Question for Tire EXPERTS

[Ed_Gee]

Looking for facts - not guesses.
In the event of a flat tire, What are the ramifications of using a same spec tire of a different brand but that has an outer diameter up to 1/2 " less than the original?
Specifically on my small motorhome I have Hankook Dynapro HT RH12 195/75R16 tires, ( which in remote areas are hard to come by in a timely fashion). Other manufacturers of this size tire with same load characteristics all seem to be spec'd at .4 to .5 inches smaller outer diameter. What I am asking is what is the harm, if any, of installing the slightly smaller diameter tire in an emergency and running for a few hundred miles? What is the harm if I leave said tire on indefinitely?

[MrWizard]

Going to Ak , I would not do that trip without a spare,
Strap the uncounted spare to the roof, a little sun and water is not going to do anything significant to the tire

[wa8yxm]

If used on a single tire position (IE: Front) handling may be affected I would get the proper tire put on ASAP but safe to drive

If used on a dual tire position (IE REAR) might as well not bother to bolt it on as it won't be sharing the road.

Though you can play a 3 tire game (put the spare on the front move the front to the rear)

IF you have to use a different size spare remember ASAP also stands for Always Say A Prayer. (That is the level of I do not recommend this on a motor home.. I'd rather call the tireman and have him bus me out a new shoe.

[ol_Bombero-JC]

Where is he when you need him ??

Who, you ask ??

The ultimate **TIRE EXPERT** the OP asked for.......

.....so where are you - FastEagle..:@

(Golden opportunity to reappear!!)

:W

[Ed_Gee]

My thanks to all. Lots to consider. The Winnebago Fuse does not really have anywhere to mount or carry a spare tire, mounted or unmounted, and in the boonies, the stock Hankook tires can be hard to get. Will have to ponder whether or not to either figure out where to carry a proper unmounted spare, or just take my chances on using an other manufacturers tire if Imget a flat. Upcoming trip to Alaska .....

[Chum_lee]

et2 wrote:


Replacement tires on any axle, must be of the same manufacturer. The
brand, model, size, and load range and must have a load rated carrying capacity equal to or greater than the original equipment tires.
Mixing tires on any axle of a different brand, model, size, load rating and load range can cause unusual handling and uneven braking due to different traction coefficient and could result in sudden tire failure or loss of control due to non-symmetrical handling.

IMO, this is good advice. (reading your owners manual usually is) In addition to those who mentioned other specific driveability issues, especially on steering axles, different manufacturers build their tire sidewalls and treads differently and they aren't necessarily symmetrical. When you mismatch tires you may find that one tire applies more side force (lateral force in either direction) than the other. This can generate an offset lateral load on the axle causing the vehicle to pull left or right. Sometimes it can be corrected with alignment or air pressure, but it's really annoying to drive a vehicle that constantly pulls left or right, even slightly. And, . . . . it's dangerous.

Chum lee

[MrWizard]

Grit dog you are correct, did not think about that 1/4" aka 0.250" in ride/axle difference

The OP, indicates he does not have a spare
If he blows a tire, he has to have road service come out and mount a new one, which he will have to buy, and thinks he won't be able to get a matching tire
I doubt he wants to buy a new tire that does not match, drive to a shop and replace with another new tire of the his brand

While you do what you have too, in an emergency, I would not want to run hundreds of miles with a miss match tire then buy another new one
Better idea to keep a new spare on hand

With the safari DP 22.5 tires, we did not carry a spare
It came without one

We drove thousands of miles with out a tire problem
Instead we spent thousands $$ on engine problems

With 3 previous RVs, we needed and used a spare tire on multiple occasions,
I don't think I would drive very far on 16 inch without a spare

One year of ownership with this RV , Ford chassis and 16" tires
And I had one flat and then the old spare blew out, a few weeks later

I have replaced 4 tires, 2 front and 2 tag and swapped the best used tires to the drive axle
The 4 on the dually drive axle are next month

[Tvov]

Ed_Gee wrote:
.... What I am asking is what is the harm, if any, of installing the slightly smaller diameter tire in an emergency and running for a few hundred miles? What is the harm if I leave said tire on indefinitely?

