Gearing down with drivers?
- Thread starter ullose272
- Start date
If the 8's are a 2.86 pitch and the 7's a 3" pitch, then its about 8%.
3" pitch drivers/tracks have 3" between teeth/window centers.... 2.86" pitch drivers/tracks have 2.86" between teeth/window centers.
A 3" driver will be larger in diameter than the same tooth count driver in a 2.86" pitch.
7 tooth 3" pitch driver = 6.68" dia
7 tooth 2.86" pitch driver = 6.37" dia
8 tooth 2.86" pitch driver = 7.28" dia
8 tooth 3" pitch driver = 7.64" dia
You will be under-driving your track by a factor of .92 when you run 7 tooth 3" compared to 8 tooth 2.86" pitch.
You will be over-driving your track by a factor of 1.05 when you run 8 tooth 3" compared to 8 tooth 2.86" pitch.
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A 3" driver will be larger in diameter than the same tooth count driver in a 2.86" pitch.
7 tooth 3" pitch driver = 6.68" dia
7 tooth 2.86" pitch driver = 6.37" dia
8 tooth 2.86" pitch driver = 7.28" dia
8 tooth 3" pitch driver = 7.64" dia
You will be under-driving your track by a factor of .92 when you run 7 tooth 3" compared to 8 tooth 2.86" pitch.
You will be over-driving your track by a factor of 1.05 when you run 8 tooth 3" compared to 8 tooth 2.86" pitch.
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B
Bowfisher
Well-known member
Good point. I didn't consider somebody changing the pitch.
And back in the day when everyone had to pay attention when they programed their Avengers or Digitrons, they had to know the circumference of their drivers too.
I remember going from stock gearing 20/39(I think) to 19/43 and then going from 9tooth 2.52 pitch drivers up the big 10t drivers.
There is a FANTASTIC gearing ratio spreadsheet that I've saved and reposted many times over they years.
You can mess with the variables in it...gear sizes, driver size and pitch...and it always tells you your final gear ratio and full shift out track speed.
I'll see if I can upload it on this newer forum software.
OK taking these no's, if ya go from 8 Tooth 2.86" P to 7 Tooth 3" P starting with 2.10 gearing ya end up with 2.273 gearing correct??
FYI I really like 2.25:1 gearing that my TKI belt drive kit gave me. Also tried 2.42:1 but it felt slow. May of needed more clutch weight? I would think this is a better way to go than changing the drivers as changing drivers changes attack angle and for all the work, you gain no improved reliability with a driver change.
I have Toms belt drive 30--63 pulleys works very nice...but I put a 3" track with 7 tooth 3" pitch drives, just cking on actual gearing ....thks
Oh come on some one is surely able to answer my ? You guys are all math people right?
Yes that is correct. 7 tooth 3 pitch vs. 8 tooth 2.86 pitch driver lowers your effective final drive ratio by 8.2 percent.
2.1 x 1.082 = 2.272
Wondering where is my math wrong??
I come up with a correction factor of .92 (1/x = 1.08695 ≈ 1.087 {8.7%} )
Where 6.68"/7.28≈.92
I've been wrong many times... so this is a sincere inquiry.
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I come up with a correction factor of .92 (1/x = 1.08695 ≈ 1.087 {8.7%} )
Where 6.68"/7.28≈.92
I've been wrong many times... so this is a sincere inquiry.
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***Note forgive my ramblings, I set out to prove who was right and who was wrong, and the truth is neither one of you is wrong, just one of you mis applied which way the conversion was going. Read on***
Diameter does not have an effect in MPH or gear ratio equations. For that is based off of the circumference (the distance around the circle that the track must follow) which is actually easier to calculate (Pitch Distance times Tooth count equals circumference at the pitch diameter of the track).
Diameter's relevance comes into effect figuring tunnel clearance and other things.
One could argue that since they are related by a constant (Pi) that you could throw out the constant and use the diameter the same way. I don't claim to be a mathematician and as such that may well be possible. I've never tried that theorem and followed it thru to prove or disprove it (Update, Yes I did, and it works). I tend to stick with the simpler formulas that have worked for me for years.
Long explanation but when I actually worked it out you are both correct in your own right one just mis-applied the last equation. See below.
8 Tooth x 2.86" Pitch = 22.88" circumference
7 Tooth x 3" Pitch = 21" circumference
If going from a 8 Tooth x 2.86" Pitch to a 7 Tooth x 3" Pitch multiply your current gear ratio by 1.09 as illustrated below;
22.88 / 21 = 1.08952381~1.09
If you were going from the 7 Tooth x 3" to the 8 Tooth x 2.86", then multiply by the 0.92 as shown below;
21 / 22.88 = 0.91783217~0.92
If you are calc'ing MPH difference the opposite or inverse correction factor applies.
These numbers are actual, if you based it on actual driver diameter then you will have some variation as the driver outside diameter is smaller than the actual pitch line of the track.
Hope I clarified that, rather than adding further confusion.
So I've been bouncing this around in my head for a bit and got to thinking...
Given the same final drive ratio, would larger drivers be more efficient? What I mean is if you were to put 7 tooth 2.86 drivers on your sled to gear it down versus keeping your 8 tooth 2.86 drivers and changing your gears to achieve the exact same final drive ratio. (Don't know if that's actually possible to get it exactly the same, but for the sake of this discussion, let's say it is) In the case of the larger drivers, you aren't having to bend the track in as tight of an arc going around the driveshaft, which would reduce resistance, right? Or am I mistaken?
Given the same final drive ratio, would larger drivers be more efficient? What I mean is if you were to put 7 tooth 2.86 drivers on your sled to gear it down versus keeping your 8 tooth 2.86 drivers and changing your gears to achieve the exact same final drive ratio. (Don't know if that's actually possible to get it exactly the same, but for the sake of this discussion, let's say it is) In the case of the larger drivers, you aren't having to bend the track in as tight of an arc going around the driveshaft, which would reduce resistance, right? Or am I mistaken?
I guess, if someone had a belt drive from the factory that does not have different ratios available... then Maybe they would use a 7 tooth driver...but I've yet to see that.
The ONLY reason to change to smaller drivers with a chaicase PRO RMK would be to accommodate a taller paddle track... Gears are the way to go (sometimes a new chain is needed)
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The ONLY reason to change to smaller drivers with a chaicase PRO RMK would be to accommodate a taller paddle track... Gears are the way to go (sometimes a new chain is needed)
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Assuming clearance is available or can be made, The larger driver will be a more efficient, better choice. That is the direction I have gone with all my builds. I had to have custom drivers machined (I went to a 9 Tooth drivers) as well as custom sprockets for the belt drive.
The majority of people are dropping to the 7 Tooth solely based on cost and convenience. There is no way in HE!! it is remotely efficient, much less more efficient.
I.E. Doing the 7 Tooth driver equals no drop and roll, press the tiny driver on the shaft and install the track, and done.
Whereas the 8 tooth requires a drop and rolled chain case or bearing plate, typically ~8.5 " center to center or ~1" longer than stock.
My 9 Tooth setup requires a slightly longer drop and roll (9") as well as a slight tunnel raise (the coolers are raised about 3/4" to eliminate the snow choke point in the front).
At least that is my thought and the laws of physics would tend to back my design up. Some will argue with me but I don't really care, the money is spent and the builds will proceed. All told, I'm easily $1000 more than the 8 Tooth D&R and about $2000 more than the 7 Tooth option. Just in getting parts CNC'd, time not included.
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