Maybe a step away from the main topic, but.. When relocating weight, I Believe we all can agree on that low is good. However do we have consenus regarding:
1) Center of mass (I Think itīs called).
I find the box to be very agile in turns, this is nice as long as you stay in Control, but when you go over the edge the Quick behaivour related to high amount of mass in the center also makes is easy to spin around..
2) Balance front/rear.
Some say... (And this time not related to The Stig) That the 911 is quicker also due to the weight distribution:
a) Better balance front/rear when breaking.
b) better grip on acceleration.
So.. How does this affect the aim of relocating weight in a Boxster? Shold we strive to relocate as much weight as possible to the back trunk?
No!
The 911 is quicker because it has more power. It doesn't handle as well as a Boxster, because the 911 has all the weight in the rear. Good for acceleration, but bad for everything else.
Moving weight to the rear of the Boxster would make it handle like a 911, which is bad. The Boxster handles better because of the weight distribution that the mid-engine layout gives you.
To the OP, relocating your battery would be one of the last things you should worry about. Yes, the battery is located high in the car, but it is still a lot lower than in most cars, because the Boxster is a low car. For street driving, you'd probably never notice the change if you moved the battery to the floor of the trunk.
Maybe a step away from the main topic, but.. When relocating weight, I Believe we all can agree on that low is good. However do we have consenus regarding:
1) Center of mass (I Think itīs called).
I find the box to be very agile in turns, this is nice as long as you stay in Control, but when you go over the edge the Quick behaivour related to high amount of mass in the center also makes is easy to spin around..
2) Balance front/rear.
Some say... (And this time not related to The Stig) That the 911 is quicker also due to the weight distribution:
a) Better balance front/rear when breaking.
b) better grip on acceleration.
So.. How does this affect the aim of relocating weight in a Boxster? Shold we strive to relocate as much weight as possible to the back trunk?
Polar moment of inertia is the point where the vehicle seems to rotate on an axis.
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1) Center of mass (I Think itīs called).
I find the box to be very agile in turns, this is nice as long as you stay in Control, but when you go over the edge the Quick behaivour related to high amount of mass in the center also makes is easy to spin around..
Not quite right, IMO the lower the polar moment the better, not only will it change directions more quickly, but it will also recover more quickly. A car with a high PMoI may "stay in control" longer, but once you loose it, it will be much more difficult to recover. Not to mention the entry understeer and exit oversteer that comes with it. If you're not trying to change F/R weight dist. , put it low and in the center of the car.
As far as weight dist. , around 55% rear (like the Boxster) is generally considered ideal, 60% rear like the 911 is too much, and can lead to quirky handling issues. This is assuming there's no odd rules in place regarding staggered tire sizes.
Keep the battery where it is and put in an electric power steering pump in the lower trunk. Cuts even more weight and eliminates the problematic PS pump on the engine. Win-Win
1) Center of mass (I Think itīs called).
I find the box to be very agile in turns, this is nice as long as you stay in Control, but when you go over the edge the Quick behaivour related to high amount of mass in the center also makes is easy to spin around..
The polar moment of inertia is a way to describe how mass affects rotation. The lower the PMOI, the easier and faster an object will rotate. The classic demonstration is how a figure skater increases the rotational speed of a pirouette as the arms and legs are brought closer to the body (center of mass).
Stephan Wilson's explanation is spot on - a car with a lower PMOI will rotate easily and quickly which is why it takes quick hands on the wheel to avoid a spin in a Boxster. Driving a 911 takes a completely different driving technique to manage the higher PMOI (slower but much larger wheel corrections to avoid a spin).
Here is a video showing how quickly I had to move my hands to avoid a spin at Laguna Seca...
Quote:
Originally Posted by Robert986
2) Balance front/rear.
Some say...That the 911 is quicker also due to the weight distribution:
a) Better balance front/rear when breaking.
b) better grip on acceleration.
Since grip is determined by the stickiness of the tires combined with the weight on the tires, more weight means more grip. But remember that grip is often a trade off; increased front grip can mean reduced rear grip - thus the concept of balance becomes important.
The secret to fast driving is managing the balance of the car to move the weight of the car to the location (front or rear) where it will provide the most benefit at any given moment without creating a condition where the reduction in grip in another location induces handling issues.
Boxster's are generally evenly weighted (front to rear) so its fairly straight forward to manage the balance of the car for maximum grip. For example, braking during corner entry puts weight on the front tires which increases the front grip for good corner turn in and reducing understeer. Then transitioning from brake to throttle at mid-corner allows for weight transfer to the rear to get good grip and build speed on corner exit. There are also other techniques that can be used in the Boxster to get though corners fast but this is the basic approach.
Conversely, a 911 has an inherent rear weight bias, so braking to get weight on the front of the car so it turns in properly is key but the rear weight bias allows for early and substantial use of the throttle in the middle and exit phases of the corner without inducing oversteer. So a 911 typically enters corners slower but can be fast though the middle of the corner and blasts out of corners with all of that weight on the rear wheels.
But at the end of the day, balance wins out. For equal power and tires, the mid-engine layout will typically produce faster corners than a rear engine layout which is why the latest Porsche 911RSR is a mid-engine design.
So.. How does this affect the aim of relocating weight in a Boxster? Shold we strive to relocate as much weight as possible to the back trunk?
As explained above, there isn't much benefit in moving weight to the rear, but there is benefit in moving weight lower in the car. But you'll have to move a lot of weight lower in order to notice any real difference in handling.
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