Recently when shopping for oddball wheel sizes for my recumbent, i stumbled upon 22 inch BMX rims, which recently came into fashion. As of writing, there are at least 4 manufacturers of these rims.
Here's some examples: https://www.modernbike.com/22-inch-rims
A few of these rims come in 457 ISO size; and 18" motorcycle wheels are also 457 ISO ( note that motorcycle tire measurements and bike tire measurements are completely different. A 16" motorcycle wheel is a 20" bike wheel, for example )
An 18" motorcycle wheel with the right moto/scooter tire roughly comes out to 24" in bike size, so for bikes with 26" wheels, you can get away with using a single 18" moto rear, as it should only drop the rear about an inch.
This is great because normally an 18" motorcycle rim and spoke combination would be about 4-5lbs, whereas with a 22" BMX rim, we're looking at more like 1-1.5lbs.
IF you want moto rims on both wheels, then this plan doesn't work and you need to step up to 19", however there is no bike rim equivalent in that size, so you're stuck with extremely heavy wheels and a difficult wheel build overall.
Here is a damned good thread showing how 19" moto rims + tires can be within an inch of 26" bicycle size. ( therefore, 18" can be within 2 inches if 26" - resulting in a rear drop of just 1 inch )
https://endless-sphere.com/forums/viewtopic.php?t=55458
In my experience, going dual motorcycle wheel is completely unnecessary on an upright bike because around 70% of your body weight is on the rear, therefore the rear is most likely to puncture and also needs the most traction. The front wheel is doing a fraction of the work, so the main reason you'd want a moto tire up front is for traveling at highway speeds, or perhaps just aesthetics.
Here's some examples: https://www.modernbike.com/22-inch-rims
A few of these rims come in 457 ISO size; and 18" motorcycle wheels are also 457 ISO ( note that motorcycle tire measurements and bike tire measurements are completely different. A 16" motorcycle wheel is a 20" bike wheel, for example )
An 18" motorcycle wheel with the right moto/scooter tire roughly comes out to 24" in bike size, so for bikes with 26" wheels, you can get away with using a single 18" moto rear, as it should only drop the rear about an inch.
This is great because normally an 18" motorcycle rim and spoke combination would be about 4-5lbs, whereas with a 22" BMX rim, we're looking at more like 1-1.5lbs.
IF you want moto rims on both wheels, then this plan doesn't work and you need to step up to 19", however there is no bike rim equivalent in that size, so you're stuck with extremely heavy wheels and a difficult wheel build overall.
Here is a damned good thread showing how 19" moto rims + tires can be within an inch of 26" bicycle size. ( therefore, 18" can be within 2 inches if 26" - resulting in a rear drop of just 1 inch )
https://endless-sphere.com/forums/viewtopic.php?t=55458
In my experience, going dual motorcycle wheel is completely unnecessary on an upright bike because around 70% of your body weight is on the rear, therefore the rear is most likely to puncture and also needs the most traction. The front wheel is doing a fraction of the work, so the main reason you'd want a moto tire up front is for traveling at highway speeds, or perhaps just aesthetics.