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Opinion: Bigger Spur or Bigger Pinion Gear

Old 07-31-2013, 06:44 AM
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Originally Posted by terry.sc View Post
Using bigger or smaller gears might have made a difference in efficiency 20-30 years ago, when we were using 1200mah nicads and we had to squeeze every last ounce of efficiency out of the car. Anyone remember having to take your car over and put it down on the start line so you didn't waste that half a lap of power getting there? Today that's not really a problem.

What changing gears does is move the motor on the chassis. The weight of a buggy or touring car means means the small amount of movement isn't going to make much difference relative to the rest of the car, but in pan cars where the motor is the biggest part of the unsprung weight, moving the motor forwards makes the car smoother and easier to drive, smaller gears so the motor is nearer the rear axle makes it more aggressive and harder to drive.
Great explanation. The weight distribution element should be more of the key factor vs. worrying about different gear combinations to reach a specific fdr. With all of the power and run time we have now, I don't see the point in obsessing. Now as a chassis / weight tuning option, for sure it is more a point of discussion.
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Old 07-31-2013, 07:57 AM
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I for one obsess about my gearing. Its not very uncommon that I would change the pinion all three qualifiers and then pick which one I thought was best based on track condition, heat, traction and driver skill. Using all that info, I can squeeze another half second or more out of a laptime. Also regarding the FDR and pinion size, we have to remember that the brushless motor also has an RPM limit. If you're using a pinion that's too small, you'll get plenty of rip but you wont get that top end. Its important to find that middle group where you're getting the most out of your motor without running too hot or wasting power.

My gearing in my T3 is 96S and 49P.. I will often jump around pinion sizes from 47 and up to a 52. Just depends on the tracks conditions.
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Old 07-31-2013, 08:22 AM
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Also, smaller gears accelerate and decelerate faster too, giving much better Performance corner to corner and better braking... I've seen lots of guys running these big pinions cooking their motors in 17.5t blinky at 4.1fdr while I was running 3.65fdr with a heavier tub tc4 and getting no heat at all(less than 120) after six Minutes... Rotational mass is not all that counts, but whether the mass is from the Center of rotation is as important...
I also think if you use 64p gears, you'll be forced to run bigger pinions to get durability versus running 48p, but whatever was thought to be gain in efficiency by using smaller tooth gears is lost by having to use a bigger 64p pinion than 48p pinion, and still ending up chewing these 64p gears twice as fast... The 64p gears lost their efficiency a long time before chewing each other anyway resulting in One blown motor after the next, while I'm still using the same five year old 48p spur gear.... It was really a perfect way to make people buy more spur gears , more pinions, and more motors/higher capacity batteries... I'm waiting for the 128p gears to come out....lol...
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Old 07-31-2013, 01:15 PM
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Originally Posted by M3Roc View Post
...

My gearing in my T3 is 96S and 49P.. I will often jump around pinion sizes from 47 and up to a 52. Just depends on the tracks conditions.
For all the others discussing gear ratios, the original poster said nothing about changing gearing, but on keeping the same gearing and using either a bigger spur and pinion, or a smaller spur and pinion.

For those suggesting using a bigger pinion and spur means more rotational mass, if you are noticing a difference there you must be using brass gears. A pinion will be 2-3g in weight and considering most of the weight is in the pinion mounting boss the weight difference between 52T pinion/96T spur and 39T pinion/72T spur combinations will be minimal.
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Old 07-31-2013, 01:22 PM
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Originally Posted by terry.sc View Post
For all the others discussing gear ratios, the original poster said nothing about changing gearing, but on keeping the same gearing and using either a bigger spur and pinion, or a smaller spur and pinion.
Mind boggling, isn't it?
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Old 07-31-2013, 01:41 PM
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I didn't think the OP was asking for anything more than which combination of spur/ pinion to reach a specific FDR was best . There is obviously more than one way to reach the desired target.
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Old 07-31-2013, 02:06 PM
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Default re-read it

since the original posted implied strain and temp differences in the motor with the ratio being the same, which you wouldn't expect to see if the FDR remains the same. I think many saw the mention of pinion size change and didn't read into that the implication of a spur change to keep the ratio the same. Which is not clear, so its easy to see this happen.

