How to PROPERLY select and size TIRES for PERFORMANCE


“What tires fit your category and size?”

Now that you have determined what your tire is going to be used for and the respective tire category, and with the newfound knowledge of how to look at tires by their true size, it’s time to select a tire.  But with all of the different stats and criteria out there, what factors make a tire good?

Feel free to read the definitions below but I’ll save you some time with this sentence:

Due to the subjective or interpretive nature of these tests; other than speed ratings (which may not apply to most people) all of the other tire performance criteria is for the most part USELESS.

Load Index

  • You can read Tire Rack’s Load Index Definition if you want, but it’s basically the load carrying capacity of the tire, which usually isn’t important unless you’re making hundreds of pounds of downforce, have a heavy car, and are driving on an oval.

Speed Ratings

  • Click the link above for more detail, but I mainly focus on tires with W (168mph), “99Y” (186mph), and “(99Y)” (Parentheses = 186mph+) based on the application.  If you never go this fast (which you can’t do legally unless you’re on a racetrack, and even so, it’s rare to go this fast on track), then this probably does not matter.

Uniform Tire Quality Grade (UTQG)

  • An arbitrary number originally developed to help consumers with a numerical value that represents the treadwear, traction, and temperature capabilities of the tire.  Since the Department Of Transportation (DOT) does not test the tires and it’s up to the tire manufacturer to come up with the value, tire manufacturers set these numbers based on how they perceive the customer will understand how the tire will perform, or to meet a random number/standard that a racing series might restrict, to have a softer faster tire as an advantage. Because of all of this, UTQG is USELESS.

Treadwear Ratings:

  • A test based on a 7,200-mile test loop with routine tire pressure and rotation adjustments during it. A 100 rating should = the tread lasting the 7,200 miles, 200 rating = 2X that distance and so on.  Since a lot is left open for interpretation and the only decently comparable data is from one tire to another within the same brand, this is also somewhat useless.

Traction Grade:

  • This is another useless test since it measures the deceleration g-forces of a locked tire across a WET road at 40mph. Other than seeing which tire will stop you the shortest distance with the tires locked; this is not relevant to cars with ABS or the braking ability of the tire under normal rack uses.

Temperature (Resistance) Grades:

  • Indicates the amount of heat generated by what appears to be an under-inflated tire at 85mph.  Since this is also outside the scope of a properly maintained tire, I find it useless.

As tire technology gets better with each new design, often driven by what is learned in motorsports, tires are performing better in the dry and wet, are lasting longer, and are quieter than their predecessors.  Keep in mind those manufacturers who are winning in multi-tire racing series tend to offer the best products to their customers as well.

These advancements make it difficult to properly classify a tire or draw conclusions that tire A lasts longer than Tire B because it’s Treadwear Rating is higher, or it will have more grip and wear out quicker because its UTQG is lower. Remember, these numbers are useless?

So back to the decision of selecting the best tire; when looking at TireRack’s subcategories

(“Ultra High Performance”, “High Performance”, “Performance”…) I usually look in the highest category.  Price is usually a major factor in selecting a tire but since tires should be viewed as an INVESTMENT in terms of both performance and safety of your car, I rarely look below the second tier of subcategories.

Tire Comparison
When comparing tires within a category, the balancing of performance, comfort, and price begins.

TireRack’s rating table is going to be one of the best sources out there.  Using a scale of 1-10, each tire is rated in terms of dry grip, steering response, wet grip, hydroplane resistance, road noise, longevity, etc…  by consumer survey ratings which can be the average from hundreds of people.  Having tracked many tires, I personally feel these figures are fairly accurate when comparing across brands and have the most credibility, especially compared to the useless UTQG or Treadwear ratings of a tire. The individual customer reviews of the tire can also be somewhat insightful, but I tend to take them with a grain of salt and use them as a secondary factor to TireRack’s rating system.

Tread Design
The tread design is something to consider when looking for tires.  The design will usually reflect its performance in Tire Rack’s rating system, but in addition, looking at the outer shoulder, rain grooves and sipes will also give a vague idea of how they will perform.  For track use, large continuous outer tread blocks will deliver more grip and stability than smaller tread blocks which tend to tear off and chunk.  Larger tread blocks tend to be more prone to hydroplaning while tires with many, small tread blocks often perform better in rain and snow.

As you start comparing different tires, it’s important to verify the TREAD WIDTH of each model, and if they run too narrow or wide, shop to see if a slightly different size would be more applicable.  If you are trying to break track records, further research would be beneficial but keep in mind that a review from a Lotus Elise owner on a set of tires probably won’t be as applicable on a heavy GTR or CTS-V, so try to find comments from someone with a car of similar weight and tire sizing.

I am not going to outright say buy this tire, or that tire sucks, but by now you have gained enough knowledge to make a more educated decision on your next set of tires with greater confidence that not only will the tires be more likely to fit, but will deliver the performance that you are looking for.


    1. Amazing article. Changes my whole perception of what i am looking for. 2017 mustang gt. Drop 1 inch, tiger grip wider. Staggered or not too. Like 275 on all 4 and do I look for height and 45s height compared to 50s height for stance

  1. Nice, but what’s the optimal weight to mm for tire width? I want a good compromise for street/weekend warrior use and looks on my 09 daily driven Scion tC. Don’t wanna take too much of a hit to mpg, but I want more room to soak up hard cornering and, as I said a more aggressive look.

