A rant about the lack of spare tires on modern cars

[JohnH]

I had a flat tire on my 72 Coronet in January, near Des Moines Iowa. At around 2:00 AM. I had a ride with me, and we took turns jumping out to do as much as we could in a minute or two - it was around 30 or 40 below zero (Fahrenheit).

are you sure it wasn't 40 below celsius?

[ken_sylvania]

I had a flat tire on my 72 Coronet in January, near Des Moines Iowa. At around 2:00 AM. I had a ride with me, and we took turns jumping out to do as much as we could in a minute or two - it was around 30 or 40 below zero (Fahrenheit).

are you sure it wasn't 40 below celsius?

Des Moines, IA - would have been Fahrenheit!

[JohnH]

The existing system has worked well for me and I can't imagine lugging around a full size spare in the back. But I also drive a vehicle with commonly tires available everywhere.

It is really annoying how bigger and bigger rim sizes seem to be becoming common. Back in the early 90s, 14" was a "standard" rim size. By the 2000s, 16" was "standard". Now it is typically 17" on a fairly pedestrian vehicle like a Honda Civic

[ken_sylvania]

The existing system has worked well for me and I can't imagine lugging around a full size spare in the back. But I also drive a vehicle with commonly tires available everywhere.

It is really annoying how bigger and bigger rim sizes seem to be becoming common. Back in the early 90s, 14" was a "standard" rim size. By the 2000s, 16" was "standard". Now it is typically 17" on a fairly pedestrian vehicle like a Honda Civic

But we're saving fuel!

[Neto]

Another thing we have in common! I need to meet this guy!

That's what we did the other day in the snow storm. A donut on the front in snow is a very helpless feeling. I had snow tires on otherwise so swapping front to back made a huge difference. It was New Year's Day but some kind men at Bradford, PA Walmart offered to do the swap front to back for free which was very nice of them since they did not have a snow tire to replace the one that got sliced.

The temporary spare will get you to a safer place to do the swap. They say it's OK to go up to 50 miles before it starts to damage the transaxle, but I would do the swap as soon as possible. (Obviously, if you have an all-wheel drive that cannot shut down the secondary drive axle, then it's either get the full-sized tire fixed before going far at all, or wait until such services are available.) If your tires are a common size, Walmart would be an option for when most actual tire shops would be closed.

I had a flat tire on my 72 Coronet in January, near Des Moines Iowa. At around 2:00 AM. I had a ride with me, and we took turns jumping out to do as much as we could in a minute or two - it was around 30 or 40 below zero (Fahrenheit).

The key is to get a donut spare that has the same diameter as your regular tire. They don't all come like that but if you are buying an after-market donut spare you can easily find one that matches the car's tire diameter and then this will not be an issue. It will still be narrower so not as durable for long distances or heavy loads. But it will be something you can drive on indefinitely if necessary.

I'm looking at after-market donut spares for Teslas and they are all the identical tire diameter as the OEM tires. Just narrower to save space and weight.

Also if you have an odd size tire, you can replace it with a more standard size tire if you are willing to buy a cheap new rim. There are often 3 or more wheel/tire size combinations that will give you the same size diameter tire. For example, the different trim models of the Toyota Prius come in the following tire sizes: 195/65R15, 205/55R16 and 215/45R17. They are all the same diameter, you are just increasing rim size and shrinking tire size. So the much more common 195/65R15 can replace a harder to find 215/45/R17. That is what I'm doing right now. In other words, my spare is 195/65R15 and the rest of the tires on the car are 215/45/R17. Works fine.

That (finding a different tire that matches the other tires you have mounted on your vehicle) might be possible for some vehicles (perhaps the smaller ones), but in my experience it is not. It might be close, but not exactly the same. How close is close enough? That's a question for the automobile engineers. I would say that it's no big deal to run different size tires on older rear wheel drive vehicles, but ever since this government "pressure" to drastically increase fuel efficiency, the weight decreases in key drive line components have made them "pickier" for precise operating conditions. It is, however, also true that the diameter will vary quite a bit over the life of the tire, as the tread wears away. So running a brand new tire on one side of the drive axle with an old one on the other side is also not advisable.

