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How Bad is it to Drive on Mismatch Tires

3K views 9 replies 7 participants last post by  JeffBett 
#1 ·
I'm currently running 265/70r16 and my spare is the stock P4X (265/75r16?). If I had to use it, what are the ramifications? I would instinctively put it on the front so it's not on a drive wheel.

Sure it's not ideal, but how bad? Don't even think about it'll ruin your front differential/suspension? Or drive carefully as the car is going to handle poorly.

According to a tire size comparison its exactly 1 inch (3.3%) bigger.

Thanks!
 
#2 ·
Though I'm not a tire expert, for a truck like the Xterra it should be alright, 1" is not too severe just don't drive too fast or aggressively.

It should be fine, but get your tire fixed or get new ones (replace in pairs or all four) asap.

The ABS and traction control could get confused a bit but it shouldn't be severe.


Kal Tire-
"Many vehicle and tire manufacturers recommend the difference in diameter among your tires be no more than 4/32”. Some manufacturers even suggest a maximum diameter variance of 2/32”."

https://www.doityourself.com/stry/5-facts-about-spare-tires-
"If you have a full-size but mismatching tire, you will be able to drive it longer than a compact or dummy tire, but it will still have to be replaced by a proper matching tire and should not be included as part of your vehicle’s tire rotation pattern. "
 
#5 ·
#6 ·
I should have searched before. Looks like using a mismatched spare to get you to the shop might not work either

A good thread here:
https://www.thenewx.org/forum/69-brakes-tires-wheels/259714-twist-unmatched-tire-size-debate.html

"[with mismatched tires] in 2wd you’d likely be getting ABS, slip, traction control codes due to the perceived difference in speed between the front wheels and rear wheels due to the difference in rpms caused be the different circumferences."

Maybe I should buy a spare winter tire to put in the back to avoid this. Or fix-a-flat, though I heard this ruins the tire. More reading!

Thanks again
 
#7 ·
The thread linked in the previous post is a theoretical discussion (aka pissing contest) concerning the effects of running two tires of one size tire on the front axle and two tires of a different size on the rear axle, not the pros and cons of using a spare of a slightly smaller or larger size in an emergency situation.

The sizes used in OP's example are 265/70R16 on the ground (30.6" dia.; 659 rev/mile) and a slightly larger 265/75/R16 spare (31.6" dia.; 638 rev/mile). The spare is approximately 3.3% larger than the tires on the ground.

If one does the math to calculate the difference in revolutions/mile between inside and outside tires of the same size on the same unlocked rear axle in a typical turn with a 50-75 radius such as one might make turning left or right from one city street to another in everyday driving, the difference revolutions/mile between inner and outer tires of the same size is far greater than than 3.3% difference between OP's 265/70 regular tire and his 265/75 factory spare when both are going in a straight line.

My Conclusion: Our Xterras don't self destruct in normal turns in 2WD with lockers off so it is unlikely that any damage will be caused if one uses a slightly mismatched spare to get off the trail or to the closest tire repair facility once back on the highway.

Supporting indicia that my conclusion is correct:

1. The California Four Wheel Drive Association recognizes that many offroaders use mismatched spares and has promulgated this rule for sanctioned/sponsored events:

"Spare tire within 3 inches diameter of other tires, or, for tires 37" or larger, run-flats or tools to repair/re-inflate tire."

2. I have been running a smaller spare than the tires on the ground in my jeeps for at least the past 20 years. No issues. I used to run a 33x9.5 BFG AT spare with 35" BFG MT tires. I am currently running a 255/85R16 spare (33.3" dia.) with 315/75R16 tires (34.6" dia.) My reason for running a "pizza cutter" spare is weight and bulk rather than cost. 35" tires are heavy. If I were running smaller tires my preference would be a matching spare.

An observation:

I have used a tire plug kit and portable compressor far more often than I have used a spare tire. It is frequently faster and easier than crawling under the rig to lower the spare.
 
#9 ·
While all my tires are matched, I understand and agree with the points made by mister Bills.

That being said, I also consider the driver/owners decision making and prioritization skills.

If you have mismatched tires due to monetary/resource challenges fine,
....I/we will help you on the trail as best we can and not leave till you are well/safe/accounted for.

If you have mismatched tires at the trail head and I/we notice you have 1k$ lights, 1k$ fancy rims, and other assorted bling$$
then maybe I WILL question you decision /prioritization skills.

And also wonder what else did you defer/omit/or cheap out on?
 
#10 ·
Right now I have a spare Xterra that I have a set of more normal street tires on an extra set of rims I own. The fronts are 31" and the rears are 32". I had these sitting around and decided to use them around town instead of burning up expensive off road tires and I know to never use 4x4 in this configuration. Running normally the truck would go into limp mode after about 6-10 miles of driving because of the mismated sizes front to back. I had already had a switch in place to kill ABS and Traction Control so I quickly found turning them off makes it work just fine. I live in San Diego and only use this config around town or short highway trips so traction control is not that important to me, the ABS would be nice to have but I can live without it.

Not the same as just 1 tire different but may provide actual information that may help.
 
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