Front tire : 100/90-16 Rear tire : 110/90-18 The V that you have before your Rim size (i.e. V16, V18) is the tires speed rating and isn't specific for the bike....you can have a V or a Z or whatever. and size 4.25/85 V18 is 4.25Inches wide which is about 108mm. So it's a 108/85-18?? Sounds odd but not too far off stock. I was going to post it here just to prove my point but the Video has been removed from YouTube :-(