realdealg35

iTrader: (2)

Posted here because most guys who are into suspension, brakes, tires, etc. are spirited drivers, roadracers, autocross, etc. This topic has more to do with weight distribution than weight reduction, I've read almost all the weight reduction threads I could find through search, and this topic isn't really touched on much at all. Here it goes:

Everybody knows that on a traditional front engine, rear wheel drive car, a LOT of weight can be removed from the rear of the car in the form of spare tire, jack, extra underbody metals, lightweight exhaust system, rear seat delete, gutted trunk, etc. and not as much from the front.

My hypothesis is as follows (and it's pretty general/simple) just want some other ideas from experienced roadracers or technical people:

Remove everything you don't need from the car (or whatever you're willing to part with) be it front, rear, whatever (I'm neglecting side to side for simplicity). Then calculate your weight distribution, and add weight accordingly. Here's the catch: you just took out a LOT of weight from the rear, and very little from the front, so your weight distribution is worse on a F/R car.

The idea: add weight to the extreme rear of the car to multiply weight realized at the rear wheels, and reduce weight from the front wheels.

Assuming a car has a wheelbase of 9' and an overall length of 15' (with a 2' long front) and a 4' long rear (G35 specifications, approximate), statics says that if you add weight to the cantilevered extreme back section of the rear end, weight will be multiplied at the rear wheels, and removed from the front wheels - altering your weight distribution to more favorable specifications.

Example: A G35 Coupe weighs approximately 3,500#. Through extensive weight reduction, you have been able to remove a total of 200# out of the car, 25# from the front, and 175# from the rear of the car, effectively. Before modification, the weight distribution was 54/46, so the front weight distribution was 1890#/1610#.

Now, with reduced weight: 1865#/1435# and a balance (worse) of 57/43.

The idea is to add back 50# to save a total of 150# (a whole person dropped out of the car) to regain a better distribution.

Addition of 50# to the extreme rear of this car will result (statics) in a lift of 22# on the front wheels, and an extra weight of 72# over the rear wheels. Effectively, a 94# weight distribution advantage. Weights change to 1843#/1507# and balance changes to 55/45 - much closer to stock balance, and still 150# lighter.

Removing weight from the extreme front end of the car will similarly increase weight to the rear by statics. Changes in the center of the car are less noticeable.

So, what do you guys think?
Can you add to the above and help me further balance out my car?
Ideas on lightening the front end?
What is the ideal weight distribution for a F/R car? 50/50, more like 55/45, or 45/55? (In regard to handling, grip, and balance.)
Is the added weight to the extreme rear going to make the rear want to step out more or less due to added rotational inertia?
Other ideas to boost efficiency - faster without necessarily increasing engine output?

Let's discuss

terrorist22

That's how teams with a healthy budget operate. Lighten the hell out of the cars, then ballast the car back to regulation weight. The lighter the car the better, because you can distribute more weight where you want it. It's also better to remove weight from the higher parts of the car.

Q45tech

AS we pointed out on the other forum remember to study polar moments of interia [remove weight from outside the springs and add weight inside the springs].
Decide whether accelerating or decelerating you want the balance point/ratio to occur. Static balance is pretty meaningless since you are almost never at a steady speed.

realdealg35

iTrader: (2)

Oh yea, I hear ya on static vs. dynamic balance. Just trying to get a general idea as to the effects - looking at static now, will contemplate dynamic based on a better understanding of static hopefully soon

Resolute

iTrader: (2)

Your static loads should only be set up to compliment any dynamic behavior you are interested in. There are a number of factors that will help determine your ideal static weight distribution, none of which you have identified and would be worth considering if you are seriously looking into the methods behind successful chassis set-up. Not least of which are-
-desired yaw rate vs ideal slip angle (need tire data and kinematic suspension data)
-desired yaw rate vs ideal roll couple (need to determine the ideal slip angle for given yaw angle)
-ideal roll couple distribution of suspended mass as function of spring and ARB(need to determine ideal yaw rate)
-weight transfer of unsuspended mass vs yaw angle (need dynamic suspension analysis)
-all of the above re-factored under dynamic loading in the longitudinal plane in addition to the lateral transfers taking place.

In general though, don't add mass on the polar ends of the car. Ideally, make the car as light as possible and adjust your spring rates and kinematics to compensate for weight distribution if you can't control where the mass is located.

Will