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Discussion Starter #1
Heres What weve got. I went to Sprocket specialties which is a sponsor for this site and did some math. I found the KFX gear ratios off a dirt bike site. This is assuming the dirt bike has the same ratio and Im not 100 percent certain. After doing the math I must say this calculator is damn close.

http://www.sprocketspecialists.com/SprocketOptimizer2.aspx

In order to use it right, you need the right numbers and here they are.

Front Sprocket Teeth : 14
Rear Sprocket Teeth: 38
chain pitch: 520
Front to rear axle distance: doesnt matter but it had 24.8 already in it.

Advanced info:
Engine minimum RPM: 2000
Engine Max RPM: 10300
Max Power RPM: 8700 (I got all this info off the dyno graphs)
Wheel rim size: 9
Tire Width Inches: 10 (guessing)
Tire Depth Percent: 27 ( I guessed cause I was tired of calculating)
Primary Drive ratio: 2.727
1st Gear Ratio: 1.750
2nd: Gear Ratio: 1.412
3rd Gear ratio: 1.188
4th Gear Ratio: 1.0
5th Gear Ratio: .875

Enter all this info and you will get the top speed I got when I used the GPS. Now go and change the Front Sprocket teeth to 15 and you get 73 which is what I got today on my GPS. So I hope this is close.


Heres what I came up with using there calculator for those of you who dont want to bother.

Remember, the stock gearing ratios are 14 front and 38 rear. A moose racing 15 tooth front sprocket for a KX450F was used on some of the tests.

With a 14 tooth front and 38 rear its 69.8 MPH (proven by GPS)
With 15 tooth front and 38 rear its 73.4 MPH(proven by GPS)

With a 16 tooth front sprocket(which I do not recommend by any means) and 38 rear is 78MPH
With a 14 tooth front sprocket and 37 rear its 70MPH
with a 14 front and 36 rear its saying 72MPH
with a 14 front and 35 rear its saying 74MPH
with a 14 front and 34 rear its saying 77 MPH
With a 14 front sprocket and 33 rear its saying 79MPH
With a 14 front 32 rear its saying 81 MPH

Now the KFX has a link so I guess you can cut it down.
I suggest keeping the stock front 14 for clearance reasons and downsizing the rear one.
Other than that I still dont have anyone to make the sprocket but I measured the center to center on the holes for the sprocket bub the best I could. I got 3 and 9/16ths of an inch and 3 and 5/8 at the most. I wasnt using the best equipment but tomarrow i will.

Ill let you all know tomarrow where I get my new sprockets and how much they are.

Jeff
 

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Discussion Starter #4
I tried to use that and I cant seem to get it to work right. What is the transmission reduction ratio?

Jeff
 

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I was screwing around and with 22 front and 22 rear and I got 186 mph for top speed. wow and with 14/22 it was 118 mph. thats crazy fast.
 

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Discussion Starter #8
Thanks man,

I talked to sprocket specialists and I am sending in my rear sprocket monday since the measurments I gave them dont match any sprocket they ever made. So next week they are assigning the rear sprocket on the KFX450R a number so if you want you can call them and order one but it wont be till the end of next week.

I will be ordering a 34 so I can do at least 77 MPH and with my 15 front in case, I can do 79 tops. Price is kinda around 50 buck or more and then 12 on top of that for hardened aluminum. Make sure you order the hardened its 12 more I think.

Ill let you know

Jeff
 

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QUOTE (PCMamerica @ Apr 13 2007, 07:59 PM) index.php?act=findpost&pid=1139
Thanks man,

I talked to sprocket specialists and I am sending in my rear sprocket monday since the measurments I gave them dont match any sprocket they ever made. So next week they are assigning the rear sprocket on the KFX450R a number so if you want you can call them and order one but it wont be till the end of next week.

I will be ordering a 34 so I can do at least 77 MPH and with my 15 front in case, I can do 79 tops. Price is kinda around 50 buck or more and then 12 on top of that for hardened aluminum. Make sure you order the hardened its 12 more I think.

Ill let you know

Jeff
I might just set aside a chain and sprockets specifically for the dunes. I hate to mix match sprockets with different wear. You guys were thinking we'll have to chop out a link or two anyway.

I'd be willing to paypal you money for a 34 tooth sprocket same as yours if your into it. I gotta have one.
 

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Discussion Starter #10
I dont know how a 34 will do in the woods but definitely good for dunes. With my front 15 its kind of perfect and has just enogh power to keep it going thu the tight stuff but its muddy and wet so idk yet.

I will order a 34 next week and let you know the power outcome. We will have to take a link out for sure. Worst case senario is that it just doesnt have enough power to take off well in first. Well see. Id hate for you to wast your money on something that might not work.

Im willing to spend my money on this stuff anf figure out how well it works. If you really wanted I could grab you a 34 and have them make 2. I just cant guarantee you will have the power to take off good. Ill post monday what the exact price is.

