This article refers to the fitting of a 'Temporary Use' spare tyre (T155/80R17), using an Australian Ford Falcon (Model FG) 'Temporary Use' wheel, under the rear floor of a 2021 Hyundai Kona EV.   Given that EVs often come without a spare, the concept might be adapted to other vehicles.
I should thank John Storey for his informative article documenting the fitting of a slightly smaller width (T135/80D17) tyre, in his Kona EV. He also used an Australian Ford Falcon (Model FG) 'Temporary Use' wheel.

The 'Tyre Mobility Kit' supplied with the Kona EV is essentially designed to temporarily repair a small puncture in the tread area of the tyre. A large puncture, a blowout, or damage to the sidewall will probably require tyre replacement. In such a situation, the small 12-volt compressor and can of liquid sealant supplied with the car will be useless.
In addition, the Kona EV is fitted with a Tyre Pressure Monitoring System (TPMS). 'Single-use sealant may not only render the tyre irreparable but also foul the TPMS.  Some tyre dealers may decline to fix a tyre that has been repaired using a temporary sealant.

Although a Kona EV full-size spare wheel (T215/55R17), would be ideal, it will definitely not fit under the rear floor. Enquiries to tyre dealers in Australia indicate that a new T135/80D17 tyre is no longer available. However at time of writing, Kumho Tyres offer a T155/90R17 'Temporary Use' tyre. This not only fits the Ford Falcon (Model FG) 17" rim, but has the advantage of a 20mm wider tread.
The Model FG Falcon has appropriate wheel offset and stud spacing and will fit the Kona EV wheel hub. Most importantly, it clears the EV's bulky rear electric parking brake mechanism.  Complete with tyre, the FG 'Temporary Spare' can be readily found at car wreckers, selling from around $50 or so.
Note: Although the FG wheel and tyre may appear unused, it has been several years since the FG Falcon was produced, so even if carried as a temporary spare, the tyre itself may need replacing.

Even though the T155/90R17 does present a challenge due to its wider tread, under-floor storage in the Kona is definitely achievable. Although the original cargo floor panel slides back into its original position, there is literally no clearance between the tyre and the underside of the floor. Obviously, the two foam storage trays have to go.

Materials Needed:
1/. Sheet of 7mm plywood (600mm X 897mm).
2/. Block of wood (about 140mm high X 350mm long).
3/. A 'Leg Plate Straight' (3/8" Whitworth thread).
4/. Piece of 3/8" threaded rod (about 100mm long).
5/. A 3/8" nut and spring washer.
6/. Large plate (wider diameter than the spare wheel centre hole), to clamp the spare in position. (I used a spare brushcutter 'wear plate'. A plywood disc would suit).
7/. A 3/8" wing nut. (I used a hammer to round over the top of the threaded rod, filed it smooth, then tightened the wing nut against it, before fitting the disc and locking the nut and spring washer up from underneath).

The mounting bolt might seem unnecessary, but it is needed to ensure the wheel stays firmly located, and clear of the exposed electrical cabling on the forward left side of the well.

The materials list is minimal. The cost was around $20


The plywood is cut to shape to fit just inside the top of the wheel well, below the horizontal surface that surrounds the well.
Although most of the wheel's weight is carried by the horizontal surface that surrounds the well, the plywood floor is positioned/supported by the sloping inside faces on either side and at the front of the well. On its rear edge, the plywood is supported by a block of wood. This is positioned in the well (on its narrow edge), against the rear panel.

Plywood floor in position with an assembled wheel clamp. Ensure the tyre sits clear of the cabling visible in the top left corner.

If substantial enough (ie; piece of the laminated beam), the wood block serves a secondary purpose. Placed under the jack, especially on soft ground, it will help to support the weight of the car, hopefully reducing the chance of the jack disappearing into the earth.
Because the Hyundai 'floor lifter' insert protrudes down into the well space, the wheel must be mounted so the tyre clears the lifter. Positioning the wheel roughly equidistant between the rear of the back seats and the rear vertical face of the wheel well will achieve this.
Before drilling the clearance hole for the clamping bolt in the plywood floor, make sure to drop the rear seats down to ensure their lower edge clears the tyre as they fold forward.

With the T155/80R17 'Temporary Spare' in place, the Hyundai Kona EV floor is a close fit. It only just slides back into its forward slots.


Although the spare only just fits, there is enough room for items in the well space under the plywood floor. Heavier items, such as the jack with its handle, an extendable wheel nut wrench, the Hyundai supplied 12 volt compressor (minus can of sealant), and the supplied towing eye, easily fit under the wheel.
A small waterproof tarp is used to wrap and cushion the above items in the well. The tarp can also be used to kneel in the mud when wheel changing. It will also be useful to wrap up the soiled flat tyre for later repair.
More frequently accessed items are probably best stored next to the tyre, immediately under the cargo floor. The Hyundai 10 amp 'trickle charger', and an 8 to 10-metre heavy duty extension lead, with 1.5 mm copper conductors to reduce resistive power loss can be packed on either side of the spare. If the wheel is mounted with its inside face uppermost, the larger recess offered can easily store a coiled 'Type2 to Type2' AC charging cable.
Although perhaps academic, the extra weight of the spare might be criticised, due to the EV's slightly increased loading and consequent energy consumption. For those interested, the Falcon FG T155/80R17 'Temporary Spare' weighs about 18 kg. The materials used to mount it (plus wheel changing tools) weigh much less.
Discovering a side-wall puncture on a cold and wet Sunday afternoon, on a lonely rural road, the driver might forgive the the slight extra weight of the spare. Perhaps the extra 20kg or so could be seen as a form of 'insurance policy' ... hopefully something you may never need.
But then ... you just might.