Technical Understanding of Mass Properties for Your Vehicle

Lets take this topic to a new level. I'm going to keep it general and vague to not lose focus.

As a design engineer, mass of a vehicle is always in consideration when planning for performance. Actually, its one of the first design keys you establish before developing the vehicle. You have various factors that attribute to this.
Such as:

• Sprung Mass - Mass of the vehicle supported by the springs
• Unsprung Mass - Mass of the susepnsion such as springs, wheels, struts and anything else not supported by the springs
• Center of Gravity - Self Explanatory
• Mass Moments of Intertia - The rotation movement about the vehicle's axii.
• Yaw, Pitch, Roll, squat, heave, bounce - Rotational movements about different axii. We'll cover this topic later in another thread dedicated solely to suspension.

All play a pivotal role, but our main focus will be on overall mass. I apologize in advance for the following:

I took a day out of my busy life, before I had my GTI, to fully decompose my 2006 Civic LX. I really wanted to reverse engineer it. So with that being said, all of the mass properties are based off this vehicle, but that shouldnt stop anyone from doing this with their own car.

Vehicle Axis

• X - Axis - Using your FRONT AXLE as your Zero, anything towards the Rear of the car is Positive and anything towards the front is Negative
• Y - Axis - Starting from the MIDDLE of your car anything towards the Passenger's side is Positive and anything towards the Driver's side is Negative
• Z - Axis - Find the LOWEST point of your vehicle. Above this point is Positive and Below it is Negative

Steps for Decomposing Your Car

1. Grab a ruler, pencil, and a pad of paper
2. Measure EVERY component of your vehicle relative to the vehicle axii. Create a table for such, and write down your numbers.
3. Estimate the mass of the component. A GOOD general estimation is go with your inhibitions. Determine whether its 100% solid or create a % of how solid you think it is. Take a steering wheel for example. If it was COMPLETELY solid it would probably weight 20lbs, seeing as though its about 30% solid, you multiply your intial guess by this percentage and you have a pretty good accurate estimation
4. Add up all your masses and, BOOM, you have your vehicle weight
5. Add up all your X's, Y's, and Z's and you should have a good center of gravity in the X, Y, and Z axis.
6. Depending on your willingness you can now calculate your moments of inertia using formulae found off the internet. I dont have the resources to post them. This will give you your yaw, pitch and roll.
7. Find your manufacturer's established vehicle weight and see how well you did.

Time for the Data

Please dont freak out, its pretty easy to sort through. I didnt include EVERYTHING like I had hoped, but this was a 4-5 hour deal. I got pretty tired and just didnt include the smaller stuff because they would not impact overall performance.

Item M M(Scaled) X Y Z X(bar) Y(Bar) Z(Bar) I(0,X,i) I(0,Y,i) I(0,Z,i) I(X) I(Y) I(Z) Lx Ly Lz

