Rear Tire Size / Power output?

[peanut_man]

Hi there,

I've always thought that the tire size for street bike are generally selected based primarily on the power requirement.  Looking at the 07 S2R 800 and the 08 696 spec below.  Why would Ducati choose to have a 160 series tire on the 696 and 180 series on the S2R 800?  The power / torque specs seems to be nearly identical on the two.  Or it's more of styling and marketing?     

(I'm not sure why they use slightly different units on the two specs, but I got all info from ducati.com):

2007 MS2R 800
Power*      56.7 kw - 77 hp @ 8250 rpm
Torque*      72.6 Nm - 7.4 kgm @ 6500 rpm
Front tyre     120/60 ZR 17
Rear tyre     180/55 ZR 17
Wheelbase     1440 mm / 56.7 in

2008 M696
Power*      58.8 kW - 80 CV @ 9000 giri/min
Torque*      7.0kgm - 50.6lb-ft @ 7750 rpm
Front tyre     120/60 ZR 17
Rear tyre     160/60 ZR 17
Wheelbase     1450 mm / 57.1 in

[Popeye the Sailor]

You know, often, these things are not chosen for their performance. A narrower tire will give you a bike that is far more nimble, except....it doesn't "look as cool". The tire sometimes just gets thrown on there for aestetics.

[caboteria]

Parts availability is a factor, too.  Where possible you want to use the same part in as many models as you can since it makes everyone's life easier.  The s2r is a single-sided swingarm bike and I don't think there's a 4.5" SSS rear rim on any Ducati, so it's probably cheaper in that case to go with the 5.5" instead of having a rim that's unique to the s2r even if the 800 motor doesn't make enough power to need the extra width.  The 696 is a double-sided swingarm and there are lots of other monster (and supersport) models that had a 4.5" rim.

[Holden]

except....it doesn't "look as cool". The tire sometimes just gets thrown on there for aestetics.

For shame. I've always loved the look of skinny tires.

[Duck-Stew]

The Coup D'etat had a hi-torque 900 motor with a 140/90/15 on it.  'Course it would light it up like a roman candle if you weren't 'aces' on the clutch lever.

GADDAMN I miss that little mo-fo...  Good times.... [moto]

[Raux]

The magazines talk about this as well. they mention how the turn in on the 696 is much better than similar bikes with the 180s