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Discussion Starter #1
A quote from Jack Hidley who I highly respect:

"Front end rise and weight transfer from the front to the rear tires do not have a cause and effect relationship that most people think there is.

It is easy to see this by taking a motorcycle, clamping the front forks so the front suspension can't move and then doing a full throttle launch. I guarantee that the motorcycle can still do a wheelie (100% weight transfer), even though the front end didn't rise at all.

A little back ground here. All of the information below only applies to a rear wheel drive car with a solid axle.

To get the most forward grip from the rear tires during launch, you need the maximum percentage of the vehicles weight on them and EACH tire should have the same weight on it.

The first part is accomplished by getting the cg of the vehicle as high as possible and as far back as possible.

The second part is usually accomplished by having very little front roll stiffness (soft springs, soft swaybar) and high rear roll stiffness (stiff swaybar).

The result of this roll stiffness difference is that the driveshaft torque doesn't make the rear tire loads as much unequal as they would be with a normal roll stiffness distribution.

More equal rear tire loads, equals more grip. More grip equals more potential for acceleration. Note that the term "weight transfer" didn't show up at all in the second part. This leads me to the second most important thing to consider.

If a drag racer uses the term "weight transfer" in a sentence, close your ears. The odds are better than 90% that the statement is false.

The formula for weight transfer is:

Weight transfer = acceleration * (cg height/wheelbase) * vehicle weight

Note that for a given acceleration, a higher cg height results in more weight transfer.

Setting up the car with a lower front wheel rate does allow the front of the car to ride slightly higher on launch, raising the cg, which increases weight transfer, which gives
more rear tire traction, which results in more acceleration, which results in more weight transfer......... This effect is not that large.

The major change from installing softer front springs is that it reduces the percentage of front roll stiffness that comes from the front suspension.

This increases rear tire grip, which results in more acceleration, which results in more weight transfer......

The important thing to realize is that the increased acceleration is the primary thing that usually results in more weight transfer, not the other way around.

For maximum forward rear tire grip, you want the cg as high as possible, the front roll stiffness as low as possible and the rear roll stiffness as high as possible.

When selecting front springs, this means make them as soft as possible. The limit is usually around 150lbs/in.

This is based around a front sprung corner weight for the car of 800lbs. The higher the ratio of sprung corner weight to spring rate used, the more distance the spring compresses at ride height. The combination mentioned here is going to compress 5.33" at ride height (800lbs/150lbs/in).

The higher this ratio, the longer the spring needs to be to not coilbind. The longest practical spring that can be packaged in the front of a Mustang is 14" long.

If you used a spring that was 125lbs/in, the spring would compress more and would need to be longer, maybe 16" long. This won't fit in a Mustang.

This puts the practical limit for a soft Mustang front coilover spring at 150lbs/in and 14" long.

There are some ways around this to use a softer spring, but they are going to get more complicated to implement.

The softest spring commercially available that could ever be used in the front of your car is a 125lbs/in x 14" model.

This would require some modifications to your struts to work."
 

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I agree 100% where he is going with it all. There are some examples that can be misleading if not read correctly but it's simple dynamics:

Front end rise and weight transfer from the front to the rear tires do not have a cause and effect relationship that most people think there is.

The above statement is a bit odd b/c I don't know what "relationship that most people think there is" and he doesn't describe what he thinks other people are thinking.
The Formula that he post proves exactly the relationship it does have..the CG Height, which changes as the frontend moves upward, gives more weight transfer if the car is moving forward:

Weight transfer = acceleration * (cg height/wheelbase) * vehicle weight

The below is debatable b/c I can launch my Harley at ANY throttle and it will either spin or hook but the frontend will not come off the ground due to other affects going on. In order for the below statement to be 100% correct other factors are needed to change.

It is easy to see this by taking a motorcycle, clamping the front forks so the front suspension can't move and then doing a full throttle launch. I guarantee that the motorcycle can still do a wheelie (100% weight transfer), even though the front end didn't rise at all.

Although he did not say it some of the statements "could" be read that: "if I raise my car higher off the ground then I will get better traction". This is NOT what he is saying. With the car at standstill there is the same amount of weight on the rear tires as there is if the car was slammed on the ground or raised up in the air. As he stated ONCE the car starts to move THEN the weight on the rear tires changes. In other words you still need traction in order to move forward and induce the transfer of weight to the rear tires. In other words if the car is on ICE there is no traction thus no weight transfer and lifting the car higher up in the air isn't going to help.

Important Key:
The important thing to realize is that the increased acceleration is the primary thing that usually results in more weight transfer, not the other way around.

ks
 

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Discussion Starter #3 (Edited)
Interesting points Kevin and thanks for the reply. I did think that he meant a car that sits higher will get better traction. Now I'm scratching my head. I'm in the middle of a new build and trying to do it right the first time.
Oh...your Harley won't pull the front wheel because it's a Harley!
Heavy hog. Lol. My mother is 77 and rides a Heritage Softail. I kid you not. She has ran the Tail Of The Dragon the last two years!
 

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I've been too busy to reply to posts but somewhere I thought I was reading into someones post that the higher the car sat the better the traction. That's why I mentioned it above.

Remember: You have to have MOVEMENT first, before you get weight transfer.
The key is to get the car moving correctly to get the "best", not the "most", weight transfer.

FUNNY, about your mother! We can all learn from her!!
ks
 
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