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Old 02-25-2003, 08:17 AM   #31
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The longitudinal weight transfer of the car with solid blocks for springs is easily calculated with the formula on page 32 of Carrol Smiths book.

Load transfer= (acceleration (g's) x center of gravity Height)/ wheelbase.

It is the same for a car with heavy springs or light springs. I agree that many other properties of the car changes with lighter springs, just not the total load transfer to any great degree. The view that the load transfer is reduced when you stiffen springs is a misconception.

Let's say we build a touring car with solid blocks for springs that has a center of gravity height of 12 inches and a wheelbase of only 4 inches. When the car accelerates, you would see the wheels move forward, the ponderously high center of gravity left behind and the car would tip. We would get 100 % weight transfer from front wheels to back wheels. The car would fall on its back. Regardless of the springs. This condition is improved, but not eliminated by lengthening the wheelbase and lowering the center of gravity.

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Old 02-25-2003, 08:42 AM   #32
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Quote:
Originally posted by John Stranahan
The longitudinal weight transfer of the car with solid blocks for springs is easily calculated with the formula on page 32 of Carrol Smiths book.

Load transfer= (acceleration (g's) x center of gravity Height)/ wheelbase.

It is the same for a car with heavy springs or light springs. I agree that many other properties of the car changes with lighter springs, just not the total load transfer to any great degree. The view that the load transfer is reduced when you stiffen springs is a misconception.

Let's say we build a touring car with solid blocks for springs that has a center of gravity height of 12 inches and a wheelbase of only 4 inches. When the car accelerates, you would see the wheels move forward, the ponderously high center of gravity left behind and the car would tip. We would get 100 % weight transfer front front wheels to back wheels. The car would fall on its back. Regardless of the springs.
I 100% agree with the Load transfer equation you listed. However you can't assume that all variables in that equation are constants. They are not. For example, the magnitude of acceleration(g's) change as the vehicle rolls (from changing camber angles and therefore maximum traction abilities of the tire), center of gravity changes in height as the chassis rolls and wheelbase can change slightly as the chassis rolls due to kick-up and antisquat angles. I don't think a simplified equation applies in this situation. It does not take into account the dominating factors that contribute to the result.
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Old 02-25-2003, 09:39 AM   #33
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The equation ONLY includes the dominant factors. Changes in center of gravity are small for both pitch and roll. When one end of the chassis elevates the other end squats. Center of gravity is relatively unchanged in the touring car. In a car with blocks for springs the equation is even more exact.

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Old 02-25-2003, 10:05 AM   #34
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Similar to cg height, the wheelbase may only change slightly during cornering. I agree that neither will change much during cornering. However, the acceleration (assume acceleration during cornering) varies a great amount depending on the camber angle of all four tires. Different amounts of suspension compression and roll(as a result of softer and stiffer springs) changes the camber angles of the tires.

Before you gave the situation of using blocks for the springs. In this simplified example there is no suspension roll and the previously stated equation holds true. My point is that with the touring cars we race, the suspension moves during cornering. This movement varies the angle between the tire and the ground depending on the amount of roll. The amount of roll could increase or decrease the traction of the tires(available cornering traction limits) and therefore change the maximum available magnitude of acceleration. The equation still holds true, but the cornering acceleration changes with different amounts of roll and therefore the magnitude of load transfer also changes.
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Old 02-25-2003, 11:35 AM   #35
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Mike- I see your point. I aggree that the roll stiffness should be adjusted to suit the traction of the track and to optimize cornering power. Generally tracks with higher traction require higher roll stiffness. I believe that there is probably a pretty wide range of stiffnesses that will work well and produce similar g's on the RC track. It is not a major change but a minor change.

I do not agree that higher spring rate will reduce weight transfer. If this were so we would all use the highest spring rate possible on every track on a 4wd touring car.

A good driver at our track did an interesting experiment. He set up two Yokomos. One with light springs medium roll centers, One with medium springs, sway bars, and higher roll centers. He got the same laptimes and race times with both cars run back to back even though the roll stiffness was quite different. Used the same motor and battery for both runs. This is just to say that many setups can produce similar g's and laptimes. The driver is the bigger influence.

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Old 02-25-2003, 01:10 PM   #36
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John - I agree, spring weight is independent of weight transfer. There are numerous suspension changes that effect cornering acceleration and weight transfer is dependent on acceleration.

The setup experiment you listed proves a very important point. Two very different chassis setups can posses similar weight transfer characteristics resulting in similar tire loading and similar vehicle cornering performance. However those setups will perform differently on acceleration(due to spring stiffness and droop), decelleration(due to spring stiffness and droop) and in bumpy conditions(due to sway bars). In this situation the setup would depend on driver feel.
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Old 02-26-2003, 05:29 PM   #37
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John,
What do you do first before you setup a car, and how should the car balance if you put a lever in between the front and rear? where should be the lever positions? or do you do this? or this another altenative?

