265/40/18 on Titan 7 T-R10 18x9.5
Finally, I upgraded the wheels to Titan 7s. I have nothing but good things to say about the purchase. I ordered them through COBB Tunning, and their customer service was always exceptional. The quality of the Titan 7 wheels is excellent and what you expect for the price, if not better. As advertised, the wheels weighed in at 18.9 lbs. The OEM STi BBS wheels are forged and very light for OEM, 20.5 lbs! Any time gained at the track will be primarily from the increased width of the tires.
Yes, yes, this is where someone jumps in to say that the contact patch for a given amount of weight per tire will be the same regardless of the size of the tire. Though technically true, it’s a bit irrelevant because what matters is that the contact patch shape changes with the wider tire, and that is what gives you the benefit. Additionally, with the wider wheel and the offset moving the wheel slightly outward, the car's track width is slightly increased by 1.96 inches. Since track with is the denominator of the lateral load transfer equation, it certainly has some effect. Anyway, that’s all for another time. Back to the wheels!
The really impressive part of the wheel setup is that The new Titan’s wrapped in V730s weighed within a pound the OEM wheel and tire setup up that is an inch thinner!
How Much Faster are 265s?
First, there are a few variables to consider. These two laps occurred several weeks apart, so the track conditions differed. I’m also a very imperfect driver. A certain amount of speed gain was simply from building more experience. The red line is my fastest lap with 245s on 18x8.5 OEM wheels. The blue line is my fastest lap with 265s on Titan 7 18x9.5 wheels. Both wheels were wrapped in Kuhmo Ecsta V730. All other aspects of the car setup are the same. The result was dropping my lap time by 2.41 seconds. Let’s take a look at the speed trace:
1. The increased gains in sunset should arguably be more, but I still haven’t sorted this corner completely. However, there was still a seven mph gain through sunset
2. Maintained five mph faster between Grapevine and Club Corner. The car felt much more planted, and the increased available grip was significant.
3. Big gains through Riverside with 12 mph faster! Part of this was me getting better at the corner. However, the 265s made it feel easy to go more quickly from Bus Stop and into Riverside.
4. Getting on the throttle sooner with more available grip leads to a significant gain exiting the Sweeper and heading into the Esses. There was an 11 mph increase exiting the Sweeper.
So 265s make you two seconds faster, right? Well, kind of. I’ll defer my conclusion to people who do actual testing, Grassroots Motorsports. Based on their testing, it seems the wider wheel enables the gains, not necessarily the width of the tire. Based on GRM’s testing, a 255 tire would be just as fast on the same wheel. The 265 tires may offer the benefit of taking longer to heat soak, but you should expect the same hot lap time.
In conclusion, moving to an inch wider wheel and rubber is worth about 1.5-2.0 seconds on 200 TW tires. The number of variables prevents me from offering any concrete numbers. However, it’s not a scientific breakthrough that wider wheels will drop your lap times. Hopefully, this gives you a rough idea of what to expect. Most of the fast Subies in Time Attack run 10-inch wheels. The fitment gets a little challenging, but it can be done. I may move up to a wider wheel in the future.
Another Data Point At Palmer Motorsports Park:
After moving to the Northeast, Palmer Motorsports Park is my new track of choice! This offered another data point on 8.5 vs 9.5 wheel widths. I typically run a few sessions on the 245s mounted on 8.5 OEM wheels and then swap over to the 265s on 9.5 wheels for the second half of the day.
Although the runs occurred on the same day, it was not a perfect experiment. This was my third time at the track, and driver consistency was an issue. There are some clear advantages in the available grip, as you can see in the speed graph below. You can also see where I botched T11 on the 148.8 lap.
The Red 1:51.76 Red Lap is on the 245 18x8.5 wheels, and the 1:48.80 Blue Lap is on the 18x9.5 wheels. The raw laps show a 3-second gain! This probably isn’t too far off the mark, but with me being somewhat new to the track and without retesting the 245s, it’s hard to make a definitive claim. However, looking at a few segments of the track shows some big gains in speed:
1. From Turn 2, Turn 3, and Turn 4, the wider wheels carried 3-5 mph faster. This section cut .74 seconds of the previous time.
2. The wider wheels kept speed higher through T5 & T6, however it was very noticeable in T7. It’s an off-camber right-hand downhill turn. The extra available grip was much more confidence-inspiring compared to the thinner wheel.
3. The wider wheels lead to maintaining 8 mph faster through Turn 9.
4. I botched it! You can see the red lap with the smaller wheel is faster through T11, but this is just a driver error. However, the wider wheels enabled me to travel more speedily through T14 and T15. However, even with the error, the lap came in about 3 seconds faster.
I once again offer you imperfect data, although somewhat more accurate since the laps were run on the same day. However, without retesting the narrower tires later in the day to account for potential improvements in track conditions or driver improvements over the day, it’s not possible to provide a definitive answer.