Engine setback/weight change
Moderator: Team
Engine setback/weight change
For a given weight and wheelbase is there a formula to calculate the weight dictribution change? I think I have it figured but would like input from others.
Re: Engine setback/weight change
Easier to explain with a diagram, but essentially, you calculate 'moments' about either the front or rear axle and determine how they change. Let's say the car weighs 3,000# and the engine/trans is 600#, wheelbase is 100" and the center of gravity (balance point) of the engine/trans assembly is originally 80" forward of the rear axle. The moment of the assembly around the axle then is 80" x 600 #, or 48,000 inch-pounds. The reaction (support) at the front axle will be in proportion to its distance from the 'pivot point' of the rear axle, so 48000/100 = 480#. Obviously the other 120# is carried by the rear axle.
Now, let's move the engine/trans back 10". The new moment is 70 x 600 = 42000 so the reaction at the front axle is now 420# leaving the rear to supporting 180#, thus the front is now 60# lighter and the rear 60# heavier. If the original weight distribution was 50% rear (1500#), the new one is 1560/3000 or 52%.
Many people are surprised at how much an engine must be shifted to get a substantial result, but try calculating the effect of moving a 40# battery from say 20" ahead of the front wheel to 30" behind the rear!
Now, let's move the engine/trans back 10". The new moment is 70 x 600 = 42000 so the reaction at the front axle is now 420# leaving the rear to supporting 180#, thus the front is now 60# lighter and the rear 60# heavier. If the original weight distribution was 50% rear (1500#), the new one is 1560/3000 or 52%.
Many people are surprised at how much an engine must be shifted to get a substantial result, but try calculating the effect of moving a 40# battery from say 20" ahead of the front wheel to 30" behind the rear!
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.