Tire Size 235/40r18 vs 235/45r18
The main difference between 235/40r18 and 235/45r18 tires is the aspect ratio. The aspect ratio is the second number in the tire size, representing the height of the sidewall as a percentage of the tread width.
In this case, the 235/40r18 tire has an aspect ratio of 40%, while the 235/45r18 tire has an aspect ratio of 45%. This means the 235/45r18 tire has a taller sidewall than the 235/40r18 tire.
| / | R |
| / | R |
| Parameter | 235/35 R18 | 205/40 R18 | Differ. |
|---|---|---|---|
| Tire Height | |||
| Section Width | |||
| Circumference | |||
| Sidewall Height | |||
| Revolutions | |||
| Rim Size |
Fitment Guide
The 235/45R18 is 3.6% larger in overall diameter than the 235/40R18, with a circumference difference of 2.91 inches.
Replacement tires should be within 3% of the original size to avoid clearance issues or speedometer error.
The 45 series may require adaptations like a lift kit on some vehicles, whereas the 40 series has a more direct fit as a replacement.
Ground Clearance
With 0.46 inches more sidewall height, the 235/45R18 provides increased ground clearance compared to the 235/40R18.
This can benefit off-road driving by reducing scrapes over obstacles. However, the larger diameter also causes a lower speedometer reading.
The 235/40R18 reduced clearance increases the risks of damage but gives a higher speedometer reading.
Gas Mileage
The slightly smaller 235/40R18 has a potential fuel economy advantage over the 235/45R18 due to decreased rolling resistance and rotational mass from its shorter sidewall and smaller overall diameter. This makes the 40 series tire more ideal for daily commuting.
Ride Comfort
The taller sidewall of the 235/45R18 absorbs road impacts better, providing a smoother ride over uneven surfaces.
The more flexible sidewall cushions bump better than the shorter, stiffer 235/40R18. This is advantageous on rough roads, but the 235/40R18 delivers a sportier, more responsive ride.
Aesthetics
Visually, the difference is subtle. The 235/45R18 has a slightly taller sidewall, which some may prefer aesthetically on trucks and SUVs over a very low-profile appearance.
However, the 235/40R18 promotes better vehicle aerodynamics with its shorter sidewall.
Handling & Stability
The 235/40R18 shorter sidewall height gives it sharper handling and quicker response on paved roads than the more flexible 235/45R18.
However, both offer stable handling characteristics. The 45 series suits off-road stability better.
Noise & Vibration
With its shorter, stiffer sidewall, the 235/40R18 transmits more road noise and vibration into the cabin.
The extra flex of the 235/45R18 better dampens noise and vibration for a more comfortable ride. However, the differences are minor.
Durability & Wear
The lower profile 235/40R18 exhibits potentially more even wear and longer tread life.
The taller 235/45R18 endures more impacts, but its added weight could increase wear on vehicle components. Both offer good durability.
Adverse Conditions
Performance in rain, snow, and off-road is comparable, but the 235/45R18 extra ground clearance gives it a slight edge.
The 235/40R18 shorter sidewall makes it a bit more responsive. Both handle adverse conditions well.
Speedometer Reading
At the same actual speed, the larger diameter 235/45R18 causes a higher speedometer reading than the 235/40R18.
For example, at an actual 20 mph, the speedometer would read 20.73 mph with the 235/45R18 but only 20 mph with the 235/40R18, a difference of 0.73 mph.
How Tall Is A 235/40r18 Tire?
The 235/40r18 tire has an approximate height, also known as the overall diameter, of 25.4 inches (645 mm). This height can vary slightly depending on the brand and model of the tire, as well as the amount of air pressure in the tire.
Can I Use 235/40r18 Instead Of 235/45r18?
Using 235/40r18 instead of 235/45r18 results in a diameter increase of 3.6%, which exceeds the recommended 3%. This can cause speedometer inaccuracies and handling issues, so it’s not advised.
What Does 235/40r18 Mean?
The tire size 235/40R18 can be converted to inches as 25.4×9.3R18. The term “235/40r18” refers to the tire size, with each number conveying specific information.
In this case, “235” denotes the tire’s width in millimeters, “40” represents the aspect ratio (height-to-width ratio), and “18” indicates the diameter of the wheel it fits, measured in inches.
How Tall Is A 235/45r18 Tire?
The tire size 235/45R18 is approximately 26.33 inches or 668.7 millimeters tall. This measurement represents the tire’s total height from the rim to the topmost tread.
What Does 235/45r18 Mean?
The tire size 235/45R18 can be converted to 26.3×9.3R18 in inches. Each “235/45R18” number in this sequence provides specific information about the tire. The first number “235” indicates the tire’s width in millimeters.
While the second number ” 45″ represents the aspect ratio or height-to-width ratio. The last number “18” informs us about the diameter of the wheel the tire is compatible with, measured in inches.
How Much Taller Is A 235/45r18 Tire Than A 235/40r18?
The 235/45r18 tire is 0.93 inches (23.5 mm) taller than the 235/40r18, representing a 3.6% increase in diameter. When properly mounted and inflated, the 235/45R18 stands 26.33 inches (668.7mm) tall, while the 235/40R18 measures 25.4 inches (645.2mm).
235/45r18 vs 235/40r18
This table provides a quick overview of the main differences between the two sizes.
Our Observation
Based on the comparisons, both the 235/40R18 and 235/45R18 offer advantages depending on usage. For responsiveness and handling, the 235/40R18 is slightly better suited to on-road driving.
The 235/45R18 has a minor edge for absorptions of impacts and off-road stability. Unless the vehicle is used extensively off-road, we’d recommend the 235/40R18 for most drivers.
Since its shorter sidewall promotes better fuel economy, handling, and aesthetic appeal. However, the differences are not significant, and both deliver overall solid performance.
Meet Caitlin McCormack, a Tire Size Expert and Blogger Passionate About Everything Related to Tires. With Years of Experience in the Tire Industry, Caitlin Has Become an Expert in Tire Sizes and Their Impact on Vehicle Performance.
