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Pinions & Spur Gears

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Old 03-26-2008, 08:38 AM
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Default Pinions & Spur Gears

Just got back into hobby went from bashing to racing.

what is the general rule for Pinions and spur gears ??

lower pinion = faster acceleration ?
larger pinion = more topspeed ?

i want to start playing with these but want to know what general
direction to start with

TIA
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Old 03-26-2008, 08:58 AM
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Originally Posted by IL_AudiRacer View Post
Just got back into hobby went from bashing to racing.

what is the general rule for Pinions and spur gears ??

lower pinion = faster acceleration ?
larger pinion = more topspeed ?

i want to start playing with these but want to know what general
direction to start with

TIA

from what i understand that is correct.works the same way with the spur gear too. smaller spur more acceleration, bigger more speed.
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Old 03-26-2008, 09:05 AM
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yep thats right

lower pinion= faster acceleration
and
higher pinion= more top speed

you have that right and like the guys said above me im pretty sure that its goes the same with the spur gears
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Old 03-26-2008, 10:48 AM
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The spur works in the opposite direction to the pinion. A larger spur is directionally the same as a smaller pinion. Larger spur lowers top speed, increases acceleration. Smaller spur, more top end, less acceleration. As long as the motor will pull the taller gearing of course.

Actually it's the number of spur teeth divided by the number of pinion teeth, that would be the gear reduction for that stage. For direct drive cars that's the Final Drive Ratio. Multiply by the transmission ratio to get FDR for tranny cars.
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Old 03-26-2008, 04:29 PM
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i was taught like this.... i worked on dirtbikes and had them my whole life and if you put a bigger sprocket on back came out to be more top end, smaller in the rear my acceleration. now with the drive sprocket bigger in the front was more top end and smaller was more acceleration. thats how i was taught.
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Old 03-29-2008, 12:26 AM
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Originally Posted by dieseldog20 View Post
i was taught like this.... i worked on dirtbikes and had them my whole life and if you put a bigger sprocket on back came out to be more top end, smaller in the rear my acceleration. now with the drive sprocket bigger in the front was more top end and smaller was more acceleration. thats how i was taught.
Unfortunately Dieseldog20, it seems that what you were taught is wrong...

Bigger pinion, or smaller spur gives a better top speed, but less acceleration.

Smaller Pinion, or larger spur gives better acceleration, and a lower top speed.

Thats just how it is..
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Old 03-30-2008, 09:20 AM
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O.K. Thanks for the info. Now we have that figured out

How do you figure out FDR do you divide the Spur by the Pinion ??

I have never messed with this stuff before, im amazed at how

much tuning is able to be done. I used to build as kit and run in parking lots

now im starting to learn about just how technical this hobby
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Old 03-30-2008, 10:37 AM
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hey you work out fdr by dividing the spur by the pinion and then timesing it by you internal gear ratio (you work it out by dviding the diff pulley by the centre pulley)
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Old 03-30-2008, 11:05 AM
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WOW So theres actually 4 gears that need to be considered ??

divide spur x Pin then divide diff pulley X center Pulley then multiply the 2 totals ?? to = FDR. maybe i should of went to math class LOL
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Old 03-30-2008, 11:15 AM
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Most transmission equiped cars have a readily available ratio, check your manual or the appropriate web site. So just multiply that by the spur/pinion division.

BTW, for the tranny ratio, the size of the center gear is irrelevant. It's the output gear divided by the input gear. Which with modern 3 gear trannys, off road anyway, is typically the diff/output gear divided by the top shaft/input gear.
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Old 03-30-2008, 12:07 PM
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Originally Posted by Dave H View Post
Most transmission equiped cars have a readily available ratio, check your manual or the appropriate web site. So just multiply that by the spur/pinion division.

BTW, for the tranny ratio, the size of the center gear is irrelevant. It's the output gear divided by the input gear. Which with modern 3 gear trannys, off road anyway, is typically the diff/output gear divided by the top shaft/input gear.
Correct, it's not that hard to figure, all you need is to figure out the outdrive ratio of your car's drivetrain, & then you'll have a basic number that'll make it easy to calculate your FDR. As an example, I'll use my Tamiya TRF 415MSX's drivetrain, its(stock) diff pulleys have 35 teeth, & my center pulley has 16 teeth, so you take the diff pulleys & divide it by the center pulley(35 divided by 16) & you get 2.1875(though we typically go by 2.187, works well enough without using that last digit). So if I have a 100 tooth spur & a 25 tooth pinion on the car, you just take 100, divide by 25, & multiply that number(4) by the outdrive ratio(2.187), & you get the FDR(about 8.75 FDR). But if you don't know exactly what gears or pulleys are on your car, just look through the car's manual, pretty much all of the manuals I've had or seen have the outdrive ratio printed in it somewhere. And just to make it clear, the lower the FDR number, the higher your top speed & the worse its acceleration, while the higher number means better acceleration but less top speed....
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Old 03-30-2008, 01:57 PM
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Originally Posted by StumpyRC View Post
Unfortunately Dieseldog20, it seems that what you were taught is wrong...

Bigger pinion, or smaller spur gives a better top speed, but less acceleration.

Smaller Pinion, or larger spur gives better acceleration, and a lower top speed.

Thats just how it is..
thanks for the tip.
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