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Old 11-24-2004, 10:54 AM   #1
Lordhowe
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Default Contacting surface?

1. Which has an wider contact surface? Pzero Nero M+S in 225-45-17 or Dunlop SP Sport 5000 Asymmetrical in 225-55-16.
2. if the tires were the same size, which one do you perfer?

thx
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Old 11-24-2004, 03:50 PM   #2
2Stroke
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In theory, they should be the same width. In reality, there will be variation in shoulder design, and there are tolerances in manufacturing, but the difference will be small. A 225/55-16 will be enough taller that the differences in ride height and gearing will be readily apparent. Effective gearing will be higher (lower numerically).

I don't know how much fender clearance a WRX has above the center of the wheel at full bump, but if I was thinking of installing taller tires, I'd find out.

The second question is harder. I like Pirelli because Italian names have more flair, but my dirt bike has very good Dunlop knobbies. It's a toss-up.
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Old 11-24-2004, 04:40 PM   #3
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There's only a seven tenths of an inch diameter difference between those two sizes, which will cause a 3.1% difference in your speedometer reading. I wouldn't expect to be able to feel any difference on the Butt Dyno between the two, but hey, perhaps your rear end is more sensitive than mine.

There's only a four tenths of an inch difference in the radius of the tires (discrepancy vs. diameter due to rounding). I seriously doubt you'd be able to observe a ride height difference without breaking out the ruler.

As 2Stroke mentioned, contact patch is not dependent on tire size. While there may be marginal differences due to tire construction, as a practical matter the total area of the contact patch will be the same regardless of the tires you put on the car.
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Old 11-24-2004, 04:50 PM   #4
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I can easily feel the gearing difference when I switch between 215/45-17's and 205/55-16's. It shows up as g-force and a difference in percieved throttle response, and is also very noticable in how much faster you have to grab the next gear when using shorter tires, or how you have to "wait it out" on taller tires.

The difference between my two sets of tires is just under 2%.
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Old 11-24-2004, 05:02 PM   #5
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If the radius difference is 4/10", then the car is higher by that amount ( I haven't checked that number).

4/10" = 10mm (actually, a tiny bit more but close enough)

Some common aftermarket lowering springs for the WRX give about 20mm of "drop". After installing these, the car is said to be "lowered".

So by this reasoning, 10mm is halfway to "raised".
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Old 11-24-2004, 05:03 PM   #6
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Hey man, I'm not denying your reality, I'm just saying that your ass must be a lot more sensitive than mine.

I got into an argument with a Nissan mechanic a while back about my 240sx. It has upsized wheels and low profile tires on it, but the outside diameter of the tires is within a couple of tenths of an inch of the stock tires (the aftermarket wheel/tire combination is actually a little *larger*). He *insisted* that the car was lowered, and wouldn't accept an alternative answer until we actually broke out the ruler and started measuring things.

Human eyes typically make terrible measuing instruments.
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Old 11-24-2004, 05:21 PM   #7
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I've never thought much about the sensitivity of my... er.. well, nevermind.

4/10" additional sidewall height will make the car look raised for the same reasons that your Nissan looks lowered. Namely, the relative sizes of the wheel vs the tire mounted on it, and the height of the top of the wheel in relation to the bodywork.

So not only will the different proportions make it look higher, it will BE higher. A WRX has about 6" of ground clearance, so thats about 7% more? Too lazy to open calc right now.

Probably OK with a WRX, because you can just say you have a gravel event coming up.
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Old 11-25-2004, 01:39 AM   #8
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ahhah, this is getting good! thx for the great info guys. I used to have a set of Yoka AVS DB s2, in the size of 225-45, but comparing the Pzero to the yoka, there is a noticible difference in shoulder width (contacting surface), where the Pzero is wider. So i just want a general comparsion between the Dunlop and the Pzero
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Old 11-25-2004, 02:10 AM   #9
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You probably won't get a full-blown Dunlop vs. Pirelli debate going in a thread titled "Contacting surface?".
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