A 35 fits in the factory under-bed spare location. A 37 does not — except on Gen 3 trucks with the factory 37 Performance Package, which got a revised carrier and a (slightly smaller-diameter spec) spare to make it work. If you've upsized aftermarket, your real options are: keep a 35 under the bed as a get-home spare, or carry a matching tire in the bed. And whichever you choose, the factory screw jack needs to be retired — it doesn't have the lift height to get a flat 37 off the ground on a drooped axle.
The spare tire question gets ignored until the day it matters, usually somewhere with no cell signal. Work it out in the driveway with a tape measure, not on the trail.
The factory spare well between the frame rails behind the axle has hard limits set by the spare winch travel and the frame crossmember:
A mismatched spare is workable within reason: a 35 spare on a truck running 37s is roughly an inch of radius difference. Fine to drive home moderately on a free rear ratio; on the front of a 4WD-engaged truck or with the rear locker active, it grinds driveline components against each other — put the mismatched spare on the rear, drive in 2WD, and keep speeds sane. The locker/Torsen guide explains why mismatched diameters and torque-biasing differentials don't mix.
Lift the truck, add tire diameter, droop the suspension when the wheel comes off the ground — the factory bottle-screw jack runs out of stroke before a 37 clears. Test it once at home and you'll never trust it again. Real options:
1. **Safe Jack-style bottle jack kit (~$200–$300):** a 6-ton bottle jack with screw extensions and a base plate for sand. Compact, stores behind the seat, lifts from the axle so suspension droop doesn't eat the stroke. The pragmatic choice for most trucks.
2. **Pro Eagle off-road floor jack (~$350–$450):** wheels that roll on dirt, huge lift range, fast. The desert-crew standard, but it lives in the bed and costs bed space — pairs naturally with a bed-mounted spare.
3. **Exhaust-air or hi-lift jacks:** the hi-lift is the wrong tool on this truck — there's no bumper or slider lift point on a stock Raptor that's hi-lift-safe, and a 6,000 lb truck on a hi-lift in sand is a guillotine. Skip it unless your armor was specifically built for it.
Whatever jack you carry, add a 12"x12" base plate (or a chunk of 3/4" plywood) — every jack is only as good as the sand under it. And confirm your lug wrench actually fits the aftermarket lug nuts on your aftermarket wheels; spline-drive lugs with a missing key have stranded more trucks than flat tires have.
For real desert trips on 37s, the answer is a matching spare in the bed: bed-mounted carrier ($300–$700, bolts through the bed floor or to a rack), or strapped to a bed rack alongside the traction boards the sand recovery guide already has you carrying. Mind the weight — a 37 on a bead-lock-style wheel approaches 130 lb, mounted high and behind the axle, which the rear suspension feels. It's the right tradeoff for remote trips and the wrong one for commuting; many owners load the bed spare only for trips and run the under-bed 35 day to day.
Get-home setup: aftermarket 35 take-off on a cheap steel or factory take-off wheel under the bed ($150–$300 used) plus a Safe Jack kit ($250). Full desert setup: matching 37 spare mounted ($600–$900), carrier ($300–$700), Pro Eagle ($400). Check the spare winch mechanism while you're deciding — they seize from dust and disuse, and a spare you can't lower is decoration. Run it down and back up once a season with the dust management habits this truck already demands.
| Part | Vendor | Est. price |
|---|---|---|
| Safe Jack 6-ton bottle jack recovery kit | Safe Jack | ~$250 |
| Pro Eagle 2-ton Big Wheel off-road jack | Pro Eagle | ~$400 |
| Bed-mounted tire carrier (various) | various | ~$500 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.