Can I use a different size spare tire?

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  #1  
Old 03-09-15, 10:05 AM
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Can I use a different size spare tire?

I purchased a used GMC Yukon that has some aftermarket 20" rims and tires on it. The tires that are on it are 285/R50-20 size. The optional size for this SUV according to GMC was a 275/R55-20.
I looked underneath the SUV and found that the spare tire, which has never been used is a P265/R70-17.
At my age I would hope that I never get a flat that I have to change in a remote area but the question I have is can I use the spare in place of the 20"??? It would not seem so but what do I know?
 
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  #2  
Old 03-09-15, 10:22 AM
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No....
Here is a handy tire chart for tire size comparison for you to look at. Just enter the size on the car & then the spare size under the vehicle.
Tire Size Comparison

According to the tire sizes you provided, I double checked just to see. There is a 1.3 inch difference in the diameter in the two tires.
Also, at 20 mph, one tire will attempt to turn at 20 mph, the other will be trying to turn at 20.3 mph.
At 70 on the interstate for example, one will attempt to turn at 70 mph while the other tire will attempt to turn at 70.9 mph.

I hope this helps... Good luck
 
  #3  
Old 03-09-15, 10:53 AM
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Hmmm~OK, TNX.
Maybe I don't have to worry about buying another rim and tire of the same size then.
 
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Old 03-09-15, 01:18 PM
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What you need to worry about is the age of the spare. If it's more than 5 yrs old it should be replaced, esp with our weather around here.
 
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Old 03-09-15, 01:24 PM
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I did look it over and there are not cracks and it's still got proper pressure after all these years. As stated, this tire has never been on the ground. But the SUV has lived in a garage all it's life and only had 52k on it when I picked it up used last year.
 
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Old 03-09-15, 01:33 PM
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If you ever read the sidewall on those 'donut' spares, it says not to be used for over 50 miles or over 50 mph [or something like that] I'd look at that undersized spare the same way. Not something you'd want to leave on the ground but it is something that will get you home or tire repair shop. It's important not to engage the 4 wheel drive if it's a 4x4.
 
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Old 03-09-15, 03:27 PM
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You can't tell by just an exterior visual inspection. The tire needs to be dismounted and the interior checked for flaking as such.

I was wrong on one thing, it should be dismounted and inspected at 5 yrs, and replaced after 10.

The age of the tire may be different than the age of the truck (which you have yet to mention). You need to check the sidewall DOT numbers and look it up. Mileage doesn't tell much. I have an 11 y/o car that only has about 65K miles. Other people probably have 2 or 3 y/o cars with that many.
 
  #8  
Old 03-10-15, 05:08 AM
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The important thing to look at is the height (or diameter) of the tire - you want that to match and it can do so even being on a different sized rim. For example, the tires on my car are 25.7" tall so I need to match that, regardless of whether it's a 16", 17" or 18" or even bigger rim.
 
  #9  
Old 03-10-15, 06:48 AM
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It is just a spare for an emergency and probably wont be on long - Definitely have it checked (dismounted and mounted) and then sleep well.

It is best to buy your replacement tires in pairs or in sets of 4. Look over the spare and chose if you want to use it as a spare or use the "best of the litter" for a spare. The odd size of the spare will not match you newer wheels and tires and any 4 wheel drive could get very dicey when it comes slippery roads.

Fortunately, I have 2 SUVs (a 1999 Jimmy with 190,000 on it and a 2000 Blazer with only 135,000 on it) and I have been able to swap between cars in pairs if necessary. The Jimmy is the best one although they are "kissin cousins". I have gravitated to Michelins because of the life and I had great luck over 30 years of replacing the rags on a new car with Michelins as soon as reasonably possible.

I had a Corvette with different sizes front to rear and it was recommended that tires should not be switched from left to right except in and emergency, so every tire was different and they were identified. - That gets a little pricey.

Dick
 
  #10  
Old 03-10-15, 06:30 PM
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It's OK to use as far as you DO NOT engage AWD or 4WD modes. Or, your car will seize moving in about 25 feet. You want to know how I know? So don't get stranded in remote dark area WINTER time.
Go to a Mexican tire place and get the right size spare.
 
  #11  
Old 03-11-15, 08:02 AM
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TNX for the replies. I am taking it down to dismount and inspect the tire today. This Yukon is not a 4 WD model so no problems there either. It's good to know that I don't have to spend $ to get a 20" rim and tire anyway. I have not had a flat tire in many years but you never know.
 
  #12  
Old 03-11-15, 06:41 PM
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If it's 2WD then don't worry about it.
Different overall wheel diameter locks transfer case when engaged.
Also, you just jinxed yourself. Sorry about that.
 
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