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Tire size question

Discussion in '360/430' started by Gary(SF), Sep 6, 2004.

  1. Gary(SF)

    Gary(SF) F1 Rookie

    Oct 13, 2003
    3,637
    Los Altos Hills, CA
    Full Name:
    Gary B.
    I'm considering trying some of the new Dunlop R-compound tires (SP Super Sport) on my 360. They are very competitively priced ($129 ea!) they're getting good reviews on the Porsche boards, and are suitable for street use to some degree so you can drive them to the track, much like Toyo RA-1s. My question is, with the closest rear being 285/30-18 vs the stock size of 275/40-18, there is a difference of 1.7" in diameter. Will that cause problems with the ABS, or any other implications, like maybe too low in the rear compared to the front? The front tires are much closer but not exact: 225/40-18 vs 215/45-18. Any thoughts appreciated. Here's the TireRack link for those of you interested:

    http://www.tirerack.com/tires/tires.jsp?tireMake=Dunlop&tireModel=SP+Super+Sport+Race

    Gary
     
  2. 4i2fly

    4i2fly Formula 3

    Apr 16, 2004
    1,330
    SF, Bay Area
    Gary,

    I noticed Max loading loading on these tires are 1433 vs. 1709 for the 99Y OEM tires on Modena. If you are going to use them for track I think they'd be o.k. but on Freeway I'd be careful.

    Matt
     
  3. Gary(SF)

    Gary(SF) F1 Rookie

    Oct 13, 2003
    3,637
    Los Altos Hills, CA
    Full Name:
    Gary B.
    Good catch, Matt, I hadn't noticed that at all. OTOH, that still allows a safety margin even at max gross weight, which I will probably never approach.

    Gary
     
  4. 4RE Bob

    4RE Bob Formula Junior

    Feb 7, 2004
    567
    Muskoka, Ontario
    Full Name:
    Bob
    I would think (I am no expert) the difference in ride height front to rear would really mess up the downforce generated by the underside of the car -- both in terms of total downforce and fore and aft balance.
     
  5. Gary(SF)

    Gary(SF) F1 Rookie

    Oct 13, 2003
    3,637
    Los Altos Hills, CA
    Full Name:
    Gary B.
    That's the kind of thing I'm worried about, just don't know if it's a fact.

    Gary
     
  6. docster

    docster Karting
    Silver Subscribed

    Apr 14, 2004
    204
    Oregon
    Full Name:
    David
    When I checked the tire info at tirerack.com, the largest size I could find was *265*/30-18. At 25.1" diameter, they are indeed 1.7" smaller than OEM Michelin Pilot Sport 275/40-18s (or 1.6" smaller than OEM Bridgestone S-02 As, and 1.5" smaller than OEM Goodyear Eagle F1 Fioranos).

    The 225/40-18 fronts, which are also listed at 25.1" diameter, are closer, at 0.5" smaller than the OEM Michelins, 0.6" smaller than the OEM Bridgestones, and 0.4" smaller than the OEM Goodyears.

    These tires sound interesting to me as well, and I share the same concerns as you regarding changing the rake. From what I've been told, ride height adjustment on the 360 is pretty simple, which should make it easy to compensate for this. ABS shouldn't be affected, as it senses wheel speed independently. Another concern for me is how the change in tire contact patches would affect handling. At first glance it looks like you'd be adding a little bit of available "stick" at the front, and taking away a bit at the rear--relatively speaking, of course, since these tires will supposedly have higher overall grip levels...

    dn
     
  7. docster

    docster Karting
    Silver Subscribed

    Apr 14, 2004
    204
    Oregon
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    David
    Since the wet/loaded (two passengers) rear axle weight on my Modena is only about 2000 lbs, 1433 lbs seems like an adequate per-tire load rating.

    dn
     
  8. SED

    SED Karting

    Nov 10, 2003
    61
    Stockholm
    Full Name:
    Thomas
    The problem with using a lower tire on the 360 is that the ASR will kick in. So you have to drive in sportsmode and ASR completly OFF.

    /SED
     
  9. docster

    docster Karting
    Silver Subscribed

    Apr 14, 2004
    204
    Oregon
    Full Name:
    David
    Anyone know if the ASR system on the 360 can be programmed to account for using different tire sizes? I seem to recall that at least one M-B I've had allowed end-user inputting of tire size changes, to keep its traction/stability control system acting appropriately...

    dn
     
  10. Tifosi66

    Tifosi66 Formula 3

    Nov 30, 2004
    1,776
    Jiang Jia Jie
    Full Name:
    Li-Ge
    If you plan to use it on the track, the lesser diameter of the Dunlops will definitely lower your gearing and provide for better acceleration. The downside is the car will be lower than before, i.e the body will be closer to the ground...too close for comfort!

    On the streets, I guess it's a definite no-no...
     
  11. Brian C. Stradale

    Brian C. Stradale F1 Rookie
    Lifetime Rossa

    Mar 17, 2002
    3,603
    Dallas, TX, USA
    I ran my 360 on the streets with Kumho V700 R-compound tires... love the tires... but the smaller rear diameter forced me to always remember to turn ASR off. It also resulted in artificially fast speedometer / odometer readings. I didn't find the lower ride height to be particularly problematic. Worse to me was the fact that the smaller diameter tires left a larger gap between tire and fender arch... didn't look ideal.

    The constant need to remember to turn off ASR did get to be annoying.
     
  12. CodeRed

    CodeRed Formula Junior

    Nov 8, 2003
    368
    LALA LAND
    I drove a GT3 at the track with the Dunlops. It is a great tire for the money let me tell you. The only ones that might be better out there would be the MPSCs (really bad for street) and the Corsa R which I also like a lot (much more expensive). I am having Corsa systems (even more expensive) put on a GT3 that I just bought before I go to Willow on the 27th. If anyone is interested I will let you know how thay are. The dunlops have a nice stiff sidewall and were surprising quiet.
     
  13. Gary(SF)

    Gary(SF) F1 Rookie

    Oct 13, 2003
    3,637
    Los Altos Hills, CA
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    Gary B.
    I'm also considering the Toyo RA-1, they are made in better sizes for the 360.

    Gary
     
  14. jrotsaert

    jrotsaert Karting

    Aug 15, 2004
    80
    Reading, UK
    Full Name:
    Jean-Marc
    Get the right size from Pirelli. They just came out with a 295/35/18 P zero corsa which is just about the same diameter as 274/40/18
    JM
     

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