WHY, do mud dragsters have smaller tires on the front than the back?

My thought is that with teh same gear in the front and rear, that the front tires would be spinning more revolutions and thus clearing some path for the rear tires.

My brother in law says that can't be it because the bigger tires would be spinning faster and the fronts would be pushing.

 

Mud dragsters dont use the same gears front and rear....
They hav the front tires spinning a little faster than the rears to pull the dragster along,
they dont need huge tires up front, because when the dragster launches it plants the rear tires. The smaller tires do fine up front and allow for less weight of the entire vehicle....
Thats my guess....
I do know that the gears front and rear are not the same though, as they want to front tires to spin slightly faster to pull the dragster along,

 

I have a friend building one right now.

A built 540 in a tube chassis with Ranger body skins, that probably is going to weigh about 1800 pounds.
They don't run through the mud, they run on top of it.

Say as an example you ran 38" tires on the rear axle with 4.56 gears.
Then on the front, you run 33" tires with 3.73 gears.

When the transfer case input shaft was turning at 3300 RPM, the front axle tire speed would be 86.8 MPH.
The rear axle tire speed would be 81.8 MPH.

The extra tire speed of the front tires helps with steering through the mud pit.
Since the front tires are turning faster it helps pull the front which ever way you try to steer.

Now for the fun part.
If you ran a 4.56 rear axle with 36" tires and a 3.55 front axle with 28" tires, the ground speed of both axles with different size tires would be close enough to run in 4x4 without major problems.
If the transmission output shaft was turning 3300 RPM the truck would be going 77.4 MPH.
The distance traveled by the front tires in one minute would be 6813.96 feet, and the rear tires would travel 6820.36 feet.

 

some guys will actually gear for almost double the wheel speed on the front vs the rear. reason for this is a faster front tire will actually keep you straight. Other then that truckin4life is right it's mostly a weight thing. and it's usually in the upper classes of trucks you see this (promod and above) running enough HP to actually lift and carry the front tires. if you put big heavy ones on the front like the rear they will actually weigh the front down and drag or slow you down. Mud drags isn't all that different from on pavement in the principles of what works.