Aww yiss finally got around to getting the tyre fitted onto the rim...the wheel fits perfectly, and it actually had room to spare around the perimeter despite it being a 235/40/R19 tyre.
The original setup, note the floorboard (referred to within parts catalogues as "cover assembly") with its offset hook set on the weatherstrip:
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Donut spare:
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Spare wheel bay:
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Parts required:
Center foam piece or "spare wheel tray"/tool tray and the clamp/"spare wheel carrier"/center fastener (64779-33250 and 90080-94031 respectively):
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The original spare wheel carrier for the donut is on the top, as you can see above, it is longer than the one for a full size spare and thus will not hold down the wheel. On a side note, does anyone know what tools fit in the various slots/cutouts in the tool tray? There's space for the jack, towing hook and tire iron but otherwise that's the only ones I can think of.
The surrounding plastic piece or "luggage box"/spare tyre cover 64429-33020:
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64770-33160 for the cover assembly/luggage floor cover, bottom and top respectively:
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In the left picture, three spacers towards the back are visible, these provide the clearance for the board to sit properly over the luggage box.
And a full size spare wheel, best to get one from a junkyard or something. I bought everything brand new because we don't have any wreckers here that have late model camrys, not even ones that are statutory writeoffs. Maybe they're too valuable for parts to let plebs like us get our grubby little fingers on them at self-serve yards.
Aftermath
Fortunately doing this is simply a matter of swapping out existing parts, no tools required. With everything in place, here's what it looks like:
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Don't mind the specks in the floorboard; that's just grass lol.
And with the floor liner in place, the whole thing actually looks rather slick. But more importantly, you can carry things like a lawnmower without scuffing the floor:
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Got a better, brighter photo this time. Full size, 19 inch spare, with the new carrier holding it down. The original carrier had the bolt head visible in the top black plastic bit that you grip but besides that and the length of the carrier, they are identical. Interestingly, the diameter of the entire wheel is actually a bit smaller than the donut spare - the tread doesn't touch the walls of the spare wheel bay at all, but it's probably not easy to see here:
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Better, brighter photo here too. Notice the curve of the cover assembly hanging off the weatherstrip - this isn't just due to gravity, but is also the way the board was created so as to be able to clear the top of the luggage box (working together with the three spacers seen previously to make it sit properly over everything). Everything in place. Note the jack handle now being placed in the plastic cover, towards the right:
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Buying all this stuff brand spanking new, the whole endeavour probably cost me about 900 AUD but I kinda did it just because I could, and also because in the future it'd be one less thing to worry about on a long road trip if a tyre should pop. It might also increase the resale value of the vehicle, but that's just a fringe benefit for me as I don't intend to sell it any time soon - I went through all this mostly just because I could lol. Another benefit of a full size spare is being able to include it in tyre rotations - you can then go 20% longer between tyre changes. If you need a TPMS sensor this may bump the total cost to 1 grand AUD.
The biggest expenses were the alloy and tyre. You could easily get a used wheel for far cheaper from a wrecking yard or something. Assuming the 17/18 inch wheels and their tyres allow for an identical outer diameter as the 19 inch wheels, you could probably just scavenge those instead if you can't get your hands on a 19" wheel.
The foam tool tray was about 40 AUD for me but I got it at cost price so expect to pay more if not buying from a junkyard. Surrounding plastic piece/spare tyre cover was about 106 AUD, while the spare wheel carrier/clamp was around 25 bucks from the dealership because I was impatient. Alloy rim was about 487 AUD cost price, expect to pay much more for a brand new one. Getting same model tyres that the car originally came with (Dunlop SP Sport Maxx 050) would've cost me 370 AUD, but the tyre shop I used let customers price match and I was able to drop the price down a bit to 305 even after the initial price match the shop gave me. Basically, if you want to save cash, hit the junkyard or make friends with someone who works at Toyota, else fork out the cash at the dealership or buy from one of those third party sites that sell OEM parts for cheaper.
Also note that if getting a full size spare, cargo capacity is slightly reduced by 31 litres from 524 L to 493 L. Not sure if that's significant enough to impact usual grocery getting, but in practicality it just raises the central floor a little bit (about 1-2 inches).