https://www.danscomp.com/bmx/Parts/Tires/ ?
generally wheel with a 451 rim is needed to get narrower tires ,
it's still a nominal 20"
but rim is bigger with the tire narrower to achieve that.
https://store.bikefriday.com/product_info.php?cPath=49&products_id=8961&osCsid=ggsghqorujpmojc80epqm4ipg7
https://store.bikefriday.com/index.php?cPath=49
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in the past there was great interest in BMX racing ,
in the Italian manufacturing companies .
On sprint Moto Tracks like used on last 2 Olympics,
for that they made sew-up tires and rims..
...