Some of the BEST aftermarket parts places for the 1978 - 1981 Yamaha XS1100

Bike Bandit:  http://www.bikebandit.com/partsbandit/OEM-Parts.asp

Parts N more:  https://www.partsnmore.com/cat_index.php?model=xs1100&category=x

TKAT fork braces:  http://www.tkat.com/forkbrace.html

My favorite tires for my XS1100 are:
Dunlop 491 Elite IIs on both front and rear:
F: MM90-90 M/C 61H
R: MT90 B 16 M/C 74H
'love em! Great for high speed, cornering, and overall handling.
I got mine from Cycle Gear - and they mounted them...