Author Topic: big or small pulleys big or small sprockets  (Read 5254 times)

0 Members and 1 Guest are viewing this topic.

Offline johntaves

  • Newbie
  • *
  • Posts: 57
  • Karma: 0
  • Gender: Male
    • View Profile
    • PNWSoft
big or small pulleys big or small sprockets
« on: June 25, 2006, 12:49:47 am »
What is better bigger pulleys or smaller, where both provide the same ratio? For example, do you prefer 8" and 4" or 6" and 3, both choices are obviously 2:1"? I would guess that smaller is better to reduce the belt and idler speeds and to reduce weight, especially rotating weight. But if it is too small it will slip. If that is true, then what is the smallest pulley you would put on a say a 20 HP. Does the faster belt speed help or hinder sliping the clutch for a smooth take off? George Herrin said that he uses A belts, and I have to assume that is to reduce weight, so George, did you minimize the size of the pulleys too?

I am upgrading to a transmission from a transaxle. What is better, faster transmission speed or slower? For example, do you prefer 6/4 pulleys and 15/54 sprockets, or 4/4 pulleys and 15/36 sprockets where both sets of pulleys and sprockets have the same total ratio but the first choice makes the transmission spin faster than the second?

I care about noise. I hated the noise the transaxle setup made due to the belts spinning at nearly 10k RPM at the input to the transaxle. My assumption is that I can minimize that type of noise, by dropping the speed of the belts and chain. I haven't seen, much less heard, a trans w/chain drive setup but I assume the chain is relatively quiet, so my  guess would be to make the two pulleys small and the same size, say 4" and 4", then make the sprockets small too say 7 and 16 teeth.

jt

Offline George Herrin

  • aka SUPERMAN
  • Superman
  • Highly Mowtivated
  • *
  • Posts: 17732
  • Karma: 102
  • Gender: Male
  • I am going to Race Every Race like its my last one
    • View Profile
    • BTMRA Home/Forum An Independant Club.
big or small pulleys big or small sprockets
« Reply #1 on: June 25, 2006, 09:24:17 am »
Every mower I have built s/p or b/p has been the same 8 on motor 5 on tranny. 1/2 inch pulley's and belt's with a two pulley twist pull type clutch. WHY because when I got started, a top driver says use this and this that with that and you will be in the ball park. SO I did I was and simply got a tach and fine tuned from there with sprockets. I have had mutiple machines in the top five in points at nationals level, and locally. So it can't be far off.
     NOW the faster you spin any of the gear boxes whether tranxaxle or tranny the more noise you are likely to hear. They were designed to run 8 mph and not the speeds we run on the track. I do know the smaller engine class like AP many run 1 to 1 pully ratio's and to get the speed they want they wind up running big sprockets like 23 to a 40 something like that. Two reasons amount of space on the smaller chassis and they don't over drive the gear boxes as much. I just know what works for me and with it working so well 3 National titles later why fix what isn't broke.
George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
4 time USLMRA National Champion
Retired from BP
www.herrinmowersports.yolasite.com
www.allamericanmowerchampionships.yolasite.com
My other racer is a 1/5th scale Dirt Late Model!!!!

 

anything