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Old 08-22-2007, 08:19 AM   #1
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Default can someone explain gearing to me!?

Ok, I've seen the gear charts, I know how to calculate roll out, FDR and pinion/spur. my question is how do you determine what FDR to shoot for? Is there a given range you want to stay in? I know with these brushless motors, you have to pay very close attention to your gearing or youre going to be buying new ESC's and motors very quickly if you get something wrong.

Is there a good rule of thumb when decided how you are going to gear your car?
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Old 08-22-2007, 10:04 AM   #2
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Depends on the track you are going to run on. Using the manufacturers Final Drive recommendations as a template, look at your set-up, type of cells and length of the straights and overall size of the track. If the track is small with a nice amount of turns, gear for torque and punch, higher FD. If the track is sizeable, nice length straights, gear for rpms, lower FD. Take a few pratice laps and monitor your temps. Make sure to have an adequate gear selection (several pinions and spurs) and do your math. With BL, 160-175 is the area that is the safe zone cut off (for Novak anyways). Anything higher than that, you are looking to thermal. Lets use the 3.5 by Novak. Safe zone FD is roughly 9.75 to 10.75, give or take. In my Pro4, I am running 100 spur/26 pinion, giving me a FD of 9.375. I am pushing the envelope, but am running an additional fan on the motor to keep the temps in check. To ensure I dont thermal, I am dropping a tooth, increasing my FD, but, lowering my temps. The downside is, lower top end. As long as you are happy with your top end and the temps stay in the safe zone, you have room to work with.
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Old 08-22-2007, 10:43 AM   #3
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thanks bx! so there is a manufacturers recommendation? that explains alot.
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Old 08-22-2007, 10:45 AM   #4
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I'm having trouble coming up with the man. rec. for a cyclone and a jrx-s. anyone know where i can find these or know what they are?
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Old 08-22-2007, 10:49 AM   #5
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Try gearchart.com for all your gearing needs!
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Old 08-22-2007, 10:56 AM   #6
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You ever have a question about anything in particular, reach out to MarcosJ on this forum. He is probably one of the most informative and knowledgable dudes on rctech.net. I also give him props because he was in the Marines like me
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Old 08-22-2007, 12:47 PM   #7
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Try gearchart.com for all your gearing needs!

gearchart creator still doesnt address the point of this thread, it just gives you a FDR. i'm trying to figure out what range of fdr you want to use as a general guideline.





thanks bx, i will consult marcos.
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Old 08-22-2007, 01:27 PM   #8
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lets see if this works....
FDR or Gear Ratio at the spur which ever u want...
1:1 is just that 1 turn of the pinion to 1 turn of the spur (applies to many different examples).
If I am looking for top end I want to be closer to a ratio of 1:1, if my memory serves me that's a tall ratio, 5.5:1. The closer you are to 1:1 the less torque u have.
A ratio further awat from 1:1 will give you more torque at the expense of speed, called a low ratio like 9:1 or 12:1

The key is to find a range that will not only suit your driving style but the track as well. If you have a tight twisty track you might want a lil bit more torque on the ground to help pull or push the car though the corners. If the track is loopy and has nice smooth corners then you might choose something that give less torque and more top end.

If your track is a blend then you need to experiment and find a happy spot for your driving.

Usually with stock motors I try and run 5-7:1 FDR, Mod I will try 8.5-11:1 all depending on the track. So lets say I have a mod 12T, I might start something like this (using a TC4 internal ratio is 2.5:1)

(spur / pinion)* Internal DR = FDR => (78/21)*2.5 ==> 3.714 * 2.5 ===>9.286 FDR

If you know your FDR (most manuals give this and so does gearchart.com) you can plus and choose your numbers to get the ratio you want. Just remember more speed move closer to 1:1 more torque move further away from 1:1

Brushless is a whole new creature and I'm still learning but the same principal applies
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Old 08-22-2007, 07:02 PM   #9
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Quote:
Originally Posted by RAP66 View Post
lets see if this works....
FDR or Gear Ratio at the spur which ever u want...
1:1 is just that 1 turn of the pinion to 1 turn of the spur (applies to many different examples).
If I am looking for top end I want to be closer to a ratio of 1:1, if my memory serves me that's a tall ratio, 5.5:1. The closer you are to 1:1 the less torque u have.
A ratio further awat from 1:1 will give you more torque at the expense of speed, called a low ratio like 9:1 or 12:1

The key is to find a range that will not only suit your driving style but the track as well. If you have a tight twisty track you might want a lil bit more torque on the ground to help pull or push the car though the corners. If the track is loopy and has nice smooth corners then you might choose something that give less torque and more top end.

