18in rear tires- sprocket help

[sprtrx300ex]

I just bought 18in razor for the rear. What sprocket do I need to change to keep the same ratio as stock?

[QuAdEr 317]

Originally posted by sprtrx300ex
I just bought 18in razor for the rear. What sprocket do I need to change to keep the same ratio as stock?

i would like to kno also....

[Jersey450R]

drop 2 in the rear

[buster369]

Drop it in the rear 1 or 2 but if you go up one, go up one on the front sprocket as well

[Rico]

Keep the 15 up front and run a 36 in the rear,, Best combo I ever used with MX tires.

[sprtrx300ex]

alright thanks guys

[hardkoratvmxr]

i run 13/16 with 20 uinch tires on my 300 it is good and i would think that maybe a 35 or 367 for 18s would be good also with my 13/36 i lost a little low end accelration so a 35 or 36 for 18s should be perfect

[wilkin250r]

When I did the calculations, I was rather surprised.

The stock drive is 15/38 gearing with 20 inch tires. Theoretically, in order to get back to there with 18 inch tires, it falls right in the middle of 16/36 and 16/37. However, this is a simple calculation for drive ratio, it doesn't account for rotational inertia of the tires and such. You can probably get just as good acceleration with taller gearing than 16/36. Probably the only true way to tell is very precise timed trials, or find somebody with a stock 400EX and race him.