If it is an emergency, I would think you would only be running a different tire for maybe 50 miles to a garage to get a replacement -- not a "few hundred miles".

If there is really such a small difference in size, you could probably run the tire without an issue. Think about when vehicles "blow" a tire, and get a replacement. That new tire most likely has 1/4 inch or more thicker tread than the older tires on the rig - and people do that ALL the time.

Note the word "probably" in the above paragraph... You SHOULD get tires all the same size, age and treadwear.

[CapriRacer]

As a general rule, in emergency maneuvers - the kind that should be of concern - vehicles tend to pivot around odd tires - and the more odd the tire, the worse that tendency.

In this case, we are talking a small motorhome with a different brand of tire that is 1/2" smaller in diameter.


First, this combination can NOT be used for duals. The larger diameter tire will carry more load, and that could cause a catastrophic failure of the larger tire.

Even assuming the intent is to replace one of the single tires, this still sounds like a very bad idea.

JaxDad wrote:
…… Are you sure about the size difference?

The tire size is literally that, the size of the tire. In your case a 195/75R16 is 195mm wide with a sidewall being 75% of that which is 147mm.

That means by definition it will have an 86.4” circumference.

Sorry, but those dimensions are only guidelines and the tire manufacturer can use any dimensions he wants. If the specs say they are smaller in diameter, then they are smaller in diameter.

[et2]

I'm no expert. But your owners manual might specifically state it. Good place to start.


Here's what mine says.



Replacement tires on any axle, must be of the same manufacturer. The
brand, model, size, and load range and must have a load rated carrying capacity equal to or greater than the original equipment tires.
Mixing tires on any axle of a different brand, model, size, load rating and load range can cause unusual handling and uneven braking due to different traction coef cient and could result in sudden tire failure or loss of control due to non-symmetrical handling.



That tire isn't that big why not just carry a spare if this is your concern in an emergency.

[JaxDad]

Ed_Gee wrote:
Specifically on my small motorhome I have Hankook Dynapro HT RH12 195/75R16 tires, ( which in remote areas are hard to come by in a timely fashion). Other manufacturers of this size tire with same load characteristics all seem to be spec'd at .4 to .5 inches smaller outer diameter.

Are you sure about the size difference?

The tire size is literally that, the size of the tire. In your case a 195/75R16 is 195mm wide with a sidewall being 75% of that which is 147mm.

That means by definition it will have an 86.4” circumference.

[2012Coleman]

Ed_Gee wrote:
Looking for facts - not guesses.

LOL

[Ralph_Cramden]

Grit dog wrote:
You guys realize the OP is talking about a tire that is 1/4" or less different in radius, right?

NO sir!.....don't think so.....

MDKMDK wrote:
This will be fun. Release the hounds......

Indeed.

[Grit_dog]

You guys realize the OP is talking about a tire that is 1/4" or less different in radius, right?
Only 1/2 to 1/3 the difference between a new and wore out tire of the same size and model.
Steer axle, won't notice anything.
SRW drive axle, won't notice anything or cause any harm.
DRW axle, I'd make sure the smaller tire is at max pressure and maybe soften up the taller tire a bit if you're loaded pretty heavy, but I'd run it, maybe not indefinitely. I've put a new spare on the back of a dually with worn tires a few times. Didn't result in any problems.

[MrWizard]

i think i would buy a spare identical tire

why keep a spare the wrong size, when you know there could be a problem

if i absolutely had to keep an undersized spare or run with out a spare

i would make sure it went on the drivers side front, and use that tire to replace any drive axis tire that had gone flat

even keeping an unmounted spare tire is a better option than NO spare and buying the wrong diameter for a mis-match