I want to try the longest possible tennis racket meaning 29 inches long, USTA rules. I use Babolat Pure Drive (68.5cm long) but I want to get it 5.2cm longer to be able to hit as high as possible in servings. I am not sure whether it makes any sense to try to get as long tennis racket as possible by that I try to add the maximum power to servings so personal height has less importance. Is it possible to lengthen an existing tennis racket or some other options to get the longest possible tennis racket?
It is possible to lengthen your racquet (at least the handle/grip) - however, you don't want to attempt it yourself unless you really know what you're doing. I would recommend looking into a service such as what is provided by RPNY where racquet customization professionals can do the modification to your racquet. I've tried playing with a 28.5" racquet before and it felt quite odd and I didn't play well with it because of the extra time it takes to swing it around (I found myself making contact late on many shots before I adjusted). 29" could end up being tough to play with until you really get used to the timing change.
Keep in mind that before you start off wanting to lengthen your racquet, you should look at your service motion/technique and start there. Having a longer racquet isn't likely to do a whole lot for your serve in terms of speed or anything like that.
Here is How I did it:
Buy a decent Wilson kid's racquet, 250g or so with a thin handle, other brands may have different core shapes that might be difficult to work with.
Remove the wrap of the handle and the butt cap.
Cut off about 3 inches of hardened glue from the bottom of the handle, expose the metal or carbon fiber core inside.
Buy a piece of square shaped aluminum pipe from the hardware store, cut 6 inches, insert the exposed core of the handle into the pipe to get an extra 3 inches. If it does not fit snugly, either wrap some duct tapes or grind some of the materials off the handle.
Drill a few holes through the pipe into the handle, screw the pipe into place.
Put a thick layer of hot melting glue around the whole handle, wait for it to cool off, use a knife to shape the handle into a smooth piece of polygon cylinder.
Find a bicycle handlebar tape and wrap it up. Done.