If you’ve stumbled upon this guide, then chances are you just bought yourself a sweet set of 18×8.5 rims for your ride, but now the next tricky bit is to actually find the right set of rubber to wrap around them.
When it comes to pairing wheels and tires, proper fitment is key to ensuring the best performance, comfort, and safety while driving (also helps them avoid looking dreadful on your car).
So if you want to find out just exactly how big and how wide you can go for your 18×8.5 wheels, stick around as we list the best tire sizes to pair it up with before you tear up the tarmac!
What does it mean when rims are 18×8.5?
A rim size of 18×8.5 means that the rim has a diameter of 18 inches and a width of 8.5 inches.
The first number of a rim size is the rim diameter in inches (e.g. 18), while the second number after the “x” is the rim width that is also in inches (e.g. 8.5).
When picking out rims, it’s important to understand how their sizes or dimensions are listed, which means primarily knowing both the rim diameter and the rim width.
If you’ve ever seen a set of rims being sold as “18×8.5”, for instance, this is your main way of telling their dimensions in inches, with the first number (18) simply being the overall diameter and the second number (8.5) being the overall width.
Sometimes, you may even find some tire sizes that are listed slightly differently, such as “8.5Jx18”. This is essentially the same thing, with the addition of the letter “J” denoting the rim’s bead profile.
Rims with “J” bead profiles are the most commonly used for passenger vehicles. Other than that, the rest of the rim dimensions are pretty straightforward as we’ve discussed.
After understanding how rim sizes work, it’ll be a lot easier to pair them with compatible tire sizes. This is more so the case if you’re trying to find the best tire size for your 18×8.5 wheel.
What is the best tire size for 18×8.5 wheels?
The best tire size for an 18×8.5 wheel is 235/40R18, which gives a good balance of performance and comfort in everyday driving conditions.
But depending on your needs, you may choose wider tires (245 or 255) for better performance, or narrower tires (225) for improved fuel economy and comfort.
When you get yourself a set of 18×8.5 wheels, then the universally accepted best tire size for it would be 235/40R18. But why is that?
In general, car manufacturers carefully consider which tire size would go with the best rim size in terms of comfort and performance when equipping a vehicle model with OEM wheels, and this is also the case even for manufacturers of bigger aftermarket wheels.
While each particular rim size is still compatible with a limited range of tire sizes, wheel manufacturers usually recommend only one optimum tire size that makes the wheels well-rounded (no pun intended) for their application.
But then again, not everyone goes for a “well-rounded” wheel setup. As such, some may opt for slightly wider 245mm tires for their 18×8.5 rims to get more grip and so that it looks more “aggressive”.
Of course, there are also some potential drawbacks to going for tires bigger and wider than what’s recommended, including increased fuel consumption and inaccurate speedometer readings.
What size tires fit 18×8.5 wheels?
An 18×8.5 wheel can be fitted with tire sizes such as 225/40R18, 235/40R18, 245/35R18, 245/40R18, and 255/35R18.
Among these tire sizes, 235/40R18 is the most recommended, while 225/40R18 is the minimum tire size and 255/35R18 is the maximum tire size.
225/40R18
If you’ll be running on a set of 18×8.5 wheels but prefer a slightly smaller setup for your rubber, then a tire size of 225/40R18 will fit the bill.
However, do keep in mind that this tire size is considered the minimum recommended for most everyday setups. How it fits and performs can still depend on the specific vehicle model.
As an example, 18×8.5 wheels wrapped around 225/40R18 tires are a common wheel setup for the Toyota 86 or Subaru BRZ. The setup is not far off from either car’s OEM tire size of 215/45R17.
It becomes a different story, however, when you opt for 215mm-wide tires on 18×8.5 wheels, as the wheels end up stretching the tire sidewalls slightly outward, possibly affecting their performance and durability.
In some cases, people already experience a bit of stretching even with the 225/40R18 tire size for their specific 18×8.5 wheels, let alone with a 215mm one.
This is why it’s generally recommended to not go any smaller than 225/40R18 for 18×8.5 wheels if you really value a well-balanced setup with little to no stretching.
235/40R18 (Recommended)
Going one size higher (or wider) from the last size, we move on to the 235/40R18, which is actually the most optimum setup for any set of 18×8.5 wheels.
With this particular tire size for 18×8.5 rims, you’re less likely to run into any issues with stretching or the tires rubbing against the wheel wells, assuming your car can even accommodate this kind of wheel setup, to begin with.
Moreover, a tire size of 235/40R18 will give you the best of both worlds when it comes to overall performance and ride comfort, which is why manufacturers recommend it the most when choosing new rubber for 18×8.5 wheels.
245/35/R18
If you prefer to go just a bit bigger than the optimal 235/40R18 tire size, then another compatible size for your 18×8.5 wheels would be 245/35R18.
This tire size is 10mm wider but also has an aspect ratio that’s 5% less, which translates to sidewalls that are just a tad bit shorter than the ones for the 235/40R18.
To explain, a 40% aspect ratio on a 235mm-wide tire would mean that the sidewall is 94mm, while a 35% aspect ratio on a 245mm-wide tire equates to an 85.75mm sidewall. That’s just under 10mm (0.4 inches) of difference.
