I'm running a 13. Right now a 12. But mostly a 13. Bike has 30,000 kms and I have replaced 3 guards, need another one right now but waiting a bit. I am going to do a full swing arm movement adjustment. I found that the more I weight the bike down the sooner the guard is destroyed. Slack is set fine for normal riding or empty bike but gear up or two up and it will be too tight.
2009 WR250R "Da Mini Bike"
"That's our colour: mud!"