whats the widest tire or widest looking tire I can put on the rear of my 2003 sportster and can I just exchange mag wheels for spoke rims without adjustments?Thank you so much.

 

You can use a 150/80 on the stock rim. Any larger than that and you risk problems of clearance inside the fender. Wider tyres usually require a significantly wider rim than stock - I have a 160/70 but the recommended rim width is 4.5", not the 3" that is stock. Some members use a 160 on the stock rim, but that ain't for me! It is actually easier to use a spoke wheel, as that is the easiest way to get a wider rim (rebuild onto the stock hub).