Recently by Eric Peters: The Little Things That Lead to BigThings
No, not the one around your middle. The one that used to be in your cars trunk.
Most cars (note: passenger cars, not just big trucks and SUVs) used to come with a full-sized spare tire.
What happened to them? And why?
Two thing led to the near-abandonment of the once-common full-size spare tire:
First, cars got smaller. A 1973 Nova considered a compact when it was new would be classified as at least a mid-sized, if not full-sized car, by modern car standards. Todays compact is a car like the Toyota Corolla a much smaller car, overall. And it has a much smaller trunk. A full-size spare would eat up most of the available space, which is the main reason why cars like the Corolla dont come with full-size spares anymore.
Even mid-sized cars today have fairly small trunks by the standards of what was commonplace a few decades ago.
Meanwhile, wheels and tires have gotten a lot bigger. Taller and wider. Seventeen and eighteen inch wheels are commonplace on current-year mid-sized family sedans. Even economy cars usually have at least 16 inch wheels. Taller and wider wheels (and the larger tires that mount on them) take up more space than the once-typical 15×7 (or smaller) wheel/tire combos of the past.
So, as a purely practical matter, the full-size spare outgrew its environment. Who wants to cart around a fifth wheel/tire that takes up a third to half the available trunk space?
Another problem was is changing styles. Many new cars (crossovers and hatchbacks) dont even have trunks, properly speaking. They have cargo areas. Now youve got the additional issue of visibility. No one wants to see a big old tire laying on the floor of their cargo area.
So the car companies (or the tire companies) came up with the mini or space saver temporary spare tire.
Early examples used a steel rim that was the same diameter (and sometimes even width) as the four regular wheels but the tire itself was deflated (and hence very compact). Cannisters of compressed carbon dioxide (or similar) came with the space saver and were used to inflate the tire when it was needed. The upside was these spares took up less room when not in use and also weighed a lot less than a standard-size spare, which helps both fuel economy and handling. But this this type of temporary spare isnt used much anymore, probably because of the hassle of having to inflate the tire and also because it wasnt uncommon for the inflator to have leaked d(or been lost) leaving you stuck and outta luck.
Ready-to-roll mini spares replaced the inflatable space saver; these are like the original space savers except the tire doesnt require inflation prior to installation.
As with the earlier inflatable type, current minis are great in the sense that they free up valuable trunk space, but have the downside of not being an equivalent wheel/tire relative to your other three still-good ones. The mini wheel will usually be much narrower, especially compared to the now-typical eight and nine inch wide alloy wheels many new cars come equipped with. Also the tire itself will not be high-speed-rated (as many new car tires are) or have the same ratings for load and heat and so on.
And here we come to the biggest weakness of these space-saving mini-spares: Theyre designed to get you to the next service station and thats it.
Most have warning stickers on them that caution against driving for more than about 50 miles or so or exceeding 50 mph. Expect your cars handling (and braking) to be affected not for the better.
The good news is you may never need to deal with this. Flats are not as common as they used to be because tires are tougher than they used to be. Theres still the potential for physical damage (running over a nail, etc.) but many people drive for years and years without getting a flat.
An alternative to breaking out the space-saver mini if you do have a flat is a can of emergency tire sealer/inflator such as Fix-a-Flat (or equivalent). Unless the tires sidewall has been flayed open, or you have a really massive hole in the tread, this stuff will usually get you going much faster (and more safely) than jacking up the car using the usually pitiful factory-provided jack/tools and trying to install the mini by the side of a busy road. Just screw the inflater bottle onto the tire stem and press the button. Usually, thats all there is to it. Maybe a 5 minute stop and you are back on the road and without your hands and clothes covered in grime and your (formerly) clean cargo area mussed up by your nasty old tire.
A few things to know, though: Like using the mini, using Fix-a-Flat is not a permanent fix. You should have the damaged tire dismounted and properly repaired as soon as possible. While handling/braking performance will not noticeably deteriorate (because youve still got the factory-type wheel/tire mounted instead of the much-smaller, less-capable mini) the tires structure could be compromised, so dont drive super fast or super hard. Also, tell the tire place you used the sealer. The goo inside the tire can be a hazard during dismounting if the tech doesnt take precautions and if you dont tell him, he may not.
Another option is to buy a real-deal spare in the same size (and with the same type tire) as the other four. If you have a car with a big enough trunk or dont mind losing the trunk space this alternative eliminates the problems of the mini and also the emergency sealer/inflator.
Be sure that the spare wheel you get is correct; i.e., that it has the right bolt pattern, diameter, width and backspacing for your vehicle. The best way to assure this is to get a a spare thats the same type of wheel as the ones that came on your car (junkyards are a great place to find these) and then mount a tire on it thats the same size/type as the tires on the other four wheels.
Reprinted with permission from EricPetersAutos.com.