my original spare tire....

[Huskyguy68]

Yesterday I needed to remove everything thing out of my rear cargo area/remove the cargo floor cover, remove the original spare tire .
I needed to fix/reinstall my muffler heat shield that came off and decided to drill holes in the floor board under my spare tire in order to secure the heat shield with new bolts/washers/nuts....job done.

I removed the spare tire and was surprised how good looking condition the tire was/is.
I have a 2006 Nissan Xtrail SUV ( similar to size and shape, performance of a 2006-11 Rav4.) .
The vehicle originally came with 215/65R16s All Seasons. Then I bought and had installed new Cooper AT3 Lite truck tires at 215/70R/R16s.

My old spare tire on the steel rim is 215R/65R/R16.
I took my spare tire and rolled it up beside my current tires to see what the height difference is. I used a two foot wooden handle off my windshield squeegee and laid it flat on top of the spare tire , horizontal to see how much off spare to current tires would be. I figured my 65 spare tire would sit lower then my 70 tire, but the opposite was true. Just eyeballing it with the wooden handle, my spare tire appeared to be about 1/2 inch taller.

So here are my questions: Is it because I have the weight of my vehicle on my current 215/65s/16s that the tires seem lower in height then the 70 spare tire? like ummm...unsprung weight on the spare tire. In other words, IF I were to put my 70 spare tire on as an emergency replacement tire to get me back on the road to a tire shop/garage, is it safe to drive on ? ( I briefly googled this question and it seems it seems to be safe as the tire size height is within 3% plus or minus. Some AWD vehicles may give issues to the AWD system/overheat, but I can disable my AWD with the dash dial switch.Normally rides in FWD ).
Second question is the age of the spare. I bought my SUV in 2015 and i'm either the second or third owner. When I bought the truck it had on 215/65/16 All Season tires. Eventually I put on the Cooper lite truck tires. The spare tire is a Goodyear tire, it has a more aggressive tread then a normal all season. I think it too is a lite truck tire. I once again read off Google that any spare tire that is 0ver 6-10 years old is old, dried out, unsafe to drive on.
I do plan to replace the spare tire (it is not a donut skinny tire but an actually full size tire) ......but for now, if I had to put on this old spare tire , is that very dangerous to drive on a few miles below City posted speed limit ? should I never use it and just go buy another similar sized used tire as my 215/70/16s?

 

[LouC]

That is hard to say, because it can look fine on the outside and be bad on the inside, when a steel belted radial comes apart, it gets ugly fast, the steel belt strands will beat the hell out of the bodywork, depending on how it fails. I would not use a spare that is older than 10 years, in fact this year I am going to replace a set of General Grabber AT2s on my '98 Jeep that literally look brand new, only have maybe 25,000 miles on them, but I don't think it's worth the risk. They are just turning 10 years old. That Jeep is only used for local driving but some of that is highway driving. The bias and fiberglass bias belted tires we had in the old days, when they failed they weren't as destructive as what a steel radial does. In fact I still use regular bias ply trailer tires on my boat trailer partly for that reason. We had a General radial fail on a '75 Olds Delta 88 (big full size GM vehicle) and the steel on those was super thick. The steel belts bent the lip of the fender up, when it failed!
In general steel belted radials are an improvement over bias ply tires but when they fail watch out. We had bias ply tires fail in the old days and they never did the kind of damage that steel radials can do.

There will be a date coded on the tire, it will give a 2 digit # first (that's the week of the year of production) and then 2 more digits, that is the year.

 

[AZjeff]

215/65-16 is 27" diameter, 215/70-16 is 27.85" diameter (calculated) so it's right at 3% difference.

So here are my questions: Is it because I have the weight of my vehicle on my current 215/65s/16s that the tires seem lower in height then the 70 spare tire?

Is this backwards?

No opinion on safety if used at low speeds and short distance. If you had to drive a 20 YO tire 200 miles at highways speeds to get home might be cause for concern. Then again there are "Will it start and drive home" videos on YouTube with guys driving OLD terrible looking tires hundreds of miles.

 

[ecotourist]

Two good ways to keep your full size spare tire fresh: (1) Replace the spare tire with the best tire when getting new tires, or (2) Buy 5 tires and have all 5 in the tire rotation.

 

[k1xv]

My Corvette has no spare tire. And the one around my waist is many sizes too large.

 

[Huskyguy68]

215/65-16 is 27" diameter, 215/70-16 is 27.85" diameter (calculated) so it's right at 3% difference.