    Stock sizes are 215/45r17 and 225/40r18. I know a 235 will fit, and I’ve seen a couple of 245 and 255 fitments online, but it’s mostly 245 or below. Currently running BFG sport comp 2 a/s tires and like them. Live in Florida and was recommended those for my application. The car is FWD with a manual and 160hp, I intend to run a square setup.

  2. Thanks for pointing out that choosing the right tires will be able to dictate the success of the race and also keep you safe from accidents. I will share this information with a friend of mine since he will be joining races once he gets his car customized. It has really been his goal to do so after being obsessed with a series of movies that focuses on this.

  3. This is probably the best ‘layman’ article on tires I’ve read! Here’s why I’m here. 2018 Mustang GT, stock except exhaust, air box and multiple tunes including E85. Daily driver with track weekends. Stock rims are 18 x 7.5 rolling on Pirelli P Zero Nero P235/50ZR18. I want more grip in the rear. Don’t care to change wheel diameter bc Ford Engineers are smarter than I. Contemplating going to 10″ in rear with MT ET Street SS 285/40R18. Not married to them and am open to any suggestions you may offer. I’m interested in grip and of course a better ET.

    1. Thank you for the kind words, it’s great to hear that feedback (which was the goal). To be honest, I’m not the best source for tire sizing when it comes to drag tires since I do not have firsthand experience testing how wheel widths affect longitudinal grip and launches of drag-specific tires.

    2. What did you end up doing? Mine is a 2017 and trying get a better stance look with a drop 1 inch with a little wider tire,but my big concern is 40 45 or 50 height tires

  4. Thanks for listing all the details which are of importance for proper tyre selection.
    Yet, I did miss the part explaining the influence of “aspect-ratio”.
    I actually trashed a set of all-weather tyres and damaged my rim, due to driving a bit to fast on a very poor rural road. Consequently, I searched for information regarding rally tyres on the web. Interestingly, the majority of rally tires of Michelin have aspect ratios of 60-65. Yet, these tyres have very stiff side-walls. What is your opinion regarding the influence of aspect ratio?

    In addition, you mentioned that you consider load-index not to be be very useful. Yet, does load index influence the strength and stiffness of the side walls? Consequently, the higher the aspect ratio, the more important load index, especially using poor roads? Appreciate your view/

  5. Mr. Johnson, your article is the most clearly explained writing I’ve found on the matter. Still it is not very clear for me what would happen to my 2019 Toyota Camry, with original 17″ x7.5 original wheels if I change original tire size of 215/55/17 to 235/55/17. My intention is to gain half an inch in underbody clearance, and of course any gain in performance would be wellcome. I appreciate any light you can give me on this matter.

    1. Going from a 215/55 to a 235/55 would give you a tiny bit of ground clearance but would also change the circumference of the tyre, which may throw off your odometer and other systems. I suspect it’s not a good idea, if you want more ground clearance the proper way to do it is to install adjustable coil-over suspension.

    2. The wider tire will lose steering response and feel more vague and ‘mushy’ as the sidewall deflects more before loading up. Peak grip will likely increase. I’m not sure you’ll gain 0.5″ in ride height from making that switch. Check out a tire size calculator to be sure.

  6. Than you for writing this article! It is very informative! What I did miss was information on what would be a balanced mm/Lb for track use. You present a table with multiple vehicles, but do not comment on whether you find those values too high or too low, with the exception of the Elise, that isn’t even on the table. What would be a good range for mm/Lb?

    1. It depends on the tire. Whatever it takes to keep a tire in its ideal operating temperature window is what should be targeted.

  7. First of all, excellent article, i appreciate the time and effort placed into explaining all the nuances of selecting a damn tire. Ive already screen shotted some portions for my digital “Car” notes.

    I just have one critique from a data driven, engineering minded geek.

    In the TTSA chart, TTSA seems to be calculated only using half of the tires….1xFront+ 1xRear… thats not total…I realize that may not be your chart, but when i come across calculations like these that aren’t completely logical, it makes me ask…why? In the end, i know it will just change those numbers by a factor by 2, but to me it makes more sense to use the TTSA that uses all four tires. Of course, if there is an industry standard that uses 1xFront and 1x Rear, then so be it; i am ignorant to it (alibi: i am new to this game)

    Once again, thanks for making your experience available for the entire world to learn.


    1. Haha, thanks. As far as TTSA goes, feel free to multiply all the numbers by 2. For comparisons sake, only looking at half the tires does not affect the results.

  8. That was very helpful, thanks. On my Lotus Elise S1 (1800lbs), I’ve always found that I could not get heat into my tires (205F/245R). For many years I was following the ‘wider is better’ gang. But this year I’ve decided to try a smaller size (195 & 225). I’ll be saving weight and hopefully heat them faster too! Over the time I’ve also came up with the thinking of choosing a tire first then get the wheels. Thanks for the great article !

    1. Glad to hear it. The #1 thing is the compound of the tire and keeping it in it’s operating temperature range.

Leave a Reply

Your email address will not be published. Required fields are marked *