Technical Note
How 35- and 37-Inch Tires Change Raptor Braking
In brief
A 37-inch tire increases the lever arm acting against the brake compared with a 35-inch tire. It often adds rotating and unsprung mass too. The brakes need more hub torque to create the same force at the road, while the larger assembly can add energy that must be managed during acceleration, suspension movement and braking.
The radius is a lever
Brake torque is applied at the hub and tire force acts at the road. For the same road force, required hub torque rises with tire radius. Comparing nominal diameters alone, moving from 35 to 37 inches increases that lever arm by about 5.7 percent.
That does not mean every stopping distance grows by 5.7 percent. ABS, tire grip, actual rolling radius, surface, load transfer and brake temperature all influence the complete result. It does mean the brake has a less favorable mechanical relationship to the road.
Weight and inertia arrive with the diameter
Two tires with the same nominal diameter can differ materially in weight and construction. A 37-inch assembly commonly carries more mass farther from the hub, increasing rotational inertia. Wheel width and material also matter.
Record the complete mounted wheel-and-tire weight rather than relying on diameter. The suspension must control that assembly over bumps, and the brakes must remove its rotational energy.
The factory 37 package is a system
Ford did not define the 37-inch Raptor only by fitting a larger tire. The factory package uses a chassis and electronic calibration developed around that configuration. Equipment also changes across model years, including the availability of later FOX Dual Live Valve hardware.
That makes factory 37-package and converted 35-package trucks different starting points. When ordering suspension or brake parts, identify the original package and current hardware instead of assuming all Gen 3 Raptors are identical.
What the driver may notice
A larger, heavier tire can reduce the immediacy of acceleration and braking. Repeated stops may create heat faster, particularly with added vehicle weight. Steering response and damper control can also change.
A strong single stop can still be tire-limited. The need for a brake upgrade often appears through repeated use: increasing pedal effort, changing friction, longer recovery or accelerated pad and rotor wear.
A practical upgrade order
- Confirm actual tire diameter, wheel offset and assembly weight.
- Verify pressure and tire grip for the load and surface.
- Service the existing brakes and establish a clean baseline.
- Select pad temperature range for the duty cycle.
- Add rotor and caliper capacity when repeated use or leverage requires it.
- Check wheel clearance with the exact brake template.
The 37-inch tire may be the correct choice for clearance and terrain. It simply needs to remain attached to the brake and suspension plan that makes it work.
View the Alcon Gen 3 Raptor brake kit