more mph in lower gears?

[honduh440]

what is the best sprocket for the 400ex to make 1st and 2nd gear larger im on 18inch tires and i want to have my 2nd gear going as fast as what lower 3rd gear does now any help would be appreciated

[400EXcrazy]

if u want more top end get a 16t front sprocket and if u want more bottom end i would go with a 14t front sprocket

[wilkin250r]

You would be surprised at how big your tire change affects your gearing.

You can't get the exact same ground speed, but you can get pretty close. If you want the same ground speed going from 20-inch tires down to 18-inch tires, you want either 16/37 or 16/36. The stock gearing and tires falls directly in between these two, so if you want slightly more acceleration, go with the 16/37, or for slightly more top end speed go with the 16/36.

These are simple calculations, in all reality you have much lower rotational inertia with the 18-inch tires, so it's entirely possible you would see more acceleration with the 16/36, even though the calculations say it is a little taller gearing.

[honduh440]

ok im kind of confused let me describe my situation of why i need this.........im ridding on a supercross track so the jumps are one after another the woops section is a 2nd gear only for me and then right after that is a jump i must hit in 3rd gear but i do not have enough time to change gears so im wanting to gear it so i can run threw the woops in 2nd gear and still come out to hit the jump in 2nd gear as well what would u say is the best gearing?

[dawnchris]

Just put a 16 on the front and try it. Nobody can say exactly what will be perfect for your situation. Changing the front is cheap.

[wilkin250r]

Now I fully understand. I thought you were comparing 18-inch tires and wanted the same gearing as stock tires.

You want taller gearing, plain and simple. Taller gearing gives you more speed, less acceleration, in all gears. You can't just change 1st and 2nd gear, when you change your sprocket, you change all gears. I can't tell you exactly the gearing change without knowing the exact RPM of the engine.

I think changing the front sprocket is probably going to be too big a change for you, so let's look at the rear. If you're still running stock, I think it's 38 teeth. So you want to go down on the rear sprocket for taller gearing, so get a 37 or 36 tooth rear sprocket.

Of course, there is always the possibility of going the other way, making all gears lower, and taking the whoops in 3rd? You lose top-end speed in 5th gear, but you gain acceleration out of the corners and the holeshot.