i searched the topic and only found one thread that had any info

so my question is... will the METZELER ME880 120/70-21 fit on my 07 FXST stock front rim with the stock fender?

 

no not without butchering the fender.90/90 is tight.

 

ok..thanks for the help!

 

This guide says yes it will without modification.
http://www.hdwheels.com/Product.htm

 

Whether or not it will fit inside the fender doesn't matter. The tire is too wide for the stock rim, which is only 2.15" wide. Yes, you might be able to shoehorn it onto the rim. You might even be able to get it to hold air. But it won't be safe, because there will be too much sidewall bulge. 2.15" = 54.6mm... that's over a 2-1 ratio with the the 120mm tire. Check the tire manufacturer recommendations. They are in the business of selling tires. If they don't recommend it, you can be sure there is a reason!