So just how do you tune tire sizes on a car?
I'm having fun playing with these tire & rear end calculators:
http://gs.tolan-hoechst.com/tirecalc.htm
http://powerdog.com/tiresize.cgi
http://www.csgnetwork.com/gearratcalc.html
Playing with these calculators, I began wondering about tires on performance cars. The Sky will come with 245/45-18s.
Now, why is it that so many performance cars have wider tires in the rear with a smaller diameter tire? Is this due to weight distribution, horsepower demand or what?
Here are some examples...
Model ........................ Front ............... Rear
BMW M3 ................ 225/45-18 ...... 255/40-18
Porsche 911 ........... 205/50-17 ...... 255/40-17
Aston Martin DB9 ... 235/40-19 ...... 275/35-19
Honda S2000 ......... 215/45-17 ...... 245/40-17
Corvette ................ 265/40-17 ...... 295/35-18
Viper ..................... 275/35-18 ...... 345/30-19
All the cars have in common wider rear tires than front, probably to induce understeer. I can understand that. But why do all the foreign cars have smaller diameter tires in the rear than the front? The 911 even steps down a full inch in aspect ratio front to rear. That is going to lower the rear end a lot and spin that rear much faster than the front tire.
The American cars step down in aspect ratio and step up in wheel diameter to yeild the same overall diameter front and rear. The foreign cars, even the Honda S2000, all step down in aspect ratio while maintaining the same wheel diameter front and rear.
Why would the engineers want the rear wheel spinning faster than the front? In addition, this change drops the ground clearance and centroid of the rear end by a half inch.
Not all foreign cars tune their tires this way as I found the Acura NSX has identical wheels and aspect ratio front and rear, merely widening the rear tires. While the Audi S8 and Subaru WRX STi both carry identical wheels and tires on all 4 corners, like the Sky.
Any hints would be appreciated.
I guess my point is, would it help handling to reduce the Sky's tires from 245s to 225/45-18s up front and drop the aspect ratio of the rears from 45 to 245/40-18s? And what affect would this have on handling. I'm a bit confused. I guess I figure if it is good enough for an all-out racing sports car like the Honda S2000, then it's good enough for the Sky.
Does anybody understand tire tuning? Can someone refer me to a technical website to try to understand these details? It is looking like black-magic at this point.
I'm having fun playing with these tire & rear end calculators:
http://gs.tolan-hoechst.com/tirecalc.htm
http://powerdog.com/tiresize.cgi
http://www.csgnetwork.com/gearratcalc.html
Playing with these calculators, I began wondering about tires on performance cars. The Sky will come with 245/45-18s.
Now, why is it that so many performance cars have wider tires in the rear with a smaller diameter tire? Is this due to weight distribution, horsepower demand or what?
Here are some examples...
Model ........................ Front ............... Rear
BMW M3 ................ 225/45-18 ...... 255/40-18
Porsche 911 ........... 205/50-17 ...... 255/40-17
Aston Martin DB9 ... 235/40-19 ...... 275/35-19
Honda S2000 ......... 215/45-17 ...... 245/40-17
Corvette ................ 265/40-17 ...... 295/35-18
Viper ..................... 275/35-18 ...... 345/30-19
All the cars have in common wider rear tires than front, probably to induce understeer. I can understand that. But why do all the foreign cars have smaller diameter tires in the rear than the front? The 911 even steps down a full inch in aspect ratio front to rear. That is going to lower the rear end a lot and spin that rear much faster than the front tire.
The American cars step down in aspect ratio and step up in wheel diameter to yeild the same overall diameter front and rear. The foreign cars, even the Honda S2000, all step down in aspect ratio while maintaining the same wheel diameter front and rear.
Why would the engineers want the rear wheel spinning faster than the front? In addition, this change drops the ground clearance and centroid of the rear end by a half inch.
Not all foreign cars tune their tires this way as I found the Acura NSX has identical wheels and aspect ratio front and rear, merely widening the rear tires. While the Audi S8 and Subaru WRX STi both carry identical wheels and tires on all 4 corners, like the Sky.
Any hints would be appreciated.
I guess my point is, would it help handling to reduce the Sky's tires from 245s to 225/45-18s up front and drop the aspect ratio of the rears from 45 to 245/40-18s? And what affect would this have on handling. I'm a bit confused. I guess I figure if it is good enough for an all-out racing sports car like the Honda S2000, then it's good enough for the Sky.
Does anybody understand tire tuning? Can someone refer me to a technical website to try to understand these details? It is looking like black-magic at this point.