Re: ZTR\'s
JimMo,
In my opion, it's all in the deck design. I have a 1996 Exmark Turf Ranger with the 60" deck. I can mow at top speed (6.4MPH) without any degradation in cut quality. Yes. I do have to slow down a bit in super thick stuff but not as much as I you'd think.
Exmark (and any Commercial grade ZTR mfg.), first and foremost focuses on their deck designs because the sole purpose of these machines is to cut great and to cut fast. Example: Exmark's top of the line LaserZ XP can mow up to 7 acres per hour. I'm sorry, but that would probably make me dizzy.
The theoretical limit on my Turf Ranger is about 3.64 acres per hour at 100 percent efficiency but a more realistic 2.91 acres per hour can be expected (80% efficiency - allowing for turns and overlapping). This is still quite respectable.
(Please Note: I'm not a lawncare professional, just happen to own a commercial unit which makes mowing akin to an amusement park ride on my less than desirable lawn).
Why a better cut at speed?
My opinion:
From what I've seen, the cutting blades feature a much longer sharpened cutting surface than what is typically found on your typical MMM. The deck is a floating design with four point suspension (Floating action is front to back and side to side) which enables the deck to follow various contours.
The deck also has flow control baffles that improve the quality of cut and no-clog discharge etc. etc. blah blah blah you get the point.
Not sure on the blade tip speed, but suffice to say it must be fairly fast (sounds like a turbo prop). The blade tips on Exmark's mulching deck reach 18,500 fpm.
My Exmark delivers a smoother ride than what my Ingersoll or John Deere did. This may be due to the oversized tires,
seat, and wheelbase. The overall comfort level may contribute to faster mowing speeds as well?
I have no experience with Simplicity or Kubota non-ZTR decks, but I've heard numerous comments favoring their cut quality over others. My Ingersoll RM44 deck gave a decent cut, but I couldn't mow as fast with it as I do with my Exmark.
I hope that helped