so how much different stock tire size you used with differnce of 124 and 120? it is negligible.
on internet variety of such sites which gives difference in readings of odo in case you change stock one
but again as i told that when i discussed with toyota service manager in japan , they told me toyota is not responsible for malfunctioning in odo and speedo redaings if some one not follows the recommended sizes mentioned by toyota, he told that analogue old meter were better as they did not did much differnce and also resume if you again put back stock size but problem with digital odo that once it gets disturb, then even if you again put back stock size, it will not resume correct reading unless you correct it again by digital meter device
in my recent trip to uae & saudi arabia, my junior used same GPS navigator and tally speed with it because he put some sporty low profile tires but many times caught by speed radar & caught by patrolling highway police
when 1 moment i interrupt & told highway police that it was under limit as we were tally with GPS Navigator but they told politely that also your navigator software might have issue ,not showing correct speed
they showed their radar software to satisfy us that what was speed during journey and surprisingly it had variation of 10
after that i strictly ordered him to drive at least 20 less than designated speed