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Old 02-26-2003, 06:01 PM   #38
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Wilfred-On the touring car the left side should weight the same as the right as much as possible. Place a knife point or blade under the center of each bumper or shock tower. When you pick it up the car should lift both sides at the same time. More details on setting up the car are on the first few pages of the TC3 Assembly tips, Factory team kit thread.

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Old 02-26-2003, 08:22 PM   #39
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john, after our discussions I am a little puzzled on your points..

can you please explain why when you go to a harder rate spring in the front of the car it induces understeeron?..

#my answer is: with the reduced weight transfer on decelleration entering a corner, the front tires have less weight transferred to them, hence they have less grip.

This is the same theory posted in all of the tuning manuals I have read.

A stiffer spring allows for quicker weight transfer initially, but to a lesser extent as the springs cannot compress to the same extent. the car will begin to understeer by mid apex, as it has less weight over the front end.

Using a softer front spring will allow greater amount of weight to transfer to the front tires, and gives the front tires more bias, as there is more of the cars weight acting apon them...this is also the case when the car is neutral set mid corner, the end with the softer spring will have more static weight over it.

Keen to hear your thoughts..

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Old 02-26-2003, 08:39 PM   #40
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Default Stiffer Front Springs

Stiffer front springs cause more lateral weight transfer at the front of the car while cornering than at the back. The stiffer front spring tries to stop the roll harder than the weaker back spring. This reduces the efficiency of the outside front tire and of the front end relative to the back; you get a push. The total lateral weight transfer is close to the same just more of it happens at the front. Tires develop their best cornering power and efficiency when lightly loaded. The ideal situation would be to have all four tires carry the same weight in a corner. This is not possible. There will always be some lateral weight transfer. The more the lateral weight transfer on one end of the car the less the cornering power on that end.

There is a good numerical explanation of this in Herb Adams book "Chassis Engineering" that goes through an example with numbers taken from a graph of cornering force vs vertical load for a tire.


Adding a front roll bar has a similar effect. More weight is transfered lateraly on the front. Front cornering traction is reduced.



Be glad to discuss this further.

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Old 02-27-2003, 02:43 AM   #41
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Quote:
A stiffer spring allows for quicker weight transfer initially, but to a lesser extent as the springs cannot compress to the same extent.
i agree with that...

all this talk about springs and compression ect... remember, that the shock angle plays a part aswell with the wieght transfere

the other day i moved my front spring 1 hole in on the lower arm, and it totaly changed the car
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Old 02-27-2003, 09:25 AM   #42
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I aggree that shock angle has a big effect. Moving the shocks upper position out stiffens the spring on a touring car.

Weight transfer is caused by the center of gravity lagging behind the tires when the car accelerates or corners. Roll and squat are the result of weight transfer. Roll and squat do not cause the weight transfer. If you use stiffer springs you do not eliminate or lessen the weight transfer, you limit roll and squat. Weight transfer is speeded up by stiffer springs.

Fore and aft weight transfer on a touring car is fairly low compared to side to side weight transfer. This is because the wheelbase is much longer than the track width. This is also because cornering g's are higher than g's accelerating or braking into a corner.

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Old 02-27-2003, 02:34 PM   #43
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Here's a simple example stolen from ol' Carroll Smith : watch a go-kart around a track. Watch the driver's body english in the corners. There is no suspension on a go kart but it still transfers weight.


Here's another question: Where does droop play into all of this? i'd be interested to hear the answers....
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Old 02-27-2003, 05:59 PM   #44
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John
Is it good to put a downstop or gravity stop for my 414m2? Is there a difference? my problem is my car now handles very well but the problem is my chassis rear edge is scratched, i have a 5mm rear ride ht., I plan to put a stopper in my shocks shaft to limit down travel, is this ok?
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Old 02-27-2003, 10:42 PM   #45
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Default Droop

My opinion on droop is that when you remove some droop (go to a bigger number on a Losi or TC3 gauge) That you slightly increase the roll stiffness. If the front end has slightly too much cornering traction, you take a little droop out and make the car push just a tiny bit more. I always get the spring positions and shocks correct first and then tinker with the droop for very fine tuning. This would be for a standard diff or one-way.

Wilfred-Using inside the shock limiters to set droop is a rugged way to do it. The droop won't change in the race. Matt Francis, I believe is setting his droop this way on a XXXS. It is a bit tedious to change the droop if you like to change it once in a while. The Yolkomo touring car and most off-road cars use this method.

Last edited by John Stranahan; 02-27-2003 at 10:45 PM.
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