If your track is a blend then you need to experiment and find a happy spot for your driving.

Usually with stock motors I try and run 5-7:1 FDR, Mod I will try 8.5-11:1 all depending on the track. So lets say I have a mod 12T, I might start something like this (using a TC4 internal ratio is 2.5:1)

(spur / pinion)* Internal DR = FDR => (78/21)*2.5 ==> 3.714 * 2.5 ===>9.286 FDR

If you know your FDR (most manuals give this and so does gearchart.com) you can plus and choose your numbers to get the ratio you want. Just remember more speed move closer to 1:1 more torque move further away from 1:1

Brushless is a whole new creature and I'm still learning but the same principal applies
'nuff said!! That's the best explanation on gearing that I've heard yet. Good job brah!
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Old 08-23-2007, 06:48 AM   #10
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No doubt. i wish we could get this pinned for newbies like myself.

thanks !
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Old 08-23-2007, 06:52 AM   #11
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that's a cool way of explaining things

The only other simplistic thing that I would add for the newbies is, smaller pinion gear to gain acceleration, larger pinion to gain maximum speed if need be
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Old 08-23-2007, 07:56 AM   #12
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Originally Posted by nc racer View Post
Ok, I've seen the gear charts, I know how to calculate roll out, FDR and pinion/spur. my question is how do you determine what FDR to shoot for? Is there a given range you want to stay in? I know with these brushless motors, you have to pay very close attention to your gearing or youre going to be buying new ESC's and motors very quickly if you get something wrong.

Is there a good rule of thumb when decided how you are going to gear your car?
Gear your motor so that it winds up 3/4's of the way down the straight away.
Works great. And its simple.
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Old 08-23-2007, 04:32 PM   #13
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Quote:
Ok, I've seen the gear charts, I know how to calculate roll out, FDR and pinion/spur. my question is how do you determine what FDR to shoot for? Is there a given range you want to stay in? I know with these brushless motors, you have to pay very close attention to your gearing or youre going to be buying new ESC's and motors very quickly if you get something wrong.

Is there a good rule of thumb when decided how you are going to gear your car?
In all the years I've been "HACK er uhh Racing" I have not paid any attention to rollout. Yes I understand that the tire diameter ultimately affects FDR etc... Just get used to judging the track and how your motor reacts to gearing, learn basics first and the rest will follow when your ready.
Ask the guys at the track questions see what range they are using and watch them on the track, one thing I like to help other with is to LISTEN to the cars (and your car when you drive the infield and back straight) what do you hear? Is the motor screaming? Is the motor still pulling at the end of the track.... if it is then adjust 3-4 teeth on your pinion and try again.

Another thing I want to suggest if your running MOD, try this and you can get a nice feel gearing... Run a 15 - 16 turn with a stock gear ratio; say 6.0-6.5. That should get you enough motor to be competitive and yet slow enough that you dont over power your car through a track. I did a race this way, and it's great to see how other reacted when they ask what I was running. If your running brushless... well you & I are in the same boat, I'm still learning on that one.

Get out there and Hacktice Practice Practice... Eventually you'll get a good feel of what works right for your style of driving & the tracks you attend.
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Old 08-24-2007, 06:37 AM   #14
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Originally Posted by nc racer View Post
Ok, I've seen the gear charts, I know how to calculate roll out, FDR and pinion/spur. my question is how do you determine what FDR to shoot for? Is there a given range you want to stay in? I know with these brushless motors, you have to pay very close attention to your gearing or youre going to be buying new ESC's and motors very quickly if you get something wrong.

Is there a good rule of thumb when decided how you are going to gear your car?
Check this article out in the XRAY forum.
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