Help - Tyre Usage

Well, I got a small problem...

Is there any problem if the tyres goes below 50% during a race?

Am I going to make worse times? 

Is there any level of percentage of the tyre that makes my driver go slower?

Newer tyres will be faster. The performance will drop off considerably around 25-30%

But I saw drivers of other teams making better times after made 10 laps with softs, with a rate of 8% per lap, that makes 80% after 10 laps... How can that be possible?

The tire wear is not linear. So while it is 8%/lap  early on, it is not as much later in the run. It also depends on how hot the tires get and how hard the drivers are pushing.

Ok. I will joke around with that things. Thank you.