# Does spindle size corespond to speed and torque?

Discussion in 'Friction Drive' started by Dockspa1, Feb 23, 2008.

1. ### Dockspa1Guest

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. :?:

Last edited by a moderator: Dec 15, 2015

2. ### kerfGuest

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.

3. ### loquinActive Member

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.

4. ### Dockspa1Guest

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.
Doc

5. ### mickeyGuest

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.

6. ### kerfGuest

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):smile:

7. ### uncle_punk13Guest

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...

8. ### mickeyGuest

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.

9. ### Jim HGuest

Oh my gosh! It's like eating ice cream too fast...

10. ### kenspiceGuest

spindle size

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?

11. ### loquinActive Member

On a friction drive, the tire does nothing more than to transfer the circumferential velocity of the drive roller to the ground. It's an idler wheel, essentially. The drive roller transfers IT's speed to the tire, which in turn, transfers its speed to the ground.

Now, the ANGULAR velocity (RPMs) DO decrease, but, in a friction system, unlike a sprocket system, the ratios of wheel size to drive roller size have zero effect. If you had a system that could place the drive roller directly against the ground, it would push you along at the same speed as if the drive roller operates through a wheel of ANY size.

Disregarding frictional losses. the speed of the roller (circumference speed, in miles per hour) is exactly the same as the ground speed. And, the circumference speed is calculated by multiplying the RPM times 60, to get revolutions per hour, then multiplying by the roller diameter and by PI, to get the number of inches per hour, then you divide by 12 inches per feet, and by 5280 feet per mile. The result is the speed in miles per hour. The wheel diameter doesn't even enter in to the picture. If you wanted, you COULD calculate the wheel RPM, but it wouldn't make any difference.

Now, if you have a smaller wheel, its RPMs will be higher, but the ground speed will be the same as with a larger wheel. IF you keep carrying this analogy down using smaller and smaller wheels, a 2.6 inch diameter tire would spin 10 times faster than a 26 inch diameter tier, but, because it's 10 times smaller, it HAS to spin 10 times faster, just to stay at the same speed. A 1 inch diameter tire (the same size as the roller) would spin at exactly the same RPM as the drive roller. And, it would be running at the same ground speed as a 26 inch tire, a 20 inch tire, a 10 inch tire or a 2.6 inch tire...

Last edited: Feb 25, 2008
12. ### kerfGuest

You obviously know little about dairy. You run the machine clockwise for ice cream and counter clockwise for butter.:smile:

13. ### Dockspa1Guest

Thanks for all the help on this one guys. It is finally, clear as ice (cream)! No, I do understand it know. When I think of someone pulling a rug out from under your feet, it doesn't matter how long the rug is, your still going to fall just as fast. Ha Ha!
Ok, Here's my story that I'm sticking too now, The wheels may be different in diameter but the surface is going the same speed. ie; MPH. Got it! Whew! I just about blew a gasket over that one. I gotta BRAIN STRAIN!
Thanks again for the patience.
Doc

14. ### Dockspa1Guest

Hey Loquin, you mispelled tire but your math gets an a+! Ha Ha!

15. ### loquinActive Member

Yeah, but I spelled "circumferential" right! So, by the "level of difficulty," rating system, I come out ahead!

16. ### Dockspa1Guest

I didn't say I was grading on the curve scale! Get it?
Doc hehheh!

17. ### kenspiceGuest

Hey Lou! Be careful of the words you use. Kerf does not know the difference between ahead, afoot, or ahorseback:smile:

18. ### kerfGuest

I r knot stupid. I knows what circumferential mean. That wat they done to me win I was a itty bitty baby.

19. ### Jim HGuest

O K, so is it solved then? BTW, I didn't know about the ice cream and the butter:shock: