what is final drive ratio???

Final Drive Ratio (FDR) is a measurement that basically expresses the number of rotations your motor must make in order to rotate the wheels one complete time. To be more specific, FDR takes into account all of the gears between the motor and the wheel - from pinion gear tooth count, to spur gear tooth count, to the number of teeth in the transmission output gear or pulley, and finally the tooth count of the vehicles differentials. The formula for Final Drive Ratio (FDR) is as follows:

FDR = (P x I)

Where P = Primary Gear Ratio and
Where I = Internal Transmission Ratio

Gearing your car correctly (that is, selecting a pinion gear and a spur gear) is a basic way of tuning your car for the course, or to change how you want the car to react when you’re on the throttle. You can set up your gearing for torque to give you that punch coming out of a turn, or you can set it for horsepower for more speed. In RC drifting, your FDR will determine if you have tire burning low-end or high velocity top-end.

In order to set up your gearing, you need to figure out how to calculate it properly. Since different chassis have different spur gears, pinion gears, gear pitch, and internal ratios, the “Final Drive Ratio” is a standard number that is good for comparison. In other words, you can compare gearing between two different chassis by looking at the final drive ratio - even if they are different chassis brands, different gear pitch, different spur and/or pinion sizes, etc.

NOTE: you may hear the term “rollout” when comparing two differently-equipped vehicles. While rollout is better than just comparing FDR, rollout has to do with the distance traveled by the vehicles tires (overall tire diameter) - and racers use rollout to determine exactly how much distance their car will travel with one revolution of the motor. While this is useful in competitions where the distance travelled is important, in drifting, distance travelled isn’t important since, unlike racing, drifting isn’t generally “against the clock.” Also, final velocity (top speed) in drifting is not really related to tire diameter, but more by the momentum gained while running while on low-traction tires.

To determine FDR, first you need to find 2 things - Primary gear ratio and Internal gear ratio. You can find these two pieces of information easily; finding your primary gear ratio is a matter of noting the number of teeth on your pinion gear (attached to the motor) and the spur gear (the gear that the pinion touches in the transmission.) As for the internal ratio, some instruction manuals list the internal gear ratio for you (usually near the assembly step that involves mounting the pinion gear to your motor.) If there is no internal ratio specified, you’ll have to do a little work to find it out (see below.)

A. Primary Gear Ratio (Primary)
To calculate the primary gear ratio, divide the number of teeth on your spur gear by the number of teeth in your pinion gear.

Primary Ratio = spur / pinion

It does not matter if you are using 48-pitch, 64-pitch, or .04-module (metric), the ratio can be found regardless. For example, if yout pinion gear has 25-teeth and your spur gear has 75-teeth, then your primary ratio is spur/pinion, or in this example 75/25= a primary ratio of 3:1 (where it takes the pinion gear 3 revolutions to spin the spur gear one complete turn.)
B. Internal Gear Ratio (Internal)
If you can’t find the internal gear ratio for your chassis in the instruction manual, you can figure it out yourself by counting the number of teeth on certain parts of the chassis, as follows. You may have to disassemble the transmission or diff casing to find this information:

For belt-driven car:
To calculate your internal gear ratio on your belt driven car, divide the number of teeth on your differential pulley by the number of teeth on your center layshaft pulley (generally the pulleys that your drive belts are wrapped around, near the spur gear; just count the teeth on one of the pulleys.)

Internal (belt) = differential pulley/ center pulley

For shaft-driven car

To calculate your internal gear ratio on your shaft driven car, divide the number of teeth on your differential gear by the number of teeth on your driveshaft output gear (generally the gear at the end of the driveshaft.)

Internal (shaft) = differential gear/ shaft output gear

C. Final Drive Ratio (Final)
With both your Primary Gear Ratio and your Internal Gear Ratio, you can calculate your Final Drive Ratio. Just take your Primary gear Ratio and multiply it with your Internal Gear Ratio.

Final Drive Ratio = Primary x Internal

You will now have the final drive ratio for your current setup. Let’s use this in an example:

Your buddy’s Hot Bodies Cyclone is running a 27t motor, with a 100t spur gear and 29t pinion gear (64-pitch.) The Cyclone differential pulley has 39 teeth, and the center layshaft pulley has 18 teeth.

Primary: (spur / pinion) 100/ 29 = 3.44
Internal: (diff / center) 39 / 16 = 2.43
Hot Bodies Cyclone FINAL DRIVE RATIO: (primary x internal) 3.44 x 2.43 = 8.35

So with the pinion gear and spur gear shown above, the motor must turn the pinion gear 8.35 revolutions in order for the wheel to turn one full time; thus the final drive of your buddy’s Cyclone is 8.35:1 (8.35 pinion gear revolutions for every 1 revolution of the wheel/tire.)

