ;) So,.. it sounds like BTS is more like 6-7 engineering. I.E. putting a performance chip in your Hot Rod. A modification to get that little extra.

  5. DennisF

    DennisF LawnSite Bronze Member
    from Florida
    Messages: 1,381

    Blade tip speed is indeed a factor in quality of cut and potential mowing speed. Engine HP is not the determining factor of BTS. Blade tip speed is determined by... Engine rpm, main shaft pulley size, spindle pulley size, and length of blade. Belt slippage also enters into the equation. Don't get caught-up in the BTS hoopla the manufacturers banter about because it will be constantly changing as you are mowing since the engine rpm will vary during the time you are mowing different grass heights. The manufacturers numbers are indicators of optimum conditions ( Just what that is... is anybody's guess). If you keep your mower operating in top running condition and use razor sharp blades, it will cut cleanly at top mowing speed if the grass is not overgrown. In the case of overgrown lawns...BTS and cut quality all go out the window.
  6. Flex-Deck

    Flex-Deck LawnSite Silver Member
    Messages: 2,845

    In my opinion, deck design must match blade tip speed. Some decks will not clear with too much blade tip speed, the air and grass just compact against the top. ( Kind of like ground effect under an airplane wing when landing) I believe that most mower manufacturers match their deck design and blade tip speed to get the best cut.

    If you really sit down and figure out how far a mower actually travels before the other side of the blade makes another swipe, even at 10 mph, (Well - lets do that now)

    6mph = 8.8 feet per second (60 mph - 88 ft per sec)

    54" decks have 18 1/2" blades more or less, = 58" circumference-divided by 12" = 4.85 feet.

    If your blade tip speed is only 16,000 ft. per min. which would be fairly low, your blade is turning 16,000 div by 4.85 = 3298 rpm. which is 3298 div by 60 = 55 rounds per second, which means the blade makes 55x2 = 110 swipes per second. That means in an 8.8 foot travel section, the one end of the blade has come around every .08 feet which is less than one inch.

    Thanks, Brad
  7. John Gamba

    John Gamba LawnSite Fanatic
    from ct
    Messages: 10,812

  8. sildoc

    sildoc LawnSite Silver Member
    Messages: 2,925

    Hey John, Have you ever approched Exmark with an offer to be a spokesman? You might as well make a couple of bucks for all of the promoting of exmark! Ha ha.
    Keep up the positive attitude.
  9. Qdriver

    Qdriver LawnSite Member
    Messages: 186


    Ever think about working for NASA in astrophysics? :)

    Those are indeed some interesting calculations.


    Love that little model! Even if I am probably going w/cousin Toro.

    I think I will just follow this advise from Dennis F. and I should be G2G.

  10. BB36

    BB36 LawnSite Member
    Messages: 171

    I once asked a owner of a dealership(Toro/Hustler) at a trade show whats the story on blade speed.He said to me that OSHA prohibits any increase in blade speed because of excessive vibrations which could lead to damage etc.. It sounded good to me at the time.

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