Stephen, you are on the right track.
The bottom line is that the weight distribution, with the driver in the
car, and the gas in this car matters, as you have mentioned, because of
the weight in the rear.
If a car with a 1/2 full gas tank has a 50/50 distribution, Who Cares,
if you don't know what the cars distribution is with the driver in the
car.
After all we do drive a car, with a person behind the wheel, and the
weight of the driver does matter.
The purpose of me weighting the car, with ME in it, was to see what I
needed to do to make the car more balanced. But first, I needed a
starting point.
Drag racers know to jack up the left or right rear for weight
distribution, but anyone needs to know where you are starting from.
Road racers do the same in tuning their suspension, but they need to
where they are staring from.
Larry
Stephen Waybright wrote:
>Great.... a chance to practice a little engineering statics.... ;)
>
>The passengers weight will be distributed between the front and rear
>axles proportional to the distance from each axle to the CG of a person
>in a seated position, which would be approximately the center of the
>seat which is roughly 53" front & 33" so with 400 lbs of passengers,
>the front should see ~247 lbs and the rear ~153 lbs added for ~100 more
>to the front than rear which in a 2500 lb car will be a 4 point (+2%
>rear, -2% front) rearward shift of the weight balance.
>
>As example if you have 52/48 balance without passengers, you'll have
>50/50 with two passengers in a Tiger.
>
>Now looking at the gas level.... empty to full adds some 70 lbs (I
>think) about 24" behind the rear axle. This actually lifts weight off
>the front proportional to the ratio of the 24" vs the 86" wheebase, to
>the tune 17 lbs.. which now are loaded on the rear along with the 70
>lbs of gas to result in 87 lb weight added to the rear, or nearly the
>same as two 200 lb passengers in the example above. Let's say it's just
>a 3 point shift instead of 4.
>
>Now the question is... under what conditions do you want to "balance"
>the car?
>
>Do you want it to always be on the same side of 50/50? or allow it to
>transition from rear bias to front bias as loading varies. Generally
>transitions from one side to the other is a indicator of instabilty, so
>Let's aim to be 50/50 at the extreme load of full tanks and two 200lb
>passengers. The shift to an empty tank and no passengers should move
>the balance by have the calculated passenger shift (+/-2 point) plus
>the gas shift (=/- 1.5) for a target of 53.5%/46.5% "empty" balance.
>
>Can't "weight" to see the numbers Larry got on the scales.
>
>Waybright
>
>--- CoolVT@aol.com wrote:
>
>
>
>>Another question might be...when a driver sits in the car does his
>>weight
>>add to the front weight of the car or the rear?
>>
>>
>
>I know that each end will benefit from the driver's weight, I'm just
>curious to know
>
>
>>if anyone
>>has calculated what portion of the weight ends up where.
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