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Old 08-01-2013, 08:08 AM   #31
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Again another person that does not understand the original question... Wow... You can't decrease the size of One gear and increase the size of the other without changing the FDR !!! To keep the same fdr, you need to decrease or increase both gears by the same amount !!! Too many folks here who don't understand ENGLISH !!!
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Old 08-01-2013, 08:20 AM   #32
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Originally Posted by narcotiks View Post
To answer your question. No. The ratio is the ratio.
There will be no effective difference in rotatianal mass, as if you decrease the size of one gear and increase the other, the difference cancels out. Assuming the gear pitch was kept the same, and the mesh was optimal, the only effect would be WHERE the motor is in the car (further forward or backward in comparison to the original position). If you multipy the number of teeth on each gear by a constant, the gear ratio will remain the same.
Not sure why people seem to think that changing sizes will give you some other advantage than mass distribution.
Bizkit, you run whatever gears will fit in your car and give you your desired FDR.
Well played Sir. The answers are very clear- good post.

gearchart.com still works last time I checked, anyone can go there and play with the numbers to see what combinations of spurs / pinions will give the DESIRED FDR. Pick an number to aim for and see what options you have to reach that particular number. If you are able to reach an FDR a few different ways, and want to try those different combinations to move weight forward or backwards, then great. Fine tuning. As stated before "the ratio is the ratio".
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Old 08-01-2013, 08:33 AM   #33
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Originally Posted by narcotiks View Post
To answer your question. No. The ratio is the ratio.
There will be no effective difference in rotatianal mass, as if you decrease the size of one gear and increase the other, the difference cancels out. Assuming the gear pitch was kept the same, and the mesh was optimal, the only effect would be WHERE the motor is in the car (further forward or backward in comparison to the original position). If you multipy the number of teeth on each gear by a constant, the gear ratio will remain the same.
Not sure why people seem to think that changing sizes will give you some other advantage than mass distribution.
Bizkit, you run whatever gears will fit in your car and give you your desired FDR.
Probably for touring car, there will not be any diff. In the 1/12 threads, there is a theory around using the largest spur to aid on car balance. Maybe for 1/12, there is some diff. I personally switched from 88t to 96t spur, maintaining the same ratio and didn't notice any diff.
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Old 08-01-2013, 08:36 AM   #34
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FDR is FRD, it does not matter what spur/pinion combination you use. However, using different gearing combinations will allow you to move the weight of the motor on the chassis, front or back.
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Old 08-01-2013, 08:50 AM   #35
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Still the question is misunderstood, and will stay that way... I guess ignorance is bliss for some.....lol... I'll pass them all forever anyway. Let them stay ignorant....
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Old 08-01-2013, 09:18 AM   #36
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Originally Posted by bertrandsv87 View Post
To keep the same fdr, you need to decrease or increase both gears by the same amount !!! Too many folks here who don't understand ENGLISH !!!
Lets try not to confuse people with bad information.
Look at this example where the number of teeth has been decreased on both gears by the same amount;

90s/30p = 3.0 FDR
80s/20p = 4.0 FDR

the FDR changed. Keep in mind we are working with a ratio in most cars that is not 1/1.

There is only one case where increasing or decreasing both the spur and the pinion the same amount maintains a constant FDR, 1.0 or 1/1, both gears would need to start out with the same number of teeth;

90s/90p = 1.0 FDR
80s/80p = 1.0 FDR
70s/70p = 1.0 FDR
and so on...

The math is simple.
I won't get into the understanding of english or not.
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Old 08-01-2013, 09:35 AM   #37
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Originally Posted by oldrcr View Post
Lets try not to confuse people with bad information.
Look at this example where the number of teeth has been decreased on both gears by the same amount;

90s/30p = 3.0 FDR
80s/20p = 4.0 FDR

the FDR changed. Keep in mind we a working with a ratio in most cars that is not 1/1.

There is only one case where increasing or decreasing both the spur and the pinion the same amount maintains a constant FDR, 1.0 or 1/1, both gears would need to start out with the same number of teeth;

90s/90p = 1.0 FDR
80s/80p = 1.0 FDR
70s/70p = 1.0 FDR
and so on...

The math is simple.
I won't get into the understanding of english or not.
+1 on this, pretty sure this is the first person to truly get it correct. good job.
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Old 08-01-2013, 10:37 AM   #38
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Originally Posted by ongbenghui View Post
Probably for touring car, there will not be any diff. In the 1/12 threads, there is a theory around using the largest spur to aid on car balance. Maybe for 1/12, there is some diff. I personally switched from 88t to 96t spur, maintaining the same ratio and didn't notice any diff.
Yes indeed. Any pan car will usually work best with the motor as forward as it can possibly go. This means using the largest spur/pinion combo you can fit for a given ratio.

