If you have a 4x4 vehicle with a TracLock (or any type of posi-traction unit) rear differential carrier, you should never run different diameter size tires on the same axle.
It could wear out the clutches in the carrier very quickly.
Another sound reason for having a spare tire the same size as the other four tires.

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05 Jeep Liberty CRD Limited
Blk Brush Guard/Hella's/LED's
Ironman Springs/Bilstein's
Yeti Stg4 MaxTune
Weeks ElbowKit/BatteryTray
NO FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pump
2mic.Sec.Fuel Filter
Flowmaster/NOcat
V6 Airbox
GM11 blade fan/NAPA HDclutch
Ironrock Trilink
98 Dodge Cummins, 5"exh. Viair, Huge K&N

If you use a five wheel rotation, then the cover becomes simply cosmetic. Yes, the spare will have ultraviolet damage, but no more so than any other tire, and will wear along with the other 4. A five wheel rotation will make a set last 20-25% more miles than a 4 wheel rotation.

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'06 Lbrty Sprt CRD 150K

Sasquatch
DSS Turbo
CAT-elimntr
Weeks Stg1&2 EGRfix
PV-200
BLING
vent gauges

IDParts
head
cams
rockers
Timing set
ARP studs
eTn1 GX2123 5v GPs

YETI Custom Tune
Flowmaster 8325508
Carter P76611M
GM 12611872
Hayden 2986
GM 15976889
PATC Custom Billet
2010 Ram Hemi Trans
Sonnax 44957
Transgo kit
Cooper 51770

IF YOU HAVE ANY 4X4 you need all 5 the same size , trust me , running around with a stock size tire on will cause issues sooner or later

Do it right from the get go and do not even think about spacers.
Even brand new stock 245-70-16s rubbed some when turning and mine was 4 weeks old then. ( yes brand new )
Spacers will only cause rubbing issues now especially now that springs are sagged

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MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 Goodyears/ 4.10's etc, 04 Kilimanjaro Edition loaded