Rear engine vs. mid engine ? Cayman vs. 911.

[Bill Verburg]

low polar moment just means the car can be rotated w/ less force than a car w/ higher polar moment because the weight is more toward the center of rotation.

A commonly seen example of changing polar moment is an ice skater spinning, when the arms are pulled in you can see the rate of rotation increase noticeably, when the arms are extended the rate of rotation slows noticeably. This is because the total energy or rotation is conserved during the transition from one geometry to another.

In a car polar moment is more or less fixed, it does decrease a bit due to gas usage

Cayman has lower polar moment than 911.

Sometimes it's better to have a higher polar moment, on acceleration and deceleration are 2 prime examples.

Another point is that the inputs don't have to be so finely controlled w/ a higher polar moment, A 911s tail will always let you clearly know what it wants to do and responds to drivers input well, you want to rotate more? OK, let off the gas, the car will rotate more. You want to stop rotation? OK, gas it it, the rear plants and the car squirts ahead. You do have to steer a bit while all this is going on. In a Cayman you will want to be more subtle and not have to counter steer as much.

Someone mentioned that you can lower the polar moment of a 911 easily, this is true, a 911 w/ f/g or c/f bumpers as opposed to the stock rugged bashers will have a lower polar moment and will rotate more easily, If you have a chance to back to back drive the difference is amazing.

[stealthn]

After getting used to the Cayman it is a completely different drive than my old SC. The 911 can rotate on a dime, sometimes whem you don't want it to but it can shoot out of corners like no tommorrow. The Cayman feels like it's on rails around a corner with no real feel of a rear break away, but a re-correct after the corner that takes a second before you can apply the power properly. Both understear but I managed to tune most of it out of the 911, I haven't had the chance to do it on the Cayman yet.

Both are completely fun cars to drive, just very different.

[masraum]

911, weight in the rear. The front of a 911, because there's not much mass/weight, is very easy to get to change direction. IE, you turn the steering wheel a little and the front end goes where you point it like it's telepathic. The rear end because it has all of the weight, wants to keep going in a straight line and takes a lot more force to get it to turn (hence the bigger rear tires). On a spirited drive, you can get that to work for you. A 911 can be a formidable car in the right hands.

A mid engined car (in this case, mid-rear), with the weight mostly in the middle (but as stated, still usually with a rearward bias, is still going to be pretty good at turning because of the low front weight, and since the weight is more centered, the rear is also a little happier to rotate for you. Because of that, a mid engined car is usually better at changing directions than cars that aren't mid-engined. But, a car that's happy to change directions (ie, spin faster) can also require very quick reflexes to catch when it does spin.

A balanced car that's forgiving and easier to drive is a car that's balanced, but has a high polar moment, think 944 with the motor in the front and the transmission and differential in the back, same as the newer corvettes. I could swear that there's an article out there where Derek Bell says that the 944 is better than the 911 because of it's balance and since the weight is divided between each end not as quick or likely to spin. I think the gist is that the 944 is very easy and forgiving to drive because it's got a high polar moment.