Tire Selection for NASA TT

Discussion in 'Corner Carver Racing Tech Discussion' started by ddd4114, Oct 4, 2018.

  1. Vorshlag-Fair

    Vorshlag-Fair Official Site Vendor Official Vendor

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    I missed some of these updates but did notice your car at Nationals. Congrats on the times, but Dennis is fast (and a customer of ours). I've run against him off and on for years, and had a perfect record against him in our S197, but he has continued to develop the car in the years since we sold that car. He is quicker than he used to be!

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    I still think you are giving up some time by not using the GOD TIRE: the 345/35/18 Hoosier. And 48 psi is waaaay higher than we ever ran. I used to go on track at 26-27 psi cold and come in at 33-35 psi hot with these and the 335s. We ran at 3802 pounds in TT3, which was the then limit for the highest bonus on minimum weight brackets.

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    The TruFiber flares look good, but since my last 2018 post here I have since found a number of options that are less costly but also less "bolt-on". I made a post about this last week on the Corner Ponies FB page...

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    We took a chance late last year and ordered some of the cheapest flares I had ever run across for my wife's 86. I had used Duraflex/Carbon Creations parts before and the quality was really hit-or-miss. In this case it was so cheap that I didn't have a lot to lose.

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    It turned out better than I had hoped, but there was a little mis-match on a few pieces that my paint and body guru will have to fix. Lots of hours of doing the "underneath" work, of course...

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    But this allowed us to fit 18x11" and 315mm Rival-S tires at all 4 corners. Made for a 2.5 second drop on the 90 sec MSR Cresson 1.7 CCW course, our biggest drop over the course of 6 track tests on the same car/track/driver over a 2 year period. You can read more about the flare install at this link - its a lot of the same technique needed for an S197 flare using Duraflex flares...

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    I don't think these flares existed last year for the 2010-14 Mustang, but they do now. And ignore the prices shown - their Minimum Advertised Pricing policy is a joke. I don't even bother selling this brand (and I'm a direct dealer) because eBay and other sites just sell these at cost.

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    They look pretty big - and might be a copy of the TruFiber flares for all I know. They say "75mm" on both, but who knows? Next time we get an S197 in here that needs big tires we'll try this new kit.

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    https://www.clinchedflares.com/universal-fender-flares/

    There is a company called Clinched that makes a bunch of styles and widths that are listed in their "universal flares" section. I've put my hands on these recently and they are kind of a game changer for cars that don't have a lot of flare options.

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    Her is a set of their "Euro" style flares on a CTSV road race car. These are made from vacuum formed thermoplastic and are very easy to cut and modify.

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    We just mocked these up on his 2 door 96 Subaru Impreza body with F14 18x12's and 335/30/18 Hoosier A7s. The ends need to be trimmed to fit, but like I said, these are easy to cut. It might be a solution for those not wanting the styling or look of the TruFiber or Duraflex bits.

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    Anyway, I have rambled enough... still wish the OP would try the 345/35/18 A7... its worth some time, you gotta trust me. We use this big boy as the drive tires on lots of RWD cars...

    Cheers
     
    knous81 likes this.
  2. ddd4114

    ddd4114 forum member

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    Yeah, Denis said he didn't really get serious into TT until ~5 years ago (can't remember exactly what he said). Since then, he's been putting a lot of focus into coaching and data review, and it shows. It's a bit embarrassing that he out-drove me at my home track with a car that has basically the same performance envelope. He shared some data with me, and our cars are VERY close. Our speed traces were almost identical except for 2 turns - where we took different approaches, and he was (obviously) faster. Otherwise, our grip seems to be the same, our top speeds were the same, etc. Hindsight is 20/20, but I think if I had also invested a little bit more into coaching, I could have beat him. Oh well, maybe in 2021.

    I'm actually considering the 345mm Hoosier in the rear, but not so much for the (possible) additional grip. I'm running out of gear in a few spots at several tracks where it's not worth shifting, and the taller tire will probably help as long as I keep my apex speeds high enough. I am struggling with rear traction issues, but I'm wondering how much of that is because I'm still running stock control arms without relocation brackets, and I'm lowered ~1.75". I'm going to try addressing that issue first to see how much a bit of anti-squat and stiffer bushings will help.