But it is always interesting to see how different people read things, if not worded clearly.

Maybe Bizkit1 could clarify the actual intent of the question...
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Old 07-31-2013, 04:11 PM
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[QUOTE=terry.sc;12401693]For all the others discussing gear ratios, the original poster said nothing about changing gearing, but on keeping the same gearing and using either a bigger spur and pinion, or a smaller spur and pinion.

QUOTE]

Yes, it was about keeping the same fdr just what would be better. I see the point of the smaller pinion being less rotation mass, but that rotating mass is now transfered to the spur or vise versa.

The point of the limit of rpm of the motor does come into play and I never would have thought about it maxing out, but yes that is a really good point.

I have to say that this is some really good information being brought up
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Old 07-31-2013, 06:56 PM
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The smaller pinion gear's rotational mass is not transferred to the spur gear in anyway here. On the contrary, you will need a smaller spur gear too to keep the fdr the same. So with the smaller pinion and smaller spur you'll save on rotational mass twice plus all the mass is spinning closer to the Center of rotation of both the motor and the shaft holding the spur ....
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Old 07-31-2013, 06:59 PM
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Originally Posted by bertrandsv87 View Post
Also, smaller gears accelerate and decelerate faster too, giving much better Performance corner to corner and better braking... I've seen lots of guys running these big pinions cooking their motors in 17.5t blinky at 4.1fdr while I was running 3.65fdr with a heavier tub tc4 and getting no heat at all(less than 120) after six Minutes... Rotational mass is not all that counts, but whether the mass is from the Center of rotation is as important...
I also think if you use 64p gears, you'll be forced to run bigger pinions to get durability versus running 48p, but whatever was thought to be gain in efficiency by using smaller tooth gears is lost by having to use a bigger 64p pinion than 48p pinion, and still ending up chewing these 64p gears twice as fast... The 64p gears lost their efficiency a long time before chewing each other anyway resulting in One blown motor after the next, while I'm still using the same five year old 48p spur gear.... It was really a perfect way to make people buy more spur gears , more pinions, and more motors/higher capacity batteries... I'm waiting for the 128p gears to come out....lol...
Wow, soooo much incorrect information in this post!

You talk about big pinions at 4.1 FDR, but if you were running 3.65 FDR (keeping the same spur), your pinion would have to be bigger to achieve that lower FDR.

And gearing largely depends on what motor you're running and track size. There is no magic FDR number. Even on a large track, I have ran 4.0-4.2 on my old Team Powers 17.5. Its more of an RPM motor. On the same track and layout, I now run 3.6 FDR on my eXpress Killshot torque motor. Temps are all fine with both setups.

And I've never heard of anyone blowing a motor just because they ran 64P gears instead of 48P gears.
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Old 07-31-2013, 07:16 PM
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Read the post again if you know how to read ! The whole club where I race on carpet had tons of racers using 64p gears and smoking motors left and right at above 4.0fdr with torque motors and 12.5mm rotors. I had my novak with a 12.3mm rotor and geared at 3.65fdr with 48p gears in a much heavier Car and had no heat coming out of the motor after six Minutes... I never used a spur or pinion that was bigger than their's because I did not have durability issues with my 48p gears , but they all did and they were forced to use larger(than my 48p gears) 64p pinions and spurs... Hopefully you'll read this correctly....lol...
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Old 07-31-2013, 07:23 PM
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Also I know their drivetrain was much less efficient too because these guys were running their Cars way below the 1380gram minimum weight while I could not get under 1472grams.... I doubt that they all were timing their motors too high.....
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Old 07-31-2013, 08:11 PM
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This thread is getting so far away from the original question, and simple answers that were presented by a few...

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Old 07-31-2013, 09:11 PM
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Originally Posted by nf_ekt View Post
This thread is getting so far away from the original question, and simple answers that were presented by a few...

+1

All, perhaps before replying to someone's comment...look at past post for said person..to see if person is actually contributing or just hitting keys trying to make soup with rock and water.

Have a wonderful Thursday to all.
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Old 08-01-2013, 12:26 AM
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Originally Posted by bizkit1 View Post
my question is does it matter what gears you run to get final ratio? If you get to your ratio with a bigger/smaller pinion does it put more strain on the motor or do you go by temp of the motor?
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.
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