Does spindle size corespond to speed and torque?

D

Dockspa1

Guest
Evidently, there some bike builders that do not understand the concept of drive ratios so I will see if I can help them out a little.
This is a beginning point.
http://eagle.csd49.org/middle/jss/Course_Transmissions_02.htm

I have been told by several well known bike builders that the driving spindle's outside diameter has nothing to do with the overall speed and or torque of the tire. In fact they have told me that it wouldn't matter what size the scrubber spindle was, they would still be going the same speed or MPH.
An inch for an inch is what one member stated.
Ok, if you are mounting a 1" spindle on a 26" tire, the motors RPM's are going to have to speed up by 26 times in order to have the same output.
It is an inch for an inch but there are a lot more inches on the diameter of the tire. The motor will have to turn 26 times for the tire to turn once.
Anyway, I had to start this thread because we started walking on someone elses.
If some one can give me a real good reason to think otherwise, I am willing to listen.
 
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K

kerf

Guest
Doc,

Roller size has everything to do with speed and torque. The larger the roller the greater the speed and the less the torque. What does not matter in a friction drive, is wheel size. Wheel size does matter if one is driving it with a chain or a belt but not if it is being driven along its circumference with a roller. A one inch roller driving a 26" wheel gives the same results as a one inch roller on a 20" wheel. The wheel is just there to fill the gap between the roller and the road.
 

loquin

Active Member
Joined
Jan 11, 2008
Messages
2,214
If you have an roller spinning at at any speed, a 1 inch roller and a two inch roller would both have the same angular velocity, but, the two inch roller has twice the circumference as the one inch roller, and would push you along twice as fast (assuming no drag). However, the torque (and subsequent acceleration) would be half that of the 1 inch roller.
 
D

Dockspa1

Guest
It just seems that if the roller size makes a difference then the wheel size should also.
I see what you mean about the tire being a filler between the road and the drive. I guess what you are saying is that, if the tire was a flat strip and you rode the spindle down it, it would be the same.
Ouch! now I gotta headache. Gotta think about it.
Doc
 
M

mickey

Guest
I guess what you are saying is that, if the tire was a flat strip and you rode the spindle down it, it would be the same.
Thats a great way to visualize it, Doc. The length of the strip makes no difference when you bend it into a circle. It does seem counterintuitive though because we general think in terms of gears or sprockets.
 
K

kerf

Guest
It does get very tricky for the very reason you stated Mickey. If the rear wheel were rigidly mounted on a shaft that turned on bearings, them we would have a gear reduction at the shaft. Since we're accustomed to dealing with chains and sprockets, sometimes it's hard to "change gears". (Pun intended):)
 
U

uncle_punk13

Guest
Correct, and yes, changing wheel size has an affect as well... One thing that I am backwards on though, I always thought that the larger the diameter of the drive roller, the lower speed and the better torque. I'm no expert, and would love to know the facts in this... :)
 
M

mickey

Guest
I always thought that the larger the diameter of the drive roller, the lower speed and the better torque.
If I understand correctly, it would be the opposite. The larger the scrubber the more inches per rotation and hence, the greater speed, at the price of less torque.
 
K

kenspice

Guest
spindle size

Oh my gosh! It's like eating ice cream too fast...
So, Jim, are you suggesting I take my engine off of my bicycle and mount it on an ice cream machine? If I do that, what size spindle will I need to turn the drum fast enough to make butter before it becomes ice cream?
 
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