HPI Racing 114587 Heavy Duty Spur Gear 43 Tooth X5mm Savage XL Mini 8IGHT Parts Kyosho describes the purpose directly:

Kyosho describes the purpose directly: the weights attach to the front knuckle to increase tire load and change steering response

Compound choice is also a balance tool rather than just a grip question

Dual ball bearing equipped motor

Two weights are supplied

Budd Coach #4704 “Silver Glow”

HPI Racing 114587 Heavy Duty Spur Gear 43 Tooth X5mm Savage XL Mini 8IGHT Parts Kyosho describes the purpose directly:HPI Racing 114587 Heavy Duty Spur Gear 43 Tooth X5mm Savage XL This is a genuine HPI Racing heavy duty 43 tooth spur gear, 5mm width, for the Savage XL. The spur gear takes the full force of the drivetrain every run, and a heavy duty factory gear is built to shrug off the punishment a big monster truck dishes out. It installs during routine drivetrain maintenance and restores clean, dependable gear mesh when the original is worn or stripped. Genuine