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Old 02-21-2003, 03:26 PM   #1
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Default how the *%$& do you work out how a motor should be geared?????

ok... I will admit it... I am now TOTALLY confused after spending time reading these forums because from what I have read here EVERYONE in My local club gears too high

how the hell do you work out how a motor SHOULD be geared... and I don't want to hear things with vauge descriptions 'cause that doesn't help... I want facts and figures

I have a Tamiya TA04R... and I race Stock (ROAR rebuildable) and I want to know where is a good place to start gearing... I use either a Trinity P2K2 or a Corally Steetracer, though I MIGHT try and get an Orion Core Stock as they seem to be doing good things here for other drivers... foam tires are the order of the day

the track is medium grip and fairly smooth asphalt, and is fairly open with one good straight of about 25 meters (62 feet) with fast full throttle sweepers at both ends... the infield has some twisty sections with no real straights, 12-15 feet being about the longest, but because the track is pretty wide only one or two corners would be consider really slow

I want to know what sort of gearing I should start with? any help is going to be greatly appreciated

but remeber I need facts and figures to start with... not vague recommendations.... and I also don't want or need people telling Me I need to buy brand X motors or a brand Y chassis....

I am sure all you experienced racers out there can manage that
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Old 02-21-2003, 03:36 PM   #2
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all anyone on here can do is give you a suggestion.....unless someone runs at your track with the car and motor you need help with all info will be a suggestion. I don't run your brand of car so I can't offer you a gearing suggestion.
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Old 02-21-2003, 03:43 PM   #3
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Quote:
Originally posted by STLNLST
all anyone on here can do is give you a suggestion.....unless someone runs at your track with the car and motor you need help with all info will be a suggestion. I don't run your brand of car so I can't offer you a gearing suggestion.
thats fine... as long as those suggestions have some figures in them that I can make sense of... I am very much a facts and figures type of person and I need them to make sense of what people say
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Old 02-21-2003, 03:45 PM   #4
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This is probably not what you want to hear but without specific experience with your chassis and your motor at your track it's the best that can be said.

Gear your motor so the motor reaches top speed at the end of the longest straight. Adjust from there.
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Old 02-21-2003, 03:53 PM   #5
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Just guessing here, but I'd start out with a 120/36 on a track of your description. 2.13 internal reduction puts you at 7.1 final drive which is a little high for a P2K2, but you're on a pretty short track.
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Old 02-21-2003, 04:04 PM   #6
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There are no specific formulas for gearing, it's all trial and error. You're going to wait a lifetime if you think you're going to get a magic formula that works for every possible condition.

All motors will be different and will need different gearing. Even two of the same brand could potentially have different gearing.

Batteries will effect gearing.

Your driving style will effect gearing.

How tight the track is will effect gearing. You can describe it all you want. People can only give a ruff idea if they don't run on your track.

If you want to be a fast you need to put in the time and practice. Experiment with different gearing and set-ups. There are no secret set-ups that will guarantee you a win.
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Old 02-21-2003, 05:24 PM   #7
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Shadow,

There are some options to find you a BASIC STARTING point but they are not very good.

Find a racer at your track is fast and find out their pinion and gear ratio, their car type, wheel diameter and use all of this to find out the roll-out. Use this information and work backwards to find out your pinion/spur ratio. This will give you a STARTING POINT ONLY, the actually gearing of your car will need to be higher or lower based on the RPM and Torque of your motor compared to the fastest racer's motor.

For an accurate method get access to a dyno and gather the RPM and Torque numbers from both motors but be sure to target the same load (the current draw). With this information you can adjust the gearing based on the motor quality. To do this take the RPM number for the two motors at the same load, find the ratio and then multiply this by the pinion of the good motor to find the pinion for your motor.
Ex:
- Good Motor RPM 20,000 @ 20 Amps
- Your Motor RPM 22,000 @20 Amps
- Ratio is 20,000/22,000 = 0.91
- Take good motor pinion and multiply by 0.91 to get your motor pinion.

This method will match your motor's performance to that of the good motor but you could still have lower performance if the good motor has more power (RPMxTorque) then your motor, in this case you would then have to apply Big Jim's tuning to your motor.

