I won't lie. My bike is not stock. Here's a list of my mods.
40mm lectron carb
ported and polished
bored to 416
11.1 JE piston
WB rev Kit
No air box lid
K&N Filter
Lrd exhuast system
xr400 cam

After all that i kept running stock gearing 15/38
A guy told me that i need to gear high b/c 4-strokes love to be in a bind. I thought he was full of it but i tried and it worked. I won the past weekend for the first time. I think it's all in the gearing. My gearing is 16/36. And it doesn't even lug the first little bit on bottom end. Just thought i would share. Everyone let me know what you think. Everyone try it.

 

If you go smaller on your back sprocket(axle), doesn't that lower your gear ratio? With a bigger front spocket and two teeth smaller in the back, doesn't your gear ratio come out about the same as before?

 

Nope, gearing was hard for me to remember at first but here's my 2 cents.

Front Counter Sprocket:
Less teeth = slower
More teeth = faster

Rear Sprocket:
Less teeth = faster
More teeth = slower

Note: (close but not %100)
for every tooth in the front = 2 in the rear. So if your stock is a 12/40 and you wanted to make a 6 teeth gear change you would change to a 14/38 or 13/36.

Hope this helps alittle. Later.

 

Bigger in the front and smaller in the rear equals higher gearing.

Smaller in the front and bigger in the rear equals lower gearing.

 

The best way to figure it out is to find the final drive ratio.

stock 15/38 = 2.53 that means the front sprocket turns 2.53 times for every revolution of the rear sprocket, and with equal tire sizes gives you the final drive ratio.

I switched to a 14 front 2 years ago to get more pull in second and I never use first, so if you went the other way a little it should make first more usable, and give you more top end for those who want it.

14/38 = 2.71 makes first like granny low but second is great.

16/38 = 2.375

16/36 = 2.25 The smaller the number the higher the top speed.

15/33 = 2.26 then you just need to buy one sprocket for the highway gear.

this is interesting enough to try my chain and sprockets are due for replacement anyway.

 

just like a 18 speed mountian bike, just look down to understand

 

You made a big change. I went up a tooth in the front and now it pulls harder and more in every gear. For the price of sprockets its worth trying. I was surprised by the change I made. Later