In order to get some mid range and torque gains, I've decided to replace my rear sprocket with a bigger one. I asked a friend of mine (experienced motorcyclist, been riding for decades) and he said I will have to get the bike dyno tuned.
My Questions are:
my bike: MV Agusta Brutale 675 ,MY: 2014
Changing your rear sprocket won't give you more mid range or change the engine power curve in any way. It will alter the torque at the rear wheel at all RPMs. The bike should accelerate faster through the gears but you will also loose out on top speed.
You don't need to get dyno tuned just for changing a sprocket. He may however have been implying that to get proper midrange gains, you need some tuning done, altering the fuel map to try up pump up the midrange. According to the MV website, the Brutale has 4 engine maps already and one spare for your own customisation. This would probably be your best bet for increasing your midrange torque.
It's possible you could keep the same chain on. If it is relatively new and unworn and you only alter 1-2 teeth on the rear and still have enough adjustment left on the swingarm. Otherwise, you will need a new chain with a couple of extra links. If the chain is worn, it's best to replace it as it will accelerate wear of the new sprocket. Might be worth replacing the front sprocket too in this case.
No, you do not need to remap your ECU
This doesn't have anything to do with your air fuel ration and ignition timing. You are simply changing the gear ratio for your final drive.
Making the sprocket larger will make all of your gears a bit shorter and reduce your top end speed.
I typically do this on most of my motorcycles as it makes for better city driving. As well, a couple of my bikes have a first gear that is over 80mph at redline. It will make your bike feel a bit more responsive and help you with acceleration a bit.
Always change chain and sprockets in pairs, they wear in together even if you cannot visually perceive it. If you change out just your rear sprocket on a chain with a thousand plus miles on it, you can expect to wear your chain and sprockets at a very accelerated rate. If you change everything together you will get good wear and life out of the overall set.
