Full Sized Spare Tire mod for Gen 3 Hatchback

After blowing a tire in the northern Yukon and using the doughnut on very rough roads, we decided to replace the doughnut with a full-sized spare. On ebay I purchased a full-sized OEM alloy rim and the black plastic tray or tub just above doughnut ($100 and $75, respectively), and had new, standard-size tire mounted on rim ($80-$90). After removing jack mounting, doughnut, and Styrofoam pad under doughnut, the new rim + tire fits perfectly in the spare tire area and can be secured with the same large plastic screw in the center:


The black plastic tray above the doughnut must be raised slightly (about 2 inches) in the rear to fit down properly over a full sized spare. I removed the padding on the bottom of the tray, cut a semi-circle to fit the circumference of the tire in the rear of the tray, cut and melted off some of the flashing on the bottom, and glued the resulting flap of plastic back to the bottom and rear off the tray. The tray is polypropylene, so you must use a glue like JB Weld Plastic BOND that is certified for polypropylene. This pic shows the rear underside of the tray (upside-down) after the final gluing step: (The yellow pieces are wedges of polypropylene plastic cut from a pill bottle, shaped to fit the necessary gap, and glued in place.)


The modified tray is then re-inserted above the full sized spare just as it was originally above the doughnut. I found that the scissors jack would not fit in the full sized spare, so I store other things like the air pumps, plug kit, and survival gear with the spare and put my modified jack (larger base and hexagonal crank handle) in the black plastic tray. The original floor and carpet fit just as they did originally over the tray.


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So this is my solution to having a full sized spare. The advantage of this approach is not having any of the limits on speed, distance, and handling that installing the doughnut incurs, and not having to do a "double-tire-change" if a front tire blows out (rear to front, doughnut to rear). The airflow from the HV battery back to the 12-volt battery is also preserved (the triangular section in lower left of last pic directs that air flow). I think the air cooling of the HV battery will not be affected, but will monitor HV battery temp with my Scanguage to check on any effect of this mod on that critical parameter. Cheers!

 

That would avoid quite a bit of "cut and paste"!
Not sure what size would work given your approach, but you might consider still removing the pad glued to the bottom of the tray and possibly trimming off the reinforcing splines of plastic on the bottom of the tray at the rear to give yourself maximum space for the 15-inch spare you select. IMO as long as the tray fits right over the spare, the sidewall of the spare essentially supports the rear part of the floor of ,the tray.
Do you plan on using an OEM alloy rim or aftermarket? The large plastic scew securing the donut fit the OEM rim's central hole perfectly, but not at all sure it would fit aftermarket rims in the same way.
I carry an air pump and considered storing the spare in an uninflated state to effectively make it narrower but was not sure that would make enough of a difference in width to use an unmodified tray. Changing a tire would then involve the delay due to inflation, and I preferred to avoid that.
Would be interested in pics of your approach if you decide to try this.

 

Ok, now I am totally puzzled.
Here are the facts from measurements I just took:
The spare is a Yokohama Avid Ascend P195/65 R15 with no tread wear and it measures 64cm or 25 1/4 inches in diameter from outer edge of tread on one side to outside edge on the other.
The new Michelins fuel-savers I just had Costco put on last fall ALSO measure 64cm from edge of tread on one side to the other.
Finally, I checked for clearance in the well around the edge of the Avid spare as it is now mounted and found at least 1/2 inch at the front (the HV battery side) and the sides, so even a slightly larger diameter tire by 1 or 2cm should fit!
I have one of the last 2012 models made which we purchased as a "leftover model" in February 2013. Did the wheel well change from 2010 to 2012? Are there differences in models sold in US, Europe, or other areas in that wheel well?
Frodoz could you possibly measure your wheel well?
At the top of the well where it broadens out a bit, my measurements are 68.5cm from HV battery side to rear side, and 74cm from left side to right side at the widest point. What does yours measure?
Wish we could put the cars side by side and get to the bottom of this!

 

I also removed the reinforcing plastic underneath the tub right where it was contacting the spare tire, before doing the "cut and paste" method of altering the plastic tub to make it fit successfully over the full sized spare. I like your method of heating the plastic so that you can bend exactly that section around the rear of the spare to make the tub fit down correctly. I suspect that your "slumping" method will result in a stronger integrity of the tub than my "cut and paste" method, but there have been no signs of failure of the glue joints yet in my case, so I am satisfied so far.
However , I chose a different place to relocate the Jack. I chose to move the jack up into the tub rather than wedge it up against the HV battery housing, as a hunk of metal right next to the HV battery makes me uneasy when I visualize rear-end collision scenarios. I was also concerned to try to keep the air flow that cools first the HV battery and then apparently circulates over to the 12-volt battery and cools it, as uninterrupted as possible to avoid overheating either one. I watch HV temperature with a Scangauge but do not monitor the temperature of the 12-volt battery.
But I'm sure that either of us will feel better having a full sized spare the next time we have a flat or a blow out! Good job!