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Tires for 355...??

Discussion in 'Technical Q&A' started by sennapanzer, Jan 19, 2004.

  1. sennapanzer

    sennapanzer Rookie

    Jan 19, 2004
    3
    Any ideas on tire choices for 355? Brand/size? Not many selections for 265/40-18s out there... should I go 225/40 f and 275/40 r?? Eeeeek, help please!
     
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  3. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,058
    Stay away from 265/35ZR18s and stick with 275/40 ZR18s.

    I use Bridgestone S03s. I can get 15 track days and 5,000 street miles on a set. Which is about 3 times as long as I can get on brake pads (5 track days)
     
  4. Robin

    Robin F1 Rookie

    Nov 1, 2003
    2,893
    Arlington, VA
    I just hopped over to www.tirerack.com and punched in a search for 265/40/18 and came up with a choice of 13 different tires. Most are low stock or back order, but there were several in stock. I still see a thread every 4 or 5 months about people not being able to find this size though... not sure what the story is, but it seems like they shouldn't be hard to find.

    -R
     
  5. BigHead

    BigHead Formula Junior

    Oct 31, 2003
    992
    Outside of Boston
    Full Name:
    Dennis
    #4 BigHead, Jan 19, 2004
    Last edited by a moderator: Sep 7, 2017
    I built an XL spreadsheet for selecting a rear tire size for my car. The Ferrari 355 worksheet was last updated back in 2002, so it's a bit dated (tire pricing info from Tire Rack), but the math still works. I just did the Porsche 996 worksheet on Saturday, as I just ordered a set for my wife's car (but the stock rear size on that is 265/35-18).

    I set it up for my use only, so it may not be that clear to others, initially. Basically, the first table provides the total diameter of the tire for a given tread width and aspect ratio. The table beneath that one converts it into a PERCENTAGE of the OEM size (265/40-18). Each of the tires sizes provided should fit stock wheels on a 355.

    I ended up going with 295/35-18 in the rear - it is a perfect match without spacers or clearance problems. The aspect ratio on the rear is almost identical between the 265/40 and the 295/35. The wider tire offers slightly more rear grip, offsetting the factory inclination towards understeer. You'll also find a lot more tire selection in the 295/35, compared to the 265/40.

    The tables to the right were done using pricing and availability info from the Tire Rack a few months back, so I'm sure that pricing/availability has changed, at least a little. Ignore the large table on top, which lists ALL sizes; the table immediately below that trimmed away those sizes that I didn't want to use because the variation in sizing from OEM was too great.

    The initial column lists the brand and the manufacturer's wear rating. The next column is the price of one front tire, always static at 225/40-18. Then I listed the speed rating. The first column under a given rear tire size is the price of one tire, the second is the price of four tires. If a cell is blank, the size isn't available for that brand of tire.

    I ended up going with the Michelin Pilot Sport last year. More expensive, but a nice tire (on my wife's 996, we got about 18k street miles and 25+ track days on the set!!!), great performance, and a good wear rating. At the time, availability for OEM sizes was tough to find (one of the reasons I went with the bigger tire in the back), back the situation may have improved as more 996 buyers seek out similar sized tires. YMMV.

    FWIW, I just ordered a set of Kumho MAX tires for the 996; I'm now running Pirelli racing slicks for track days, so the MAX tires were a nice, inexpensive compromise for a street tire.

    [the second tab was for 348 tire sizes that I did for a friend of mine]

    vty,

    --Dennis
    Image Unavailable, Please Login
     
  6. sennapanzer

    sennapanzer Rookie

    Jan 19, 2004
    3
    Brilliant!!! Thanks guys.
     
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  8. ze_shark

    ze_shark Formula 3

    Jul 13, 2003
    1,273
    Switzerland (NW)
    Wider rear tires offsetting understeer ??
    30mm wider tires on the same rims sounds like an awful lot, are you not concerned about upsetting the damping characteristics ? I read in many places that the 355 is extremely sensitive to tires rigidity, and strong advice to stick to OEM alternatives.
     
