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Well there are plenty of videos and articles on the internet, but I haven't practiced it by myself. Most of them uses the shunt break to increase the speed, but i am confused about it.

I am studying in China and this place is crawling with e-bikes, pretty cheap here. These comes in 24 to 96v (may be more) with different speeds. In smaller bikes (24-60v) speed is the major problem. The circuitry and controllers are almost the same for all. Controllers are very cheap here and its not a bad idea to experiment some. However, there is a button called 'speed increase', if that turned on, the speed might have a 5-10 km/hr increase.

I have just seen one of it (48v), and it was pretty much easier to deal with. I saw a shunt in there but was afraid that the circuit will smoke, because my bike was already going at 45 km/hr. The speed controller button and various other wires were disconnected (by a service person), due to that I had no speed issue.

But i am planning to get another used e-bike and do some experiments with that. Could you people kindly share your experiences with speed upgrades

I just got an e-scooter from scrap, so i want to upgrade it. I can increase the voltage from 48v to 60v, which will be more than enough for me. I can replace the controller as they are cheap. But I don't know about the voltage capacity of the motor. Their is a code written on the rear wheel, but I don' t understand what is the wattage.. There is written 48v but the wattage is confusing... Because my friend is using 60v 20A battery with a bike whose motor is 48v 800w. I tried to upload the images here but there is some problem with the website

BTW i know to calculate the watts if i have voltage and amps. I will change the controller and charger for sure, but what about the maximum voltage a motor can take? Is there any formula or something like that to calculate it?

I checked the controller, it was 450w, so i thought to give it a go, and worked like a pro.. First I tested it with original 48v 12Ah while the bike was on double stand. Then tested it with 60v 12Ah, speed was almost double with the bike whumping. It was for a few minutes, and I checked the motor, controller and wires temperature, nothing was hot.. I didn't test it on road, bcz the 60v battery setup I made was from a 48v lithium and 12v lead-acid, so I was afraid of battery explosion.. Though it worked well for few minutes.. I checked the lighting, that was fine, but the horn wasn't giving good sound. So the test was clear.  During the test on double stand, it was alright. However, before the test, there was a glitch in this bike. Whenever I increase the speed (pull accelerator to the fullest) the bike shuts off, and then after removing the battery socket off and then back on, it resets [this problem was also told by the person who sold this bike]. I thought the wiring might be a problem, for that I solidified all the connections, but again on the road it shuts off with maximum accelerator. I am so confused whether this problem is in the controller, motor, battery or accelerator.

Sounds like there might be some sort of over current protection---sudden acceleration draws more current which may be above the trip level. Just a thought.