Rear tire

[jimride]

How big of a tire can you put on the back of a 2008 Road Glide (factory rim)

 

[HDDon]

The rule of thumb is usually one size up on the stock rim. Check to see what type of clearance you have between the tire and the belt, or tire and the belt guard. I think your bike has a 140 rear so check the different tire manufactures for their specs.

 

[Hobbit]

remember tho that a wider tyre might not mean you get a wider tyre - explanation i know - right the size might be wider on the side wall but when you put it on the rim remember you squeeze the sidewalk together so pushing the tyre taller not wider, but when you put it on the correct sized rim it will go wider as the sidewalls are stiffer and don't like flexing so they push the tread up - hope that makes sense