When the grip start to change color or lost it's shine. Also, I change it when I start to play bad too.
When it gets really yucky and smelly, tearing of the grip, loses performance, and umm when there's too much bacteria on the grip.
when so much bacteria grow on it that it feels like sponge. which is like 2 weeks of good play? a month or 1.5 of less play? If you want your grips to last, wash your hands before playing.
I change my grips once every 3 weeks . As i choose to have bright and coloured grips and i have training 3 times a wekk , i have to change it very often.
Depends on what type of grips I use but nowadays I prefer using towel grips. I change normally change them after every 4-6 sessions. Towel grips are pretty pretty cheap anyway (abt S$0.50 per piece) since I can get them from friends who go to Indonesia or Thailand. Using a towel wristband will help prolong the grip usability as well.
You must be mercifully free of acid sweat... I'd have to change mine every two days after I get a new one, heh!
That's why I switched to darker coloured grips. I found I was changing them way before they needed to be just because of the dirt. I change every 2-3 months or when the grip starts fraying.
Between 1 to 2 weeks depending on how warm and how much I play. I really like tackiness so I'm picky about my grip.
i change my grip every two months or so and i play 5 times a week. my favourite are karakal pu grips. i h8 the feeling of towel grips. my favourite colour is white becoz they go with all rackets but they go dirty so quickly