Changing Tire Size On Same Rim (Different Tire Size On The Same Rim)[Explained]

Last Updated on August 19, 2021 by Viva Elizeee

Do you want to change your tires but keep your rims? Well, that’s easy, but you’d have to understand how tire sizes work. Don’t worry; I’ll break things down in plain English.

You can change to a different tire size on the same rim. But, the new tires need to have the same inner bead diameter as your car’s rims. So, you need to know tire measurements before you change anything.

In this article, you’ll know:

1. If you can change tire size without changing rims

2. What to focus on when finding the right tire size

3. Where you can find your car’s tire size

4. The meaning of the sequence on your tire’s sidewall

5. And the tire sizes that you can interchange

Let’s go!

Can I Change Tire Size Without Changing Rims?

Yes, you can. But, you need to know what may happen.

Let’s take an example. Say you want to buy larger tires – ones with a larger outside diameter. Of course, they’ll fit well if their inner bead diameter is the same as that of your rims. But here’s how things will play out:

1. Since the tires have a larger outside diameter, they’ll take longer to complete rotations.

2. If rotations take long, your car’s computer will process incorrect data. Besides, other systems may fail.

3. For example, your speedometer will show slower speeds. That is if compared to the rotation of your wheels.

4. Also, the oversized tires will prevent the anti-lock brakes from engaging well.

What Do You Look At When Finding The Right Tire Size?

To find the right tire size, you need to focus on physical measurements first.  According to a Quora answer, you measure tires in three aspects. They are:

1. Section width

2. Sidewall height (as % of section width)

3. Inner bead diameter

Then, you need to consider other details, and they include:

1. Load index

2. Speed rating

Where Can I Find My Car’s Tire Size?

Whoever makes your car recommends a tire size. Then, they put that information in specific places for you to check. The places include:

1. The door jamb on the driver’s side

2. Inside the door of your glove box

3. Within the car’s gas tank hatch

4. On the sidewalls of your current tires

Have you seen some letters and numbers on your tires’ sidewalls? If yes, they should be something like this: P225/60R/16 91S. Car lovers know it as the tire sequence.

To better understand it, look at the following table:

Reading On Your Tire Size: P225/60R/16 91S
Tire Sidewall InformationMeaning
PMetric Tire Size
225Width
60Aspect Ratio
RConstruction
16Rim Diameter
91Load Index
SSpeed Rating

Meaning Of The Tire Size Sequence

Now, let’s see what the sequence means:

1. Metric Tire Size (P)

For many cars, P comes first in the number sequence. It is short for P-metric, meaning that the vehicle can carry passengers.

Now, where does the P come from? The TRA (Tire and Rim Association) has different designations, and P is one of them. So, a tire with P will go with passenger vehicles like:

1. SUVs

2. Cars

3. Minivans

4. Light-duty pickup trucks

For other vehicles, you’ll see the LT-metric instead of P. That means the tires are for light trucks. Also, they’re for other cars capable of pulling trailers and carrying heavy cargo.

Apart from the LT and P metrics, we also have T and ST:

1. T – Temporary

2. ST – Special Trailer

2. Width (225)

This number is in millimeters and gives your tire’s width. To explain, the width refers to the measurement from a sidewall to the other. So, for 225, the nominal width of the tire is 225 millimeters.

3. Aspect Ratio (60)

You’ll see the aspect ratio next to the width and after the forward slash. It describes how tall the tire is. Also, the figure is in percentage, and it relates to the width. But how? 

When making tires, cars divide a tire’s height by the width and multiply by 100. So what they get is the aspect ratio.

For example, in P225/60, the tire’s height is 60% of 225. So, to get the tire’s height, we can do some math:

Height / Width * 100 = Tire Ratio

Height / 225 * 100 = 60 

Height = 60 * 225 / 100

Height = 135 millimeters 

4. Construction (R)

Construction is a technical term that refers to tire stability. For most tires, construction is in two types: Radial or Diagonal/Bias Ply. And here’s what they mean:

1. Radial Tires

These are the vast majority in the US today, so you’ll often see tires with the R designation. Radial tire construction means the tire’s ply lines move in a radial direction. To explain, the lines move from one bend and over to the other.

RADIAL PLY

2. DIAGONAL TIRES

Here, the ply lines are diagonal from the center of the tire.

BIAS-PLY

5. Rim Diameter (16)

Next up is the rim diameter in inches. The rim is the part of the wheel where the tire fits. So, for our example, a P225/60R/16 91S tire will fit in a 16-inch diameter rim.

Other rim diameters include:

1. 22-Inch

2. 21-Inch

3. 20-Inch

4. 19-Inch

5. 18-Inch

6. 17-Inch

7. 15-Inch

8. 14-Inch

6. Load Index (91)

As you can guess, the load index marks the weight (in pounds) that the tire can support. But hey, can our tire only support 91 pounds? No, and I’ll tell you why.

Indexes are numbers and not weights. They begin with 0 and end with 150. And more, those numbers correspond to a specific weight.

Here’s a table giving some examples (from TirePlus.com):

Load IndexLoad (Pounds)
911356
099
10132
30234
50419
70739
901323
1102337
1304189
1507385

7. Speed Rating (S)

And finally, the last character in the tire size sequence is its speed rating. Tire makers use letters to limit the speed (mph) of your tire. For example, S is up to 112 mph and R up to 106 mph.

But don’t disregard legal speed limits because your wheels are S or R.

What Tire Sizes Are Interchangeable?

Well, interchangeable tires sizes are those that have identical tire sequences. So, it is crucial to know your tire’s sequence. Then, once you’re at the dealership, pick the ones that match your tires.

Since you already know the alphanumeric sequence, it shouldn’t be a problem. So, ensure the tires you’re changing to check all these boxes:

1. Metric Tire Size

Don’t get an ST-metric tire for your sedan or a P-metric for your RV.

2. Width

The tire’s width should be similar to what the manufacturer recommends.

3. Aspect Ratio

The thicker the tire, the longer the aspect ratio. But if your tire is longer, you will mess up with the car’s computer system.

4. Construction

Don’t mix constructions unless you changed your suspension. So, radial tires for radial wheels and diagonal tires for diagonal wheels.

5. Rim Diameter

If the inner tire diameter doesn’t match with the rim diameter, the tire won’t hold. So, for 16-Inch rims, you need 16-inch wheels, not any other thing.

6. Load Index

Ensure your tires do not exceed the manufacturer’s recommendation. For example, if your car’s manual says 110, why would you buy a 91?

7. Speed Rating

Again, it would help if you got this from your manufacturer.

Conclusion

Now, you know if you can change to different tire sizes while maintaining your rims. As you change the wheels, have the alphanumeric tire sequence in mind.

Also, check what your manufacturers recommend. They’ll guide you in making the best choices. You will find their comments inside the car’s manual.

And that was it!

Thanks for reading till the end, and I’d love it if your share the article.

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