Before installing your new grips, make sure the handlebars are clean of the old grips. Do whatever you need to do to remove any traces of the old grips before you move on to installing your new ones.
Hair spray or not to hair spray. Here's the deal. Hairspray will work in an environment where there is no moisture or humidity. If you are still confused, NH is VERY WET! Hairspray DOES NOT WORK HERE. We tend to get a lot of rain on average and when it's not raining the humidity can be 90% or more. Hairspray get's slippery when it get's wet... not what you are looking for in a grip.
So what's the secret to a nice tight grip? Rubbing alcohol! Yup. That's how the factories install grips and so should you.
Grab your favorite rubbing alcohol and put a healthy dose in the grips. Then put some on your handlebars. The alcohol acts as a lubricant making it pretty easy to just slide the grips right on your bars. Now let the grips set overnight and they'll be glued right to your bars.
