I know I will get some heat for this - but I've been doing some research (and didn't see any small cars running them here - just trucks) and I think it might work! They have stiffer sidewalls (for lower rolling resistance) and are way cheaper. Here's the points I thought of.
Pros:
I drive 55-65 max anyway so speed isn't an issue
I think the ride couldn't get much worse
The load rating on a trailer tire is higher then a passenger car
Easier to find 12" size in a trailer tire
Cons:
Trailer tires (supposedly) don't have the same quality regulations
Trailer tires on the front could make steering difficult at low speed
Trailer tires say 'for trailer use only' and could be an insurance liability
Okay, so flame on - why isn't everybody doing this??