I do accept paypal if you wanted to. I actually own an internet business. I still have to see is they can make a 34. The person there said it might be possible to go to a 34 or 33 but not 100 percent if they can. Definitely a 35 they said. In order to know for sure they have to have it in there hands.

Ill let you know what they say.

Jeff
 

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You need to understand gear ratios. Not just sprocket sizes, but actual gear ratios, and what they do, how it affects power, etc.

QUOTE (NormalZ @ Apr 3 2007, 12:37 AM) index.php?act=findpost&pid=592412
Gear ratios aren't too difficult, once you figure out the "final drive ratio." Most of us on bikes and quads don't even know what "final drive ratio" means. Think about trucks, Jeeps, etc.

You'll hear Jeepers talking about gears, saying they have 4.11s, 4.56s, or 4.88s (or more). That's the final drive ratio they're talking about, and it has everything to do with the ring and pinion gearing - bear with me - in the axle differentials.

For the most part, Jeepers don't know the tooth count on the pinion gear or the ring gear, but they certainly know the ratio. All that means is this: the ratio is the number of crank revolutions the motor makes, against the number of turns the axle makes. For a "4.11 ratio," the motor will turn 4.11 revolutions in order to turn the axle one full revolution. A "4.88" would turn the motor 4.88 revolutions to move that axle one full revolution - the motor is turning more just to get the axle to turn one full time.

Numerically higher gear ratios are "lower gears," and crawl better (better acceleration). Numerically lower gear ratios are "higher gears," and offer better topend (more flat-out speed, provided you have the horsepower to turn it). Example: Jeeps... you can have 3.55s in your axles, and someone with 4.56s in the axle will be idling up hills that you'll stall on. The 4.56:1 gears are lower gears, and that specific Jeep can "crawl" much better than the one with 3.55:1 gears.

Numerically higher = lower gearing
Numerically lower = higher gearing

Dragstrip racers might swap out 3.55s for a set of 3.08s for better topend on the strip... They also might swap out those 3.55s for a set of 3.83s so they can get off the line quicker. It's a trade-off, for sure... Depends on how much motor you have.

To find out your true gear ratio, divide the number of teeth on the rear sprocket by the number of teeth on the front sprocket.

Example: stock LTZ gearing is 14/40... 14 teeth on the front sprocket and 40 teeth on the rear sprocket. Almost everybody lists it like that("14/40"), but that's not necessarily how you divide it. It's NOT 14 divided by 40, though that's what it looks like when people say what gearing they have. It's really 40 divided by 14, but hardly ever listed as 40/14. 40 divided by 14 = 2.8571. If you were a Jeeper or a Dragger, you'd say you had 2.86 gears, because the final drive ratio is always rounded. You want more acceleration, or more topend? You'd need a lower gearing for the acceleration, and a higher gearing for topend.

Let's say you want acceleration: Remember, a lower gear is numerically higher, so you'd need a number higher than a 2.86 ratio. switch to 13/40 gearing - 13 front, stock 40 rear. 40 divided by 13 = 3.0769, or about a 3.08 gear ratio. A 13 t front is about the smallest you can go on a Z, so if you want "lower" gears than that, you'll need to increase the back sprocket size. 42 divided by 13 = 3.2307, or a 3.23 ratio. That'll take off for ya, but it'll also kill your topend.

If you want more topend: The baseline was the stock 14/40 gearing, which yielded a 2.86 ratio. For more topend, you'll need a "higher" gear ratio, which is actually numerically lower. For topend, you'll need something that works out in a lower number than a 2.86.

Look at a 14/39... That comes out to 2.7857, or a 2.79 ratio. All things being equal, that'll give more topend speed than a 2.86 ratio. A 14/36 would give you a 2.5714, or a 2.57 ratio - if you have the horses to turn it, that thing will FLY on the topend. It'll also be an absolute slug off the line.

A general rule is that one tooth on the front equals three teeth on the back. Example: 14/40 gearing = 2.8571. 15/43 gearing = 2.8666. 13/37 gearing = 2.8461. All three are damn near identical, and will yield similar results on a track, in the dunes, and racing around in the woods.

Let's say you determine you need three more teeth on the back sprocket, for 14/43 gearing. That will give you a final drive ratio of 3.0714, or a 3.07 ratio. The back sprocket is much harder to change than the front sprocket, and you'll also need a new chain for the added circumference around those gears. Why not swap out the front 14 tooth for a 13 tooth sprocket, and keep the stock rear sprocket (one on the front equals three on the back). You can keep the same chain, it's easier to change, and your final drive ratio still comes out to 3.0769, or a 3.08 ratio. Damn near the same. Something to think about...

Hope that makes some sense...

