Scientific comparrison of modifications

[jonsolbe]

++++++ATTENTION PILOTS AND SCIENTISTS++++++

I'm tired of our community being reduced to relying on "case-based" information and advice when it comes to soliciting help choosing accessories and parts for our vehicles. When I'm considering a certain component, or performance modifier, I want facts, not opinions! I think the Ramp Travel Index is one such instrument which allows scientific, fact based comparrison of different suspension components. You can take your rig to an RTI and get a number, then make a modification and see how the RTI changes. Whether the information is inherently applicable to the average off-roader is a topic for another forum, but the concept is interesting none-the-less.

Would it be of value to take a scientific approach to weight and balance issues also. In aviation, aircraft performance can be compared using the concept of weight and balance. Each airplane has a scientifically calculated center of gravity (the point on the fusalage at which the aircraft would balance on a fulcrum). Then, any weight (passengers, fuel, baggage, accessories, etc) can be plugged into a formula based on leverage's effect on the plane (another application of the torque concept). The [weight] of the object, times the distance from the center of gravity [arm] is equal to the [moment].

weight (lbs) x arm (inches) = moment (lb-inch)

If there were standardized stations such as 1) front bumper, 2)front seat, 3) rear seat or baggage compartment, 4) fuel tank, 5) rear bumper

then, various changes including bumper and winch combos, rear bumpers and tire/fuel/jack carrying configurations could all be compared in a standardized way. This is applicable when considering weight transfer and traction to front tires when going up hill, or vice versa when going downhill.

Just as weight's effect about the lateral axis (pitch, or front to back) could be comparred, so too could weight's effect about the longitudinal axis (roll, or side to side).

If someone took a stock jeep, and used blocks and jacks along the frame to find the point where the whole thing balanced front to rear, it would be easy to establish a standardized "arm" for front bumper, rear bumper, fuel tank, etc. Then, the only variable would be the weight of the object you're considering installing, and its effect on center of gravity could be measured. This specific calculation would, of course, only be applicable to going up or down a hill; however, if the same measurements (the arm) were established for various heights (frame height, cargo/passenger compartment, and roof rack), then the same formula could be used to compare different components and their effect on the jeep's tendency to roll.

These computations would certainly be affected by various heights of lift kit. Would this be a worthwhile pursuit, or in the experience of those older and wiser than I, does weight and balance not make that much of an issue in the long run.

Anxiously awaiting some responses,

Jon

 

[superj]

maybe for the guys who are going up and down those super steep walls of rock or mud, but i don't think it would effect the rest of us

 

[elevatorman]

The mathmatical approach is a great idea however,Your Rubicon came equipped from the factory designed by engineers with most likely greater mathmatical skills and car building experience than the "average" person.
You added 33's,They didnt design that jeep with 33's so now it has changed.Say the average driver is 200lb per thier calcs,and your wife only weighs in at 115lbs.
Then all the math in use to design that jeep will not create a perfect vehicle than can continually keep up and react to the variables that will continually change throughout the life of the vehicle.
add more weight,a winch,high lift jack accesories,wife goes to 300 lbs!
Freeway to offroad, hills to creekbeds etc....

I think if it could be achieved we would have one car company hopefully JEEP desining and building cars.
but would it be a Wrangler? a Cherokee? or a truck? could they please us all?

 

[larrymo49]

Half the fun of owning and building up our Jeeps is through some trial and, unfortunately, some error.

Since most of us do not have engineering degrees from MIT (or other institutions of higher engineering excellence) we usually have a steep learning curve to deal with, which often relies on what has and hasn't worked for others in the real world.

Like Elevatorman implied...there are so many variables to consider in building the perfect vehicle...no combination will please everyone.

Larry

 

[superj]

finding the center of gravity, like listed above is very simple. (well, more so then it reads out to be) it is used all over the USA by normal aviation mechanics working in non-air conditioned hangers, just like most of us work. i didn;t enjoy doing it so i won't be doing it on my jeep and for what i do, its useless, as it would be for most of us. it is done to keep an airplane as closed to balanced so you fly efficiently with only minor trim adjustments so you are not front or aft heavy. we don't need to worry about that in driving. we could use the firewall as the fuselage station 0 though

 

[mud4feet]

Regardless of all the math and the "perfect" vehicle, there are two unkowns that affect the driving experience. The terrain or surface you're riding on (traction?) and that all important little part............the nut behind the wheel!!!

