Games 2.5.0 feed the beast, minecraft version 1.12. I searched the whole internet and found nothing, or only old 2014 tutorials that are no longer valid.
Do you play on a server or single player?
Server
Lag (spikes), especially with modpacks and especially with newer versions, often result from "bad" hardware, especially from insufficient memory.
I suspect the server has too little RAM.
When exactly do the lags occur?
With multiple players on the server?
For e.g. Bigger explosions?
What I once had, that too many items (through Buildcraft) were in tubes and because of that I had lags whenever I was around.
The spikes occur pretty much all the time. A friend on the server told me I have to change my settings somewhere with my RAM myself, he doesn't remember exactly how he did it.
So the server itself should get at least 8 GB of RAM, preferably 16.
how much RAM does your pc have?
With the FTB, I don't know how to add more RAM myself, but I can tell you that you should allocate about half of your available RAM (e.g. With 8 GB RAM: 4GB)
ingame, if you have changed the assigned RAM, you can use F3 to check whether everything has worked (at the top right next to "Mem:", is given in MB)
