Hi, right now i have a 40t front chain ring with a 15t cog in the back. i love this ratio but unfortunately the crank i am using is old and not really made for fixed gear use. it gets loose allot, the chain line is off and its ugly so my question is if i move up to a 46t crankset like IRO what tooth cog should i get to have the same feel. i dont think i said that right but i hope you guys understand what i'm talking about.

thanks
-David

17 in the rear would be the closest with a 46t in the front. It'll be a little harder/faster but not much.

40/15 = 2.67
46/2.67 = 17.23

Edited due to uncalled-for hostility towards your lack of math skills.

thanks onetwentyeight that was my guess.

i didnt really think to do the math notfred, i was just asking a simple question. Internet forums and those who dwell on them tend to always have bad things to say about every single post. the real question is not that i suck at math, its that if you spend so much time on here as your "senior member" status implies, why would take the time to answer a stupid question?

...because people need to be slapped down for answering what you yourself call a "stupid question".
gears operate on ratios. that's 4th grade math, even in kentucky. some promotion advice - if you read sheldon brown's website and browse past threads here, you will never need to ask a question again. then, and only then, will you enter the ranks of the elite, where you are bequeathed the power to post rants and talk smack.

notfred, eurotrash - you both posting in this thread keeps it up near the top. if it annoys you, ignore it. yes its an easy question, but it's been answered, no harm done, move on.

just use brown's calculator

I prefer this one: https://www.basementfreaks.com/member...ring/index.php