While this kind of setup may give you more handling performance, having the shorter and thinner sidewalls means that you’ll also sacrifice a bit of comfort in that you’ll have less cushioning when going over bumps.
245/40R18
Another 245mm tire size that you can pair up with your 18×8.5 wheels is 245/40R18. Unlike the last one, this keeps the same 40 aspect ratio as the optimal 235/40R18 size.
However, if you actually do the calculations again, a 40% aspect ratio on a 245mm tire would give you a 98mm side wall.
This makes the sidewalls for the 245/40R18 tire size 12.25mm (0.48 inches) taller than that of the 245/35/R18. Be sure to keep this difference in mind when fitting this bigger and wider tire size on your vehicle’s wheel well.
Fitment aside, going for this 245mm tire size over the last one will not only give you a slightly bigger contact patch with the road than its 235mm counterpart, but it’ll also still provide respectable levels of comfort.
255/35/R18
If you’re looking to have the widest setup for your 18×8.5 wheels safely, then a 255/35R18 is just about as wide as you can go.
Among all of the compatible tire sizes that we’ve discussed, a set of 255/35R18 tires will give you the best handling and cornering performance as long as correct fitment is achieved for your particular vehicle.
As to be expected, opting for the widest tire size in the “recommended” range for 18×8.5 wheels will mean that you’ll have the most rolling resistance, which means that you’ll consume more fuel.
In addition, depending on your specific vehicle model and suspension setup, you might be more likely to run into fitment or rubbing issues with 255 mm-wide tires than with any of the narrow tires discussed.
What is the smallest tire size you can fit on 18×8.5 wheels?
The smallest recommended tire size that you can fit on a set of 18×8.5 wheels is 225/40R18.
While you can technically get smaller 215mm tires to fit on some 18×8.5 wheels, they may end up getting a bit stretched, resulting in poorer ride quality and increased tire wear.
If improved fuel economy is more of your thing rather than downright performance, then you can consider the smallest recommended tire size for your 18×8.5 wheels, which is 225/40R18.
This tire size has a 90mm sidewall, which when combined with its slightly narrower width over the all-around 235mm tires, results in a more comfortable ride and less rolling resistance.
We recommend not going for anything smaller than 225/40R18 for 18×8.5 rims, as it can cause the tires to stretch more, possibly reducing performance to a dangerous degree and wearing out the tires quicker than usual.
What is the biggest tire size you can fit on 18×8.5 wheels?
The biggest recommended tire size that you can fit on a set of 18×8.5 wheels is 255/35R18.
While it’s still possible to mount 265mm or wider tires to fit on some 18×8.5 wheels, they may not give the most optimum performance, can rub easily against the wheel wells, and wear out faster.
There’s always a safe limit when choosing to put bigger and wider tire sizes on your rims, and in the case of an 18×8.5 wheel size, that limit would be 255/35R18.
With a 255mm section width and an 89mm sidewall section height, the 255/35R18 tire size is the biggest that you can safely mount on an 18×8.5 rim while still giving you good performance over smaller sizes.
In some applications, fitting a slightly wider 265mm is still possible, but this is generally not recommended as you’re more likely to rub against the wheel well/fender liners, not to mention there’s a risk that the tire’s performance will be worse off.
What does 235/40R18 mean on a tire?
235/40R18 is a specific tire size, which means that it has a width of 235mm, an aspect ratio of 40, a radial construction (R), and a diameter of 18 inches.
The size and dimensions of tires can be found printed on their sidewalls, which can be useful when you’re trying to pair your rims with the correct tire size.
There are three main parts of a tire size that you should keep in mind, namely the tread width (first number), aspect ratio (second number), and the rim diameter it can fit (third number).
Using “235/40R18” as an example, 235 would be its tread width in millimeters (mm), 40 would be its aspect ratio (in percentage), and 18 would be its rim diameter in inches. The “R” in between simply means that the tire has a “radial” construction.
In some tires, you may even see the tire size written with a “P” in the beginning (e.g. P235/40R18), which means that the tire is rated for “passenger car” use.
Other info you may see printed on a tire sidewall can include the load range, speed rating, DOT tire identification number (for U.S. tires), max cold inflation pressure, and more.
What does aspect ratio mean on a tire?
Tire aspect ratio is the percentage that’s calculated when dividing the tire’s section height (sidewall height) by the tire’s section width (tire width).
In other words, the tire aspect ratio tells you how high or tall your sidewall is compared to the width of the tire.
An important part of any tire size is the aspect ratio, which is the second number right after the indicated width. It gives you an idea of how much sidewall there is in proportion to how wide your tires are.
To be more specific, the aspect ratio takes the height of your sidewall from the edge of the rim to the edge of the tire (section height) and divides it by the width from sidewall to sidewall (section width).
For instance, if you have a 235/40R18 tire, it would have an aspect ratio of 40, which means that the section height of the sidewall is 40% of the section width (235mm). Going by this example, the sidewall would be 94mm tall.
Frequently Asked Questions (FAQs)