Go Ride! :lol
QUOTE (leopardturtle @ Apr 11 2007, 03:13 PM) index.php?act=findpost&pid=594840
What about tire size? How does that come into play?
QUOTE (NormalZ @ Apr 13 2007, 10:26 PM) index.php?act=findpost&pid=595783
Front tire size won't affect gear ratio at all, but rear tire size has a great affect on choosing the right gear ratio.

In short, let's say you have all stock drivetrain parts: 14/40 gearing, and 20" rear tires. Putting a set of 18" rear tires on there, and not changing anything else, is just about the same as putting on a 13t front sprocket onto a set of 20" rear tires. Rear tire size plays a huge part of the equation...

From the post above, you know how to use the front and rear sprocket tooth-count to actually figure out the "gear ratio" of the machine. Here's the formula you need to use to see how those gear ratios will affect the power, either with higher or lower gearing through the selection of tire size:

New Tire Diameter / Old Tire Diameter X Old Gear Ratio = New Gear Ratio

That's "New Tire Diameter" divided by "Old Tire Diameter" times "Old Gear Ratio" equals the "New gear Ratio" you'll need to install in order to have the exact same power as you had with the old tires on there.

Example: 14/40 gearing, 20" rear tires. 14/40 gearing equals a 2.8571 gear ratio. Let's say you want to mount 18" rear tires for MX, but want to keep the exact same gear ratio and exact same power that you had with the 20s on there.

You'll have to apply that formula from above above...
New Tire Diameter / Old Tire Diameter X Old Gear Ratio = New Gear Ratio
18 / 20 X 2.8571 = 2.5713

You need to figure out what gearing combination you'll have to make (front and rear sprockets) to end up with a new gear ratio of 2.5713 for those 18s, and they'll perform exactly like a set of 20s with the 2.8571 (14/40) gearing...

Make sense?

The gearing target would be a 2.5713 gear ratio for the 18s. Two easy choices would be 15/40 (2.6666) or 14/37 (2.6428). Both those rear ratios are very close to the target gear ratio of 2.5713. The 15t front is cheaper than a 37t rear, but a 37t rear will give you more ground clearance with the smaller rear tires. Lots to consider, but gearing isn't too difficult to understand. Hope that made sense - if not, let me know.
 

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THANKS for the info
 

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Discussion Starter #13
I am well aware what axle ratios do. lol

I tune cars and trucks for a living and that includs Jeeps, Corvettes and yout typical S10 or Chevy Full size pickup. I work with axle ratios every day and tire sizes. There isnt a rear differential on my KFX450r but the rear sprockets in my eyes arnt any different then going froma 3.73 to a 4.10 or 4.10 in my case to a 3.73. Instead of rock crawling I wanna drag race.

The higher the gear ratio obviously the slower and more power you are going to have to the ground. In a car it really doent matter most people get 3.73 cause a 4l60e tranny has a relly low first gear and some in jeeps do 4.10 and somtimes 4.88's but thas cause of that 4l60e having wierd gear ratios that most people dont even like. So some are old school and do 700r4's.


Really I think its all up to your application. If you have a stock machine and go trial riding, id say a 15 tooth is all you will want. It obviosly takes away from the bottom end and taking off. But when you get in the tight stuff you have to play alot with the clutch. This is cause they added the dirt bike tranny to a atv. its got a medium forst gear and all clode ratio thereafter.

U=Tis is very unlike a wide ratio tranny like Kawasakis new KLX450 which has a wide ratio. Meaning the first gear after the primary reduction is lower than a close ratio. this is to achieve the higher top speed and still be able to take off well. Like my YFX450 with a wr(wideratio) motoin it from the yamaha wr450 bike. It has a low first gear and then tall thereafter. I like it this way cause it works perfect for me but its crap on the track.

So after doing some research, as I need more top end I will lose bottom end, its just a close ratio tranny made for the trails and track, not top speed. its that simple.

My theory is that i If I add all my mods, camshafts, esr pipe, power programmer and a intake when its available I will increase boottom end torque and will be able to push a smaller rear sprocket. If I didnt do those mods, going through the woods wouldnt be very easy.

SO when I get my mods and my rear sprocket we will see. I will test it stock and not stock and see how it does.

Jeff
 

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QUOTE (PCMamerica @ Apr 14 2007, 09:49 AM) index.php?act=findpost&pid=1178
I am well aware what axle ratios do. lol

I tune cars and trucks for a living and that includs Jeeps, Corvettes and yout typical S10 or Chevy Full size pickup. I work with axle ratios every day and tire sizes. There isnt a rear differential on my KFX450r but the rear sprockets in my eyes arnt any different then going froma 3.73 to a 4.10 or 4.10 in my case to a 3.73. Instead of rock crawling I wanna drag race.
Great. My comment wasn't aimed at you, like an attack or anything. My comment about understanding ratios was for everyone else. Sorry you took it the wrong way.
 
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