Plus Sizing is a fairly recent trend (I think it started in the late 80’s or early 90’s). Well when I say recent, I mean compared to the 50’s and 60’s when I was getting into cars and making them street cool. The basic idea of Plus Sizing is to replace the stock wheel size with a larger diameter wheel and still maintain the same original tire and wheel combination diameter. Back in the early days, up to and including the 70’s, the only thing that happened when you put larger diameter tires on your rod, was the speedometer read slower than you were actually going. That only worked when you said “but Dad, the speedometer said I was only going 50”.

In today’s world, when you change the wheel and tire combination diameter, it effects a number of things with your ride. Not only will it change the speedo reading, but the ABS braking system, the engine management system and with some cars the suspension control system. Computers don’t take kindly to changes of input components.

So to make sure you don’t alter the input from the wheel and tire combination, the diameter of the OEM combination needs to be maintained. To accomplish this you need to understand the meaning of Plus Sizing. A simple definition is to take the original wheel diameter and plus up from there. A Plus 1 conversion is upping the diameter of the original size by 1 inch (i.e. 14″ to 15″). In some extremes I’ve heard of a Plus 9 conversion (i.e. 17″ to 26″). That’s a bit radical for me, but to each his own. Most tire and wheel dealers are very aware of the Plus Sizing concept and can guide you as to the proper tire size to fit your wheel diameter choice and maintain the original tire and wheel combination diameter. It’s pretty difficult to get the exact match, but if you are within 5% you’re okay.

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Now let’s discuss the Pro’s and Con’s of Plus Sizing.

The Pro’s – First of all, you’ll be cool if you Plus Size. The bigger the diameter, the cooler you are (at least some folks think so). The biggest benefit from Plus Sizing is the increased road handling. By increasing the wheel diameter (and maintaining the original overall diameter), the height of the tire side wall deceases. This has the effect of less tire sway or roll, and increases the stability or cornering ability of your ride. Other than those 2 attributes, I’m hard pressed to come up with more Pro’s.

The Con’s – The first thing that comes to mind is the loss of suspension. By deceasing the side wall of the tire, you will increase the effect of road bumps, pot holes, expansion joints and all the other deformities of our roads and highways. Road noise will be increased also. In addition to the loss of ride comfort, you will also experience a loss of free time. I come to this conclusion based on the theory that the bigger the wheel, the more time it requires to keep it shining. Another Con is the tire mounting folks that have to put these tires on these wheels (20″ and up) aren’t real thrilled with the whole concept.

A few things to beware of when choosing to Plus Size. The larger the diameter of the wheel, the more difficult it is to meet the load requirements for a safe and reliable wheel. Some manufacturers solve the problem by adding material to the wheel so it will pass the performance standards (see TECH Stuff 3). By adding material, the weight of the wheel becomes heavier than the suspension the vehicle is designed to take and function properly. The tire and wheel are considered unsprung weight, and can cause excessive wear on the struts or shocks, bearings, spindles and brake systems.

Plus Sizing is not a bad thing when done properly.

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9 Responses to The Pros and Cons of Plus Sizing


    • Leroy, we don’t list 18×8.5 as working on your vehicle, sounds like it’s working for you. Our system recommends between 7 and 8″ width for 18″ rims, our fittings are fairly conservative so that rubbing is not an issue. The largest 18″ we recommend is 8″. For a 18×8 you can go up to 235/45-18.

  2. I noticed on just plus tire sizing you don’t list a 245/40/18

    I have a 2017 BMW 330i Xdrive and I am happy with the factory 18” x 8” wheels squared set-up
    I was going to replace the 225/45/18 with 245/40/18 and 245/45/18 is to tall
    245mm is the widest you can put on an 8” rim, not to mention rubbing issues if you tried to go wider on the front? And I’d have to replace all the wheels
    There won’t be much difference in looks, probably unnoticeable
    Would there be much benefit to braking handling
    I know the diameter is a little lower, so the car might launch faster, but use more gas? Lower the gear ratio?
    And the 245/40/18 is 1 pound heavier adding to the rotational and unsprung weight
    Diameter 25.72 vs. 25.97 = 0.25 = 1/4″ less
    Width 245mm vs. 225mm 20mm = 3/4″more
    So I was thinking 3/4″ wider x 4 wheels is 3″ more contact patch on the pavement?
    I know the numbers are section width and not tread width, but are probably proportional Sidewall for ride/handling trade-off
    Sidewall 3.86 vs. 3.99 = 0.13 = 1/8″ less
    Speedometer will read 62.8 mph at 60 mph
    Cost difference is negligible
    Is the difference so small, you wouldn’t even know the difference?

    Thank You

  3. Hello, my family recently bought a toyota tacoma that was plus-sized, came with some big tires. When you look at the wheel space and the rubber wall, they are about an inch or less away from each other. Would you say that since the space is small, it can cause the wheels to rub against the walls and cause the truck to brake on its own? This happened while making a sharp turn on some curvy roads while going downhill. Thanks!

  4. I want to move to a 265/50R20 inplace of the 255/50R20’s that come OD on the 2018 VW Atlas RLine. Any issues?

  5. 20 inch rims 255 30 20 for a 2007 volk’s jetta.

    What else should I upgrade on the car to get the most out of the ride with 20in rims.

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