Sorry. I wasn't thinking "at rest" because I don't judge handling and traction at rest.
I should have been clearer though.
I'll try to offer some input as an engineer, hopefully it'll make sense to everyone.
This is my thinking.
If I put a marble in the bed of a truck with rake the marble will roll forward. Gravity is the dynamic force. I don't now the technical physics terms but something like (gravity/angle) - friction = acceleration.
Careful how you define the boundaries of your analysis: to compare a marble in the bed with a rake, would be like the truck sitting on a downhill slope, where the entire earth (mountain slope) is accelerating.
This is not the same as the truck itself having a rake / slope, acceleration on FLAT ground.
In that case, yes, the Sin(angle of slope) * 32.2ft/s^2 - rolling friction = acceleration of truck.
Likewise, drop a marble on a non-moving truck, with a certain rake, and the marble will accelerate at sin(angle of rake) * 32.2, minus friction.
If I accelerate the marble rolls backwards at (gravity/angle) - friction - rearward energy/angle = backwards acceleration.
If I brake the marble rolls forward at (gravity/angle) - friction + forward energy/angle = acceleration. NOTE: This acceleration is considerably greater than the backwards acceleration.
Flatten the rake and you get friction - rearward energy/angle = backwards acceleration = friction + forward energy/angle = acceleration
As mentioned above, this is akin to the entire mountain slope moving, with a truck parked on its slope.
For the truck ITSELF, with a rake, the acceleration and braking forces are only altered very minutely. Most of it is an optical illusion - more rake gives the illusion of less squat, and more brake dive.
The only real physical change, is the slight shift in center of gravity. When you accelerate or brake, the forces act on the center of mass (gravity), about the point of contact (tire patch). This force moment is what creates dive and squat forces.
To turn those forces into actual dive / squat measurement in inches, we need to couple it to 2 things: suspension geometry (which dictates roll center), and suspension stiffness (both spring rate, and damper rate).
Contrary to optical illusions, a leveling kit, because it raises the CG, would create MORE brake dive (in inches), assuming suspension is kept equal. It may *feel* less because the truck is more level. The only exception is if, by lifting the front, you've altered the longitudinal roll center MORE than the raise in CG.
Example, you lift the front 2", CG goes up by say 1.7", and your roll center (due to short radius arms) raises by 4". In this case you may end up with less brake dive. But it's important to understand why - due to CG vs roll center relationship, NOT just because the truck is level.
The above makes no consideration for squat/dive and it's already getting interesting. Lets say I brake AND turn. Marble rolls forward at (gravity/angle+dive angle) - friction + (forward energy/angle+dive angle) AND sideways at (gravity/angle+roll angle) - friction + (forward energy/+roll angle) = acceleration. AAAAACK! BRAIN HURTS! But this is the situation where I feel a raked truck suffers the most. Brake and turn at the same time and the outside front wheel wallows.
See above.
Dynamic motions of the truck is primarily dictated by the relationship between:
1) primary force: height of CG to tire patch (increased with leveling kit)
2) primary force vs suspension stiffness (unchanged with a spacer lift, usually stiffer with a spring + monotube shock suspension)
3) primary force vs suspension roll center (usually increased due to greater angle of radius arms)
The marble analogy does not work, because now we're confusing ourselves with a totally different system (the moving mountain side scenario)
Manufacturers have created many ways to mitigate the squat/dive/roll forces but often there is a compromise to off-road performance. EG: Ant-Roll bars. It's always a compromise... and when you have solid rear axle/leaf springs going on much of the compromise has already been made. No anti-dive/squat there.
Agreed.
Though with leaf springs, analyzing the geometry / roll center changes would be more difficult, as we don't have radius arms / control arms to use as a visual aid.
I feel like drag racing proves my point. Dragster/Funny car design = frames that are flat to the ground with no rake and pretty much all of the weight on the rear wheels. This is the pinnacle of design for traction when drag racing. Now a 69 chevelle owner might jack up the rear end to FIT big drag slicks but I think that has a lot more to do with the tire size and counteracting too much rear weight transfer.
Best regards,
Matt
As I mentioned previously, the rake vs weight transfer is mostly an optical illusion. A high rake APPEARS to put more weight on the front wheels, and vice versa. A fellow engineer did the calculations (backed up with measurements) on a sportscar forum, and the actual difference was around 1 to 2 lbs! In other words, very little STATIC weight transfer.
Drag cars depend primarily on suspension tuning: soft springs, very low compression shock damping, and high rebound damping, to allow "squat" upon launch and increase DYNAMIC weight transfer.
The only direct correlation a rake has toward anti-squat / dive, is as mentioned before, by altering the longitudinal roll center. This is not to be confused with lateral roll center, which dictates lateral body roll during cornering.
So, in conclusion, a "leveling" kit does not affect the weight transfer much, either static or dynamic, except due to changes in roll center. Most of that is an optical illusion: squats more because truck sits level to begin with, and dives less because level to begin with...
Hope that helped somewhat, feel free to correct me or discuss more!
