18×8.5 Tire Size: Perfect Rim

The 18×8.5 inches rim can accommodate several tire sizes including P 215/30 R18, and P 225/30 R18. However, among these options, P 235/40 R18 is considered the most optimal fit for the rim. At its maximum, the LT 38/15.5 R18 tire with a diameter of 38” is the largest tire that can be fitted on this rim. Conversely, the smallest tire that can be fitted on these rims is P145/40R18. Here
“LT” stands for Light Truck and “P” for Passenger car.

Thus, this is not the whole scenario that answers your question. So, go through further segments.

Tires Size Chart For 18×8.5 Rims

If you’re looking for tires for your 18×8.5 rims, here is a tire size chart to help you find the right fit. The tire sizes range from LT 35/12.5 R18 to P 255/45 R18, with various wheel diameters, sidewall heights, and load index ratings.

Tire sizeWheel diameterSidewall heightLoad Index Rating 
LT 35/12.5 R1835″8.50″123
LT 38/15.5 R1838″10.00″123/120
P 215/30 R1823.1″2.55″80/84
P 225/30 R1823.3″2.65″1389 lbs 
P 215/35 R1823.9″2.95″84
P 225/35 R1824.2″3.1″87
P 235/35 R1824.5″3.1″95
P 285/30 R1824.7″3.35″97
P 215/40 R1824.8″3.4″89
P 245/35 R1824.8″3.45″92
P 255/35 R1825.0″3.5″89
P 225/40 R1825.1″3.55″92
P 265/35 R1825.3″3.65″97
P 235/40 R1825.4″3.7″95
P 275/35 R1825.6″3.8″95
P 215/45 R1825.6″4.1″93
P 245/40 R1825.7″3.85″97
P 255/40 R1826.0″4.05″99
P 225/45 R1826.0″4.1″95
P 235/45 R1826.3″4.25″98
P 240/45 R1826.5″4.35″94
P 245/45 R1826.7″4.4″100
P 255/45 R1827.0″4.55″103

From the table, the first row of 35 represents the overall tire diameter in inches. And 8.50 inch refers to the sidewall width of the tire and the load index refers to the maximum load the tire can bear. Furthermore, the tire construction is R for radial, P fro passenger cars, and LT tires are classified as Light Truck tires. 

What is the Smallest Tire On 18×8.5 Rims?

The P 215/30 R18 tire is theoretically the smallest tire that can be installed on 18×8.5 inch rims, but it is strongly advised against doing so. This is because the tire width should be matched with the width of the rim, which in this case is 8.5 inches or 225mm after conversion.

However, the smallest tire width that can be installed on this rim is 145mm, which is significantly narrower than the rim. This mismatch can result in issues such as accelerated tread wear and tearing.

Furthermore, there will be a noticeable gap between the rim and the tire contact patch, which can lead to the tire being ripped off or dislodged at high speeds. Hence, despite the fact that this size tire can be mounted on 18×8.5 inch rims technically, it is not recommended for safety reasons.

What Is The Biggest Tire I Can Put On A 18×8.5?

On 18×8.5 inches rims, you can fit up to 38-inch tires which are the biggest that can fit on modified SUVs and pickup trucks. This is indicated by the tire size code LT 38/15.5 R18, where “LT” stands for “Light Truck” and indicates that the tire is designed for use on a truck or SUV. 

However, fitting such a large tire may require modifications to the vehicle, including fender trimming to accommodate the increased size of the tire, and the use of a lifter and spacer kit to create additional clearance.

These modifications are necessary to prevent the tire from rubbing against the vehicle’s body or suspension components, which could cause damage or safety issues. Additionally, in this setup, the tire width is much greater than the rim width. The wider contact patch can cause flexing, ripping, and rapid wear.

Furthermore, larger tires can improve an automobile’s off-road capabilities and aesthetic appeal. But, it can also affect the vehicle’s handling and fuel efficiency. Hence, it’s essential to carefully consider the benefits and drawbacks of modifying a vehicle’s tire size before making any changes. The pros and cons of this setup are listed below. 

Pros Cons
Smoother ride: Its taller sidewalls can provide a softer and more comfortable ride than low-profile tires.Less durable: For the greater contact patch with the track, this tire can wear out rapidly.
More cushioning: The increased sidewall height of these tires provides greater cushioning, which can help absorb shocks and reduce road noise.Risk of ripping out: Because the tire is too wide, it won’t fit perfectly and can rip out.
Better traction on rough terrain: The additional cushioning of this tire can provide better traction and handling on rough or uneven surfaces.Not ideal for regular road conditions: Higher sidewall is not ideal for regular road conditions if you want acceleration.
Improved fuel efficiency: High-profile tires tend to have a smaller contact patch with the road, which can result in less rolling resistance and improved fuel efficiency.N/A
Aesthetics: It can increase the aggressive and bold look of a vehicle.N/A

However, this tire is not recommended on a 18×8.5-inch tire for being too wide compared to the rim.

What Is the Ideal Fit For The 18×8.5 Rims?

P 235/40 R18 is the ideal fit for the 18×8.5 Rims according to the general rule of thumb. Numerous individuals have also reported a noticeable improvement in their vehicle’s performance after adopting this tire-rim combination, as seen on various online forums.

In accordance with the aforementioned rule of thumb, it is advisable to use a tire that is 20 mm wider than the width of the rim for optimal performance. In the case of an 8.5″ wide tire, which is equivalent to 215 mm, adding 20 mm to it results in a recommended tire width of 235 mm.

Furthermore, the aspect ratio of 40% is deemed ideal, as it is neither too high nor too low profile. As a result, this tire can perform effectively across various road conditions. However, it is important to note that there are both advantages and disadvantages associated with this tire-rim combination, which are listed in the table below.

1. Better handling and grip on dry roads
2. Improved cornering ability and stability
3. Enhanced braking performance
4. Better overall performance in wet and rainy conditions
5. Improved aesthetic appearance of vehicle
6. Availability of a wide range of tire brands and models
1. Reduced comfort due to lower aspect ratio
2. Reduced fuel efficiency due to wider tire
3. Increased road noise compared to narrower tires
4. Potentially higher initial cost compared to other tire sizes
5. Potential for compatibility issues with certain vehicles or suspension setups


Can I Use The Wrong Tire Size?

No, It’s not recommended to use the wrong tire size for your vehicle. A different size tire can affect your speedometer accuracy and may cause damage to your vehicle’s anti-lock braking systems and stability system calibrations. It’s important to stick with the tire size recommended by your vehicle’s manufacturer.

Can Tire Size Affect Speed?

Yes, tire size can affect speed. Up-sizing, or installing a taller tire, will lead to a speedometer reading that is slower than your actual speed. This is because a taller tire will have a larger overall circumference, causing it to need to travel more distance per rotation than the original equipment tire.

Why Do People Put Wider Tires In The Back?

People put wider tires in the back of their cars for better traction and a sportier appearance. Wheelspin is less likely to occur with wider tires on rear-wheel-drive cars with high horsepower. This helps to improve the car’s performance and handling, making it more enjoyable to drive. Additionally, wider rear tires can give the car a more aggressive and balanced look.


Well, now you know the 18×8.5 tire sizes. It is anticipated that the information provided will aid in selecting the appropriate tire dimensions for your vehicle featuring 18×8.5 inch rims. It is advised, however, to consider the benefits and drawbacks mentioned prior to altering the tire size by either increasing or decreasing it. See you later!

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at Autoglobes.com with a passion for the automotive industry.