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Old 02-21-2003, 05:56 PM   #8
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try a roll out of anywhere between 28 and 34mm. or the best way is to get the motor to peak near the end of the straight and adjust depending on how hot the motor is or if you need more punch in the corners etc.
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Old 02-21-2003, 06:10 PM   #9
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You could install an AMB transponder and check out laptimes The track dyno never lies and the computer usually backs that up!
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Old 02-22-2003, 02:05 AM   #10
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Quote:
Originally posted by rtypec
You could install an AMB transponder and check out laptimes The track dyno never lies and the computer usually backs that up!
Bit hard to do on a car park track that is only set up once a month... but I can understand the point

Hey Mal... I've been racing close to 8 years so I am no beginner here... I've raced outdoors,indoors, oval, pro-10, nitro-tourers, circuit cars and probably some I've probably forgotten about right now....

I've just read so many DIFFERENT posts from people talking about all sorts of different way of getting the best from a motor that I find it a little "hard" to beleive that so many different ways can exist to acheive the same thing... thats what I find confusing... espically as I've seen some pretty wild gearing locally recently... I posted My car and track info so people that post can perhaps focus their posts... I was hoping people might supply similar information BACK so I can do a little mental comparing

what I am trying to do is find out if there is some sort of concenus or basic theory that can be applied... more as a intellectual exercise then anything to actually apply to My day to day racing... I have my own theories I am just interested in other peoples
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Old 02-22-2003, 02:19 AM   #11
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Quote:
Originally posted by ruf
Just guessing here, but I'd start out with a 120/36 on a track of your description. 2.13 internal reduction puts you at 7.1 final drive which is a little high for a P2K2, but you're on a pretty short track.
I am running 112/45 currently, but mind you My tires are down to about 60mm diameter, which gives a final drive of 5.31 and a rollout of about 35.5
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Old 02-22-2003, 02:35 AM   #12
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I've seen P2K2's geared as low as 4.6 so it all depends on how fast you want to go and how long you want the motor to last. P2K2's can be geared low but don't try to do the same with the Monsters or you will end up with cooked motors.
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Old 02-22-2003, 08:33 AM   #13
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well not all motors are made the same, so they tend to vary on the gearing.

I used a plot based on real numbers and came out with this chart,

http://www.schumacher.clara.net/setupguidegearing.htm

its based on the MR4TC but shoudl be ok for most other cars as the overall drive ratio is given.

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Old 02-22-2003, 11:18 AM   #14
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You HAVE to come up with your gearing based on lap times. Nothing else matters.

You can try copying a good driver, but if you are not of equal skill that gearing probably won't work quite right, your car will probably be slower and your motor will probably be too warm by the end of the run. A good driver/car setup combo will carry lots of cornerspeed and can handle higher gearing as a result. A lesser driver or car setup won't have the same cornerspeed and will probably have better results geared a bit lower.

If you have a reference motor that gives good lap times, you can figure where to gear the other motor based on the gearing and RPM as tvromero mentioned.

There is NO formula for determining gearing. Every track is different, every car is different, every driver is different.
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Old 02-22-2003, 02:47 PM   #15
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Me thinks Me made a mistake posting something like this

I am certain people don't always read the first post on these threads on its merits... they read the subject and then skim through the rest and then they write what they THINK the subject is about... of course always making the assumption that the person who first posted the subject knows nothing about the subject they are asking about, or some inexperienced newbie who needs to be told the facts of life

Some people have tried to get into the spirit of what I intended and that has been interesting to read

The point of this subject was for people to post their ideas on how THEY, not Me, would gear a car based on the track information that I first provided because EVERYONE has to START somewhere... ok its not the same as seeing it, but at least you have SOME idea of what the car has to do... its not like you have weeks of track time to get it right or access to 20 different motors and a dyno....

What gearing would YOU put on YOUR car for that first ever run on the track and how do you arrive at it?

I am talking about how YOU would gear a car if YOU went to a track like that for say a titles meet where you maybe have a days worth of practice maximum....

I know I didn't supply that exact information at the start and maybe I should've
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