Is this backwards?

No opinion on safety if used at low speeds and short distance. If you had to drive a 20 YO tire 200 miles at highways speeds to get home might be cause for concern. Then again there are "Will it start and drive home" videos on YouTube with guys driving OLD terrible looking tires hundreds of miles.

yes, thanks for the advice, I think I need to track down a good used tire of the same size as my 215/70/16s and just stay in the safe range.

 

[Huskyguy68]

Two good ways to keep your full size spare tire fresh: (1) Replace the spare tire with the best tire when getting new tires, or (2) Buy 5 tires and have all 5 in the tire rotation.

I need to do a tire rotation . I'm gonna look for a good used lite truck tire as my spare.

 

[CapriRacer]

First, my comments on the fact that a loaded 70 series tire appears smaller in diameter than the unloaded 65 series spare.

There is no requirement that a tire match the published numbers. They can be both larger or smaller than the "nominal" dimensions. Tires deflect a lot, so it is no surprise to me that this happened.

Problems for the differential? - highly dependent on the drive system. Some systems are very tolerant and some aren't. Be very careful here!! These things can be expensive to repair.

Rolling diameter: The rolling diameter of a tire is about 3% less than the free-standing diameter. There is nothing than you can measure to determine the rolling diameter - either loaded or unloaded - except as I mentioned, the free-standing diameter - and even then, it's an approximation!

EXCEPT:

You can actually measure the rolling circumference by measuring the length a tire traverses in a single revolution. Please note: This is highly dependent on the inflation pressure and the load!

What this means is that if you have 2 different tires, you can NOT tell if the rolling diameters are different unless you actually measure it this way!

Interestingly, if you look at a tire load table with the relationship of load to inflation pressure - all those have the same deflection, and therefore that same rolling diameter! (For a given tire! Different tires will have different deflections.)

Is an old tire "safe"? Tire aging is highly dependent on the temperature it sees throughout its life. A tire in - say - Phoenix, will age much faster than a tire in - say - Minneapolis!

So to answer the OP's question: You didn't tell us where you live, and that could be the difference between being OK, and not!

 

[Huskyguy68]

so I called around 4-5 tire shops in my area, mostly to inquire about a used tire to mount on my 16'' steel rim spare.
One shop owner said i'm good/safe to drive on my 215/65/16 , that he drives frequently on his own older tires back and forth to work long distances/travels long distances and never has had any issues. I mentioned my spare tire could be from 2015 or older and he said not to worry, perfectly fine.
Having said that,I do not know what the inside of my spare tire looks like, so this will be just a temporary usage spare, still going to hunt down a good used spare tire in the 70 series..

First, my comments on the fact that a loaded 70 series tire appears smaller in diameter than the unloaded 65 series spare.

There is no requirement that a tire match the published numbers. They can be both larger or smaller than the "nominal" dimensions. Tires deflect a lot, so it is no surprise to me that this happened.

Problems for the differential? - highly dependent on the drive system. Some systems are very tolerant and some aren't. Be very careful here!! These things can be expensive to repair.

Rolling diameter: The rolling diameter of a tire is about 3% less than the free-standing diameter. There is nothing than you can measure to determine the rolling diameter - either loaded or unloaded - except as I mentioned, the free-standing diameter - and even then, it's an approximation!

EXCEPT:

You can actually measure the rolling circumference by measuring the length a tire traverses in a single revolution. Please note: This is highly dependent on the inflation pressure and the load!

What this means is that if you have 2 different tires, you can NOT tell if the rolling diameters are different unless you actually measure it this way!

Interestingly, if you look at a tire load table with the relationship of load to inflation pressure - all those have the same deflection, and therefore that same rolling diameter! (For a given tire! Different tires will have different deflections.)

Is an old tire "safe"? Tire aging is highly dependent on the temperature it sees throughout its life. A tire in - say - Phoenix, will age much faster than a tire in - say - Minneapolis!

So to answer the OP's question: You didn't tell us where you live, and that could be the difference between being OK, and not!

First, my comments on the fact that a loaded 70 series tire appears smaller in diameter than the unloaded 65 series spare.

There is no requirement that a tire match the published numbers. They can be both larger or smaller than the "nominal" dimensions. Tires deflect a lot, so it is no surprise to me that this happened.

Problems for the differential? - highly dependent on the drive system. Some systems are very tolerant and some aren't. Be very careful here!! These things can be expensive to repair.

