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Old February 4th, 2010, 02:41 PM   #11
ChrisZang
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Originally Posted by Duster View Post
I'm trying to decide between these sets of tires: Dunlop Direzza Star Spec Z1 or Kumhos Ecsta XS? I'll use them mainly for AXs.

Any recommendations?
If it's mainly for A/X, then all I read about these two tires they seem to be about equal. If you also want to go on the track I'd go with the Dunlop
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Old February 4th, 2010, 03:04 PM   #12
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I agree with Chris
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Old February 4th, 2010, 03:42 PM   #13
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I just read and compared the Dunlops to other "Z" rated tire on Tire Rack and I'm convinced as well. I'll need new rubber about mid year and will put four of the Direzza Sports on. I'm still a little in the dark though about going from a 205/50-17 in the front to a 225/45-17. Will both fit on the same stock front rim and is the 225/45 lower profile and wider?
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Old February 4th, 2010, 03:45 PM   #14
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225s will fit on the stock front wheels with no rubbing or other issues. 225x45 has almost exactly the same overall diameter as the stock 205x50s.
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Old February 4th, 2010, 04:13 PM   #15
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225s will fit on the stock front wheels with no rubbing or other issues. 225x45 has almost exactly the same overall diameter as the stock 205x50s.
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Then why change from OEM recommended size?
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Old February 4th, 2010, 04:16 PM   #16
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Rolling diameter not tread width
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Old February 4th, 2010, 04:23 PM   #17
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Rolling diameter not tread width
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Ok, so smaller diameter= less rolling resistance=increased handling? I need a glass of wine.
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Old February 4th, 2010, 05:26 PM   #18
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Then why change from OEM recommended size?
Simple: When Porsche designed the Boxster it was targeted for the mass market, not for driving enthusiasts which were familiar with how to deal with oversteer.
Therefore the OEM tire/suspension/alignment combo was dialed into understeer (which is deemed safer than oversteer). This might be a safe thing for a commuter car. But as soon as you go to the track or do A/X you are probably more interested in a more neutral handling. Before you start playing with alignment the easiest method to dial out some of that understeer is to put on wider tires in the front.

Definition of understeer vs. oversteer by (my hero) Walter Roehrl:
Understeer means that you see the tree that you are about to hit
Oversteer means that you only hear (and feel) the impact
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Old February 4th, 2010, 05:27 PM   #19
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no, the rolling diameter is about the same for the two tire sizes, but the 225 is 20mm wider....bigger foot print gives you a better turn in, and less push (understeer). With the rolling diameter being nearly equal, the larger size will not upset the computer for the ABS or traction control. If the tire diameters are too far off % wise front to rear it will cause the computer to believe there is a braking discrepancy or traction problem. The sensors are in the hubs of each corner of the suspension.
The wider tire patch helps eliminate the heavy understeer the factory built into the suspension. This gives you a better balanced handling.
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Old February 4th, 2010, 06:56 PM   #20
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Thank you Chris and Doc I get it now. So here's my next question. My Boxster has a tendency for the rear end to swing out in high speed turns and I turn into the "swing" and keep on the gas to straighten it out. Isn't that oversteer? My suspension has been aligned for track use and I first started noticing this after I installed the Pedro Technobrace. I have to add that as I'm getting more used to the handling characteristics of the car I'm driving more aggressively but my car seems to be handling in the opposite of what the factory intended or do I need another glass of wine?
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