Author Topic: Sprocket size choices.....does it make a diffrence?  (Read 16624 times)

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Offline Dave Cox

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #15 on: May 23, 2008, 01:09:45 AM »

[/quote]

3 of my old HDs have auto chain oiling, I think 1 of them is intentional...  :|
[/quote]

funny! but so true.

Offline smcleod007

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #16 on: May 23, 2008, 02:08:34 AM »
Rex is right. At the drag strip, the high horse powered busas that run a 15 tooth front sprocket are harder on their chains and are more prone to rounding the teeth on the front sprocket. As you use more teeth on a sprocket, the individual tooth and chain roller load gets reduced because your engaging more links simultaneously. It would probably also help reduce the heat generated by a really dirty chain.  :-D

Scott

Offline Jonny Hotnuts

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #17 on: May 23, 2008, 12:52:28 PM »
Here is where I am having the problem:
Quote
At the drag strip, the high horse powered busas that run a 15 tooth front sprocket are harder on their chains and are more prone to rounding the teeth on the front sprocket



I am not talking about changing one sprocket that will change ratio, ture many drag bike guys lower the counter to get a harder launch (and becaue most busa are not doing 200mph in the 1/4 and dont need that high of gearing) but they dont also decrese the size of the drive sprocket. True a smaller counter sprocket will lower the ratio and pull harder on the chain. I am talking about increasing both sprocket sizes incrementally, retaining the same gear ratios.

I am certain that a larger sprocket will have a heat reducing affect….based solely on the fact that friction is reduced because the amount the links pivot is lower. This is because the larger radius they have to travel around the sprocket. Let face it, if a chain did not have to go around any bends it would not build heat. 

I am NOT convinced that the chain load (X) will change between examples if torque loads and speed loads are identical if the gear ratios are the same.



« Last Edit: May 23, 2008, 12:54:37 PM by Jonny Hotnuts »
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Offline Loose Goose-Terry#1

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #18 on: May 23, 2008, 01:44:48 PM »
 :-D Hi Jonny,

In the scenario that you have illustrated, you are nearly correct. Your ratios DO remain the same, however if you consider the radius of the countershaft sprocket as a “lever”, the shorter the lever, in this case, the more torque or "force" you will apply to the chain.

Back in the 70’s when I was doing a lot of Karting (Sprint and Enduro) we found the kart pulled harder out of the turns when we used the smallest countershaft sprocket that would allow the chain to “live” for the duration of the last practice session (to get rid of the chain stretch) and 1 hour race. The top speed was the same with either sprocket as verified from the maximum RPMs. Sprint proved to be the same but wasn’t quite as noticeable because of the abundance of torque due to the lower gearing. Again, maximum RPM proved the same top end speed.

Since the very small benefit in torque you may obtain from the smaller countershaft sprocket won’t make any difference in your top speed, you should use the largest sprocket combinations to keep your chain alive. 8-)

Hope this helps a little.

Yours in Sport

Terry A. Hume
If I had it all to do over again...I would!

Offline willieworld

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #19 on: May 23, 2008, 01:52:21 PM »
jonny i think you are right --there is something to consider though the bigger the sprockets the faster the chain speed --what i try to do is run a big enough sprockets so the sprockets dont wear out and small enough to keep the chain speed as slow as possible--i buy cheap chains and expensive sprockets --i race 3 races at el mirage and throw the chain away --speedweek and throw the chain away --3 more races at el mirage and throw the chain away --total cost 3 chains 104 dollars and the sprockets still look new -  willie buchta
willie-dpombatmir-buchta

Offline Jonny Hotnuts

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #20 on: May 23, 2008, 07:21:11 PM »


For argument sake lets say you could progressively add identical weight to the 25 LBS blocks.
Because the gear ratio is identical both 50 LBS blocks would raise at the same time AND at the same rate.

I would think that the chain load between the sprockets would be the same if this were true.
 
jonny_hotnuts@hotmail.com

"Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully."
*Andres Segovia
(when Im not working on the car, I am ususally playing classical guitar)

Offline Peter Jack

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #21 on: May 23, 2008, 07:31:40 PM »
Wrong Jonny. Because of the size of the larger sprockets the weight on the right would raise twice as far in the same length of time as the weight on the smaller sprockets. The circumference of the larger small sprocket is twice that of the smaller one. Remember, the small sprocket is driving and not just an idler.

Pete
« Last Edit: May 23, 2008, 07:35:09 PM by Peter Jack »

Offline willieworld

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #22 on: May 23, 2008, 08:25:12 PM »
if the ratio is 2 to 1 on both sets of sprockets then if you turn the small sprockets 1 turn then the big sprockets will turn 1/2 turn the only differance is the chain speed ---you might pick up some leverage on the smaller front sprocket but you will loose it when the rear sprocket transfers power to the rear wheel---   i think--  willie buchta
willie-dpombatmir-buchta

Offline Loose Goose-Terry#1

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #23 on: May 24, 2008, 08:07:52 PM »
 :-D All very good arguments. But, when you boil it all down, it is still better to use the largest sprockets that will fit and give you the ratio you need. Keep the chain speed as slow as possible.  8-)

If you race on a different type track and you need to come out of the corners hard, then use the smallest sprocket pitch diameters to give the added leverage on the countershaft sprocket. Just remember, your chain will run hotter due to the constant flexation from the smaller pitch and may not last in a long race. :wink:

Terry
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Offline Geo

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #24 on: May 24, 2008, 09:24:47 PM »
Nice discussion.  I looked at this for a couple of days and used all my spare time thinking about it.  Not much time which is why it took so long to find the missing piece.

