"In order to earn the circled 'E' on their sidewall, tyres have to pass the ECE R30 high-speed test, which ensures they can carry a specified percentage of their rated load at close to their rated maximum speed without failure. But there are no statutory tests of braking, handling or aquaplaning performance, and even the R30 test is considered inadequate by many car makers. In other words, just because a tyre can legally be sold in the UK, that is no guarantee of its performance in safetycritical aspects of normal driving."
Like has been said before if you can't afford to maintain your Lexus properly then buy something cheaper you can afford the upkeep on. Budget tyres don't have a place in this end of the market IMO.