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Old 07-31-2008, 04:35 AM   #1
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Default Pinion Madness.....???

Can someone point me to a website or help me understand the gear ratio and pinion gear thing?

I'm not quite understanding what the different sizes are for and what they do, etc...
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Old 07-31-2008, 05:25 AM   #2
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Well, I know there are a lot of others who can articulate it better than I can, but I'll try and give you the basics as simply sounding as I can...
First, find out what your internal gear ratio is of your car. Every cars gearbox has a different size diff gear, idler gear, etc. and that adds up to an Internal Drive Ratio and from that you can find other things you need to know like FDR or Final Drive Ratio and Rollout. I wont even get in to rollout because it will confuse you, but the short explanation is it figures how far of a distance your call will travel on one full revolution of the wheels. It takes in to account pinion/spur size and tire diameter.
FDR will be what you'll need to find. Right HERE is a nice chart for Losi's that explains it pretty well. Every track or certain motor combos and whatnot have a good FDR starting point to begin gearing at. Check that link, then calculate what your FDR is and see where your at. ALSO, please give more info on your car and motor and everything and you will get some much more specific info to your car.
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Old 08-01-2008, 12:31 AM   #3
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Ok.. there was another thread that started to drift into this subject.. here is what I posted there (example was a TC5R).

Explaining gear ratios is easy...

To get what is called your Final Drive Ratio (FDR) you take the number of teeth on your spur gear stock is an 87T and divide by your pinion gear tooth.

Take this number and multiply by your internal drive ration (IDR) of 2.0:1 on a TC5R

Ok.. confused?

87T spur divided by 24T pinion = 3.625 x 2.0 IDR = 7.25 FDR

Thats the equation part... now comes the hard part...

You are going to need to do a lot of testing and talking to others at your track. There isn't a magic FDR for every motor and all tracks...

There are many factors to take into consideration.
  • Track size
  • Traction conditions
  • Tire selection
  • Weather/Ground Temp
  • Driving skill/style
Probably other things someone will remind us in following posts...

Try to find someone at your track first with the same type car and motor.. see what they are running.. If you find someone with the same motor and different car, get their gearing and car's IDR so you can do the math to figure their FDR.. then do some more math and figure what your spur/pinion combination equals their FDR.

It's a lot of work when you first start.. but if you truly want to understand what's going on.. it's worth it!

Remember, a change in tooth of the spur is less drastic than a pinion tooth change... buy a range of both so you have them!

Now your probably thinking.. ok I got the math.. what does it mean?


First off.. the Final Drive Ratio tells you how many times the motor has to spin to turn the axle once.

You need to do some research at the track.. you'll have to find the "sweet spot" in the power band for your motor/track/traction/driving.. The FDR gives you a number to compare to.

I wouldn't even worry about roll-out..


What kind of car and motor are you running?


Jerome
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Old 08-01-2008, 03:38 AM   #4
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Quote:
Originally Posted by JeromeK99 View Post
Ok.. there was another thread that started to drift into this subject.. here is what I posted there (example was a TC5R).

Explaining gear ratios is easy...

To get what is called your Final Drive Ratio (FDR) you take the number of teeth on your spur gear stock is an 87T and divide by your pinion gear tooth.

Take this number and multiply by your internal drive ration (IDR) of 2.0:1 on a TC5R

Ok.. confused?

87T spur divided by 24T pinion = 3.625 x 2.0 IDR = 7.25 FDR

Thats the equation part... now comes the hard part...

You are going to need to do a lot of testing and talking to others at your track. There isn't a magic FDR for every motor and all tracks...

There are many factors to take into consideration.
  • Track size
  • Traction conditions
  • Tire selection
  • Weather/Ground Temp
  • Driving skill/style
Probably other things someone will remind us in following posts...

Try to find someone at your track first with the same type car and motor.. see what they are running.. If you find someone with the same motor and different car, get their gearing and car's IDR so you can do the math to figure their FDR.. then do some more math and figure what your spur/pinion combination equals their FDR.

It's a lot of work when you first start.. but if you truly want to understand what's going on.. it's worth it!

Remember, a change in tooth of the spur is less drastic than a pinion tooth change... buy a range of both so you have them!

Now your probably thinking.. ok I got the math.. what does it mean?


First off.. the Final Drive Ratio tells you how many times the motor has to spin to turn the axle once.

You need to do some research at the track.. you'll have to find the "sweet spot" in the power band for your motor/track/traction/driving.. The FDR gives you a number to compare to.

I wouldn't even worry about roll-out..


What kind of car and motor are you running?


Jerome

Thanks Jerome...that was awesome!

I'm just running my stock Slash at the moment....
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Old 08-01-2008, 04:42 AM   #5
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The easiest way to determine what gear ratio you should start with would be to find someone at the track that has a similar setup and ask him/her what they are running in their car...

If not, just experiment. Start out at a low gear ratio (weird how "low" gear ratio means a higher number, i.e. 12:1 is a "lower" gear ratio then a 9:1 )

If you find yourself constantly topping out in speed (meaning, your car won't go any faster), you have too much acceleration, AND your motor is relatively cool (meaning it's hot but doesn't burn your fingers when you touch it after one battery pack), then you should up a tooth on the pinion. Always step up/down pinions with one to two teeth. One tooth or two teeth in pinion makes a DRASTIC difference in the way the power/speed feels on your car and the temperature of your motor...
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