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365 GTC TIRE PRESSURES

Discussion in 'Vintage (thru 365 GTC4)' started by Cobraownr, Sep 18, 2020.

  1. Cobraownr

    Cobraownr Formula Junior
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    Feb 6, 2008
    899
    Edgewater, MD
    Full Name:
    Donald Silawsky
    I have two year old 205VR14 Michelin XWXs on my 365 GTC and would appreciate comments from
    330/365 GTC owners on tire pressures.

    The 330 GTC Owners Manual shows the following for Dunlaps of the same size as the XWXs:
    <110 mph = F29/R33
    >110 mph = F33/R37
    >135 mph = F38/R42

    The 365 GTC Addendum to the 330 GTC manual shows:
    <124 mph = F27/R31
    >124 mph = F31/R37

    Interesting that the manuals show a 4-6 PSI differential front/rear even though the weight is near balanced 50/50.

    I don't have an educated enough butt to discern much seat of the pants differences in the tire pressures I have tried other than 38/38 is waayyy to high. I started out with those pressures on a drive from Maryland to Watkins Glen, New York in September 2018 based on the recommendation from a Ferrari tech and had one of the scariest drives of my life. The car felt like it wanted to swap ends in sweepers (~80 mph) on the Interstates. I'm guessing the pressures had increased to the low 40s PSI at the 80 mph Interstate speeds and the warm air temperatures (mid 80s).

    Last weekend I used 30/32 on a 200 mile group drive with my local Ferrari club. A friend with many track sessions in a variety of cars was driving my GTC and said it was understeering, which I guess is not surprising. I don't drive the GTC aggressively, nor have I done any track sessions with it but might, understanding that would require different tire pressures. I am looking for suggestions for normal street driving with an occasional blast to 95-100 mph and some fun in corners but nothing extreme.

    I appreciate your comments and suggestions.
     
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  3. TTR

    TTR F1 Rookie
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    Mar 29, 2007
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    Timo
    #2 TTR, Sep 18, 2020
    Last edited: Sep 18, 2020
    Regardless of make or model car, my advise is and has always been, start with factory recommendations* (and they are just that, nothing more) and adjust according to load, speed, road & weather conditions, personal preference, etc.

    *Usually based on same basics as all other driving or suspension setting recommendations by most car manufacturers, i.e. full fluids, 2 (or 4) passengers, luggage, spare & tools... (consult your owners and/or service manuals)
     
  4. Edward 96GTS

    Edward 96GTS F1 Rookie
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    Nov 1, 2003
    4,554
    30/32 seems like a good compromise. understeer is safe.
     
  5. Bob Zambelli

    Bob Zambelli F1 Rookie
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    Nov 3, 2003
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    Manning, SC
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    Robert G. Zambelli
    I have no experience with the 365 GTC but since there is not a lot of difference between it and my 330 GTC, I’ll elaborate on my own 330 GTC experience.

    I have put close to 160,000 miles on my car, having owned it for 45 years.

    Approximately 10,000 of those miles are from track events and very aggressive driving.

    I will express my own opinions based on nothing more than my experience with the car and the various tires I’ve used.

    First off, there are no specific tire pressures for the GTC, no matter what the manual or anyone else says. I know that this thread is about tire pressures but these are a function of tire size, brand and driving styles.


    Here are my ratings and comments on the different tires I’ve used, from best to worst, based on ride comfort, road noise, longevity, dry weather handling and heavy rain handling. As far as alignment, all four wheels were checked when I got the car and found to be right to spec. I check alignment regularly:


    1) Uniroyal Tiger Paw AWD II. Best all-around tire I’ve tried. Great in all weather conditions. Not high-speed rated but I don’t drive all that fast anymore. AND, they’re whitewalls! 36/38 psi work best for general driving.

    2) Yokahama Y-12 and Pirelli 4000. Nice all around but a bit short lived. Pretty good on the track. 38/38.

    3) BF Goodrich Comp T/A. SUPER on the track but not so good in heavy rain. Moderate life. More of a track tire than a road tire. 38/38.

    4) Goodyear. Can’t remember the type or pressure but OK as I recall.

    5) Pirelli CN-72. They came with the car when I bought it and they seemed OK but I only drove them a few hundred miles. Don’t remember anything else.

    6) Michelin XWX. My least favorite tire. I tried all sorts of F/R pressure combinations and nothing worked for me. At my first track event, I spun out twice. Terrible in the rain and they only lasted around 8,000 miles.


    Whenever I installed a new set of tires, I started with 30/32 and experimented with pressure until I felt comfortable with the overall performance.

    People have all sorts of different driving styles and habits. Experiment a bit and find the pressures that work best for you. And insure that your alignment is spot-on and keep an eye on tread wear.


    This is my story and I’m stickin to it!

    Bob Z.
     
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  6. Cobraownr

    Cobraownr Formula Junior
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    Feb 6, 2008
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    Edgewater, MD
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    Donald Silawsky
    Bob Z., thanks for the details regarding your long experience with tires for the GTC. As the Michelin XWXs I have are a little over two years old, they will be on my 365 GTC for some time to come. I just did two group drives with the car during which a friend with quite a lot of track time under his belt drove for about 200 miles, at times pretty aggressively. The Michelins performed admirably at F31/R34 PSI (cold).
     
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  8. Longstone Tyres

    Longstone Tyres Formula 3
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  9. fasthound

    fasthound Formula Junior

    Nov 23, 2003
    391
    Potomac, Maryland
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    Kevin
    Per Ferrari Circolare Technica No. 108/3 dated January 27, 1975, recommended pressures for Michelin’s 205 VR 14 WXW are:

    low speed F 27.1 psi R 32.9 psi
    High speed F 30 psi R 37.1 psi

    Same for both 330 GTC and 365 GTC.

    Got this info from FERRARI TUNING TIPS AND MAINTENANCE TECHNIQUES by Roush and Apen
     
  10. fasthound

    fasthound Formula Junior

    Nov 23, 2003
    391
    Potomac, Maryland
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    Kevin
    Michelin XWX….dyslexia strikes again.
     
  11. Longstone Tyres

    Longstone Tyres Formula 3
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    Feb 2, 2006
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    Hi

    The 205VR14 XWX has been out of stock for a while, but we recently got them back in.

    https://www.longstonetyres.co.uk/tyres/205-14/205wr14-michelin-xwx.html

    the current date code on my shelf is 2021. I know there is a lot of scare about brexit in Europeland and the old Coroney, but we have maintained our service. we also deal with the taxes and duties, so if you are buying from Europeland don't worry your tyres from Longstone will not get held up by customes and there are no extra hidden charges.
     
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