There are tire size calculators on-line, as I'm sure you are aware. We are running 17" rims on our 2019 CR-V for winter tires, where as the stock rims are 18s. I chose the tire that is closest to the same, but there is no 17" tire that exactly matches the 18" tires designated by Honda. Well, at least with the added requirement that it be a Blizzak snow tire. So maybe if one were considering all types of tires, there might be a closer match. (I also never mix the Blizzaks with the standard size M&S tires we run in the summer.) But drastically different tread types can also create unusual mechanical wear on the drive line components. I think that another reason this is more important now than it was on older cars (and, I would infer, also with a narrower tire like a temp spare, even if it is the exact same diameter) is that all older vehicles used narrower tires, and like mixing a bias ply tire with radials, the traction rating is different. (There's a technical term for that, but I cannot remember what it is right now.) New laws are also pressuring tire manufactures to increase traction ratings while maintaining mileage efficiency ratings. (The "stickier" the rubber on the tread the better the traction, but this also increases "rolling resistance", which decreases the mileage rating.) But generally speaking, narrower tires will allow more slip than the wide tires used now-a-days, so this tire scrub allowed the tire to road surface parameter to absorb some of the difference, not forcing the drive line itself to deal with the added stress of uneven traction (due to different contact surface amounts). (This is also complicated by increasing awareness of environmental damages caused by some elements of modern rubber, specifically those that have been used to comply with the traction rating requirements. These materials are, for the most part, no longer being used on tires produced in the USA, but foreign manufacturers are not as forthright in revealing the makeup of their rubber products. (I read about these concerns in a magazine that is produced for the rubber industry. Not sure now, but I think it is called "Rubber World". I have interest in this field because of the need to eventually get some rubber replacement parts cast for my old car, like engine mounts and body to frame mounts, where the durameter - hardness - rating is crucial. When I originally rebuilt the car back in 80-81, I reused the original parts, but they have deteriorated in the intervening years. Unfortunately most replacement parts now available are made in China, and the experiences of other old car restorers reveal these products to be either extremely hard, or very prone to deterioration in a short span of time.)

[Ken]

The existing system has worked well for me and I can't imagine lugging around a full size spare in the back. But I also drive a vehicle with commonly tires available everywhere.

It is really annoying how bigger and bigger rim sizes seem to be becoming common. Back in the early 90s, 14" was a "standard" rim size. By the 2000s, 16" was "standard". Now it is typically 17" on a fairly pedestrian vehicle like a Honda Civic

You can easily swap back to the smaller rims and bigger tires if you want. They actually provide a better ride than the big rims and low profile tires that seem popular today. The base model stock cars like Civics still come with smaller rims and larger tires.

The current Civic comes with 215/55R16, 215/50R17, and 235/40R18 tire sizes depending on the level of trip. All of them have the same tire diameter (or very close to it). You are just exchanging tire diameter for rim diameter to get to the same place.

[Neto]

The existing system has worked well for me and I can't imagine lugging around a full size spare in the back. But I also drive a vehicle with commonly tires available everywhere.

It is really annoying how bigger and bigger rim sizes seem to be becoming common. Back in the early 90s, 14" was a "standard" rim size. By the 2000s, 16" was "standard". Now it is typically 17" on a fairly pedestrian vehicle like a Honda Civic

But we're saving fuel!

I suspect this trend is mostly 'driven' by stylistic preferences - a fad. The larger the wheels and tires, the greater the 'unsprung weight'. This requires beefier suspension components, because the tires and wheels themselves are also MUCH MUCH heavier than their older counterparts. Back in the 20's (the NINETEEN 20's) larger wheel diameter was important (due to the poor road conditions). My 46 Plymouth came with 16" wheels. By the end of the Plymouth P15 manufacturing cycle (the cars were nearly identical from 1946 until early 1949) they had dropped to 15" rims. Part of it is of course the fact that "I'm no longer 23", but at three times that age I struggle a bit to mount the 18" wheels on the Honda - I have to "get creative" to get it up there and align the wheels with the studs.

[ohio jones]

It is really annoying how bigger and bigger rim sizes seem to be becoming common. Back in the early 90s, 14" was a "standard" rim size. By the 2000s, 16" was "standard". Now it is typically 17" on a fairly pedestrian vehicle like a Honda Civic

If you want a pedestrian vehicle, get a Ford. Hondas are more reliable than that.

[Ken]

The temporary spare will get you to a safer place to do the swap. They say it's OK to go up to 50 miles before it starts to damage the transaxle, but I would do the swap as soon as possible. (Obviously, if you have an all-wheel drive that cannot shut down the secondary drive axle, then it's either get the full-sized tire fixed before going far at all, or wait until such services are available.) If your tires are a common size, Walmart would be an option for when most actual tire shops would be closed.

I had a flat tire on my 72 Coronet in January, near Des Moines Iowa. At around 2:00 AM. I had a ride with me, and we took turns jumping out to do as much as we could in a minute or two - it was around 30 or 40 below zero (Fahrenheit).

The key is to get a donut spare that has the same diameter as your regular tire. They don't all come like that but if you are buying an after-market donut spare you can easily find one that matches the car's tire diameter and then this will not be an issue. It will still be narrower so not as durable for long distances or heavy loads. But it will be something you can drive on indefinitely if necessary.

