Originally Posted by mreed

The tire size is a formula for the overall diameter & width of the tire. For instance a 150/80-16 breaks down like so:

150 is the width in mm, 80 is the percentage of that width that equals the sidewall height, and the last is the rim diameter.

150x.80=120

120x2=240 (multiply by 2 since the overall height includes the sidewall on the top and bottom of the rim)

240/25.4=9.45 (divide by 25.4 to convert to inches)

9.45+16=25.45" overall diameter.

Using the same formula to find the appropriate sidewall for a 180 tire will give you a 180/65-16 and that equals an overall diameter of 25.21".

You'll end up with a 180 tire that is less than 1/4" shorter than stock but if you don't change the rim hoop to 4" wide and opt to keep the stock hoop, the sidewall "bulge" will force the width taller. Right at 1/4".

Lol...follow that? Anyway, a 180/65-16 will only add width. Not height. Therefore, your speedo will read correctly. You can get that tire in a Dunlop (407 I believe).

Originally Posted by TheEdge

Has anyone tried to throw a bigger rear tire on their Nightster? Its got a 150...I think, I was thinking a 180-190 would look pretty sweet, but I don't know up sizing on motorcycles. I would imagine one or two sizes would be ok, but can the rim hold a 180? Will it fit in the swing arm?

Originally Posted by Fig0341

Yes it fits. I did put a 180 on the rear to the factory rim and swing arm. No issues so far. Now, it will look better with a 200. I’m researching now for that answer.