Block 520 543.12 -7 5.5 17.25 -1.47 1.15 3.61 905.2 1584.1 1629.4 112174.3 119217.5 28483.9 20 35 36
Oil Pan 10 10.44 -7 5.5 -1 -0.03 0.02 0.00 0.0 0.0 0.0 323.8 518.0 821.1 0 0 0
Oil Filter 1.5 1.57 4 10.875 17.75 0.00 0.01 0.01 0.0 0.0 0.0 678.1 518.1 210.1 0 0 0
Fuel Pump 3 3.13 -2 13 18.5 0.00 0.02 0.02 0.0 0.0 0.0 1598.1 1082.3 540.8 0 0 0
Intake 5 5.22 -6.75 -10 18 -0.01 -0.02 0.04 0.0 0.0 0.0 2205.4 1922.2 757.1 0 0 0
CAT+Exhaust Manifold 10 10.44 -15.5 5.875 10 -0.06 0.02 0.04 0.0 0.0 0.0 1393.7 3525.2 2846.8 0 0 0
Exhaust Piping 40 41.78 52.5 8 0 0.85 0.13 0.00 0.0 0.0 0.0 2588.4 111471.9 114060.3 0 0 0
Muffler 10 10.44 127 16 3 0.51 0.06 0.01 0.0 0.0 0.0 2745.6 167201.3 169760.4 0 0 0
Radiator 20 20.89 -23.5 0 9.5 -0.19 0.00 0.08 0.0 0.0 0.0 1855.0 13206.1 11351.0 0 0 0
Power Steering Pump 8 8.36 -15.5 12 5 -0.05 0.04 0.02 0.0 0.0 0.0 1403.0 2202.1 3190.0 0 0 0
Coolant Pump 2.5 2.61 -14 -1.875 18.5 -0.01 0.00 0.02 0.0 0.0 0.0 901.0 1402.6 519.9 0 0 0
Coolant Resevoir 2 2.09 -18 -21.5 17.875 -0.01 -0.02 0.01 0.0 0.0 0.0 1630.4 1342.1 1639.8 0 0 0
Fan(s) Assembly 4 4.18 -22.5 0 9.5 -0.04 0.00 0.02 0.0 0.0 0.0 375.8 2484.1 2108.2 0 0 0
Battery 50 52.22 -15 1.625 17.875 -0.30 0.03 0.36 0.0 0.0 0.0 16153.3 27302.6 11414.1 0 0 0
Alternator 15 15.67 -15.5 13.5 14.75 -0.09 0.08 0.09 0.0 0.0 0.0 6188.4 7086.2 6539.6 0 0 0
Transmission 250 261.12 -9 -7 17.25 -0.91 -0.70 1.74 500.5 701.8 609.3 73686.1 80645.0 28154.6 23 32.25 28
Gas Tank 50 52.22 95 -3 7.5 1.91 -0.06 0.15 0.0 0.0 0.0 3271.7 455343.7 452974.5 0 0 0
Rotor (D) 9 9.40 0 -27 5 0.00 -0.10 0.02 0.0 0.0 0.0 7036.5 233.3 6803.2 0 0 0
Rotor (P) 9 9.40 0 27 5 0.00 0.10 0.02 0.0 0.0 0.0 7036.5 233.3 6803.2 0 0 0
Caliper (D) 13 13.58 -4 -27 6 -0.02 -0.14 0.03 0.0 0.0 0.0 10278.7 698.7 10010.0 0 0 0
Caliper (P) 13 13.58 -4 27 6 -0.02 0.14 0.03 0.0 0.0 0.0 10278.7 698.7 10010.0 0 0 0
Master Cylinder Assm 11 11.49 13.5 21.5 14 0.06 0.10 0.06 0.0 0.0 0.0 7495.9 4307.4 7339.3 0 0 0
E-Brake Assembly 10 10.44 38 -4 8 0.15 -0.02 0.03 0.0 0.0 0.0 828.9 15624.0 15126.7 0 0 0
Drum (D) 20 20.89 105 -27 6 0.85 -0.22 0.05 0.0 0.0 0.0 15723.9 227349.7 241593.8 0 0 0
Drum (P) 20 20.89 105 27 6 0.85 0.22 0.05 0.0 0.0 0.0 15723.9 227349.7 241593.8 0 0 0
Brake Pedal 3 3.13 18 -13.5 7.5 0.02 -0.02 0.01 0.0 0.0 0.0 745.5 1188.6 1582.5 0 0 0
Gas Pedal 2 2.09 18 -9.5 7.5 0.01 -0.01 0.01 0.0 0.0 0.0 305.5 793.0 863.9 0 0 0
Spring (DF) 10 10.44 0 -23 26 0.00 -0.09 0.10 0.0 0.0 0.0 12484.7 7003.8 5480.8 0 0 0
Spring (PF) 10 10.44 0 23 26 0.00 0.09 0.10 0.0 0.0 0.0 12484.7 7003.8 5480.8 0 0 0
Spring (DR) 10 10.44 105 -23 26 0.42 -0.09 0.10 0.0 0.0 0.0 12484.7 121230.8 119707.8 0 0 0
Spring (PR) 10 10.44 105 23 26 0.42 0.09 0.10 0.0 0.0 0.0 12484.7 121230.8 119707.8 0 0 0
Strut (D) 10 10.44 0 -20 20 0.00 -0.08 0.08 0.0 0.0 0.0 8288.6 4144.3 4144.3 0 0 0
