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Old 12-02-2003, 07:07 PM   #1
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Default TC Internal Ratio

Hi,

I would like to know whether internal ratio plays a part in the performance of a TC? For example, if my SD has an internal ratio of 2.353 and I geared it to arrive at a final ratio of 8.0, would it have a performance advantage/disadvantage over say an Xray T1 with an internal ratio of 1.77 and geared at final ratio of 8.0? Thanks!
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Old 12-02-2003, 07:13 PM   #2
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That's a really good question Kenneth. Since the cars are geared the same for a particular motor, but have different internal drive ratios, in theory they should be the same. But since they are two completely different cars, one belted the other shaft, you will feel and notice a difference in performance. As far as the internal drive ratio specifically has a performance advantage or disadvantage, keep in mind the tire/wheel rotation compared to the motor's rotation. If the SD car has a IDR of 2.353, that means that the wheels are turning 2.353 rotations for every one rotation at the motor.
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Old 12-02-2003, 07:29 PM   #3
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What if you compare the stock ratio pulleys and low ratio pulleys on the Xray T1, given that both of them are geared to have a final ratio of 8.0?
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Old 12-02-2003, 09:24 PM   #4
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Well with belted cars and their pulleys, the Xray's new low ratio pulleys freed the car up by not bending the belt at such a steep angle. Xray did this by making the center pulleys larger and the diff pulleys smaller. The car freed up so much, it improved the acceleration of the car.
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Old 12-02-2003, 09:36 PM   #5
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so mr. tan, what's this internal ratio thingy troubling you about?
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Old 12-02-2003, 09:45 PM   #6
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what if the drivetrains are the same, lets say both are shaft driven or both are standard dual belt designs, but still have different internal ratios, what advantage or disadvantage will one car have over the other? or is there even any difference?
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Old 12-03-2003, 07:49 AM   #7
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If two cars are geared overall the same but with different internal ratios normally the car with the with the higher internal ratio will accelerate faster and the other one will have more top end.

If all would be equal and you would race in a straight line one with the 2.35 internal would pull ahead in the beginning of the race and the car with the 1.77 internal would start catching up at the middle of the track. At the end of the drag and everything being the same they would cross the line at the same time, that is if everything could be made equal.

In my racing it always seems that the cars with higher reduction transmissions accelerate faster out of the corners (shaft or belt) and the cars with a lower internal ratios seem to come on strong in the mid to longer straights.
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Old 12-03-2003, 08:49 AM   #8
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i would have to respectfully disagree with wyd on this issue.

from a physics and theoretical standpoint, the lower ratio should increase overall accelleration based on the fact that the layshaft, in either case, will be rotating less due to the lower internal ratio to produce the same overal vehicle speed.

the importance here is that kinetic energy is a linear function of rotating mass, and a squared function of rotating speed. therefore, the intent with the lower ratio is to minimize the amount of kinetic energy required to accelerate the drivetrain to it's maximum speed.

another benefit of the lower ratio for belt cars comes with the increase in layshaft pulley size that is needed to acheive this lower ratio. this results in a more effecient drivetrain, since the belt won't have to form such a small radius through the wrapping of the layshaft pulley. additionally, the belt can be run even more loosely since it will have more teeth to contact it to prevent what is known as "ratcheting" or skipping of the belt under loads.

realistically, it may be insignificant, because the pulley mass increases due to its larger size, the spur usually needs to increase to get the external ratio high enough to maintain the same FDR.

there are always design compromises that will be made, but i do believe the intent of a low internal ratio is to gain a better spool up time through minimizing the KE required.
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Old 12-03-2003, 10:52 AM   #9
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I hope you didn't lose anyone with your explaination seaball. It's been awhile since I took physics and calculus in college. Back then I spelled physics with a "F".
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Old 12-03-2003, 12:35 PM   #10
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hey neil,

i hear ya. i certainly didn't mean to sit back here and print alot of stuff that sounds pretty for amusement.

the trouble with any type of internet sounding board is that anyone can sit there and utter an opinion, observance, or other subjective statement and call it a fact. sometimes it is, and other times it is not. facts to me, are backed either by empirical data, or scientific theories or laws. (that's why my posts are often, so long.)

while i certainly wish i had the skill to run right behind your man alex lopez this past weekend, i do not. so i can't, and wouldn't anyhow, say that i am right because i am fast. what i can do is say that i believe i am correct, and state what has led me to believe this.

i'm not much on blind faith.
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Old 12-03-2003, 02:11 PM   #11
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Seaball,

uuuh what you said...

My direct drive (int 1:1 int rat) Corally Assassin agrees with you...
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Old 12-03-2003, 03:35 PM   #12
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Quote:
Originally posted by Neil Rabara
If the SD car has a IDR of 2.353, that means that the wheels are turning 2.353 rotations for every one rotation at the motor.

thats not right. it takes 2.353 rotations of the spur gear for one full rotation of the wheels. and to further the equation. if you have a 87t spur and a 32t pinion it takes the motor 2.71875 times to rotate the spur once. and that gives you a final of 6.397. and that is how many times the motor spins for one full rotation of wheel spin.


or, it takes in a shaft car= 2.353 revolutions of the pinion for one full turn of the ring gear.(ring and pinion diff.)

Last edited by stumper; 12-03-2003 at 03:54 PM.
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Old 12-03-2003, 03:41 PM   #13
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If I'm correct the wheels have nothing to do with the internal drive ratio, hence the word internal. The internal drive ratio is just how many times the pinion turns to how many times the spur turns. The roll out ratio is how many times the pinion turns to how many times the wheel turns.
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Old 12-03-2003, 03:46 PM   #14
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nope, the internal has nothing to do with the spur and pinion. thats the spur/pinion ratio which is what you need to get your final drive raito.......

or another word for it is "gearbox" ratio. or trans mission ratio. its just the ratio before the motor.
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Old 12-03-2003, 03:49 PM   #15
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and to answer your other question. yes having a lower internal ratio does have an advantage........it give you more acceleration.
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