Good to see you still on here Fred....how about that video series now!??!

I wish I had the time. I just don't. Anyone can always pm me if they need help though.

good info here, the big thing for me on my vehicle I am working on is getting the rear end to stick more, and work on its nose down jumping issue.

I think for me at least, its a combo of the two as the recommended stiffer springs also seem to take away the traction I am needing. I need to get an equal drop in rates to a happy medium for the conditions to get both the traction I want, but the in air jump performance too.

Have someone else drive your car and see if they have the same issues driving. If not, it may not be a set up issue more so, how you drive it issue....just a thought.

The biggest problem that I see with many people and jumps is that they hit them at full throttle, never letting off at all. In some instances this may be fine but watch motocross riders hit jumps. Often times they'll quickly let off and then blip the throttle on the ramp before the wheels leave the ground. This automatically gets them in a slight nose up orientation. Lowering the nose just requires a tap of the brakes.

One thing to remember, and I know it wasn't just mentioned here, is that vehicle layout has nothing to do with pitch while in the air. I've seen it stated elsewhere that a rear motor car will jump nose up and a mid motor will jump more level or nose down. That's a physics violation. Remember that a feather and a bowling ball will fall at exactly the same rate in a vacuum. It is only due to air resistance that this isn't so. We don't have that problem with an rc car. What this means is that it's either off balance spring rates, driver technique, or both.

the funny thing is that it was commented that oriented the battery more rear-ward on the vehicle (the battery tray mod) will help with the nose down jumping condition, in particular since the vehicle doesn't have a rear wing.

In general what I am seeing I am getting consistently regardless of approach to the jump or how I take off, etc. and its pretty much one particular jump, and i have had others try it with the same effect. Now, I know the saying is "well just roll it since its just that one jump" however you lose a good bit of time in comparison to vehicles that don't have that issue, they take the jump without any problems.

I feel though I may be on the right track as it seems some others have gone with a softer spring setup up front relative to what I am using on the rear. So will see how it goes. Just wish it wasn't the winter season to really get out there and try the ideas, so I got to find a way to try and simulate the effect.

I'm going to disagree with you a bit on both of these points. One of the main reasons motocross riders jump like they do is to get back down to ground as quickly as possible to be putting the power down and not sailing through the air. If you are in the air you are losing time compared to someone who is already on the ground and accelerating. The point is to minimize total flight time and still clear the jump(s). This is also the reason you see many guys "scrub" the jumps any time possible.

On the second point...the weight distribution does have an impact the car flight pitch once it is in the air. Think of the car like a teeter-totter once it is in the air. If you have a teeter-totter and take a 10 pound weight and put it 1 foot from the fulcrum you will create a torque force that will push that side of the teeter totter down. Now take that same 10 pound weight and put it 10 feet from the fulcrum. At this point we have now created a larger torque force that wants to push that side of the teeter totter down. The masses of the teeter totter and the weight added are the same in both instances, so M1 = M2. However F2 > F1....and we know F=MA (force = mass * acceleration)...therefor the increased force shows up as increased acceleration. Just like a teeter totter that is just out of balance will slowly drop to the side that weighs more, add weight to that side and the teeter totter will drop more quickly. So why does that matter? Well if the car is a teeter totter in the air, then a car more centralized mass will cause less pitch change in air than a car with all the weight far to one end or the other.

Geez after all that I think I may agree that weight distribution does not alter the pitch just after leaving the jump, however weight distribution will affect how the pitch changes while flying through the air.

@wanderer: I don't think you have a "fulcrum" in the static sense you are referring to when the car is in the air.

Take that teeter totter and drop it from an airplane. That fulcrum does nothing without the ground.

does the motor spinning and hence spinning the wheels in turn affect the teeter-totter in air? So if one end is heavier, it has to work that much harder to bring it up, etc?

Yes. Motor rotation does affect this. There's no reason to have such a strong effect that you can do backflips though. Keep in mind that while motor rotation direction can have a benefit, it also has drawbacks. Everything is a compromise somewhere.

good stuff thanks for the info. Was wondering if i was missing something in my understanding

If I drop my rc car towards the ground and all of the weight is centered it will drop basically flat. If I move 90% of the weight to the rear and drop it, will it not want to pitch and rotate wanting to land rear first? I understand the whole falling in a vacuum feather, bowling ball analogy, but there is to some extent a "fulcrum" here...it's air resistance. If air resistance is equal across the bottom of the buggy, and one end is heavier (the bowling ball) will it not want to drop "faster" than the other end (the feather)?

See the second to last and next to last sentences of post #1850.

Keep in mind that since it's air resistance that we are saying affects it, which way is the air moving from while your car is in the air? Is it falling straight down like you dropped it, or is it moving forwards where there is essentially little to no air pushing directly upwards on the bottom of the chassis?

Personally I'd say that the air resistance acting on the bottom of the car is the same regardless of if I drop it straight down or if it is flying through the air and dropping in height. The bottom of the car still has to "force" its way through an equivalent vertical column of air. Think of the physics thought experiment of a bullet shot vs. a bullet dropped from the same height. Both will hit the ground at the same time. Both are encountering and overcoming the same upward air resistance force. If this force went away because the bullet had horizontal velocity, then the fired bullet would land later than the dropped bullet, but that is not the case.