According to Motor Trend and TFL, Ford told them the 37 has a different frame.
Road and Track says less travel with the 37's, see below
Is Road and Track a reliable source?
From Motor Trend
https://www.motortrend.com/cars/ford/f-150/2021/2021-ford-f-150-raptor-first-look-review/
Time For New Frames
Ford needed two new frames for the Raptor lineup; both modified to accommodate the new five-link coil-sprung rear suspension, and one further revised to accommodate a 37-inch spare tire mounted under the bed. In fact, the 37s are part of a whole system, including wheels and tires, a different frame for the spare, different shock hardware, and different overall tuning. The standard Raptor will come on 35-inch tires, which don't get the frame modification to fit the spare.
It is a pretty big change, Ford Performance Chief Engineer Carl Widmann says: "We probably should have put a second step board on it to get down from the vehicle. When you grab the steering wheel to get in, you will notice it right off the bat. And it definitely gives it a different appearance."
Back in the day, 35s were seen as a big step. "To get a factory-delivered vehicle with 37s that is all integrated in the chassis electronics, versus what people been doing when their 35s wore out, that's why we spent time to do this," Widmann says.
Ground clearance is 12.0 inches with the standard 35-inch tires and 13.1 inches with the 37s.
FROM Road and Track
https://www.roadandtrack.com/news/a35383467/2021-ford-f-150-raptor-details-photos-specs/
With the standard-fit 35-inch tires, Ford says the new Raptor offers 14 inches of suspension travel up front and 15 inches at the rear. Step up to the optional 37s and that travel decreases slightly, down to 13 inches at the front and 14.1 inches in the rear, to stop those big Raptor-specific BFGoodrich All-Terrain T/A KO2s from chewing away at the wheel wells. To fit those huge optional tires, Ford engineers had to lower the front differential slightly (it still sits higher than the frame crossmembers, so there's no decrease in ground clearance), relocate the front spring perches, and fit larger-diameter rods on the front shock absorbers. Trucks with the 37-inch option package get a special mount to fit a full-size spare under the bed, too—don't expect to outsmart the automaker by buying a truck with 35-inch tires and swapping on 37s.
Road and Track says less travel with the 37's, see below
Is Road and Track a reliable source?
From Motor Trend
https://www.motortrend.com/cars/ford/f-150/2021/2021-ford-f-150-raptor-first-look-review/
Time For New Frames
Ford needed two new frames for the Raptor lineup; both modified to accommodate the new five-link coil-sprung rear suspension, and one further revised to accommodate a 37-inch spare tire mounted under the bed. In fact, the 37s are part of a whole system, including wheels and tires, a different frame for the spare, different shock hardware, and different overall tuning. The standard Raptor will come on 35-inch tires, which don't get the frame modification to fit the spare.
It is a pretty big change, Ford Performance Chief Engineer Carl Widmann says: "We probably should have put a second step board on it to get down from the vehicle. When you grab the steering wheel to get in, you will notice it right off the bat. And it definitely gives it a different appearance."
Back in the day, 35s were seen as a big step. "To get a factory-delivered vehicle with 37s that is all integrated in the chassis electronics, versus what people been doing when their 35s wore out, that's why we spent time to do this," Widmann says.
Ground clearance is 12.0 inches with the standard 35-inch tires and 13.1 inches with the 37s.
FROM Road and Track
https://www.roadandtrack.com/news/a35383467/2021-ford-f-150-raptor-details-photos-specs/
With the standard-fit 35-inch tires, Ford says the new Raptor offers 14 inches of suspension travel up front and 15 inches at the rear. Step up to the optional 37s and that travel decreases slightly, down to 13 inches at the front and 14.1 inches in the rear, to stop those big Raptor-specific BFGoodrich All-Terrain T/A KO2s from chewing away at the wheel wells. To fit those huge optional tires, Ford engineers had to lower the front differential slightly (it still sits higher than the frame crossmembers, so there's no decrease in ground clearance), relocate the front spring perches, and fit larger-diameter rods on the front shock absorbers. Trucks with the 37-inch option package get a special mount to fit a full-size spare under the bed, too—don't expect to outsmart the automaker by buying a truck with 35-inch tires and swapping on 37s.