Rolling diameter: The rolling diameter of a tire is about 3% less than the free-standing diameter. There is nothing than you can measure to determine the rolling diameter - either loaded or unloaded - except as I mentioned, the free-standing diameter - and even then, it's an approximation!

EXCEPT:

You can actually measure the rolling circumference by measuring the length a tire traverses in a single revolution. Please note: This is highly dependent on the inflation pressure and the load!

What this means is that if you have 2 different tires, you can NOT tell if the rolling diameters are different unless you actually measure it this way!

Interestingly, if you look at a tire load table with the relationship of load to inflation pressure - all those have the same deflection, and therefore that same rolling diameter! (For a given tire! Different tires will have different deflections.)

Is an old tire "safe"? Tire aging is highly dependent on the temperature it sees throughout its life. A tire in - say - Phoenix, will age much faster than a tire in - say - Minneapolis!

So to answer the OP's question: You didn't tell us where you live, and that could be the difference between being OK, and not!

Vancouver Canada.
So in this part of Canada (where my city sits next to the Canadian/American border/Pacific ocean on the west/mountains 30-50 klms to the north)we really do NOT get a true north American winter. More like...it's either raining or not raining. Summers are nice, not too hot, actually cooler compared to most of Canada and USA, some warm humid days in the summer.
Precipitation, mostly in the form of rain, about 169 days per year. The rainy months are Nov/Dec/Jan and mostly half of January .
Forget what they call the climate here....Rainforest coastal ----Vancouver, Canada has a temperate oceanic climate [1, 2] (Köppen climate classification Cfb) featuring mild, dry summers and cool, wet winters. Protected by the mountains of Vancouver Island and warmed by Pacific Ocean currents, it is one of the mildest and warmest cities in Canada.
We go by Celcius, so summers might be from 19C to 26C, with some days in late June/July/August going to 30-35C . It can get humid in these summer days, but honestly, mostly a perfect balance of sunny skies and averages of 20-25C .

Winter it can go to 7-9C daytime, rain or sunny. Very rarely gets to zero overnight. The spare tire was under cover in the spare tire wheel well, most sunny days I lower my windows to let the fresh air in.
If you ever visited Seattle, very similar climate and amount of rainy days/sunny days, temperature very similar...they may have a few more hotter summer days as they are about 2.5 hours/230 klms away from Vancouver.

One thing I will repeat, I have not had this tire dismounted from the factory spare steel wheel....so really, I have no idea if it has degraded from the inside out.
That is the really scary part. The tire can look great from the outside, but might be total junk on the inside.
So I'm thinking I should just go buy another good used tire that is not more then 5 years old and be done with it.

I don't want to change a flat tire, far from home, thinking my spare is good to travel on the freeway..then it shreds when i get it up to speed, lose control and crash head on to a semi truck or over a cliff, hurting/killing myself or others on the road.

 

[k1xv]

Lots of confusion about tire aging..

First, a tire mounted on a car, out in the sunlight and weather, flexing, and temperature changes, both ambient and due to heating while driving, It is aging at the "normal" rate for an in use tire.

A mounted tire sitting in a closed enclosure is not seeing sunlight. Is not heating and cooling from driving. Is not hitting bumps, or having its tread subject to physical stresses of acceleration, braking, and cornering. Its aging slower.

A tire sitting out of the sun in a temperature controlled garage or warehouse is seeing even less stress. Aging even slower.

Does anyone think the safe life span of a tire in years is the same under all three circumstances?

 

[Huskyguy68]

Lots of confusion about tire aging..

First, a tire mounted on a car, out in the sunlight and weather, flexing, and temperature changes, both ambient and due to heating while driving, It is aging at the "normal" rate for an in use tire.

A mounted tire sitting in a closed enclosure is not seeing sunlight. Is not heating and cooling from driving. Is not hitting bumps, or having its tread subject to physical stresses of acceleration, braking, and cornering. Its aging slower.

A tire sitting out of the sun in a temperature controlled garage or warehouse is seeing even less stress. Aging even slower.

Does anyone think the safe life span of a tire in years is the same under all three circumstances?

You brought up good points.
I read similar on the internet a few years ago.
And yes, my spare tire sat for at least a decade in the spare tire wheel well , all covered up , no sunlight, no real extreme temperatures.
I suppose the tire aged out to some degree with tire rubber oil naturally drying out to some extent.
I should take it to a few tire shops and ask what they think.

Maybe pay to dismount from steel rim and inspect inside the tire?
I just want to be able to safely use it and not harm myself or others out on the streets and highways.