Strut (P) 10 10.44 0 20 20 0.00 0.08 0.08 0.0 0.0 0.0 8288.6 4144.3 4144.3 0 0 0
Shock (D) 5 5.22 105 -20 23 0.21 -0.04 0.05 0.0 0.0 0.0 4832.0 60096.2 59425.2 0 0 0
Shock (P) 5 5.22 105 0 23 0.21 0.00 0.05 0.0 0.0 0.0 2751.5 60096.2 57344.7 0 0 0
Lower Control Arm (DF) 15 15.67 0 -20 2 0.00 -0.12 0.01 0.0 0.0 0.0 6253.2 61.9 6191.3 0 0 0
Lower Control Arm (PF) 15 15.67 0 20 2 0.00 0.12 0.01 0.0 0.0 0.0 6253.2 61.9 6191.3 0 0 0
Lower Control Arm (DR) 15 15.67 105 -20 2 0.63 -0.12 0.01 0.0 0.0 0.0 6253.2 170710.1 176839.5 0 0 0
Lower Control Arm (PR) 15 15.67 105 20 2 0.63 0.12 0.01 0.0 0.0 0.0 6253.2 170710.1 176839.5 0 0 0
Upper Control Arm (DR) 10 10.44 105 -20 10.5 0.42 -0.08 0.04 0.0 0.0 0.0 5286.6 115369.2 118371.2 0 0 0
Upper Control Arm (PR) 10 10.44 105 20 10.5 0.42 0.08 0.04 0.0 0.0 0.0 5286.6 115369.2 118371.2 0 0 0
Front Sway Bar 15 15.67 4 0 1 0.02 0.00 0.01 0.0 0.0 0.0 15.5 263.1 247.7 0 0 0
Rear Sway Bar 15 15.67 90 0 1.5 0.54 0.00 0.01 0.0 0.0 0.0 34.8 125409.0 125374.2 0 0 0
Body 750 783.35 53 0 19 16.01 0.00 5.74 11410.8 4504.3 3590.4 149146.8 1213986.3 1076250.3 174.8 69 55
Front Seat (D) 20 20.89 52 -14.5 23 0.42 -0.12 0.19 0.0 0.0 0.0 15194.7 66451.6 59900.0 0 0 0
Front Seat (P) 20 20.89 52 14.5 23 0.42 0.12 0.19 0.0 0.0 0.0 15194.7 66451.6 59900.0 0 0 0
Rear Bench Seat 50 52.22 84 0 27 1.69 0.00 0.54 0.0 0.0 0.0 36552.8 390348.3 353795.5 0 0 0
Rear View Mirror 1 1.04 16 0 41 0.01 0.00 0.02 0.0 0.0 0.0 1754.3 2021.5 267.2 0 0 0
Dash Module 250 261.12 20 0 27 2.01 0.00 2.72 522.2 1392.6 369.9 154469.4 239810.1 85862.9 24 64 17
Middle Console 15 15.67 43 0 9 0.26 0.00 0.05 0.0 0.0 0.0 1253.7 29873.1 28619.4 0 0 0
Shift Knob 0.6 0.63 34 0 22 0.01 0.00 0.01 0.0 0.0 0.0 303.2 1027.3 724.1 0 0 0
Head Light (D) 5 5.22 -21 -25 20 -0.04 -0.05 0.04 0.0 0.0 0.0 5331.4 4374.3 5544.6 0 0 0
Head Light (P) 5 5.22 -21 25 20 -0.04 0.05 0.04 0.0 0.0 0.0 5331.4 4374.3 5544.6 0 0 0
Tail Light (D) 5 5.22 128 -25 30.5 0.26 -0.05 0.06 0.0 0.0 0.0 8089.4 90057.2 88469.5 0 0 0
Tail Light (P) 5 5.22 128 25 30.5 0.26 0.05 0.06 0.0 0.0 0.0 8089.4 90057.2 88469.5 0 0 0
Side Mirror (D) 3 3.13 23.5 -34 36 0.03 -0.04 0.04 0.0 0.0 0.0 7664.6 5777.3 5339.7 0 0 0
Side Mirror (P) 3 3.13 23.5 34 36 0.03 0.04 0.04 0.0 0.0 0.0 7664.6 5777.3 5339.7 0 0 0
Wipers 2 2.09 4 0 29 0.00 0.00 0.02 0.0 0.0 0.0 1754.0 1787.3 33.4 0 0 0
Washer Nozzles 1 1.04 0 0 29 0.00 0.00 0.01 0.0 0.0 0.0 877.7 877.7 0.0 0 0 0
Washer Fluid Resevoir+Lines 4 4.18 -10 23 17 -0.02 0.04 0.03 0.0 0.0 0.0 3406.5 1620.0 2619.4 0 0 0
Steering Wheel 5 5.22 38 -16 29 0.08 -0.03 0.06 0.0 0.0 0.0 5705.9 11885.0 8842.3 0 0 0
Tie Rods 2 2.09 2 0 3 0.00 0.00 0.00 0.0 0.0 0.0 18.8 27.1 8.3 0 0 0
Steering Assembly 45 47.00 -1 -1 12.25 -0.02 -0.02 0.22 0.0 0.0 0.0 6845.0 6845.0 90.6 0 0 0


