KFX 450 HQ Forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
67 Posts
Discussion Starter · #1 ·
I figured I would post this on this site in case some of us didnt go to the other site and we might not ever see it.

Heres What weve got. I went to Sprocket specialties and did some math on there gearing calculator. 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
 

·
Registered
Joined
·
44 Posts
Jeff, you are out of control, like a mad Scientist working on your KFX. Thats cool! B)

So if we run a tiny little sprocket on the back (32), what is the speed for 1st gear?

What I'm wondering is how high will 1st actually end up being just to gain a few MPH on the top.

Now you have me thinking too. What about an average /range of speed per gear. like my car has in the manual that 1st is good from 1 to like 19 MPH or something like that.
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #4 ·
I am a mad scientist. lol, not really tho. I just want to find a sloution to our speed problem. I wanna keep up with all those modded 450's. And I will figure it out.

I already ordered my ESR exhaust and power programmer. No intake available yet but Tomorrow seems to be the day I get my sprocket answers. It seems we did some measuing and the 400ex sprocket has the same bolt pattern but the bolts that hold the ex on are tapered so its no good. When I buy my set of sprockets I will make a huge page on the KFX450r and what mods do what and what I thought. I think it will help new KFX450r buyers to easily mod there atv so they stay competitive.

You have some very good questions tho. I will look this up when I get a chance( the sprockets). Do you want me to just look up the 32 rear or do you want a couple others. Let me know.

Jeff
 

·
Registered
Joined
·
588 Posts
I am a mad scientist. lol, not really tho. I just want to find a sloution to our speed problem. I wanna keep up with all those modded 450's. And I will figure it out.

I already ordered my ESR exhaust and power programmer. No intake available yet but Tomorrow seems to be the day I get my sprocket answers. It seems we did some measuing and the 400ex sprocket has the same bolt pattern but the bolts that hold the ex on are tapered so its no good. When I buy my set of sprockets I will make a huge page on the KFX450r and what mods do what and what I thought. I think it will help new KFX450r buyers to easily mod there atv so they stay competitive.

You have some very good questions tho. I will look this up when I get a chance( the sprockets). Do you want me to just look up the 32 rear or do you want a couple others. Let me know.

Jeff[/b]

Sounds great, I'm sure you'll love your ESR pipe. Give us a ride report when you get her dialed in.
 
1 - 5 of 5 Posts
Top