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Old 02-01-2005, 07:11 AM   #1
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Default HPI Pro4 gearing

Hi guys,
I am getting the HPI Pro4 kit, I will be racing 17T Spec class, but the manual syas nothing about gearing for 17Turn motor.
Does anyone here have idead about the gearing ?

plz comment
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Old 02-03-2005, 12:54 PM   #2
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I also driven 17t class. Gearing...it always depend on what is the size of the track? Is it carpet or asphalt? Tell more if you want some more info
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Old 02-03-2005, 02:39 PM   #3
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This is actually a great thread to start!
Lets all post some of our gearing for certain track conditions.
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Old 02-03-2005, 03:21 PM   #4
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Hi Trinity2, nice to get some feedback.
I am running on a rather tight carpet track.
Handwound motor, 17x1 and 17x2.
Ill be using LRP Quantum Pro Sport w/4700 power cap and GP 3300 matched cells.

I was thinking of somewhere between 35 and 37 teeth pinion, plz tell me what you are using.
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Old 02-04-2005, 10:03 AM   #5
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Quote:
Originally posted by Snikkari
Hi Trinity2, nice to get some feedback.
I am running on a rather tight carpet track.
Handwound motor, 17x1 and 17x2.
Ill be using LRP Quantum Pro Sport w/4700 power cap and GP 3300 matched cells.

I was thinking of somewhere between 35 and 37 teeth pinion, plz tell me what you are using.
Hey there Snikkari.

C`moon scoobydoo man...

At first i recommend you to try gears like: spur 98 and pinjon 35 = 6.83

That is what i liked to use our carpet track what is also technical and tight.
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Old 02-04-2005, 11:08 AM   #6
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35 and up for large track tracks using 58mm trued tires
If your not afraid of cutting the comm alot you can also go up to 37-38
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Old 02-04-2005, 01:39 PM   #7
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Quote:
Originally posted by 710baby
35 and up for large track tracks using 58mm trued tires
If your not afraid of cutting the comm alot you can also go up to 37-38
Nah. I mean 63mm rubbertires with that gearing
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Old 02-04-2005, 01:49 PM   #8
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When considering gearing always ask "What's your rollout?", by using rollout numbers you can tune for different size tires, different cars, etc..

Here's how to calculate it:

MMPR (MilliMeters Per Revolution, It's how far the car will travel in mm when the motor makes one revolution)

W= Wheel diameter in mm

S= Spur gear teeth (ex: 96T spur)

P= Pinion teeth (ex: 25T pinion)

For cars with internal drive ratios (Like a TC3 or a Pro4, it has an internal drive ratio of 2.5:1) Check your user manual for the drive ratio and add it to the above equation like so:

DR=Drive ratio (Ex: DR=2.5 for a TC3)

MMPR= (1/DR)*(P/S)*(3.1416*W)

Example: I'm running a 19T spec motor in my TC3, what pinion do I use. Guys at the track say that 25 MMPR is a good start.
I measue, W=65mm (full size TC tire), My spur is 100T

P=(MMPR*DR*S)/(3.1416*W)
P=(25*2.5*100)/(3.1416*65)
P=30.6
Round it off to 30T or 31T

Select the 30T or the 31T and try it out.

Ask people around at your track what rollout they use and you can find out your gearing with the above equations.

For a 17T motor on a fast flowing track I would use 30 MMPR to start, for a tighter track try 24 MMPR. Go up or down depending on on how you drive, the temp of the motor, etc..

Hope this helps.
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Old 02-05-2005, 02:03 PM   #9
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Quote:
Originally posted by ddesros2
When considering gearing always ask .......

That was great. Totally explains how to tackle the question head on. Great post! Thanks ddesros2.

Last edited by scoobydo; 02-05-2005 at 09:53 PM.
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Old 02-05-2005, 03:08 PM   #10
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With 48P gears...
72 spur
anything from 22-30 depending on your track/size etc.
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Old 02-05-2005, 09:58 PM   #11
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Quote:
Originally posted by ddesros2

MMPR (MilliMeters Per Revolution, It's how far the car will travel in mm when the motor makes one revolution)
So basically when you say the motor makes 1 revolution,
you are in essence saying the "pinion gear" making 1 revolution since they are in direct connection to each other right?
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Old 02-06-2005, 01:29 AM   #12
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right
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Old 02-06-2005, 05:50 AM   #13
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Hey the por4 has an internal drive ratio of 2.4374:1 for any trying to get rollout.
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Old 02-06-2005, 02:30 PM   #14
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I been surfing around and nobody is including the internal drive ratio for shaft cars? They are just multiplying pinion/spur and tire diameter*Pie and getting numbers like 71.xxx and such.
Is this for pan cars with 1:1 ratios and belt cars without bevel gears?
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Old 02-06-2005, 10:03 PM   #15
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I don't get it ... why ask a bunch of people who have never driven or seen your track advice about how to gear?

The best way to find out, is ask the fast guys at your track and then adjust the gearing 3-4 teeth up and down. Gear based on laptime ....
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