Wheel diameter differences?
Thread Starter
Racer
Joined: Dec 2001
Posts: 301
Likes: 3
Wheel diameter differences?
I asked this in another thread but no one answered so I thought I'd give it another try.
I was wondering why Porsche put tires on a 200Mph (nearly, anyway
car that differs in diameter from front to rear. I mean, isn't that exactly what they shouldn't have done!? The stress on the differential must be enormous when approaching 200! But then I (actually my brother helped me out) thought, Wouldn't the rear tire expand more, given the 60mm extra width, than the front when driving so fast!? Maybe it should be a 1.4% difference so that at higher speeds, when the stress is most, the wheels have basically the same diameter...
If this is true, then the difference of diameter should be less if the difference of witdh is smaller between front and rear...
thoughts people!?
I was wondering why Porsche put tires on a 200Mph (nearly, anyway
car that differs in diameter from front to rear. I mean, isn't that exactly what they shouldn't have done!? The stress on the differential must be enormous when approaching 200! But then I (actually my brother helped me out) thought, Wouldn't the rear tire expand more, given the 60mm extra width, than the front when driving so fast!? Maybe it should be a 1.4% difference so that at higher speeds, when the stress is most, the wheels have basically the same diameter...If this is true, then the difference of diameter should be less if the difference of witdh is smaller between front and rear...
thoughts people!?
Racer
Joined: Jun 2001
Posts: 471
Likes: 0
From: Atlanta
Not sure I understand your question but I'll tell you what I think.
First, in standard configs, the diameter of fronts and rears are nearly identical (e.g. D(225/40/18)= 637.2 mm and D(265/35/18)=642.7 mm) so 1/5 of an inch difference...
With regards to widths now: In RWD2WD cars, the job of the rears is to transmit power and therefore you want to have as much surface as possible to get that power to the ground. The job of the front wheels is to provide steering and up to a point, very thin tires can do that. Look at F1 cars to understand what I mean.
So, diameters are near even and Porsche did exactly what they needed to. One last thing, new P-cars understeer until you get passed a point and that is the safest thing for most drivers as when you understeer your "untrained" reaction when going too fast it to lift off. This brings the car back in line... So, for "driver x" the understeer is just what they need... Smaller front tires also contribute to that.
Hope this helps
JM
First, in standard configs, the diameter of fronts and rears are nearly identical (e.g. D(225/40/18)= 637.2 mm and D(265/35/18)=642.7 mm) so 1/5 of an inch difference...
With regards to widths now: In RWD2WD cars, the job of the rears is to transmit power and therefore you want to have as much surface as possible to get that power to the ground. The job of the front wheels is to provide steering and up to a point, very thin tires can do that. Look at F1 cars to understand what I mean.
So, diameters are near even and Porsche did exactly what they needed to. One last thing, new P-cars understeer until you get passed a point and that is the safest thing for most drivers as when you understeer your "untrained" reaction when going too fast it to lift off. This brings the car back in line... So, for "driver x" the understeer is just what they need... Smaller front tires also contribute to that.
Hope this helps
JM
Addict
Rennlist Member
Rennlist Member
Joined: Jun 2001
Posts: 1,586
Likes: 67
From: Virginia USA
Don't know about the 993TT, but I recall reading that the first series C4s ran different front and rear wheel diameters to bias the torque split front to rear. Could be nonsense, but since you're looking for guesses I thought I'd share!
