i think the heavy duty ones are 4 mm

Depends a bit on the brand, but usually. Some heavy duty tubes are 4mm

Pls pic the f***ed tube. I want to find out who's the maker by official trademark record http://wsjs.saic.gov.cn/

Hi,

I note the Kenda K761s are slightly wider than the originals (10mm or slightly over 1/3 of an inch) but it seems they are working fine out there with the Hawk 250s?

-Kenda Back: 120/80-18
-Original Back: 110/100-18
-Kenda Front: 90/90-21
-Original Front: 80/100-21

The clearance up front (shocks) and back (chain) seems so tight as it is. Are there success stories out there with the K761?

I have the 705s on my bike and love them. they handle SO much better on the street.

http://chinariders.net/showthread.php?t=21276

Yep the 705's are great for bikes that mainly see the road.

If you never plan on leaving pavement at all, then you can go one step better and put actual road tires on your bike.

As far as size and fitment. 120/80-18 and 90/90-21 are the exact sizes I ran on my 705's and I had no fitment issues at all. Plenty of room. If you want to stay true to the rear tire diameter, then a 120/90-18 is almost the same exact diameter as a 110/100-18. 120/80-18 works just fine, but the decrease in diameter is effectively the same as going up 1 or 2 teeth on the rear sprocket, so you may need to adjust for the size difference.