Does Speed Add Weight?

[nathane]

Oh and it doesn't really make much difference at the kind of speed my unimog is capable of

 

[BritKLR]

Cool, so as a aircraft lifts it weighs less?

 

[Hillbilly Heaven]

Cool, so as a aircraft lifts it weighs less?

Not exactly, it is inversely proportional to the derivative of the quotient of the speed it gained to generate that lift.

 

[LeftCoastKiteboarding]

You guys are getting weight and mass mixed up. Mass does not change. (For all practical purposes). Weight as a measure is dependent on a number of factors. In the above post, the plane has the same mass but may ‘weigh’ less due to lift. If you stand on a scale holding a big bunch of helium balloons your mass has not changed but the scale will say you weigh less. Food for thought.


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[Joe917]

I think we can can assume mass is fixed, apart from fuel use.
So we are back to weight only being changed by airflow (or stopping to buy helium balloons).

 

[s.e.charles]

Grampa Clarke used to say "if the dog didn't stop to poop, he'd a-caught the rabbit".

 

[ultraclyde]

Mass of a loaded vehicle does not change with speed. (Well, okay, not at measurable amounts at speeds less than approaching light speed.)

Weight is the downward force of gravity on a certain mass. Since we can assume here we are talking about driving the vehicle on Earth, Mass and Weight can be assumed to be numerically interchangable. I'm ignoring the variations produced by aerodynamic lift verses downforce. While interesting they don't have any bearing on the force experienced in a collision unless the vehicle is free falling straight down. But then you've got bigger issues.

What does change is force. Things like mounting brackets and bolts may see several times the "weight" of a vehicle in a crash at speed. This is usually talked about in terms of equivalent static weight. In other words, a 5000lb vehicle in a crash can easily experience FORCE equivalent to the FORCE generated by a 10,000lb static weight.

 

[s.e.charles]

so … maybe the original question should have been phrased differently, because I think you hit upon my intention of what I was asking. the other component of many responses seems to be "bridging the gap between theory & practice."

the best example I can use is detailed in the above 3rd paragraph. so, I my black & white world (it's okay, "they" like me there), if a truck was rated to carry 1,000#, it may be to my advantage to use a cut off point a little lower, maybe 925#, so if I had to do any evasive maneuvering it could be assured I wasn't pushing things to the maximum stress point(s).

clear as mud …?

 

[Hillbilly Heaven]

This was my thinking the original intent was in the original post. Yes I may have gotten sarcastic in my later post.

To put it simple most vehicle generate downforce. The amount of downforce is based on speed. Yes downforce not lift. If they generate lift then the vehicle could become airborne, not flying per say.

So yes as speed increases, the force load on chassis, suspension, and tires increases. Think of Big Foot pushing down on the vehicle from the top, what is going to see the added load. One other thing to consider is the condition and type of surface you are driving on. A smooth level surface the forces will remain normal. Any rough or irregular surface will induce increased loads especially spikes in instantaneous loads as the suspension tries to keep up with the surface.

Without actual recorded data there is no way to tell you how much force to compensate for. Without outfitting your vehicle with travel sensors and load cells there is no real empirical way to gather data. There is however some things you can do to help you know how much change you see at various speeds. And old school trick we used before the cost of sensors dropped was to put O'rings or Rubber bands around the shock rods. Place them on the rod up against the shock body while the vehicle is sitting at ride height. Find a smooth road surface to run at speed. Hold that speed for one minute. Stop and measure the distance between the rubber band and the shock body. That is the amount of travel caused by downforce. If you knew spring rate you could extrapolate downward force created by speed in pounds.

 

[Scoutn79]

The only true way to answer your question beyond a doubt is to schedule some time at a wind tunnel with scales....As has been said the weight your specific vehicle applies to the road surface is dependent upon many may different factors and will change with the attitude of your vehicle and what you have on the outside at the time of the test. Driving in a vaccuum your road weight would not change but add aerodynamics with either lift or downforce and things can change.

Darrell

 

[s.e.charles]

… So yes as speed increases, the force load on chassis, suspension, and tires increases. ...

that's pretty much what I needed someone to validate.

 

[Umbrarian]

there must be some engineering - physics calculation that applies. for example: i'm driving a 6,000# vehicle with an additional 1,000# payload = total weight (static) of 7,000#. this is distributed over the entire vehicle although most likely not an even distribution. anyway, now we're getting going to say 50 mph. leave out altitude, grade change, or wind force other than whatever the vehicle is "generating" if that's the correct term.

could the conclusion be the vehicle now "weighs" more than static weight? less?

Weight is a force caused by gravity. Changing velocity (speed) alone does not increase or decrease gravitation force.

 

[LeftCoastKiteboarding]

And not to toss a wet towel on the party....but the engineers that design all this stuff build in a LOT of overhead. Not uncommon to factor in 1.5x safety factor. More on some things. So ya, theoretically a 10k rig could be loaded at 9500 to avoid breaking the 10k force point.....but given that there is a ton of overhead capacity built in the only thing you would be doing is shorting yourself a few hundred lbs of capacity. ALL that stuff is already baked into the cake.


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[s.e.charles]

well alrighty then. "load up the wagon, momma. we be goin' fo' a ride!"

 

[javajoe79]

This was my thinking the original intent was in the original post. Yes I may have gotten sarcastic in my later post.

To put it simple most vehicle generate downforce. The amount of downforce is based on speed. Yes downforce not lift. If they generate lift then the vehicle could become airborne, not flying per say.

I wouldn't say most vehicles do. It's the opposite. Especially anything that we're talking about on this site.

Taken to the extreme, enough speed will lift the front of any vehicle that doesn't make downforce because air will pile up under the front of the vehicle and lift it up. I would say that on at least some vehicles that means the vehicle is being pushed back on the rear tires not unlike driving up a steep hill. For example, I raced a 96 Sonoma at Bonneville. Sitting still the front air dam was almost on the ground. At 220mph it was 4" off the ground and the steering got very vague for lack of force on the front tires. That is a relatively small and slippery truck with an air dam and splitter, weighing around 6000lbs evenly distributed. If I was able to approach speeds like that with my NPR, I would expect it to blow over backwards.
So at a steady state speed with most any vehicle on here, I would expect the tires to "feel" less weight than sitting still but hit a big bump and that tire "feels" much more weight than it does sitting still.