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Above is a chart which indicates many combinations of front and rear sprocket teeth count for the desired gear ratio.

Keep in mind that this chart excludes the effect of tire diameter changes.

In general, increasing the diameter of the rear tire and keeping the gear ratio the same will increase your ratio.

In other words, make your quad have more top end and less low end power. It will be slower to get up to speed but when its reached, it'll fly!

Keeping your tire diameter the same (as before), and decreasing the rear sprocket teeth count will also have the same effect.

It'll fly on top, but take longer to get there.
Reducing the teeth count on the front counter shaft sprocket will provide tons of low end power, but the motor will rev quickly.

Reducing the front sprocket teeth count is preferred by most hill climbers, assuming no increase in displacement was performed on their motors to get them to the top of the hill.

OK, use the chart to figure out which combination best fits your quad with the typical load (with your fat ass on it). The GOAL is to utilize all of the power band of the motor without bogging it down to quickly.

Thanks to www.pinnedoutracing.com
 

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I found this site is epic for speed calculations for a 400ex. It shows the top speed for each gear and if you plug in different # of teeth for both sprockets, the speed different you'll see. Very good for understanding basic "How will different sprockets affect my top end, top speed for each gear, etc etc. That's good knowledge for all quads.
400ex gear ratio converter.


I also found this from 4Strokes.com (Gear Ratio Chart)
Gear Ratio Chart (WARNING, PDF!! File size is small however.)


The general gist of said chart is that
( # rear sprocket teeth /divided by/ # front sprocket teeth = Gear Ratio)
Higher # = Acceleration
Lower # = Top Speed


On my 400ex when I got it, it was set for more race track type running. Shoot out of the pocket setup, major Acceleration.
Higher Gear ratio (15 front teeth, 40 back teeth = 2.67)
Using the first link, my top speed in 5th would be = 65.19mph*

I want more top speed instead.
Lower Gear Ratio (16 front teeth, 38 back teeth = 2.38)
Using the first link, my top speed in 5th would be = 73.19mph*




* I used the default settings of 20in tires and rpm of 8250. With my 426 and aftermarket tires, these calculations are way off probably, but for the purpose of understanding how gear rations work it still helps.
 

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You won't get a 16 tooth front sprocket on there. You will rub a hole in your case.
 

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I could be wrong, I know the 450 doesn't have the room. You can always adjust the rear sprocket to match. If your gear ration 3.0, it is 3 teeth in back for 1 in front.
 

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No prob man. I just like being able to contribute some finally instead of always picking your brain for help with my yellow bird. I love playing with that web program thingy that will tell you the top speeds for your gears.

I've got a lot of weight reduction stuff (aluminum hubs, lighter swing arm, etc etc) on mine when I bought it. Plus the 426 and the Lectron carb. But it was set for track big time. I want to put her up further on the top end, while still maintaining some balance of acceleration. So Gear ratios have been interesting me a lot lately.

I've felt one extreme (the 15/40 ratio). Now I'm thinking of trying another (16/38 or 16/36), Though I'll lose my Acceleration. I don't track, but I still wanna whip those other 400's on the trails.

Decisions, Decisions....
 

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I like that idea. Think I'll go with a full 16/38 when I get some more cash.



I've got a 15 tooth in good condition on it. but the 40 is shot. I COULD be a cheep skate and just do the back with a 36 until I get a few more bucks. Keep the front and the old chain for now.
WARNING: DO NOT DO THIS!! You will spend more money in replacing your chewed parts then getting a full front, back, and chain at once. I'm just doing it to experiment for now with different gear ratios until I decide on a permanent one when I WILL buy a full combo very soon.
 

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If your chain is like the one on the 450's there is no master link. You have to grind off a link...
 

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i am lookin to do a sprocket set up on my 2007 400ex. ride trails and dunes. do some racin/flat track. what size should i do in the front and rear. Stock is 14 in the front and 39 in the rear. what should i go with. not wanting to lose alot of my speed but want a little more speed to get up a dune or a hill.
 

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Use the 400ex speed calculator to get a rough idea on whats speeds your quad will top out for each gear depending on the # of teeth you plug into the calculator.

It's posted on the 2nd post, but here is the link again

400EX Converter
 

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i am lookin to do a sprocket set up on my 2007 400ex. ride trails and dunes. do some racin/flat track. what size should i do in the front and rear. Stock is 14 in the front and 39 in the rear. what should i go with. not wanting to lose alot of my speed but want a little more speed to get up a dune or a hill.
13/18 is a good combo
 

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I run 14/38. Love climbin' them hills.
 

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Has anyone tried to put a bigger front sprocket on a 1986 trx125? the sprocket isnt like a normal one. It has like a hollow shaft attached to it and they arent cheap. I was thinking about cutting the old sprocket off and welding a new bigger sprocket back ontop of whats left of the old sprocket. tractor supply has a bunch of sprockets that would fit with a little modification and they are only $10 compaired to $39 for just the front sprocket.
 

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13/38 for the woods. Wakes these bikes up, If you have a big bore it REALLY wakes them up. With a few mods you can run with a 450 in the fields but kill them in the woods (rider skill allowing).
 
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