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Old 09-23-2005, 04:56 AM   #1
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Default Bigger Spur Or Smaller Spur?

I would like to know the difference Big spur and a small spur? Do you get better acceleration with a small spur, but lower top speed and with a bigger spur, slower acceleration and better top speed?
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Old 09-23-2005, 05:10 AM   #2
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A bigger spur= more acceleration/ less top speed. A smaller spur= more top speed less accl.
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Old 09-23-2005, 05:28 AM   #3
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Thanks Geeunit
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Old 09-23-2005, 08:44 AM   #4
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Quote:
Originally Posted by geeunit1014
A bigger spur= more acceleration/ less top speed. A smaller spur= more top speed less accl.
Sorry, I can see quicker acceleration, but if you are using a small pinion with a larger spur or a large pinion with a smaller spur and the final drive ratio is the same, how can one or the other have a higher top speed?
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Old 09-23-2005, 09:01 AM   #5
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"Sorry, I can see quicker acceleration, but if you are using a small pinion with a larger spur or a large pinion with a smaller spur and the final drive ratio is the same"

Can you provide an example where a small pinion and large spur has the same FDR as a large pinion and smaller spur? This is impossible!
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Old 09-23-2005, 09:08 AM   #6
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Hi one question is not trivial :

What is the difference between 64DP 100 spoor / 50 pinon ... and 64DP 50 spoor / 25 pinion ???

Does the 50/25 has always an advantage since has less mass to rotate ?

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Old 09-23-2005, 09:10 AM   #7
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That is backwards....bigger pinion or smaller spur does the same thing. Use the biggest spur you can. 25/100=4 or 20/80=4.
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Old 09-23-2005, 09:15 AM   #8
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Quote:
Originally Posted by Ted Flack
That is backwards....bigger pinion or smaller spur does the same thing. Use the biggest spur you can. 25/100=4 or 20/80=4.
i always try and use the smallest spur and pinuion for less internal resistance and weight on the transmision
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Old 09-23-2005, 09:19 AM   #9
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smaller mass will have less inertia and will accellerate faster given the same force input. also, there will be less teeth in contact which should produce less friciton.

realistically, this is not something to even worry about. choose a spur that will give you the correct range of rollouts for the tires sizes you'll be running.

Quote:
Originally Posted by e_lm_70
Hi one question is not trivial :

What is the difference between 64DP 100 spoor / 50 pinon ... and 64DP 50 spoor / 25 pinion ???

Does the 50/25 has always an advantage since has less mass to rotate ?

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Old 09-23-2005, 11:03 AM   #10
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Quote:
Originally Posted by TraceRacing
Can you provide an example where a small pinion and large spur has the same FDR as a large pinion and smaller spur? This is impossible!
You don't have to flame me, and you can just hit the quote button instead of typing out my quote, then you would not mis-quote me.

Off hand I can't find it exactly but on the Yoke BD for example:

96 Spur 30 Pinion (64P) = 6.40 FDR
109 Spur 34 Pinion (64P) = 6.41 FDR

94 Spur 31 Pinion (64P) = 6.06 FDR
112 Spur 37 Spur (64P) = 6.05 FDR

Now are you saying that the 109 Spur will have a higher top end than the 96 Spur? That the top end will make a difference of greater than 1/100th?

I am not sure that a smaller or larger spur will accelerate faster, this has been argued about on this site many times. I am pretty sure that the top end is ultimately decided by the final drive ratio and roll out though.
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Old 09-23-2005, 11:39 AM   #11
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Any two larger gears meshed together are more efficient then small ones. A larger gear will weigh more but we are not talking much in the rc world. A larger spur is easier to climb. Ask any real drag racer, he will ask for a specific gear with the LARGEST ring or spur, because it is easier on the motor or power plant. So I would say go with as large a spur as you could run, with maintaining the gear ratio you need.
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Old 09-23-2005, 11:46 AM   #12
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I think using different sized gears while maintaining the same overall ratio is more of a way to tune weight distribution. The motor is one of the heaviest parts of the car, and the ability to move it forward or backwards using different sized gears can have a dramatic effect on handling. This will have a much greater effect on your laptimes than the small potential gains in gear effeciency and a few grams of rotating mass.

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Old 09-23-2005, 12:27 PM   #13
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I can tell the difference between an 88 tooth spur and a 100tooth spur w/ the same FDR. I think it is because the 100tooth spur and big pinion have more teeth, so the acceleration/braking is smoother. Also, less noise is putout by the gears.

On the other hand...

A small spur and pinion will move the car closer to the centerline on an SD car. That would help with transitioning speed, but most guys running SD cars put weights on the outside of the motor to balance the chassis, so maybe the small spur/pinion is unnecessary.
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Old 09-23-2005, 05:39 PM   #14
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dont have the gear chart in front of me but somewhere around 110 or 112 with a 37 pinion is 7.0 thats 64 pitch, 72 with a 24 or so is also 7.0 thats 48 pitch, the car does drive different and accellerate different using the same gear ratio however top speed is the same. btw, thats on a yok bd.
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Old 09-23-2005, 05:51 PM   #15
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I guess one way to compare spur sizes is to a 10 speed. Your bigger gears in the back make for easier acceleration like a bigger spur gear. Where the smallest gear where the crank is on your 10 speed gives you easier acceleration as well, translates to smaller pinion.

Therefore, a smaller pinion and larger spur gives the best accelleration but less top end.

Similar gear ratios with differnt spur/pinion combinations translates to the spur/gear combo with the bigger spur gear will have the quicker acceleration but will overall end up at the same top speed.

SO, a final drive of a 6.0 for both grear ratios will end up in the same top speed, just one will get there quicker than the other.
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