If you are looking for performance, tires are where you start and where you end. Every move your car makes, it has to do through those black rubber donuts slapped around your custom wheels. For folks who like to take their cars out and dance around the cones at an autocross or four-wheel-drift toward a corner exit at a High Performance Driving Event (HPDE), you are looking for the best performance possible out of your tires. The question is, which tires should you choose?
The question of which tires you should choose is simple. It is the answer that is complex. As you search for a tire for your car, you need to navigate all types of terms you may not be familiar with, like load rating, treadwear and aspect ratio. We covered all of that jargon previously at TURNology, in an article titled “Tires: Sizing, Pressure, Load, Speed, And Treadwear — Understand It.” Gleaning information from that article we realized we had a lot of choices when it came to sizes. Our goal for this article was to pick the best size for the fastest times around a track.
Our Ford Fiesta ST project car for FordMuscle as part of the “Way of the FiST” series is being built for SCCA autocross competition. That means we needed some sticky tires for zipping through the slaloms. We liked the Yokohama Advan A052 we used in previous tests, but we wanted to explore the best size tire to use on the Fiesta. The rules in SCCA’s Street Category dictate the types of tires we could use (200 treadwear, commercially available). Upon further inspection of the rules we found something very interesting. Rule 13.4B Wheels, states, “Any type wheel may be used provided it complies with the following: wheel (rim) diameter may be increased or decreased 1” from the standard part. This change may be applied to the front, rear, or both axles.” The Fiesta ST came from the factory with 17-inch wheels, but based on the above mentioned rule we could switch to a 16-inch wheel (smaller and lighter) and fit a different size tire on it. Time to search the internet!
Our search revealed there were a multitude of Yokohama tires available for the Ford Fiesta ST. The car came from the factory with 205/40R17 tires. We knew we would want a larger contact patch for racing. The first tire we considered was the 215/40R17. Wanting to go even wider, we would have to go down to a 16-inch diameter wheel in order to find a 225/45R16. So, we found a wider tire, however the aspect ratio was bigger (45 versus a 40), which means it would have a larger sidewall. But, with a smaller rim, how much larger would the tire actually be? Time to search the internet again!
Using the tire calculator from TireSize.com, we were able to determine how much bigger the 225/45R16 was versus the 215/40R17. The circumference would be about 0.8% larger on the 225. That would essentially be like changing the final drive to a higher gear, which (for most racers) is not what we are looking for. We would rather have a lower final drive for accelerating out of the corners. However, even with the slightly higher gear ratio with the 225s, we would have a wider tire. Generally in racing, the wider the tire the better because it creates more surface area between the tire and roadway. Decisions, decisions. Let’s grab both tires and test them!
We ordered a set of 17-inch and 16-inch wheels and two different sets of Yokohama Advan A052 tires. After some much needed mounting and balancing from our friends at Sanger Tire, we were ready to test these tires out.
In order to provide a fair test of each tire, we ensured the pressures were the same, the wheel weights were similar and the offset of the wheels were the same. We wanted any change during the performance of the test to be the tires and nothing else.
The different wheel combinations were within one pound of each other. The obvious visual difference between the 215/40R17 and the 225/45R16 was the 225 was wider and had a much taller sidewall.
We used the shop at DNN Motorsports to swap out rubber, weigh the wheels, and verify our tire pressure numbers were spot on. Then, we headed to an autocross to beat up some tires.
The first thing that came to mind about the Yokohama Advan A052 was that it felt like an R-spec tire, and not a 200 treadwear tire. This thing was sticky. The sidewall was solid, and turn-in felt good. The tire warmed up quickly, and once heat was built into the tire it was very consistent. We liked it!
I’m not going to blow tire smoke up your skirt, testing tires is really hard work (if you consider sliding a car around a parking lot, hard work). I was having the time of my life zipping the little Fiesta ST around the cones and feeling the roadway through the Yokohamas. I had a great connection between my steering wheel and the corners because the tires let me know what was happening with the car. It was very easy to drive on the limit.
We put a ton of laps in with the 215/40R17s until each lap was consistent (within a tenth of a second). Once that was done we brought the car back into the shop to try the wider tires. As we were doing this test I had my own beliefs about what the data was going to tell us. I was pretty sure the wider tires would be faster. In my mind, bigger is always better.
We let the brakes cool down and then had the Fiesta back on the rack to swap out to the meatier version of the Advan A052s. The fatter 225 version of this tire was also on a slightly lighter rim (by one pound). I was sure it would be faster.
Some people said they didn’t think the 225 would fit on a Fiesta. They were sure it would rub on the fenders or the front strut. We found that the 225 fit perfectly and didn’t rub on anything. The clearance was close, but in this case close was good enough for us.
We again got to work by driving the Fiesta like a madman around the cones. The immediate difference – to the driver – between the wider 225 versus the thinner 215 tires wasn’t obvious. The car loved the tires and zipped around cones with reckless abandon.
We pushed the 225 tires hard, just like we did the 215s, and got our lap times down to within a tenth of a second per lap. Once we felt like we had the best time could get out of the 225s, it was time to compare the two best laps and determine which tire was faster. In my mind, it was probably going to be the wider tire.
They say in racing the B.S. stops when the checkered flag drops. I had a preconceived notion that the 225s would be faster, but our AEM CD-5 data logger told the hard truth. The 215s on the 17-inch rim were faster around the course. Why? Both tires felt great, but the lower gear ratio of the Yokohama Advan A052 215/40R17s helped the Fiesta get through the low-speed tight autocross better than the 225/45R16s. Both tire sizes were stable and provided excellent grip between the cones, but in the end, it was the narrower tire that got it done.
Another possible factor for the narrower tire’s success is the 215 fit on the 7-inch-wide rim better than the 225 did. A better tire/rim fitment helps with sidewall stability and that may have also helped the 215 come out on top.
In the end, we had a great time beating up our “The Way of The FiST” Ford Fiesta ST project car and sanding down some really great Yokohama rubber. What we learned is that you can spend lots of time on the internet “figuring things out” and you can have your own “preconceived notions” about what makes cars faster, but it is testing that proves theories and creates results. For this test the Yokohama Advan A052 215/40R17 was the fastest tire we tested.
Photos by Keith Kramer, Rob Krider, and Anthony Topalian.