I have a 12 tooth on front now it has made a weird poping noise like the chain doesnt roll well on it since ive put it on so i want to put my 13 back on and as of now i have a 38 tooth on back how close would a 40 tooth on back be to the 12 on front.I like the extra power of the 12 and would like to keep it but im tired of that noise. any help would be great.~~~Jeremy

 

Did you readjust the chain tension after putting the 12 tooth on?? Mine had to be.

stock is 13/40.
13/38 is the same as 14/40. You lose accerration.
If you did 12/38 its like having stock gear.

Remember more teeth in rear is more accelration.. Less teeth in the front is more accerlration..

MIke.

 

Assuming that you have the proper chain tension, it almost sounds like the 12 tooth sproket may be worn out. Did you check it's condition to see how much wear is on it?