In the end it seems that the driver would make a bigger difference than the tires?🤷♂️
Photography Credit: Anna Overman
How do you determine the ideal wheel-and-tire setup for your car? Sometimes you need to do a little testing.
As we prepped for this year’s One Lap of America, we needed to make one key decision as early as possible: What tires should we run on our Honda CRX?
[One Lap of America: How competitive can a daily driver actually be?]
First, the rules: The Tire Rack One Lap of America presented by Grassroots Motorsports requires a 200tw tire or better that must be purchased through Tire Rack to avoid one-off ringers. Further, there’s a list of eligible tires. And finally, teams only get one set of tires, and it’s gotta last the whole week. That’s 3500 highway miles plus about 40 laps of track use. Replacement is only allowed for verifiable road hazard damage–which does not include camber wear or overzealous driving.
Now add sizing to the equation. Despite its flared fenders that allow up to a 275mm width, our Honda’s old-school internal wheel well dimensions limit it to about a 23-inch-tall tire–which typically means a 15-inch wheel. As OE fitments have tended toward ever larger diameters, however, the availability of suitable tires meeting that outside diameter has become severely limited.
Most competitors choose a tire from Tire Rack’s Max Performance Summer category, which gives a good balance of both dry and wet performance. The latter is important because the event always includes a wet skidpad competition, and spring weather typically offers up rain other times during the week. The Continental ExtremeContact Sport 02 and Michelin Pilot Sport 4S are popular choices, but neither comes in a CRX-friendly, 23-inch-tall tire.
So that leaves Extreme Performance Summer tires–aka Super 200s. Within that category, the only ones that have acceptable wet performance, at least at full tread, are the Bridgestone Potenza RE-71RS and the Yokohama Advan A052. We successfully ran the Bridgestones last year on our GTI, and the brand does offer a couple of suitable sizes for the CRX, including a 225/50R15.
But something else caught our eye this time: Yokohama offers its Advan A052 in a unique size. It’s marked as a 215/40R17 that’s 23.7 inches tall, yet despite what it says on the sidewall, it’s even wider than the 225/50R15 Bridgestone.
Another possibility from Yokohama: the same model in a shorter 205/40R17. Plus, the line also includes a 205/50R15 and a 225/50R15, which are essentially the same-diameter donuts as the 17s but with a smaller hole.
We already have some 17x9-inch wheels for this car, but which setup will provide the best combination? Will the shorter gearing and lower cg of the smaller-diameter tires deliver an advantage? Will the wider tires outperform the narrower ones via better cornering potential? Will the short sidewalls of the 17s feel more responsive? Only one way to find out for sure: a test.
When we last compared 15s and 17s, we ran the latest Nankang CR-S on our Triple Threat ND Miata. In that test, the shorter 15s were substantially slower than the 17s, with most of the time differential being in corner exit power up.
We also found that we could pinch a 245mm Nankang onto a 9-inch wheel. In fact, it outran a 235mm tire that was a theoretical better fit.
But every tire is different, and the A052 is typically not happy being pinched. Of course, with the available A052 tire sizes for our CRX, pinching was not going to be a factor. In fact, the 205s were fairly stretched on 9-inch-wide wheels, with the 215s and 225s being a normal straight-up fit.
Now to see which tires our CRX preferred. One logistical shortcut we took was to change only the front tires for each round of testing–the rears were kept constant at 205/50R15.
With our nose-heavy, front-drive application, the fronts do most of the work anyway, so this shortcut has served us well in the past. It did make for some rather odd-looking combinations, though.
From left to right: 205/40R17, 215/40R17, 225/50R15, 205/50R15
As we always do, we heat-cycled our tires prior to test day. In this instance, the entire operation was done at the track. We built heat into them by doing some skidpad circles in an empty paddock area before running six laps on each set of tires. Tires were then removed and allowed to cool for 24 hours, better curing the rubber for optimal performance.
Not all tests go as planned. We typically do our work on weekday mornings when the track is mostly empty. This minimizes track evolution beyond an initial dust-off, and also allows for uninterrupted lapping for evaluating heat-sensitive tires. But this weekday was different, as a slew of cars began to fill the paddock not long after the track opened. Still, we were hopeful we could find gaps in the flow to make it work.
After 20 minutes of lapping on some old scrubs to clean the line and get our shifting and braking points dialed in, we mounted up the 205/50R15s to set our baselines. With the A052 at full tread, the first lap is typically the quickest. Heat soak sets in soon after, dropping the performance potential.
Our next size was a little wider but also had much shorter sidewalls. Compared to the 15s, these were definitely quicker to respond to driver inputs, counteracting some of the A052’s typical vagueness. The car also had less torque steer and felt steadier over bumps, as the 17-inch wheels had 8mm less offset. This reduces the scrub radius and is possible because the front suspension upright is curved, allowing for more clearance the farther from the center you go. In short, the car felt more natural and the times reflected that.
Add a little more tread width to all that 17-inch goodness and you get the 215/40R17. Grip was up, and lap times dropped some more.
Our final comparison size was 225/50R15. By now, traffic was becoming a major problem, with gaps becoming few and far between. This session got cut short as a large group of cars entered the track just after our second hot lap.
Before calling any test final, we always retest the first setup. Why? We want to make sure track evolution and driver improvement haven’t contaminated the data.
So we again mounted up our 205/50R15 baseline tires for that final bracket session. And then came a dose of reality: Traffic wouldn’t die down enough for a clean session. We waited and waited–for 2 hours. And then, as quickly as they had arrived, everyone else left.
