I cut mine with a Dewalt Sawzall using a 7" Lennox Bi-Metal blade.
It cut through the runflat like butter.
I really don't know why everyone is so worried about them catching fire. They are a Mag-Al alloy, and will take much more heat than a spark to set them ablaze.
After I cut mine, I used a grinder with a 80G flap disk to smooth them out.
After I was done I did some playing with the scrap and even a propane torch would not set a large piece on fire. If it was a pile of shavings it would though.
MAPP gas would do it all though.
No sparks from the sawzall, used a milwakee "the torch" blade about one blade per runflat.
My grinder tossed a spark or two. The propane torch got the pile of shavings hot enough that if you toss some water on it, it will flame up.