13-Turn Motor - Gearing

[GuyIsDamGood]

I have a 13-Turn Reedy Ti Worlds Edition Motor.

In a 1/10 Touring Car; would a 25-Pinion and a 55-Spur be Too Much for the 13-Turn Motor?

The Track has alot of Long Straights.

I know some of you guys know the Facts about this Motor - Gearing stuff.

Thanks

Take Care.

[highroller]

Gearing is going to be a trail and error method. Even when racing with other guys using the same vehicle and motor my final gearing may vary by 1-2 teeth. Best method I can give is to check the Associated site to see what kind of gear ratio they recommend for the type of vehicle that is similar to the one you have. Either figure your vehicles transmissions ratio to get the final drive ratio they suggest with a motor 13 turn motor. Even then your final gear ratio can vary. There is also a area that explains figuring the vehicles transmission ratio to get the final drive ratio, rollout is generally used with direct drive vehicles or with vehicles using foam tires.

My problem with suggesting gear ratios is that there are too many varibles involved even when vehicles and motors are the exact same type. Vehicles may have been assembled differently, even though I have a 13 turn Ti it may have a different setup (more timing, different brush and spring) that if I put in your vehicle would require a different pinion size to get the same results. Didn't you mean a 75 tooth spur. For TC I prefer the 64 pitch gears with a 95-115 spur range and pinions in a variety of sizes 19-48 teeth while 48pitch has a varitey as well pinions 14-39 spurs 72-90. Finding the numeric gear ratio is key then using a spur of the correct size can also help fine tune motors power to track conditions.

[highroller]

Associated's suggested gearing (final drive ratio) may not be 100% accurate since they maybe using the power of the older Rage versions or a KR based 13 turn. Since the Ti develops a different power band it would need to be geared lower (smaller pinion) than a KR based motor.

[GuyIsDamGood]

Thanks highroller.

I have the 13-Turn Reedy Ti Worlds Edition Motor in a Tamiya TT-01.
I can set-up the Gearing in a few ways:
19-Pinion - 61-Spur
22-Pinion - 58-Spur
25-Pinion - 55-Spur
-Those are the Only Gears it can take.

They say the Fastest Gearing Set-Up would be the 25-Pinion - 55-Spur.
-I thought/think the 25-Pinion - 55-Spur would/will be Too Much for the 13-Turn Motor.

I`m using the 19-Pinion and 61-Spur to Play it Safe for the motor.

But if anyone can help me on this Gearing Stuff; it would be cool.

Thanks

Take Care.

[highroller]

I think they have the gearing wrong, normally you find the numeric ratio that works for a particular motor and run that. So whatever the nummeric ratio is what using a larger spur (61) you use a larger pinion, when using a smaller spur (55) the pinion should be smaller than the one used with the 61 spur.

For the TC3 Assocated suggests a Final Drive (transmission ratio x spur/pinion) 7.83 (72 spur x 23 pinion) transmission ratio is 2.5:1. According to Tamiya's site the TT01 stock gearing is a 8:35:1 (whatever the supplied spur and pinion size is).

[cmdj_chris]

After painstakingly scouring the web and my local racers, this is what I have come up with:

Every single car whether it be nitro or electric is going to have a different drivetrain ratio. Drivetrain Ratio (DTR) is a value concerning the the model's transmission. Your owners manual should have this information. The DTR in most cases can't be changed. Some model's, such as the X-Ray, offer a kit that changes the DTR. The ratio between the pinion and spur gear is the Primary Drive Ratio (PDR). Spur/pinion=PDR.

The next step in this process is to determine the Final Drive Ratio (FDR).
PDR*DTR=FDR. Why is this number important? The FDR is used to figure rollout. Rollout is the magic number. When you go to the local track, ask around about each driver's rollout. If they don't know what it is, move on quickly. Once you find a driver in the class you want to race in that tells you his rollout, you will then be able to match your rollout to his as closely as possible. Then the only factors that will affect your laptimes are driver skill and power output of the motor. What is rollout? Rollout is the distance the car will travel in one revolution of the motor shaft. Take a shaft car and a belt car with the same exact motor and same exact rollout, and they will have the same exact speed. The higher the rollout number is, the slower you will be off the line (less accelleration) and the faster the top speed will be.

Tire Diameter*3.14=tire circumference.
tire circumference/FDR=Rollout

These equations can be used in an Excel spreadsheet. I set up mine so all I enter is the pinion and spur gear value and excel does the rest. If you race at a track that can give you laptimes, you can also figure out your speed in MPH (if you know the running track length).

It seems like a lot of confusing numbers and equations, but when you can assign a number to how your car acts on the track, all you have to do is a little simple math to figure out what pinion and spur combination will give you the best lap times.

[GuyIsDamGood]

Thanks again guys.

I`ve called Tamiya and they told me to use the Stock Gearing-(19-Pinion and 61-Spur).
They said the Higher Speed Gears(22 or 25-Pinion and 58 or 55-Spur) will/would be Too Much for the 13-Turn Reedy Motor.

Take Care.

[yellow15]

a shamless plug.. if you guys have problem calculating your final drive/pinion gear, there is a free software that can do all this here:
http://www.dwork.co.nz/rcalculator/

very good software :D

[highroller]

For transmission vehicles using rubber tires you generally use final drive to determine the pinion size (transmission ratio x spur divided by pinion) rollout is generally used in Pan Car or where foam tires are used. That uses a equation to calculate changes in tire size to obtain a consistant rollout as tire size changes transmission gear x tire diameter x Pi (3.14) x spur divided by pinion.

You can also determine the transmission ratio by using the supplied kit spur and pinionand the manufacturers final drive ratio of 8.35:1.
8>35 divided by 61 (stock spur) x 19 (stock pinion) = 2.60 (vehicles transmission ratio. To see how close of what pinion you will need based on Associated's 7.83 suggested ratio (using a TC3 with 13 turn motor). 7.83 divided by 2.60 (your vehicles transmission ratio) x 61 (spur) = 18.37 18 pinion. Even the manufactuers' suggested ratios may not be ideal, you may still need a 1-3 tooth spread in each direction to find a good point.

[cmdj_chris]

Using final drive ratio was the one point I was having a problem with. I ran a stock class with motor handout and I had the same car as another guy. But he had foam tires and I had rubber. He told me what his gearing was and I matched it, but he was always faster. Rollout is the one value that is constant. If car A has foam tires and car B has rubber, and one is shaft and one is belt driven, if both cars have the same rollout and the same powerplant, they have the same (theoretical) top speed, accel, etc. Figuring the rollout takes all of 2 seconds to do if you know the FDR. I have heard for years the the FDR is the number to know. If you know what the competition has for a FDR then all you have to do is match it. Not so. You have to account for the tires, both rubber and foam.