So here is the simplest way to cut your handlebars shorter; all you need is a G Clamp and pipe cutters (with the cutters you need to have a blade that cuts metal not just plastic). I must say it is really easy to cut handlebars and pretty tidy too. No muscle strength needed and took me just 5 minutes! (and the practice drum pad featuring in the 3rd photo is optional, although it did help to clamp the bar without sliding!)
To put the grips on you will need some hairspray: it helps them slide on the bars and once that happens, it sticks them nicely. The other thing to do is to make a little hole on one of grips so no air is trapped in the hollow bit of the bars (if there is no hole then the air pressure makes the grips move which is a hassle when you ride)
