Indeed, usually the bots are not a problem so it is the combination of a lot of people + the bots. Except for cases like Thursday when I added the feature when many bots are there at the same time.
Filtering the bots is only removing a part of the load, there are still a lot of people I suppose at some time.

For the site, I think the heaviest things are editing comments (especially old ones) and changing car info (something done a lot of course).
Adding new info is much easier for the database, even if it is still more work for the server than just browsing the site.
Among the browsing activities, the search in comments is probably the heaviest task.

Technical info: in addition to the actual data (vehicle info, comments, etc.) stored in the database, there are also indexes. These help to find/sort data more quickly, but it means that when you update the data you also have to update these indexes.
It makes browsing faster but insert/update slower.
I may have put indexes on too many fields, e.g. timecode, episode id, country, etc. These are not used so much for sorting/searching, but each update of a car requires updating these.
I'll try to remove some of the indexes, and we'll see if it works better. Difficult to tell the result in one day, we'll see in the next days if it seems to improve or if it is worse. Maybe it won't have any impact