    Regarding tire pressure, my settings came from multiple iterations of taking tire temperatures (the correct way, not using a silly infrared gun in my paddock spot), and the trends I saw are pretty repeatable. Maybe we were running different enough setups, but until I was in the upper 40's (front), my center temperatures were colder than my outside temperatures. I know you guys have a lot of track experience, but I just don't see how you can run 35psi hot in a 3800lb car (with aero) using the exact same tire and a smaller wheel size than me. If anything, I'd expect you'd need higher pressures with the smaller rim. How did you establish that pressure target? Did you take tire temp data? If so, what was the spread if you don't mind sharing? I've noticed the tires wear a lot better with the higher pressures, and I don't seem to be losing any grip. Hoosier recommended 50psi, but the tire temp data doesn't support going much higher than I already have. Another benefit of the higher pressures is the reduced aligning moment and higher cornering stiffness makes the car easier to drive. This was really the biggest difference I noticed.
     
  3. Norm Peterson

    Norm Peterson corner barstool sitter

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    Seems to me if you're running out of gear while having traction problems, solving or at least mitigating the corner exit traction problem is only going to make you run out of gear sooner and/or more often (and be in and of itself a push to go 345-wide).


    Norm
     
  4. ddd4114

    ddd4114 forum member

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    That's a good point, but the 345/35 is a lot taller than the 335/30 (27.5" vs 25.9"). That would give me another ~6mph in 3rd gear (the one that usually causes issues), and it's very unlikely that I'll be exiting corners 6mph faster with a tire size change. I'd be thrilled to exit 2mph faster.
     
  5. Vorshlag-Fair

    Vorshlag-Fair Official Site Vendor Official Vendor

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    Yea I have just never heard of tire pressures being used on the wider Hoosiers anywhere near that 50 psi range. Have run 100s of Hoosiers (with probed pyrometer testing) on .... 7 of my own cars (had to go count), and the R6/R7 and A6/A7 generations always seemed to find their happy place in the 30-38 psi range hot. I tried lower pressures, but not much higher...

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    Never even thought to go that high - I guess I need to test with 50 psi hot and see if I am missing something? There might be time available that I never knew of. :) #500psi

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    They always wore well, with fairly even temps across the tire, etc. And yes, wider wheels tend to help in many ways. We ran the 315s on an 11" wide wheel for 2 seasons then moved to 12" wide wheel, and they wore better on the 18x12s. We always ran the 335 fronts on an 18x12" and even ran the 345/35/18 rears on an 18x12", unfortunately (it should do much better on a 13" or 14" wide wheel). It was the widest wheel we could get affordably at the time (Forgestar makes an 18x13" now) but as you can see above... it didn't look super squeezed on the 12... but of course we would have run it on a 13" wheel if we could have. I was worried the 314s would wear funny, but they wore evenly, even with this squeeze.

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    The only "big tires" that we noticed very weird wear patterns on were these Conti slicks (not the re-branded Hoosiers) from the Daytona Prototype series. These wore the outside shoulders off very rapidly, in one day on track, using our "normal Hoosier" tire pressures. I would have spent time dialing in these tires for better wear we had pallets of new ones) but being 5-6 seconds off the pace of an A6, I wasn't going to waste any more track time or tires on such a slow, poorly wearing and slow tire. ;)

    Your results may vary! :)
     
  6. ddd4114

    ddd4114 forum member

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    Hey man, you never know until you try! I might drag a nitrogen bottle to track next time!

    For years, I ran in the 36-38 psi range with everything from a 245mm to a 315mm Hoosier R7 on my S197, and they always felt "fine". Actually, similar to you, when people with lighter cars told me they were running 40+ psi, I advised them to try lower pressures. You would think (or at least I thought) that for TT, you'd want to run on the lower end of the useful tire pressure range because it's more compliant, should heat up a little faster, and should offer a little more mechanical grip. However, I think what I overlooked is how stiff Hoosier sidewalls are - especially with a 30 aspect ratio (i.e. 315/30 and 335/30) - and its effect on tire pressure settings.

    When I was brainstorming setup ideas last year, I called Hoosier and told them my configuration (which was ~37psi hot at the time), and they told me I was running WAY too little pressure. I was skeptical but tried 42 psi at the next event, and... it felt better but wasn't magically faster. It wasn't until I started taking tire temps and using that data to adjust alignment and pressure that the car really started responding, and at that point, I was at the 48psi setup I mentioned. Of course, we're talking tenths and not seconds assuming your car is remotely dialed in.

    Of course, as you said, "your result may vary". The more I think about it, if the 345/35R18 Hoosier is that much better, I can see needing less front tire pressure because you can shift load transfer further rearward to achieve the same balance. Furthermore, you probably won't need any more tire pressure in the back because the sidewall is much taller and should be a bit more tolerant.

    Anyway, I'll get off my high-pressure soap box. I'm definitely interested in playing around more with setup next year to see what happens. In fact, I'll have to give you or Jason a call in a few weeks to order another set of rims to prepare myself... ;)