alexb76

I am curious to know how has our weight distribution been calculated? with a full tank you'd have easily 150 lbs of extra weight upfront... wouldn't that make a big difference?

wc11

Our 997's take 14.1 Imperial gallons of fuel totaling 104.2 lbs. I would think balance was calculated with all fluids at max. levels.
The tank is behind the front wheels so effects based on volume should be minimum

iammulva

Using my car (997.1 S), the stated weight is 3131lbs. Assuming 50/50 front/rear distribution with no gas, adding 150lbs to the front end would make it 53.3/47.7. I'm not an engineer, so I know i'm missing about a bazillion variables in my calculations. I have no opinion on whether that result is a "big difference" or not. I also got to wondering how much my fat self contributes to overall weight distribution.

peteb3

911 is rear engined
It's not 50/50 weight distribution even with a full tank of gas

iammulva

I'm an idiot.

alexb76

Correct, what I'd like to know how the stated weight distributions are calculated? full fluid or empty? Specially with fuel. 100 lbs on the front axle does make a difference.

PhilD

These are the figures I have:

Porsche 997 C2 : 38% front , 62% rear
Porsche 997 C4 : 40% front , 60% rear

I would expect Porsche, and any other auto manufacturer, to take into account the weight of a full gas tank, drivers of various sizes, passengers, etc, when designing the suspension of a vehicle.

Most manufacturers vehicle weights are quoted dry as far as I know, so I would expect the weight distribution to be the same.

Also adding weight at one end isn't always added purely to that end, if it is behind the front axis point, it will add weight to the rear too, not to mention different spring rates at either end, etc.

As to making a difference, what exactly for? Way out at the limits, maybe, the rest of the time, not really.

Jake951

Published numbers should be taken as only approximate. They can vary with the options and accessories on the car. Furthermore, assumptions about whether they include fluids, passengers, etc. are usually not stated and one can only guess.

FWIW the actual distribution on my '07 GT3, as weighed on a scale, is 38/62 F/R, with full fluids except for 3/4 tank of fuel, and a 140 lb driver (me).

alexb76

Ok, thanks guys... just being curious that's all. Like if it's 40/60 without fuel, would it be 45/55 with fuel? Like theoretically give it less of a front bias? That's all...

PhilD

The gas tank is behind the front axle, so the weight of 104 lbs of gas will not be completely all at the front, but let us guesstimate that 90 lbs is placed at the front.

Depending on options, etc, your vehicle is going to be somewhere north of 3250 lbs. Given a 40/60 weight distribution that would equate to 1300 lbs over the front axle. Add the guestimated 90 lbs of fuel to the front and 14 lbs to the rear, and you now have a 41.4/58.6 distribution ratio.

To decide if that makes a difference you first have to define what it is you are actually expecting a difference in.

I would take a good guess that Porsche designed the suspension to perform within expected parameters with a given variance on the weight distribution. That variance will take into account gas, driver weight, passengers, etc.

A race car will be set up to work with a much narrower variance, but you are not driving a race car, nor driving it at anywhere near the limits of one, so I'll take a guess that a 100 lbs here or there doesn't really matter for the majority of us.

The effect of the weight of a tank of gas is far more complicated to work out than just looking at weight distribution anyway. Where is the weight added in relation to the CoG, how does it change the CoG, how does it effect spring load, etc, etc. All factors that will effect handling and performance, weight distribution is just one part of the bigger picture, and to be quite honest by itself does not really mean much.

Edgy01

For many years the assumption has been that things were calculated as wet, and 40-60. It moves a bit from model year to model year but unless you're doing some complex inertia mass momentum problem that is all most of us need to know.