Now say you drive a Yokomo MR4-TC SD, with a 27t motor also, but you currently have a 75t spur gear and a 20t pinion gear (48-pitch.) What pinion do you use to match up to your buddy’s Hot Bodies Cyclone setup?

The Yokomo MR4TC-SD differential gear has 40 teeth, and the input gear on the end of the center drive shaft has17 teeth. Let’s calculate:

Primary: (spur / pinion) 75 / 20 = 3.75
Internal: (diff / center) 40 / 17 = 2.35
Yokomo MR4TC-SD FINAL DRIVE RATIO: (primary x internal) 3.75 x 2.35 = 8.81

Close! But not quite. Now if you were to go up 1-tooth on the pinion to a 21t and recalculate, you’ll get this:

Primary: (spur / pinion) 75 / 21 = 3.57
Internal: (diff / center) 40 / 17 = 2.35
Yokomo MR4TC-SD FINAL DRIVE RATIO: (primary x internal) 3.57 x 2.35 = 8.38

You’re now at an FDR of 8.38, and your buddy is at a slightly lower FDR of 8.35. Sure they’re not identical, but close enough to feel similar on the track. By changing pinion or spur gear teeth #, you might be able to get the ratios even closer. Note that we compared two different vehicles - a belt drive vs. a shaft drive, 64-pitch gears vs. 48-pitch gears, and two different chassis brands. Yet by getting your final drive ratio as close as possible to that of your buddy’s, both vehicles should exhibit nearly identical acceleration, torque, and top speed. This shows that regardless of drive type or gear pitch, in the end it’s the Final Drive Ratio that matters.

So if you find that you need a little more top speed compared to the competition, or you need a little more torque down low to break the tires loose like the car you’re battling, matching up the final drive ratios (provided both of you are running similar motors) is a good place to start.

Some good info there, but I like sticking with the rollout calculater, I understand it better.

???whats that???

jeepers bedtime stories too,only roll out I know ,is roll out of bed in the morning,whats roll out dt or sam?

I am waiting for someone to tell me the same thing and to post info on it?
trying to find on the net...

dt_insane wrote:I am waiting for someone to tell me the same thing and to post info on it?
trying to fond on the net...

Did you not read the info you posted??????? It is outlined quick clearly although it doesn't give you the formula how to do it. Here let me help you with a paragraph from your post.lololol

""NOTE: you may hear the term “rollout” when comparing two differently-equipped vehicles. While rollout is better than just comparing FDR, rollout has to do with the distance traveled by the vehicles tires (overall tire diameter) - and racers use rollout to determine exactly how much distance their car will travel with one revolution of the motor. While this is useful in competitions where the distance travelled is important, in drifting, distance travelled isn’t important since, unlike racing, drifting isn’t generally “against the clock.” Also, final velocity (top speed) in drifting is not really related to tire diameter, but more by the momentum gained while running while on low-traction tires.""

It's a pleasure.

no i Know what it is am looking for the formula to work it out.
(next time i will however read what i post )
thanks though.

But it's nice to see everybody on an even playing field in this class, except for that hefty fine coming your way to keep the silence.lolol Nice chart, will print and put in toolbox.

I COULDNT RACE MY CAR is set up for drifting...

will have to buy new car in near future to race.
but want brushless and to race with big boys

is nice printed it last night on my board on wall above rc car table...

dt_insane wrote:I COULDNT RACE MY CAR is set up for drifting...

Why not, just a quick tyre change and voila.

dt_insane wrote:but want brushless and to race with big boys

Baby steps, baby steps young lad. Master what you have before taking the leap, it would be a sad day to see your fancy new chassis parked so far under a pipe that everythings broken inside because of inexperience, thats throwing money into the wind just for the thrill of it. If you've got plenty, there are some of us that are looking for donations.hinthint.

no the new car is for the drifting - going to up the pace a bit.

tt 01 for racing cant break them easily...

dt_insane wrote:tt 01 for racing cant break them easily...

Wanna bet???? Jittery nerves of an anticipated close race, a rival standing next to you on the stand, not to mention there are now 10 cars on track, not just you and a buddy anymore, oh yes, don't forget the 6 erratic driving innexperienced newbies you were squaded with just to throw an extra spanner in the works, and welcome to the big leagues, those diff covers snap for nothing, not to mention the driveshafts popping out after some serious impact, it happens.

its all good, drifting is safer

www.gearchart.com
if there is something you still dont understand, please feel free to ask. I got into this a bit late. For stock my guesss is a 44 rollout will work well and superstock about a 32 rollout should be a good starting point if you are farely smooth.
I could be wrong but should be able to held after the weekend. There were guys on50mm/rpm rollouts and they say it is the fastest way around. The proof is in the pudding