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Old 07-06-2006, 08:42 PM   #1
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Default small spur gears

what would be the outcome if you use lesser or in other words smaller spur gear? or large spur gear.... not in terms of fdr numbers.... but would small spur gears creat more torque??

cause i have an extra 70t 48p spur gear that comes with a car that i bought from somebody. just wondering if small spur is still usefull
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Old 07-06-2006, 08:44 PM   #2
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roll out or fdr is going to determine correct gearing.alot of guys like bigger spurs for the use of larger pinions.they mesh better and run more efficiently that way
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Old 07-06-2006, 08:49 PM   #3
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The bigger the better I used 115 tooth @ 64 pitch on my BD
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Old 07-07-2006, 12:31 AM   #4
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Correct me if I am wrong, but larger spur gears also give you smaller gaps between gear ratios. For a hugely exaggerated example consider the following.
You take a test in school. There are 10 questions (spur gear). If you wanted to score a 87 on the test (FDR) you only have the choice to get 8 right or 9 right. (pinions) to get as close to your goal as possible. If you have 100 questions on the test (spur) you can get 87 right (pinion) and hit your intended goal (FDR). Sorry for the convoluted explanation. I am a teacher.
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Old 07-07-2006, 12:36 AM   #5
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Quote:
Originally Posted by andrewdoherty
Correct me if I am wrong, but larger spur gears also give you smaller gaps between gear ratios. For a hugely exaggerated example consider the following.
You take a test in school. There are 10 questions (spur gear). If you wanted to score a 87 on the test (FDR) you only have the choice to get 8 right or 9 right. (pinions) to get as close to your goal as possible. If you have 100 questions on the test (spur) you can get 87 right (pinion) and hit your intended goal (FDR). Sorry for the convoluted explanation. I am a teacher.
I think this will make it easier to understand:
With only 10 questions, if you miss one question, you're already down to a 90%.
With 100 questions, you can miss 10 questions and still have the same score.
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Old 07-07-2006, 01:45 PM   #6
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A final drive ratio is a final drive ratio. Bigger spur gears do give a little more choice in ratios, but running 64 pitch and having a variety of different size spur gears (114, 115, 116, 118 are all in my box right now) will get you all the fine tuning you could need. But some people think that larger spurs give more high end and smaller give more torque or vice versa etc... Not true IMO. A 9.0 FDR is a 9.0. It doesn't matter if you achieve it with a 128 tooth spur or a 114. What Jason said about larger spurs and pinions meshing better is true. It's easier to set mesh on a larger set of gears and may run a little quieter. But it will not effect your top end or acceleration. A gear ratio is a gear ratio. It doesn't matter how you get there.
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Old 07-07-2006, 03:55 PM   #7
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exactly.it will change the efficiency also to a point.if you run mod for instance or brushless 4.5,you need to run very small pinions which do not run efficiently.the pressure angle of each tooth do not blend very well during rotation.this is when i hunt a bigger spur that will allow me to run a larger pinion to have a more efficient mesh and still maintain my same FDR or rollout.
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Old 07-07-2006, 05:19 PM   #8
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ok i though it would give alittle bit of an effect to the top end or torque......
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