 

[jonsolbe]

finding the center of gravity, like listed above is very simple. (well, more so then it reads out to be) it is used all over the USA by normal aviation mechanics working in non-air conditioned hangers, just like most of us work. i didn;t enjoy doing it so i won't be doing it on my jeep and for what i do, its useless, as it would be for most of us. it is done to keep an airplane as closed to balanced so you fly efficiently with only minor trim adjustments so you are not front or aft heavy. we don't need to worry about that in driving. we could use the firewall as the fuselage station 0 though

All astute points, gentlemen. The point of the thread, however, is to stimulate some discussion which may eventually result in someone saying "aha! here's a way with which we could measure this modification objectively!" Which is exactly the way the RTI and dynamometer (for measuring horsepower) were developed.


I am guilty of many posts on here asking questions such as "which winch is best?" or "how much smoother riding is a long arm vs short arm lift?" Not unexpectedly, the vast majority of respondants reference what's referred to in medicine as a "case study," whereby an observer simply relates the subjective observations of his or his friends' own personal experience. It would be nice to have some objective data.

If, for example, you're going to install a K&N air filter because you want more MPG, it would be interesting if you compared pre- and post- MPG data, to share with the rest of us. -OR- if you were going to install a roof rack and move your spare tire, highlift jack, and 2 5ga jerry cans to the top, you somehow objectively measured your rig's center of gravity before and after the install, and shared with the rest of us.

If my suggestion to devise a weight and balance equation for jeeps was taken to mean that it is the best idea, and now we post 50 reasons why the idea sucks, then the inginuity, openness, and nurturing environment of this forum has spoken for itself. If, however, jeeprs like "superj" can apply his experience as an A/P mechanic and suggest establishing the firewall as the "datum," or senior members such as "mud4feet" can observe that reported observations should be free and clear of driver variability in order to remain objective, then we have spawned a thread in which other jeepers (universally known for their boundless creativity) can discuss ways for objectively measuring results and helping newbies avoid some of the costly pitfalls into which the rest of us have fallen. Then and only then will it be considered a success.

 

[jps4jeep]

I am a huge fan of this Math you speak of, and most if not all of my builds require specific calculations for design, but I always seam to revert back to one principal that in all my offroad vehicle building experience has been the best principal;

KISS

Keep It Simple Stupid

personally, excessive weight in a wheeler is bad, extra un-needed stress on components; think of the shock load on a NP231 when hammering up an obstical in a 3000K lb vehicle, now think of the same load in a 4500K lb vehicle. I LOL when I see people roll up to a trail ride with every silly doo dad and gadget that they could stick on their vehicle... a huge bumper with a winch neting 150 lbs of front end weight; 4 pairs of fog lights on the hood, windshield, bumper; spare tires on roof racks (<- this one still baffles me) people mounting steel tool chests up on the wheel wells; every gosh darn tool and fluid ever known to man in the back of their jeep (I understand if it si an expo type trip, but still, bring only what you think you will need, not enough spare parts to rebuild a NAPA space shuttle)

now there is just weight that can't be avoided, and in such a case, my preference is to keep the weight low as possible and un-sprung. I (and my collegues) have started working on a buggy that will be used initially in RCrocs comp then will evolve into ultra4; the car needs a winch, so we sourced one of the lightest winches we could find (a t-maxx EW9000) instead of mounting the winch up on the frame as it would be traditionally, we're putting it on the front axle. The chassis it's self will be driver built with minimal amount of head room (but within the sanctioning body's specs) looking to have about 18" of ground clearence at ride height and 14" at full bump. we are mounting as many components as we can as low as we can with in regulation.

so to essentially reiterate, really no need for a mathematical approach if you use a common sense and approach with a littlle inginuity.