If it is truly underreading then that is an issue for Lexus to deal with as it is illegal for a speedometer to underread.
The main reason for speedometers overreading (up to 11%) is to allow the fitment of various option wheel and tyre combinations that the manufacturer may offer.
INACCURATE SPEEDOMETER?
in RX 300 / RX 350 / RX 400h / RX 200t / RX 450h Club
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If it is truly underreading then that is an issue for Lexus to deal with as it is illegal for a speedometer to underread.
The main reason for speedometers overreading (up to 11%) is to allow the fitment of various option wheel and tyre combinations that the manufacturer may offer.