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One of first things I did after buying the F was to upsize the tires. MANY F owners have done this as it is generally believed that the car came under-tired from the factory. I think most manufacturers prefer understeer vs oversteer possibly for safety reasons for the average driver.
I went from 225/255 OEM sizes to 245/275 on OEM wheels which helped (I even ran the AS3's like you). I still run those sizes in the winter (but switched to DWS06). But then I went 275 square for summer/track as you point out. Even after dialing in the suspension to a reasonable setting, the car still would be biased toward understeer on the track. These cars are heavy. I could power-out of turns but it would just push the front end out (understeer) rather than rotate the car (oversteer). But after having the upgraded diff for a few weeks (but not on the track just yet), I feel that the open diff wasn't helping induce any oversteer either. I certainly get that now!
So the wider fronts definitely cause the car to "track" (pull to the side with uneven pavement) a bit. But yes, I did notice better turn in with the front tires, but the upgraded front LCA bushings made an even bigger impact on turn in and more linear braking.
So my advice would be to go up in tire size a little like so many do and to upgrade the LCA bushings (RR or Figs). They are simple and relatively inexpensive mods that have very nice improvements in the areas that you mention.
The biggest thing with replacing the bushings is improvement in straight line braking from high speed. The back of the car feels like it wants to wander under heavy braking without them. You also get massive toe-out under hard braking that kills the inside edge of the front tires very early.
Warning...lengthy update post...last month I went to my 3rd IMSA race at Mid Ohio compliments of Lexus Racing Hospitality. They did a fantastic job of treating us like VIPs as usual! Hung out with the racing and marketing teams and the CEO of Toyota NA. Saturday was qualifiers for the Lexus team and a few other races followed by a Lexus owner hot lap session.
Seeing as I tracked Mid Ohio many times, I let my son drive my ISF. I thought it was going to be a slow parade lap, but everyone created space in order to send it pretty good (maybe 70% got up to 128mph). He had an absolute blast and of course I was a nervous dad riding shotgun. As we were waiting to hop on track, #1 Lexus racing driver Jack Hawksworth leaned in the car and said he how much he loved my F. Wow! Then we got to be part of the Lexus video promo (see below).
Before Sunday's big race, we stopped by the Triple F car show (TripleFCollection on Instagram) on Columbus to see the exotics. The family owns over $100m in 1 of a kind cars (Bugatti, McLaren, Pagani, etc). Not something you see, especially in Ohio.
The #14 car broke down, but the #12 car was able to take the podium with a 2nd place finish.
I'll be hitting the track myself in about 2 weeks. Longer promo video (Instagram)
Finally got around to editing my videos from my track day at Mid Ohio back in June. This was the first time out with the new APR wing and OS Giken differential.
They both made a difference for sure as the rear of the car was more planted. As expected I picked up a few mph in the corners and lost a little on the long straight. And I finally turned the nannies off (long push) to also help exit speed.
I discovered that the downforce of the wing is just a bit too much for the 12k springs as I was rubbing some on the track (but never rubbed on the street). While I could have just raised the rear height, Rafi recommended I go stiffer 16k rear springs as I was getting some understeer still.
I also got a P2241 code again (both times day after a track day). So I'm thinking the full chassis splitter is limiting airflow. So I'm going to add a braided wire high temp sleeve. If that doesn't work, then a vented hood is next.
New personal best of a 1:42.9.
The highlight of the day was running with a Jaguar XJR-16 that was there practicing for an upcoming vintage race (was the 1992 Mid Ohio IMSA champ). Check out the video for a glimpse.
The P2241 code (Oxygen sensor pumping current circuit low B2S1) seems to be common for those with headers. I've had my headers for several years of tracking without any codes. Then the last 2 track days (only 2 I've run with the splitter) resulted in the code about 24 hours after the track day. This code is often related to heat issues (hence ppl with headers). Since I only got the code after installing the splitter, my theory is the engine temps are even hotter than before (when I wasn't getting a code). This splitter is huge and has zero vents underneath. My coolant temps seem to be running 5-10 degrees higher as well.
August 2021 - Stiffer rear springs and National Corvette Museum track day
Track day update!
As previously mentioned, the wing created so much downforce that it was rubbing in the rear. Rather than just raise the height, I went with stiffer 16k springs (vs 12kg before).
So off to National Corvette Museum motorpark for a track day. What I discovered was that the increase in rear oversteer was quite significant. Went off the track once and nearly 1-2 more times. Will definitely take some getting used to. Will also try to soften the coil settings but they are only 1 way adjustable. So the nannies came back on and I sent it.
Ended up with a 2:26 which is 5 seconds better than my previous personal best. Yay! Video of fastest lap below (but no traffic).
I aIso had a special treat from a fellow ISF owner who let me ride shotgun in the Toyota team's 2GR swapped 99 Camry 😁.
I installed a new A/F sensor and this time added braided heat-resistant sheathing. Track day temps were a very hot mid-90s and so far so good. If I kill this sensor, I'll either install hood louvers or a vented hood (if Seibon ever re-releases theirs).
Stopped by the National Corvette Museum before the track day. I've attached a some pics of the damaged vettes recovered from the sinkhole collapse (look it up if you aren't familiar with the story).
Is your splitter covering the bottom of the engine more? I wonder if it is boxing in the heat. Based on Visual performance cues, I think the novel vented hood may be more effective, but that comes at a pretty high cost. It sounds like you really are at the point you need to vent the engine bay.
Yes - it covers the entire bottom with no ventilation. See post #13 for a pic. I still believe it is an airflow issue.
I would love Novel but it's pricey. Next choice is Seibon but it is not currently available or being produced I believe.
So 3rd choice is hood vents. Pete's Red Devil SC RCF is running www.racelouvers.com
Not sure how they would look though.
I’d base your decision on designs that real race cars use. I can’t recall seeing the Seibon style on much other than on tuner cars, but I’ve seen Novel style pretty often on full aero cars. Heat is hands down the biggest enemy of a race car. William has logged some experience with this, as well as his custom hood. I’m wondering if a full splitter is related, as he has one as well.
Oh the Novel looks to be a much better design but expensive. I also drive year round, including rain and snow. So lots to consider.
In the meantime...track day photos!!!!
Yes - it covers the entire bottom with no ventilation. See post #13 for a pic. I still believe it is an airflow issue.
I would love Novel but it's pricey. Next choice is Seibon but it is not currently available or being produced I believe.
So 3rd choice is hood vents. Pete's Red Devil SC RCF is running www.racelouvers.com
Not sure how they would look though.
did you ever think about removing the access panle for the oil filter for air flow?
I thought about removing the oil filter cover as a simple test. But I think it would create turbulence. Plus I wanted to see if the heat sheath on the o2 harness worked. While I haven't gotten the P2242 code like before, I have been getting the P0101 (MAF sensor code) almost daily since the track day. Once again the pattern of getting a code right after a track day continues.
Vented hood seems like the next best option for me. We will see what happens with this CEL.
06-03-21, 02:18 PM
