Question: My 1997 Honda Accord came with a 115/70/14 donut spare tire. I had to use it for the first time recently, and it is now totally dead and needs to be replaced.

I looked on Ebay and there are a few people selling 115/70/14 Accord donut tires. But there are also a few people selling different sized Accord donut spares that they say will work on a 97 Accord. Those are sized 135/80/15, 125/70/15, and 125/70/14.

***Do I have to get a 115/70/14 tire, or will one of those other sized spares work as well?***

Answer: 
There is a huge pile of information about tire sizing around the internet. I'll attempt to summarize its application here.

Tires have 3 numbers, which work together to describe the tire's size. The first number is the section width, the second number is the sidewall ratio and the third number is the rim diameter.

**Section Width**

The section width is the width of the tire in millimeters at the largest point. This is important when trying to fit a tire to a rim, but in your case the rim is already matched to the tire so we're good. The number does still matter for us because of what we're calculating.

**Sidewall Aspect Ratio**

This is the distance from the rim to the tread. It is described as a percentage of the section width, so a 70% sidewall with a 130 section width will be taller than a 70% sidewall with a 110 section width.

**Rim Diameter**

This is the most obvious of the numbers. It is the rim diameter in inches. Why is the section width in millimeters and the rim diameter in inches? My guess is the same reason many manufactured parts in America are dimensioned in inches, but sometimes they hang out alongside parts manufactured to metric dimensions.

We can use these numbers to (roughly) calculate tire diameter...

Let's start with a standard factory sized '97 Accord tire (yours may vary depending on trim, but it will probably have a similar outer diameter):

185/65R15

185 / 25.4 = 7.283" (Metric to inch conversion) 

7.283 \* 0.65 = 4.734 (Sidewall height as a percentage of section width)

4.734 \* 2 = 9.468 (Double the radius to get diameter)

9.468 + 15 = **24.468** (Sidewalls + rim = outer diameter)

So following the same calculation:

115/70/14 = 20.339

135/80/15 = 23.504

125/70/15 = 21.890

125/70/14 = 20.890

It looks like your other 3 options are between your original spare and your standard tire diameter. As long as they'll fit in the spare tire well any one of them would likely be an adequate spare as long as the bolt pattern matches. I would favor something as close to the standard tire as possible if you know it will fit the tire well.

Please see [this link at the Tire Rack](http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46) for a more detailed explanation of tire sizing.

There is a calculator for tire diameter [here](http://www.csgnetwork.com/tiresizescalc.html).
**tl; dr** You can run it, but there is a cost.

You'd need to double check to ensure the rotations per mile (RPM) are almost/nearly the same (if not exactly). If it's off by more than a few percentage, you are going to have a problem with your anti-lock brakes (ABS) throwing codes on you. If you run a mis-matched donut on the front, you will have issues with over-heating your transaxle due to the mismatch of tire sizes. This is due to the differential having to make up the difference in . This will provide extra wear and tear on the differential, especially if it has a posi-traction style differential in it (not sure if Honda even has one, but it is something to consider). 

Bottom line - find one which is the same size. You'll be happy doing so and so will your car.