For anything else, it really doesn't matter one bit. The gears are light enough that the mass and moment of inertia differences are pretty negligible. The only real exception being that you don't want to go below a certain pinion size or the mesh gets really inefficient. That's not usually a problem since for 48p (not sure what the point is in other pitches) that point is like 14 teeth or so.
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Old 08-01-2013, 10:46 AM   #39
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Well I believe I got my answer, as far as fdr goes. This is going in a FF03 and the front to back weight transfer doesn't matter, unlike a touring car or buggy/truck. Thanks for all of the insight and for giving me more to think about in the future.

George
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Old 08-01-2013, 10:49 AM   #40
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Originally Posted by oldrcr View Post
Lets try not to confuse people with bad information.
Look at this example where the number of teeth has been decreased on both gears by the same amount;

90s/30p = 3.0 FDR
80s/20p = 4.0 FDR

the FDR changed. Keep in mind we a working with a ratio in most cars that is not 1/1.

There is only one case where increasing or decreasing both the spur and the pinion the same amount maintains a constant FDR, 1.0 or 1/1, both gears would need to start out with the same number of teeth;

90s/90p = 1.0 FDR
80s/80p = 1.0 FDR
70s/70p = 1.0 FDR
and so on...

The math is simple.
I won't get into the understanding of english or not.
Yep, but notice that to maintain the same ratio, you have to change both gears in the same direction by the same RATIO.

In other words, take a 20/60. That's a 3 to 1 ratio. If your smallest pinion is 30, what spur do you need? Well this case is so obvious that anyone can tell you a 90. 30/90 is also a 3 to 1. Notice something about the change? Pinion went up by 10. Spur went up by 30. 10/30 is also a 3 to 1 ratio.
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Old 08-01-2013, 11:13 AM   #41
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Originally Posted by wingracer View Post
Yep, but notice that to maintain the same ratio, you have to change both gears in the same direction by the same RATIO.

In other words, take a 20/60. That's a 3 to 1 ratio. If your smallest pinion is 30, what spur do you need? Well this case is so obvious that anyone can tell you a 90. 30/90 is also a 3 to 1. Notice something about the change? Pinion went up by 10. Spur went up by 30. 10/30 is also a 3 to 1 ratio.
What was being talked about though was going with a larger pinion and spur or smaller by increasing or decreasing the same # of teeth. Like going from a 35p 85s then going 40p 90s by adding 5 to each. This is just an example though. They both give different ratios. The only way to do this is by having the pinion and spur the same number of teeth.
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Old 08-01-2013, 11:37 AM   #42
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Originally Posted by ThePanda View Post
What was being talked about though was going with a larger pinion and spur or smaller by increasing or decreasing the same # of teeth. Like going from a 35p 85s then going 40p 90s by adding 5 to each. This is just an example though. They both give different ratios. The only way to do this is by having the pinion and spur the same number of teeth.
That was not what the original post was asking. He wanted to know if there was an advantage in using different size gear combinations (larger pinion & smaller spur or smaller pinion & larger spur) and maintaining the same FDR. He was trying to determine if the rotaional weight of a pinion gear, or gear mesh, has any effect when choosing what he uses.
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Old 08-01-2013, 11:42 AM   #43
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Originally Posted by Csaari77 View Post
That was not what the original post was asking. He wanted to know if there was an advantage in using different size gear combinations (larger pinion & smaller spur or smaller pinion & larger spur) and maintaining the same FDR. He was trying to determine if the rotaional weight of a pinion gear, or gear mesh, has any effect when choosing what he uses.
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Old 08-01-2013, 12:22 PM   #44
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Originally Posted by Csaari77 View Post
That was not what the original post was asking. He wanted to know if there was an advantage in using different size gear combinations (larger pinion & smaller spur or smaller pinion & larger spur) and maintaining the same FDR. He was trying to determine if the rotaional weight of a pinion gear, or gear mesh, has any effect when choosing what he uses.
That's impossible. To keep the same ratio, both have to be bigger or both have to be smaller.
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Old 08-01-2013, 12:25 PM   #45
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What was being talked about though was going with a larger pinion and spur or smaller by increasing or decreasing the same # of teeth. Like going from a 35p 85s then going 40p 90s by adding 5 to each. This is just an example though. They both give different ratios. The only way to do this is by having the pinion and spur the same number of teeth.
I know this. That is why my post started with the word "Yep". Merely pointing out a bit of math inherent in the problem.
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