I see where you are coming from coldel but in defence of the charts/data there has to be a baseline and then a proportionate improvement gap. Ie 3 tyres do a 50,52,54 sec lap. Tyre 2 shows a 50% improvement over tyre 3 when compared against tyre 1. Now overall the 2 second difference is just 4% but when comparing against each other the percentages/difference feels much greater.
I mean for the tests above, he could have done laps with no tyres (just rims) and still set a time, maybe twice as long but we wouldnt say that driving without tyres is only 50% worse than with tyres.
Not having a go at all, just explaining my view on it and why they may have presented it like they have, not saying its right either but they have to display the results somehow and displaying a bar chart from zero would not get across the required effect (or deception) delete as necessary.