<VV> Temp Tire Myths

Sat Aug 31 19:17:54 EDT 2019

Jack,

Thanks for the response.
I agree with your position that we should always "study test results and make an informed decision."  That is why I asked you for a link to the Motor Trend article you referenced.  I am asking for the same regarding your Car and Driver reference.  I didn't spend a lot of time researching but I couldn't find either online.
Please understand that I am not challenging your memory or knowledge but I also believe that we are all subject to what is known as "confirmation bias."  In effect, we tend to filter things we read or hear or see to confirm an outcome we prefer.  In the articles you reference, there might be words like, "During limited testing." or "Under controlled conditions."  I don't know if that is the case but that is why I want to read about the parameters of the tests and the results. 

I will repeat my concerns from my previous post and add to them. Please note that these concerns are fairly obvious.
1. The tread depth on the mini is minuscule compared to a regular tire.  Therefore, the tread life would be much less.  The depth of tread is barely at wear limit where you would be subject to an officer issuing a ticket if you had a standard tire.  Is this as safe as a normal tire?  This issue is aggravated by the smaller contact patch between the tire and the road.  A smaller contact patch will wear faster than a larger patch with the same weight, speeds, etc. in use.
2.  The rubber composition of the mini is harder than a standard tire.  In addition, the tire pressure is higher.  I believe this is because they want the mini to retain pressure over many years without attention.  A harder and stiffer tire will have poor braking and handling characteristics.  As in item 1 above, a tire with higher pressure and a harder substance will have a smaller contact patch.
3.  Due to both 1 and 2 above.  The already poor characteristics of the mini tire in normal use are far, far worse in the rain or snow.  While many areas of the country do not have rain and or snow year round most do have a rainy season as in Southern California.  I do not expect that people living in these areas will refrain from driving during this season or will choose to change their tires to go driving when the roads are wet.  Deeper treads and a more compliant tire are critical for safe operation under these conditions.
4.  To save weight, both the wheel rim and tire are made of much thinner material.  The metal rim is probably made from a less dense material though I am not certain of this.  This makes them much weaker if you were to hit a rock, pot hole or curb.  Further, with even moderate handling efforts, the more pronounced flexing of both metal and rubber could easily cause unexpected handling characteristics.  Even standard wheels are subject to deformation but are designed to stay as safe as is reasonably possible under expected conditions. 

5.  The perimeter and side walls of the mini/compact tires are very thin with fewer plies than you would normally have in even the cheapest of tires. This is one reason why they are inflated to almost double that of standard tires.  Mini spare tires do not need to meet the government's standards for normal use.  This is why they are approved only, I repeat ONLY, for very limited and low speed use.  In fact, the government does not require that a spare be included with any car.  Many new cars sold today do not have spares of any kind as standard equipment. The only reason any are included is because it is traditional.  The reason compact spares are even minimally safe under strictly limited conditions is because manufacturers want to avoid lawsuits.

6.  If you have a limited slip differential, the use of a compact spare on one side of that axle is of great concern.  Limited slip differentials are designed to slip minimally when you drive around a corner.  With a smaller diameter wheel on one side, that differential is slipping constantly.  It will be destroyed in short order.  Your warranty will not cover this.  All wheel drive vehicles will have this problem whichever corner has the mini wheel.  For this reason, it is far, far more important for you to use a mini wheel only for a very short distance with one of these vehicles.  Of course, if you have a compact wheel of the same size at all four corners, this is not an issue.
Regarding your aggressive driving with a compact spare, I am very happy that you survived the experience.  I have seen this sort of logic before.  Here is a story to drive home my point.
In the days of my youth, I had an acquaintance who was a degenerate drug abuser.  One evening, he decided to play a solitary game of Russian roulette.  He survived the attempt and a friend of his took the gun away immediately.  Using the logic that "I did something without negative effects." would you conclude that it is perfectly safe to play Russian roulette?  The fact that you have survived aggressive driving with mini spares doesn't mean you will continue to survive.
I suggest that you and anyone reading our posts read each of my stated concerns.  Consider as to whether they are false in any way then consider if they lead to the same conclusion that I came to.  Put simply, the every day normal use of compact/mini spares on your car is tempting fate.  Sooner or later, their use will lead to catastrophic consequences directly attributable to their misuse.
Here is "a thinker."  If compact spares are direct and safe replacements for regular tires, why aren't all regular tires built to the same specifications as the mini spares?  They are lighter and cheaper. These are two attributes that are very attractive to manufacturers.
Doc~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 8/31/2019 1:25:18 PM Pacific Standard Time, socalcorvairs at yahoo.com writes:

I don’t recall Motor Trend article date.Try Car and Driver’s test published Jan 2017.Believe what you want as a belief is just a myth, even from your favorite car manufacturer.Or study test results and make an informed decision.Many people still believe Corvairs are unsafe at any speed, even after testing that proved their superior handling.I have used a skinny spare on my Corsa in aggressive driving with no noticeable difference, but don’t often drive in rain or snow here in Paradise. (I live in California as testing proves it is the best!)Regards,Jack Pinard
Salty but Nice!

Jack Pinard iPhone 8s805.340.6533

On Aug 31, 2019, at 10:05 AM, roboman91324 at aol.com wrote:

Jack,

Do you have a reference to a Motor Trend article?  Is the test you mention available online?  I couldn't find it in a quick search.
I find it difficult to believe that the mini spares are virtually the same as the full size tires for the following reasons.

1. The tread depth on the mini is minuscule compared to a regular tire.  Therefore, the tread life would be much less.  This issue is aggravated by the smaller contact patch between the tire and the road.  A smaller contact patch will wear faster than a larger patch with the same weight, speeds, etc. in use.
2.  The rubber composition of the mini is harder than a standard tire.  In addition, the tire pressure is higher.  I believe this is because they want the mini to retain pressure over many years without attention.  A harder and stiffer tire will have poor braking and handling characteristics.  As in item 1 above, a tire with higher pressure and a harder substance will have a smaller contact patch.
3.  Due to both 1 and 2 above.  The already poor characteristics of the mini tire in normal use are far, far worse in the rain or snow.  Deeper treads and a more compliant tire are critical for safe operation under these conditions.
4.  To save weight, both the wheel rim and tire are made of much thinner material.  The metal rim is probably made from a less dense material though I am not certain of this.  This makes them much weaker if you were to hit a rock, pot hole or curb.  Further, with even moderate handling efforts, the more pronounced flexing of both metal and rubber could easily cause unexpected handling characteristics.
Car manufacturers offer very explicit warnings about the use of the spares.  They warn that they must be operated at lower speeds and for strictly limited duration.  This is due to the things I mention above and probably for additional reasons.  These tires are for temporary, emergency use because of their very real limitations.  The warning labels are there because the manufacturer knows that normal use can lead to accidents and law suits.
Periodically, I have seen people on VV who contend that mini spares are perfectly acceptable for every day use without reduced speeds and without handling concerns.  I believe that anyone who uses one or more of these tires on a car as if it/they are the same as a regular tire is tempting fate.  DON'T DO IT!
Doc~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 8/31/2019 7:12:16 AM Pacific Standard Time, virtualvairs-request at corvair.org writes:

Message: 5Date: Fri, 30 Aug 2019 12:59:25 -0700From: John Pinard <socalcorvairs at yahoo.com>To: virtualvairs at corvair.orgSubject: <VV> Temp Tire MythsMessage-ID: <61B04664-1B06-441A-8AF0-EC404917C067 at yahoo.com>Content-Type: text/plain;    charset=utf-8
Motor Trend tested many years ago and found no substantial difference in braking or handling at highway speeds, and tread life similar to full size tires.I don?t like a tire blocking access and view of enhanced engine bay, so temp lays flat up front only on long trips where there could be long wait for AAA.Found in discard pile at tire shop for five bucks.1966 Corsa convertible1964 Greenbrier Deluxe1965 Race Car ?97?
Jack Pinard87 Years in No. 1 State