I know a guy who had the same bike as mine and he got a magic gear of 37x14 to work. I have a 16t freewheel with a 38t chainring and it doesn't work. If I get a 39t should it work ok? According to the magic gear program thing it should but just checking.

Not sure I understand your question, but this might help if you are having trouble getting correct chain tension.

Play around with this

https://eehouse.org/fixin/formfmu.php

You should be able to find something that works.

Maybe I'm talking out of my hat If I know a 37x14 works, therefore a 38x15 should work and then 39x16 right? Obviously the chain gets longer but by whole links. yep probably got it wrong

Seems i didn't. The 39x16 should work with same tension as the 37x14 just a longer chain

As long as the number of teeth in the cog and chairing are the same it will work. I run a dingle speed on my s/s mtb. 32x16 and 34x14. Same chainlength.

is it the same size frame as well? provided the length of your chainstays is identical then yes, if 37x14 works then 39x16 should as well. as long as the total tooth count increases by 2's you are okay.. or you can use the 38 and get a halflink and that should work.

just know that chains stretch over time and not all chainrings are identical, so there's no guarantee of a perfect fit.

Didn't check the frame size forgot the stay length might be different. There are only 2 sizes but I checked mine with the online calculator in the previous post and should be ok now. with a half link the 39x16 is bang on. could have gotten a 15t instead but not guaranteed to work with hub i have. thanks for help

^while his thread title was misleading, he is not asking if they are the same ratio, he is asking if one works for the "magic gear" will the other as well.