I'm looking at after-market donut spares for Teslas and they are all the identical tire diameter as the OEM tires. Just narrower to save space and weight.

Also if you have an odd size tire, you can replace it with a more standard size tire if you are willing to buy a cheap new rim. There are often 3 or more wheel/tire size combinations that will give you the same size diameter tire. For example, the different trim models of the Toyota Prius come in the following tire sizes: 195/65R15, 205/55R16 and 215/45R17. They are all the same diameter, you are just increasing rim size and shrinking tire size. So the much more common 195/65R15 can replace a harder to find 215/45/R17. That is what I'm doing right now. In other words, my spare is 195/65R15 and the rest of the tires on the car are 215/45/R17. Works fine.

That (finding a different tire that matches the other tires you have mounted on your vehicle) might be possible for some vehicles (perhaps the smaller ones), but in my experience it is not. It might be close, but not exactly the same. How close is close enough? That's a question for the automobile engineers. I would say that it's no big deal to run different size tires on older rear wheel drive vehicles, but ever since this government "pressure" to drastically increase fuel efficiency, the weight decreases in key drive line components have made them "pickier" for precise operating conditions. It is, however, also true that the diameter will vary quite a bit over the life of the tire, as the tread wears away. So running a brand new tire on one side of the drive axle with an old one on the other side is also not advisable.

There are tire size calculators on-line, as I'm sure you are aware. We are running 17" rims on our 2019 CR-V for winter tires, where as the stock rims are 18s. I chose the tire that is closest to the same, but there is no 17" tire that exactly matches the 18" tires designated by Honda. Well, at least with the added requirement that it be a Blizzak snow tire. So maybe if one were considering all types of tires, there might be a closer match. (I also never mix the Blizzaks with the standard size M&S tires we run in the summer.) But drastically different tread types can also create unusual mechanical wear on the drive line components. I think that another reason this is more important now than it was on older cars (and, I would infer, also with a narrower tire like a temp spare, even if it is the exact same diameter) is that all older vehicles used narrower tires, and like mixing a bias ply tire with radials, the traction rating is different. (There's a technical term for that, but I cannot remember what it is right now.) New laws are also pressuring tire manufactures to increase traction ratings while maintaining mileage efficiency ratings. (The "stickier" the rubber on the tread the better the traction, but this also increases "rolling resistance", which decreases the mileage rating.) But generally speaking, narrower tires will allow more slip than the wide tires used now-a-days, so this tire scrub allowed the tire to road surface parameter to absorb some of the difference, not forcing the drive line itself to deal with the added stress of uneven traction (due to different contact surface amounts). (This is also complicated by increasing awareness of environmental damages caused by some elements of modern rubber, specifically those that have been used to comply with the traction rating requirements. These materials are, for the most part, no longer being used on tires produced in the USA, but foreign manufacturers are not as forthright in revealing the makeup of their rubber products. (I read about these concerns in a magazine that is produced for the rubber industry. Not sure now, but I think it is called "Rubber World". I have interest in this field because of the need to eventually get some rubber replacement parts cast for my old car, like engine mounts and body to frame mounts, where the durameter - hardness - rating is crucial. When I originally rebuilt the car back in 80-81, I reused the original parts, but they have deteriorated in the intervening years. Unfortunately most replacement parts now available are made in China, and the experiences of other old car restorers reveal these products to be either extremely hard, or very prone to deterioration in a short span of time.)

I wouldn't mix up different brands of tire on the same car even if they were the same size for all the reasons you cite. And worn tires are measurably smaller diameter than new ones.

But if you are spec-ing out a full size spare or replacement wheel/tire in a pinch then it is going to be fine. \

For example, the Prius that I'm currently driving that was the subject of the original post? It has 215/45R17 tires. I bought the full size spare about 9 years ago when I punctured the sidewall of the tire at my daughter's soccer practice and was stuck there with no way to move the car without a spare. I went to a local tire shop which didn't have a replacement 215/45R17 tire in stock on a weekend and so I just bought a 205/55/R16 tire on a generic steel rim to get the car out of the school parking lot and that became my full size spare. It is 1% larger diameter and 4% narrower in width. But is perfectly fine as a full size spare. That is within the range of new to worn tread. Or for that matter, two tires that have slightly different levels of inflation.

[Neto]

It is really annoying how bigger and bigger rim sizes seem to be becoming common. Back in the early 90s, 14" was a "standard" rim size. By the 2000s, 16" was "standard". Now it is typically 17" on a fairly pedestrian vehicle like a Honda Civic

If you want a pedestrian vehicle, get a Ford. Hondas are more reliable than that.