Understanding section width is important for ensuring you get the proper tire size your wheel is capable of fitting. It can be a little confusing but we’ll cover the units of measurement, where to measure, and other important tire size widths that are related to section width.
What Is Section Width On A Tire?
The section width (in millimeters) is the first number included in the tire size sequence. It is the measurement from the widest point on the inner sidewall to the outer sidewall. Not including raised lettering and other decorative and protective protrusions.
There are different tire widths that people measure and different reasons for a mounting narrower or wider tire to the wheels on your vehicle.
Let’s take a closer look.
What Does Tire Section Width Mean?
Section width is the measurement from inner sidewall to outer sidewall when properly mounted, inflated, and without vehicle load. The measurement is in millimeters and doesn’t include ornamentation molded into the sidewall such as the lettering, protective ribs, and similar extensions that aren’t part of the structural sidewall.
Where Is The Section Width On A Tire?
The tire’s section width is the first number of the tire size sequence. The section width is measured in millimeters and is usually 3 digits followed by a forward slash.
How To Measure Tire Width
Measuring the section width of your tire requires beginning with it mounted onto an appropriately sized wheel with the correct wheel diameter and rim width for the tire being measured.
The tire must be inflated to the proper air pressure but not mounted onto a car or truck for measurement.
Measurement is performed using a tool that can properly span the entire width of the tire and accurately contact the widest point on each sidewall.
Official measurements are performed with the tire mounted to an industry assigned measuring rim.
Tire Width And Aspect Ratio
The aspect ratio (also know as section height) of a tire is a percentage of the tire’s section width. The tire’s width and aspect ratio are linked and changing one will have an affect on the measurement of the other.
The aspect ratio can be a complex topic in and of itself so we created an article specifically for explaining aspect ratio.
Section Width Vs Tread Width
Tread width is the measurement from the inner tread edge to the outer tread edge. Tread width isn’t included as a number with the tire size sequence and it is not listed on the sidewall of the tire.
Section width is usually slightly wider than this measurement since it includes the sidewall and any slight bulge that may be a part of the sidewall. These measurements are very similar and the names are sometimes used interchangeably.
How To Measure Tread Width
Measuring the tread width is difficult to do accurately since tread shoulders can either be very well defined or very gradual. This makes them a poor metric to unify around.
Section Width Vs Overall Tire Width
The tire section width is very slightly less than the overall tire width. The overall width is slightly greater since it includes lettering, protective ribs, and other elements tire manufacturers may include on a tire’s sidewall.
How To Measure Overall Width
Measuring the overall width is difficult to do accurately since the tallest protrusion from the sidewall must be found and measured to the tallest protrusion on the opposite sidewall. This makes them a poor metric to unify around.
Section Width Vs Rim Width
Specific tire widths require specific a rim width. However, one rim width is capable of accommodating multiple tire widths. Slightly wider tires or slightly narrower tires can be mounted to the same rim.
By increasing or decreasing the width of your contact patch you can increase cornering performance or reduce fuel consumption.
It should be noted that changing a tire’s width will change the tire’s section height slightly which will affect the overall diameter slightly. This can have a minor impact on speedometer readings.
How To Measure Rim Width
Rims are measured from bead seat to bead seat. This means that when measuring rim width you will measure from the inside of one rim lip to the inside of the other lip.
Tire Width Chart
Below is a chart/table of rim widths and tire section widths of recommended minimum, maximum, and ideal section widths for common wheel widths.
| Wheel Width | Min Section Width | Ideal Section Width | Max Section Width |
|---|---|---|---|
| 5.0″ | 155mm | 165-175mm | 185mm |
| 5.5″ | 165mm | 175-185mm | 195mm |
| 6.0″ | 175mm | 185-195mm | 205mm |
| 6.5″ | 185mm | 195-205mm | 215mm |
| 7.0″ | 195mm | 205-215mm | 225mm |
| 7.5″ | 205mm | 215-225mm | 235mm |
| 8.0″ | 215mm | 225-235mm | 245mm |
| 8.5″ | 225mm | 235-245mm | 255mm |
| 9.0″ | 235mm | 245-255mm | 265mm |
| 9.5″ | 245mm | 255-265mm | 275mm |
| 10.0″ | 255mm | 265-275mm | 285mm |
| 10.5″ | 265mm | 275-285mm | 295mm |
| 11.0″ | 275mm | 285-295mm | 305mm |
| 11.5″ | 285mm | 295-305mm | 315mm |
| 12.0″ | 295mm | 305-315mm | 325mm |
| 12.5″ | 305mm | 315-325mm | 335mm |
| 13.0″ | 315mm | 325-335mm | 345mm |
| 13.5″ | 325mm | 335-345mm | 355mm |
| 14.0″ | 335mm | 345-355mm | 365mm |
Resources
Below are some links you may find helpful when learning about tires
Final Thoughts – Tire Section Width
Section widths can seem confusing, and if I’m honest, it can get a little overwhelming if you’re new to tires.
Hopefully you know have a good understanding of the differences between section, tread, rim, and overall width.
Good luck and happy motoring.
