21" front as "emergency spare" on rear?

[Trogdors_Peasant]

Has anyone ever driven (not just mounted) a 21' stock wheel on the rear for a 4s or higher? I'm thinking of picking up 1 extra front to use for any front/rear tire incidents.

A past car didn't have a spare and with non-runflat 20-21" tires, it was susceptible to flats from bad roads.

A front wheel/tire could be used on the rear with no issues, and it came in handy to have one spare in the garage for the random flat near the house that could be used front/rear. Grab the floor jack and the mounted wheel/tire and get the car home and then to a tire shop without needing a flat bed tow. Out of the 3 flats I had from our vicious local potholes (hard to identify them when they're full of water), all were easier to handle that way versus waiting hours for a tow.

I checked on a wheel offset calculator, and it looks like it should fit just fine. Same inner barrel diameter for brake clearance, 2.5mm Diameter overall increase. 19.5mm more clearance on the inside towards the suspension, 31.5mm less poke, and only 1.25mm arch gap loss.

So it'll look silly, but the calcs say it should clear just fine.

I'm more concerned if the stability/traction control systems would have a freak-out with the diameter difference side to side in the rear.

Again, not asking for feasibility to drive long distance on this. It's just for 2-10 miles around town on back roads to get home and to the tire shop.

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[JAGMAN]

Haven’t tried what you’re suggesting, but that method is exactly the procedure for using the emergency spare on a 911. If a rear tire goes flat, put the front tire on the rear and the donut spare on the front.

of course one would have to buy the spare wheel kit, but I’d imagine it would work fine.