Heading back out, we were greeted with a completely different track surface. Due to all the extra cars on track, grip was clearly up in many key areas, with our lap time plummeting by a full second. This is not even close to what we were looking for in a confirmation bracket session.
Could our earlier data be trusted? Or was the pace increase progression simply the track getting faster as we swapped to ever larger tires? Our intuition said we were fine, but the science called for a do-over.
So we did it all again.
Round 2
With limited time on hand, we could only do three more sessions. Since the 205/40R17 wasn’t as fast as the 215mm and 225mm tires, we skipped that one. Our new, faster 205/50R15 times would serve as the baseline for this round, and the final retest session on that tire duplicated the baseline nicely. Success!
Photography Credit: Anna Overman
For sure, we confirmed a lesson we’d already known: A wider tire is always quicker if properly supported by a wide enough wheel. Or, as we saw with the Miata test, were the faster laps from the taller diameter of our wider tires?
Given the limited sizing availability, those two variables could not be fully isolated. Either way, we now had two good choices for tire sizes for our One Lap of America journey. How do we decide between them? One more round of testing.
Having now verified fit and function, we headed back to the track the following week with just the two larger candidates. This time, we really focused on the subjective strengths and weaknesses of each combination in addition to pure lap times. Here’s that data:
While the 17s again felt a bit more natural due to the stock-like offset of the wheel fitment, the short sidewalls made the tires more edgy at the limit. Further, the reduced amount of rubber in the 17-inch setups contributed to earlier heat soak. All that energy generated during a hot lap has to go somewhere, and the tire is that place.
As a result, the big 15s were easier to consistently drive fast. And with One Lap time trials being a three-lap affair and every circuit being scored, consistency is key.
Back to our original question. How do you determine the best wheel-and-tire setup for your car? Ideally with some methodical testing.
In the end it seems that the driver would make a bigger difference than the tires?🤷♂️
"Get the widest one" :)
Keith Tanner said:"Get the widest one" :)
I was surprised, but apparently there are exceptions. :) IIRC 949 did some testing of low-powered Miatas at big tracks and it was possible to go too wide on on the tires/wheels and slow down. I think the hypothesis was that diminishing returns on extra grip didn't make up for the increase in drag.
This subject is perfect timing for me....big decession.
First yea yea not the first or even fifth choice for a CAM T car. 1964 Mercury Comet.
Ive got an OK fit with 17 x8 with 5.5" BS 255/40 tire. My "hard limit" is the inside 5.5BS is maximum.
My plan is a square set up.
Both front and rear will require some outer fender minor work for that set up,but with more work(cutting) ..... well you know.
From reading GRM my 255 should work better on a 9.5 to 10" wheel , now if I have to do the work do I stop at a 275 with an 11" wheel or jump to a 3xx on an 18"?
My other limit is 26" tall.
All limits are structural .
Goal is minimum CAMT weight.
So biggest tire or am I killing myself with a 275 on a17"?
Keith Tanner said:"Get the widest one" :)
Keith while I respect your accomplishments and input here you are so wrong on this one.
You want skinny tires so you can do glorious 4 wheel drifts everywhere.
Your big mistake here is thinking faster lap times are an actual goal........like anyway cares about that.
codrus (Forum Supporter) said:Keith Tanner said:"Get the widest one" :)
I was surprised, but apparently there are exceptions. :) IIRC 949 did some testing of low-powered Miatas at big tracks and it was possible to go too wide on on the tires/wheels and slow down. I think the hypothesis was that diminishing returns on extra grip didn't make up for the increase in drag.
I'm not sure that was 949, I think it was done before they really came on the scene. Iirc it was with Spec Miatas and 205/50 vs 225/45 - and since SM uses 15x7 wheels, the 225s were not well supported. Could have been drag, could have been that the fatter rubber just wasn't being used well. I'm pretty sure that the SuperMiata race series ran 225s on 15x9 wheels, and that was before 245/40s were really available.
I just found it funny that Andy did all this testing and ended up with "the widest that fit" :)
My arm-chair thinking on this comes up with "the widest tire that maintains proper temperature."
Budget plays a large part in the setup of my track car so the 16 x 8 E38 Style 5 wheels that no one really wants work great (I have 10 at an average price of $40 CAD/wheel) along with 225/50R16 Hankook RS4 at $180 CAD/tire that never seem to die means I actually get to be on a race track pushing as hard as I want.
Would a lightweight 17 x 9 with around a 245 new hottness tire be faster? Of course but that's well over $2500. That buys me two full sets of RS4's (which should last 4+ years) and leaves $900 for entry fees, gas, etc.
kb58 said:My arm-chair thinking on this comes up with "the widest tire that maintains proper temperature."
Yes, this.
Not too hot, not too cold – just right. Kinda like porridge but black and really chewy.
adam525i said:Budget plays a large part in the setup of my track car so the 16 x 8 E38 Style 5 wheels that no one really wants work great (I have 10 at an average price of $40 CAD/wheel) along with 225/50R16 Hankook RS4 at $180 CAD/tire that never seem to die means I actually get to be on a race track pushing as hard as I want.
I'm jealous of that width. My car wears CLK Lightweights in 16x7 so my 225/50R16 race rubber is way ballooned out. I'm looking at moving up to 17x8s so I can get a 235 tire that fits well. But like you were mentioning, it's a $20 difference per tire.
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