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Old 09-10-2003, 07:16 AM   #1
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Default gearing confusion

Hello everyone,

i am very confused now how to get the best gear ratio for my FT TC3, in fact i am now very confused how gear ratios works.

a) does anyone know of a site that i can go to to explain to me how gear ratios work.

Tonight i got very confused when someone told me that by using a small diameter tyre, and using higher gearing is faster then say using a larger diameter tyre and a lower gearing, but both will give me the same roll out, WHY IS THIS?

How do i know what the best ratio is to getting my motor to peak at it highest rpm in the shortest time down a straight.

If you can explain or pm me with a link to a rc site that better explain it i would be very happy. help me guys

regards BRAD P
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Old 09-10-2003, 08:08 AM   #2
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Thumbs up Gear Ratios

Checkout this site:

http://www.arroyoc.com/index.cfm?fus...utilities.gear


Just scroll down to the bottom.

Later,
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Old 09-10-2003, 08:46 AM   #3
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Roll-out- how far the vehicle will actually move with 1 revolution of the motor. This does not take into account free rolling. SO....

A larger tire will have a larger circumfrence, which means 1 revolution will carry the vehicle farther, so we gear up (smaller pinion) to achieve the same roll-out.

A smaller tire will have a smaller circumfrence, which means 1 revolution will carry the vehicle a shorter distance, so we gear down (bigger pinion) to achieve the same roll-out.

Also remember roll-out is only a good starting place. different equiptment such as motors, batteries, and even speedos (to some extent) can have an impact of gearing. So when you come across a new track layout what you wanna do is ask someone who is fast for their roll-out. from there you gear the car and go thru your normal "feel-out" to get the best ratio for your application. Usually you will be within a tooth or 2 once you use their roll-out.

Roll-out is much more important for foam tire racing, with rubber tire racing you can just assume your tires are within 1-2mm in heigth.... so gear ratio is all you need..... It helps alot to mentally or physically log the internal gear ratio of most of the popular car so all you really have to ask for is their pinion/spur which people are more apt to remember on the fly.....

As to why a small tire/big pinion would be faster this would only be true on a tighter tract where the reduced rotating weight would help with acceleration. However on a larger flowing track where you don't brake much a bigger tire/smaller pinion would help you carry more speed which would be more of an advantage........

Hope I didn't further confuse you!!!
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Old 09-10-2003, 03:30 PM   #4
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And I believe the reason you were told that a smaller diameter tire would help is because a smaller diameter wheel & tire can also have lower rolling resistance(& possibly less rotating mass), so the car should accelerate better, even with the same rollout as before.....
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Old 09-12-2003, 05:15 PM   #5
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Default MORE INFO

Hi guy anymore infor would be great, i would more like and article or web site i can read alot more about gearing, i am looking for more technical information

regards brad.p
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Old 09-17-2003, 02:53 PM   #6
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is there some sort of "magic number" i am trying to achieve when it comes to gearing? is it different by mod or stock motors, or by car, or? ? ? ? ? ? ?
i'm trying to get more torque out of my Evo 3 SL. i am running a 33 tooth pinion and a 90 tooth spur gear
thanks for the help
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Old 09-17-2003, 03:44 PM   #7
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hierog,

Unfortunately, there is no "magic" number. It can only be measured on the track by way of laptimes, and battery runtime. Gearing the motor higher to run faster doesn't necessarily guarantee that you car will be faster all the way around the track If you overgear, the car may be sluggish out the turns, hurting your overall laptimes.

If you're looking for more torque, then going down to the next lowest ratio would be the logical choice to make. You will get a little more torque, but the bottom line is, are you faster around the track? If not, then you need to go back to the gear you last used. If you are, then you might want to try going a bit lower to see if you can go faster still. The goal is to find the gear combination that will give you the fastest lap times, assuming that your suspension setup is optimal (but that's another story).
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Old 09-17-2003, 10:54 PM   #8
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so, should I change one thing at a time, meaning change the pinion number and keep the same spur gear number, and then vice versa? or should i change them at the same time? the way i'm looking at it is like a bicycle, the larger the gears, the harder it is to get going at first but the top speed is always faster then if you were running on the "little" sprockets. am i on the right track? there are so many combinations, it just seems like there ought to be some starting point as to what combination to start with!! aaarrrggghhh!!
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Old 09-18-2003, 06:54 AM   #9
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I know it is extremely confusing The best thing to do in my opinion is change one thing at a time. Change the pinion one round then the spur gear etc... Trying to keep the same gear ratio and rollout. Then check your lap times and see which combination is faster or if they are almost the same.