Summary

Phew, that was rough. Attached is the file for better viewing. But now, we can accurately deteremine the important factors were wanted from the start. You can probably sit back and grab a cup of coffee and just read through you're findings. You can see where every part is in your vehicle and see how it affects the center of gravity.

Center of Mass(X,Y,Z): 27.31 0.76 17.42
Vehicle Weight(M) (lbs): 2482.6
Vehicle Weight (A) (lbs): 2593
Percentage Off: 4.3%
Scale Factor: 1.044
Vehicle Weight Scaled: 2593.00

I(X) 849010.0 R(X) 163.71
I(Y) 4791281.9 R(Y) 923.89
I(Z) 4356581.1 R(Z) 840.07

I'm not sure if my moments of inertia are correct or not, but my center of gravities are. I went through some data from Honda engineers and found that it was so close that I crapped my pants when I actually got within 2% of the actual value. It all determines how much effort you put into it. With these numbers you can even try and distinguish between sprung and unsprung weight and really try and remove the unneeded weight you might have for tracking purposes. If you actually calculate the moments of inertia for every component, you might find some surprising things. I set up a basic formula to eliminate the lesser impacted components.

*********EDIT******** After reviewing my data, I COMPETELY FORGOT THE WHEELS!! WTF?!?!?!?!? Oh, well. My mistake.

A couple of wonderments:

• By seeing this information, can you now see the importance of tracked weight reduction?
• Heavier wheels and their impact.
• Big Bulky body kits and their impact
• Lighter weight engine components and how they can help
• Can you see a need for some possible carbon fiber suspension components?
• Racing seats and their impact
• Engine mass moment intertia and controlling the movement.
• Lowering the Suspension Pros and Cons(I'll make another thread for this)

Theres so many things you can see by doing this analysis. Its ALWAYS a good idea to understand your vehicle's weak points and its strong points. What can you do to continously improve your performance?

Very nice.

For this forum, I think that the "lowering the vehicle" analysis would help. I suspect a surprise or two is lurking there.

I would personally welcome insight on "mass of wheels," as I experienced less subjective gain there than I expected. (Caveat: I haven't tracked the car.)

Thanks,

Bob

I'd like to see the lowering of the vehicle thread posted ASAP.

I'm interested in seeing if there is a clear point where lowering improves handling...and the end of that benefit where lowering beyond a point hinders performance. If that exists, I would assume it can be calculated based upon the above data where that point is that achieves the greatest gains and where the point is that the drop begins hindering performance beyond stock height.

Hilfloskind said:

I'd like to see the lowering of the vehicle thread posted ASAP.

I'm interested in seeing if there is a clear point where lowering improves handling...and the end of that benefit where lowering beyond a point hinders performance. If that exists, I would assume it can be calculated based upon the above data where that point is that achieves the greatest gains and where the point is that the drop begins hindering performance beyond stock height.

Click to expand...

I think the problem with lowering is that usually people are modifying only one aspect of the suspension (springs and shocks) without taking into consideration every other part. It's like an orchestra. To add insult to injury, few aftermarket suspension part manufacturers are performance-oriented as there's too much money on the table selling people parts to make their ride supa-slizammed.

A lower car FEELS better because the car responds more readily to steering inputs due to the decreased body roll, but it might actually reduce the maximum grip, input feedback, and handling capabilities of the car due to actually softer springs, less suspension travel, narrower grip threshold, reduced alignment capabilities, unmatched spring rates and shock valving, poor slip angles, etc. Race engineers will even setup the suspension specific to the tire they plan on putting on the car.

It's not so much that there would be a certain point at which lowering would produce bad results, it's all in relation to the other suspension parts in the car. This, coupled with lack of easily measured objective handling measurements, is why suspension tuning is so difficult. With an engine we have dynos and quarter mile times, which produce reproducible results, and many of us have access to. Very few of us have regular access to a safe way to test the handling of our cars, so our "butt dyno" is how we do it, which if you've ever done road course or autoX, is so terribly unreliable.

Well, the thing is...

I'm sure that lowering beyond a certain point puts those orchestral components into conditions that they cannot handle. I feel the argument that any lowering is not outright beneficial is incorrect. Without any further evidence than the following, I would say it's obvious that some degree of lowering helps...

Volkswagen has an entire racing division, with a website to buy these components from in the UK, that further modifies their cars to be race optimized. In fact, many of these changes we also do on our own (ie engine mounts, tunes, etc...). They even sell...you guessed it...racing springs and entire suspension kits...these result in a modest drop and increased performance (their own words).

In my own personal case, I have a modest drop. I only went so far simply because I didn't want the car undriveable around our area and didn't want to go beyond the point where the drop helps handling. I think my own drop is only slightly lower than the VW racing springs, if at all.