  9. BigHead

    BigHead Formula Junior

    Oct 31, 2003
    992
    Outside of Boston
    Full Name:
    Dennis
    Sorry, sorry. I took my old post from my archives and edited it for this forum. Typing too fast without proofreading - Where I wrote, "The wider tire offers slightly more rear grip, offsetting the factory inclination towards understeer", should read "The wider tire offers slightly more rear grip, offsetting the factory inclination towards TTO" or "trailing throttle oversteer".

    I haven't had any problems with these tires, and in fact I've been able to dial back some of the negative camber I used to run to get better rear grip. This will mean better tread life, mehopes.

    Since my research and upgrade, including advice from a LA friend who had great success with the same, several other 355 owners I know have done the same and every single one of them likes the bigger rear tire.

    vty,

    --Dennis
     
  10. rossofiorano355

    rossofiorano355 Karting

    Dec 22, 2003
    210
    NOLA - Bham
    Full Name:
    Ron
    stuck with the Bridgestone Expedias in stock size, found some still available. like to stick to OEM when possible - but that is just me
     
  11. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,058
    Trailing throttle oversteer can be controlled by rear ride height. Given a rear tire width, there is a ride height that will allow the same pressures to be used front and rear.

    Few people are aware of how tunable this handling characteristic is. Too much understeer, get out the spanner and take 2-3 turns out of the rear ride height, too much oversteer; add 2-3 turns to the rear ride height. Lowering the rear ride height lowers the effective stiffness of the rear end, and this causes more of the roll to be handled by the front, causing the front end and the car to understeer more.
     
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  13. 1) How many trackdays do you get from the Pirelli racing slicks?
    2) Are they still the 295/35 rears?
    3) How much of a difference do you notice in terms of lateral and/or braking G's...or qualitatively for that matter...or track times?
    Thanks, for all to answer
     
  14. Mickey

    Mickey Formula Junior

    Jan 20, 2004
    409
    Linnet Drive
    Full Name:
    Mike
     
  15. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,058
    265/40ZR18 and 295/35ZR18 have the same rolling radius and therfore dont' upset the ride height or spedo calibrations.

    I know nothing about Michelin tires

    The weight of the tires has nothing to do with straight line speed. But even if you put 295/35ZR18s on the stock wheels, you are only adding 10mm to the outside of the tires (e.g. insignificant with respect to aerodynamics).
     
  16. BigHead

    BigHead Formula Junior

    Oct 31, 2003
    992
    Outside of Boston
    Full Name:
    Dennis
    1. It completely depends on your driving style, the track, the temps, the # of sessions, # of heat cycles, whether Mercury is in retrograde, etc. Safe to say that ultimate grip will fade quickly (within a few heat cycles), enough that you'd need a new set if you're competing. But still WAY sticky if you're just using them for DE events. Overheating them can wear them out more quickly. If I had to guess, if you're just using them for DE events and running 4 sessions a day, and you're reasonbly aggressive and take care of your rubber, that you could safely get 6-12 track days out of them. Maybe 16-18 if you're really thrifty.

    2. Racing slicks are not categorized the same way as street tires (using an aspect ratio). The second number is total diameter, in mm. For example, 680mm = 26.77". Subtracting 18" for the wheel diameter, you get 8.77", and divide by 2 = 4.38" for the sidewall height.

    Compare that to a 295/35-18 street tire. The 35 indicates that the sidewall height is 35% of the section width. This tire size's section width is 295mm, so converting that to inches (295 ÷ 25.4 = 11.6") and multiplying it by 35% gives us a section height of 4.1".

    Here are typical Pirelli P-Zero racing slick sizes for Ferrari:

    >235/645-18 - fits 8" rims
    >245/645-18 - fits 9" rims
    >285/645-18 - fits 10" rims
    >295/680-18 - fits 10" rims
    >305/660-18 - fits 11" rims

    3. HUGE. Even a well-worn, old slick will crush any street tire. Lateral G's of 1.2 should be easy, and hugely improved braking and acceleration too.

    vty,

    --Dennis
     

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