Please describe those exceptionally tough races whose eventual race conditions were fair, clearly stated... but that for some other reason the race couldn't be won.

This first tough race of mine described below had challenging conditions, at the most, but all doable. Problem was: flash fast bots ahead, aggressive bots behind.

Path of Defiance, last day goal four. We had to tailgate someone for 60 seconds, and that was a cumulative goal (easily done in the first lap, considering bots go slow at the turns,right?)
We also had to be the leader for 90 consecutive seconds, so just pass the leader by mid-lap 2, and you're alone, right? 

Yes, but NO!! Even though I did have tediously slow bots in the previous days in this event, in this goal I simply couldn't get a hold of the leader. I could just drive my best to reach second place and from there, sight.... could only SEE the leader in the turns, maybe get one or two seconds of his tail and then he was gone. And his crew brothers bumping and crashing at me all the time.

The first photo I took was when I first noticed something was off (this was after a handful of fails). Pretty intimidating crew chasing me...

One second or two later, their leader was preparing to attack. 

And they were pretty rough. Anyway, a few attempts later I managed to get the 60-second tailgate...

Managed to PIT the overall fastest bot only after another handful of attempts...

Then his bodyguards attacked again...

Jaguar from the left:

Or Porsche from the right:

Or both at once:

Nothing seemed to work. Once, I managed to merge in the "chasing crew", tailgate their leader for 20 seconds (totalling 30 smthng at that moment), and he flew. Another few turn later, I was alone searching him to finally get a total of 58-ish seconds! Ouch. 
Reached that bot (then 2nd place to finally beat the first task), and a few (or lot) of turns later I reached the BOSS.
After I could see him, don't know how I reached him so fast.
PIT.
Pass.
His bodyguards were at no reach from me. 
Cross the finish line. Red flag. 

Have got just over a minute as a leader. Not an easy run that one. Gave all I got but the fastest four or five bots were just... too... fast. 

Lots of upgrades and a 170 GC engine up. And I had to skip one more task. The previous one skipped was a 142 avrg mph. Bots were too slow (as usual in these special events for me), but I couldn't overtake the poor bastard as per the second task.

At least this last tough race described above was awesome. "Pretty awesome", uhu. :-/