You guys are definitely on the right trail, however, I feel the "lowering" to be a bit off topic.

I have an ENTIRE suspension technical theory thread in development right now for your enjoyment. This should all be reserved for that topic. This thread is about mass properties and your baseline center of gravity and sprung and unsprung mass.

I can go ahead and say that when you lower your car, you change the COG(Z-Axis). This has a HUGE impact on roll centers (angle phi), which impacts roll stiffness which impacts lateral forces, which impacts tire patch friction, which impacts whether your car will flip at high speeds.

Quick side note:
American standards require cars to be a certain ride height ratio. Europeans dont. That is why volkswagen offers us "lower springs" which are basically Euro spec springs. Some maybe lower, but nothing really outside of the car's capable means

grambles423 said:

Quick side note:
American standards require cars to be a certain ride height ratio. Europeans dont. That is why volkswagen offers us "lower springs" which are basically Euro spec springs. Some maybe lower, but nothing really outside of the car's capable means

Click to expand...

Same reason we don't get lip spoilers and do get side markers...both I've spent the cash to restore to euro spec/look.

CofG Benefit of lowering is real, but where that puts the rest of the suspension kinematics of the vehicle is not trivial neither. On top of making the car losing more bump travel, which makes it more nervous on uneven surface.

Bump for more discussion

bump again.

I think there are only a few people here with the background necessary to facilitate such a technical discussion. While I myself enjoy reading this stuff, most of it is way over my head...I'm sure I'm not alone in this statement, either.

Please don't let that be a deterrent from posting valuable information, though. I just don't want you discouraged by lack of responses.

Hilfloskind said:

I think there are only a few people here with the background necessary to facilitate such a technical discussion. While I myself enjoy reading this stuff, most of it is way over my head...I'm sure I'm not alone in this statement, either.

Please don't let that be a deterrent from posting valuable information, though. I just don't want you discouraged by lack of responses.

Click to expand...

Heck no man. Its all good. I understand some of it is a bit dry and non intuitive. Trust me, learning wasnt the greatest either.

BUT

I welcome questions as well. If anyone doesnt understand something, I'll be more than happy to explain.

Next steps...?

Grambles,

Here's my two cents...

First, your post was seminal in its high content-to-BS ratio, not just for this forum but for all enthusiast forums that I play in. Major kudos.

But here's why dialog is sparse IMO:

• Most members lack the backgroud to talk the math/physics
• The link from statics (CG, etc.) to dynamics (turn rate, lean, etc.) hasn't been made; and
• Lacking #2, the link to members' *mods* hasn't been made…and mods drive forum discussion

This is why I tried to nudge your consideration to "lowering," even though it is not germaine to your excellent exposition of vehicle statics.

But, as you say, it's all good and I get a lot from your fine posts.

Bob

untangle said:

Grambles,

Here's my two cents...

First, your post was seminal in its high content-to-BS ratio, not just for this forum but for all enthusiast forums that I play in. Major kudos.

But here's why dialog is sparse IMO:

• Most members lack the backgroud to talk the math/physics
• The link from statics (CG, etc.) to dynamics (turn rate, lean, etc.) hasn't been made; and
• Lacking #2, the link to members' *mods* hasn't been made…and mods drive forum discussion

This is why I tried to nudge your consideration to "lowering," even though it is not germaine to your excellent exposition of vehicle statics.

But, as you say, it's all good and I get a lot from your fine posts.

Bob

Click to expand...

I appreciate the kudos. Its been hard pressed to try and develop such a thread with how busy it is here at work. We have a lot of development going on right now, so the forums must stay a secondary priority, but I MUST say....it will be done.

Suspension dynamics is quite an ellaborate subject and in order to accurately portray it to forum speak...is rather difficult. I'm sure microsoft paint will be my friend when I start working on it.

Its easier to relate to suspension parameters than inertia. As while you change parts on the car have an impact on inertial properties of the car, that is usually not the reasons why someone do it. At the same token the manufactures of the parts, be it as brand name or home fabricator, usually don't make something as say, "low inertia A-arm", more likely as "adjustable, high strength, fabricated a-arms". Now it might perfectly have the desirable effect in the first category, that probably was not necessarily the goal(aside from making it light). Obvious exclusions maybe light weight flywheel, crank, and engine parts.

I'd say open up the whole shebang to suspensions and vehicle dynamic as well....as it might be more easily for someone to relate directly...its always good to talk about these cars aside from just to slamming them and get the stance....