I want to buy a fat bike.?

A 21-speed would be a 3x7 drivetrain.

Today, that would mean a freewheel.

Freewheels are weaker than freehubs.

Bad choice.

But so is using a Fat Bike for road riding.

You’ll pay for that look in speed and sweat every mile you ride.

The wider the tire you want, the wider the hub and the bottom bracket has to be for the chain to clear the tire.

There’s a reason - well, several - why most Fat Bikes use 1x drivetrains.

Why, oh why, would any rational being want to ride such a bike on paved roads?

Is something seriously wrong with you? A FAT tire bike on "Mostly paved roads"? I don't know what you've been smokin' - but...can I have some?

I dunno.

Have you ever ridden a fat bike? They are simply awful on pavement, the wide tires actually make them feel unstable on smooth surfaces. Fat tire bikes are designed for riding on soft uneven ground and they are used often for riding on snow covered trails. Before you buy one, try renting one to see what it is like. My son has a mountain bike with 3" wide tires and he hates riding it on pavement, finds he has trouble riding it in a straight line. Off road it is great however

I WILL RIDE A FAT BIKE ON PAVED ROAD. FULLSTOP. THANKS.

Why on earth (ha ha) would you want a fat bike to ride on pavement?