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 Post subject: weight distribution
 Post Posted: Fri Oct 23, 2009 11:42 am 
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Joined: Wed Mar 11, 2009 4:14 pm
Posts: 116
my car weighs 3744lbs with me in it,, front 1766lbs,, rear 1978lbs.. about 53% rear and 47% front.. one of the things i am considering is moving the engine(sbc) 8 inches back in the car. at the moment the car leaves fairly well, 60ft 1.3s..
would moving the motor cause 8 inches cause a problem with the launch,, ie cause the front to lift excessively,, at the moment the front wheels lift about 5-6 inches but is totally manageable... how much weight bias is good


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 Post subject: Re: weight distribution
 Post Posted: Sat Oct 24, 2009 8:39 am 
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Joined: Tue Apr 18, 2006 9:54 pm
Posts: 1619
Location: Western Illinois
Weight bias for most of us is something you sneak up on. Guess what I'm saying is we have a problem like too much transfer or not enough, we start moving weight, front to back or up and down. This still comes down to a love triangle of Power/ traction and center of gravity. When it's right, you love it and if any part is off it's frustrating. You will find sooner or later that all good working race cars came about this in one of two ways. Dumb luck or fine tuning all three from previous experience. All of the pro class cars are evolution. What worked before and what can make them better. they nibble at their combination over years.

This is one of the most important speed secrets you will ever learn. How much power your delivering to the rear wheels and how much traction determine where your center of gravity should be. On the other hand how much traction and where your center of gravity is, determines how much power you need. And even how much power and where your center of gravity is determines what you need for traction to be efficient.

Horsepower to weight pretty much determines where you want your center of gravity.high HP to weight, likes forward and low. Low HP to weight likes high and to the rear. What you look for when thinking about changing Center of gravity is how the car transfers weight. Transfers to the rear smooth, carries rear weight and lets it come back to the front smooth is optimum. How high the front gets don't mean much. Any where from sliding a piece of paper under the front tire to turning the car into a star gazer is 100% weight transfer. No matter how high you go there just isn't anymore than 100%.

You can get that 100% and still miss the boat if it fails to carry and set down smoothly. If you see this, you will notice the front springs compress. This means they have more weight on them. If they have more weight, it can only come from the rear. This unloaded the rear. You may say, well the car will set down eventually anyway and unload the rear but this is where wheel speed comes into play. The more that rear tire is turning, the harder it is to break traction. If you know what your spring rates are at the wheel, you can see how much transfer you get by the pound, by watching the front separation or compression. This does not hold true for the rear spring rate, there are other forces at work there.

Ok here is the hard part. It's not getting weight to the rear. It is carrying it and letting it down smoothly. this has a lot of things that effect it. Most of the short comings come from Power, or more so being in the power curve at the right spot. Anyone can get transfer from just stored energy from your engine. I had a 46 dodge 3 ton truck that would pop a wheelie. It just wouldn't hold it. Don't do this at home kids, it will tear a carrier bearing out about every time. So you see having the right gear and in the power curve of your engine can be very important, not just for going fast but eliminating unloading of the rear tires. This is juggled to find the right gear, tire and RPM. Sometimes even shifting you power curve up or down. I hope this is understandable.

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 Post subject: Re: weight distribution
 Post Posted: Sat Oct 24, 2009 12:40 pm 
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Joined: Wed Mar 11, 2009 4:14 pm
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bubstr,, thank you very much.. very understandable..george


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 Post subject: Re: weight distribution
 Post Posted: Tue Oct 27, 2009 6:48 pm 
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Joined: Sat Nov 03, 2007 4:44 pm
Posts: 1423
Location: Clawson, Mi.
Very good explaination Bubstr, very understanding. I could use you in my corner when time comes to test my Elky with the new 4 link and 14 x 32's under it, although I have been told to run my I/C high and far out due to the weight of my Elky, around 1700# front and 1400# rear, but that will be changing once all the new lighter weight parts are on, and the total weight is figured, and C/G is found, then I can buy the rear springs. Can I get ahold of you later?

John

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 Post subject: Re: weight distribution
 Post Posted: Wed Oct 28, 2009 6:25 am 
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Location: Western Illinois
Hey John, It's always exciting to do a new or rebuild. This is when you make gains or not. Every time I did this, I sat down and asked questions of myself. What did you do right? What did you do wrong? What can you afford to make better? I'm sure we will all be around to help anytime you need it.

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