If you add a wheel to the bigger sprocket and attach the rope/chain/line from the weight to go around the wheel, which will be the same size on both examples, then we find the lift speed is the same.  A full turn of the small sprocket will turn the large sprocket a half turn, turning the wheel a half turn.  The same for both examples.

Clear as mud!

Geo

Offline Rex Schimmer

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #25 on: May 26, 2008, 04:08:50 PM »
Jonny,
Regarding your second drawing of the two sprockets and the 25# and 50# weights, the tension in the chain from one end to the other is 25# the ratio and the sprocket sizes have nothing to do with the tension in the chain. To make the 50# block to move upward you will need to add 25# plus in efficiencies to the 25# side and this will make the tension in the chain 50#. Again, per your drawing the ratio between the two sprockets will have nothing to do with the tension in the chain, it is 25#.

Rex
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Offline smcleod007

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #26 on: May 27, 2008, 01:51:52 AM »
Here is where I am having the problem:
Quote
At the drag strip, the high horse powered busas that run a 15 tooth front sprocket are harder on their chains and are more prone to rounding the teeth on the front sprocket



I am not talking about changing one sprocket that will change ratio, ture many drag bike guys lower the counter to get a harder launch (and becaue most busa are not doing 200mph in the 1/4 and dont need that high of gearing) but they dont also decrese the size of the drive sprocket. True a smaller counter sprocket will lower the ratio and pull harder on the chain. I am talking about increasing both sprocket sizes incrementally, retaining the same gear ratios.

I am certain that a larger sprocket will have a heat reducing affect….based solely on the fact that friction is reduced because the amount the links pivot is lower. This is because the larger radius they have to travel around the sprocket. Let face it, if a chain did not have to go around any bends it would not build heat. 

I am NOT convinced that the chain load (X) will change between examples if torque loads and speed loads are identical if the gear ratios are the same.








Hi Johnny,

I'm not sure how to do all the math but If I visualize leverage points I can see how the torque on the chain would go down as the diameter of the countershaft sprocket gets larger. If I take one of my bath fan motors and try to stop it spinning by pinching the shaft I have to apply a lot of force. If I install a 10 inch disk on the shaft and pinch the outside diameter its pretty easy to stop even though its spinning way faster. This is because I have a big lever arm advantage the further I pinch the disk from the centerline. This tells me that max torque on a driven shaft is at the centerline and as you move farther away from the center as in a larger sprocket the torque at any giving instant is smaller but the chain speed is higher. The rear wheel should work in the same fashion. Power is applied to the center of the wheel and the torque gets applied to the ground by the outside diameter of the tire. If I sit on my bike in the driveway with the front brake on and hold the tach at 3000 rpms and drop the clutch with a 30 tooth rear sprocket the engine would die. If I did the same test with a 100 tooth rear sprocket the tire would break loose. This is because the distance of the lever arm between the outside diameter of the rear sprocket and the outside diameter of the rear tire has been shortened. So now it takes less of a chain yank to bust the rear tire loose. When I apply the current images in my head to my bike with a 15 tooth front sprocket and a 30 tooth rear, I see the chain applying a lot of force to the rear sprocket to get the rear tire to bust loose. When I change the sprockets to 30 teeth front and 60 teeth rear I see less force being transmitted through the chain and less force being required to bust the rear wheel loose since it has a bigger sprocket. In the end I see a difference of chain pull and chain speed between the 2 combinations but the amount of torque that hits the ground is the same.

Scott M

Offline Loose Goose-Terry#1

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #27 on: May 27, 2008, 09:53:30 PM »
 :-D Yep! That be correct thinken.  :wink:
If I had it all to do over again...I would!

Offline salt27

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #28 on: May 27, 2008, 11:07:19 PM »
From what I've seen, the most efficient sprocket setup is a ballance of chain speed and sprocket radius.
The weight, power, and drag of each machine has its own requirments, so like most things you have got to fool with it a bit before you get it right.
Just my opinion,
Don

Offline Jonny Hotnuts

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Re: Sprocket size choices.....does it make a diffrence?
« Reply #29 on: May 27, 2008, 11:17:57 PM »
Originally I posted this because I was fighting with the idea of sprocket sizes VS HP VS tire size (and growth).


I decided that a 19 would be the best choice this year because it makes the hypothetical top speed 210 at redline in 6th but the motor stops making power @ 9500 (red is 10900). If the tires grow 1/2 inch 9500 rpm is just around 201.

And with enough spray anything is possible!!!!!
jonny_hotnuts@hotmail.com

"Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully."
*Andres Segovia
(when Im not working on the car, I am ususally playing classical guitar)