Later,
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Old 09-18-2003, 09:04 AM   #10
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The most important thing to bear in mind when finding a suitable ratio is 'how hot is my motor?' after a SHORT run. If you use completely the wrong ratio, you could damage not only your motor and ESC but potentially even your cells by the end of a 5 minute race. There is even a potential risk of fire! So you'll need to get it in the ball park BEFORE you hit the track in competition. If you're not using foams, don't concern yourself about roll-out. Sort out what motor you'll be using and whether or not you'll be racing indoors or out. The TC3 has an internal ratio of 1:2.5, so whatever ratio you have between your chosen motor pinion and spur will have to be multiplied by 2.5. eg 72 tooth spur divided by 32 tooth pinion = a ratio of 2.25. 2.25 x 2.5 = 1:5.625 overall. In other words, your motor will rotate 5.625 times to turn your wheels once. You manual will have a chart of recommended pinion sizes for different wind motors - read this!! AE tend to recommend ratios that are slightly on the high side, so start a tooth or 2 lower than they recommend and work your way up. Bear in mind that if you are racing on very tight circuits or indoors, you maybe running up to 5 or 6 teeth lower than recommended Why? Because you are never fully unwinding the power available in the motor - your gearing to the track, not to obtain the most speed or use the available 'juice left in the cells'. Once you are certain you are not cooking your motor by all means check your consistent laptimes only (discount crashed laps etc) to determine whether your revised gearing is making the car quicker on the track or not - this is the only true guide, as everyone drives differently. DON'T copy different manufacturers ratio's. DON'T copy the fastest guy's gearing, cos you'll almost certainly overheat your car if you do! Copy his lines first Then attempt to match his times Experience on the track will teach you ALL you need to know about getting your car geared right. Good Luck!
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Old 09-18-2003, 11:44 AM   #11
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okay, i'll start with that. thanks for all the information. my manual does have a short list of pinion and spur gear combinations, i just need to figure out what the internal ratio of the car is (i can't find it in the book)
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Old 09-18-2003, 12:00 PM   #12
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As I said, the internal ratio of your TC3 is 1:2.5. Coount the the teeth on your diff ring gears (40) and also the teeth on your drive pinion at either end of your drive shaft (16) - 40 divided by 16 = 2.5

Hope this helps
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Old 09-18-2003, 01:51 PM   #13
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One more thing! If you think about your bike, you're on the right track. Your legs are like the motor turning the pinion and the gears on the hub of the bike are like the spur gear. Only thing is, to change gears on the TC3 you generally only need to change the pinion. The 72 tooth spur stays put - you don't really need to change this unless it breaks!! Just by changing the pinion between 19teeth - 32teeth, you can find overall ratios between 1:9.47 (lowest ratio for low wind modifeds/tight circuits) - 1:5.63 (highest ratio for stock motors/wide open circuits). Just by going up or down by 1 tooth on the pinion makes quite a significant change to the ratio - have a play around with a calculator. Much finer changes can be made by changing the spur - going up or down 1 or 2 teeth on the spur has a much smaller effect than changing the pinion. AGAIN, check it out with the calculator and you'll see exactly what I mean. Once you've grasped this, you'll never look back
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Old 09-18-2003, 03:12 PM   #14
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i think you mean Evo 3, but I get the idea. My transmission is 2.6 so I can fool around with the calculations (pinion, spur gear, trans ration). thanks again for the help
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Old 09-19-2003, 08:01 AM   #15
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I kinda mixed you up with Ohbrad - apologies On your Evo 3, 1:2.6 makes it slightly lower geared than a TC3 so adjust the examples I gave accordingly - sorry to add to the confusion! Evo 3 is a nice car - good indoors, they certainly 'nerf' well!
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