Subject: Urquattro wheels/tires - less is better!?!?

[C1J1Miller@aol.com]

Jouko Haapanen wrote:
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>>I've had a few days now to evaluate the Pirelli P-Zeros Asimmetricos
>>(225/50ZR15) mounted on my new 8x15 Ronal R8's.  I previously ran 215/45ZR17
>>Goodyear Eagle F1's on 8x17 BBS RS II's on my car, and the differences are
>>significant.  As expected, the ride is more compliant and quieter, but at
>>the same time the steering response and and ultimate grip seem to have
>>improved at the same time.
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Joukoh:  I have a couple comments on your change.  First, here's some numbers 
off a good comparison spreadsheet I grabbed off the web, to compare the two 
setups you've had on the car.

                                  15"                    17"        
Difference from 15"
Sidewall height:         4.43"                   3.81"          (0.62")
 Tread width:              8.86"                  8.46"           (0.4")
Tire diameter            23.86"                 24.62"           0.76"
Tire+wheel radius      11.93"                 12.31"          0.38"
Tire circumfrence       74.95"                 77.34"          2.39"
        (this is a 3.18 percent difference)
Tire revolutions/mile  845.33                819.24           (26.09)
Tire revolutions/km    524.95               508.75            (16.2)
matched spedometer     70mph            67.84mph      (2.16)

My initial thoughts are that both sets of wheels are very comparable, high 
quality, same width, and the 17" wheels probably weigh the same as the 15" 
OEM Ronals (lightweight and forged BBS, correct?).
You've changed too many other factors, though, to make a meaningfull 
comparison.
One, different tires... could explain entire difference, IMO.  Haven't used 
either tire, myself...
Second, you've geared down the car about 3.18 percent; should also give you 
3.18 percent more perceived horsepower... thus better response, too?
Third, the tire width went up 10 mm (over 4%)... might give better grip on 
dry cornering...

My thoughts on benefits of 17" over 15" are:  better or more aggressive 
looks, probably stiffer sidewall, more room around brakes (for upgrades, 
perhaps cooling?), and possibly quicker turn-in due to stiffer sidewall.  
Detriments are probably a worse ride, easier to damage, and often higher 
weight.

Not meant to defend the 17 vs 15s; just present more info.
chris miller, windham nh, c1j1miller@aol.com