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Needing to improve the rear suspension grip in this car and knowing the Winter doldrums are approaching it's now time to take another look at options for better stick out back.
It wasn't until recently with Bernie's bolt in three link that a better option appeared. It's to late in the game now to junk the 8 1/2" rear so a weld in third leg can't replace the two UCA there now, needs to be a bolt in 3 link like Bernie's. That's what makes Bernie's three link viable for me, essentially a bolt in. But the one downside is how to deal with the tailpipes, or the lack of room for tailpipes. That's for me is a huge disadvantage, no tailpipes, couldn't tolerate the noise level.

One of my projects for the car this Fall, reupholstering the driver's seat with added bolstering to fit my torso, is now also a Winter project, the upholstery shop's slow time. A visit there this past week started the ball rolling for the seat mods and possible harness install. That in process it's time to spend time on the rear roll.

First I think i need to get under the car and do a full workup on what i actually have for all the pick points needed to find the roll center I have now. Don't expect it's much different that a 100 other G similar to mine, but I don't trust answers when someone says "it about 18". I like number and like exact numbers, not almosts. it's not a big deal to get precise pickup points and angles for all the moving parts, just got be persistent.
And because I'm a modeler, making a full scale rear suspension to mimic what's under the car isn't difficult either once you nave the numbers.
Yes much easier on software available to play with design, but I'm just an uneducated type who like to hold stuff in their hand and watch it break.

So measuring, thinking, reading, understanding, looking at all the possible avenues to approach rear roll center is the new Winter project.

This Thurs at my local tire/repair/alignment/racers shop i need to get my PA annual inspection stickers on the windshield. If the computer alignment rack is available when I go there we may throw the pickups on the wheels and see if his computer rack gets the same numbers as my alignment rack in my shop using old school tools. Have done that comparison before and we deviate very little and it's not anything to be concerned about.
One check that is important is I can see bump from ride height to full droop on his screen while raising the front of the car on the rack and compare it to the last bump number I got with my bump gauge. Bump on this car has been an ongoing correction for 20 years. Currently it's actually very good, the computer should verify that.
A good thing about a 4 wheel align computer rack is you get all the number for the rear suspension, camber and toe per wheel and also thrust angle. These are useful number to know for the next project.

I have four corner scaled this car before using that shop's Intercomp scales. After asking about using them he said we can throw them in the trunk and take them home with me for a few days. That I will do. Scale the car with driver as i did before. I doubt the number changed much since done 10 years ago.
But there is a method to find the center of gravity using scales that i will look into. Everyone always say, "oh, it about the centerline of the camshaft". Sure would be nice to really know how high that number is. When we talk about roll center the guesstimated center of gravity usually is just a guess.
Being one of those anal people i'd like to know just exactly where that is on my car.
There is a process to do that accurately, just need to find the procedure, acting it out ain't that hard.

So finding, modifying, improving the rear roll center seems to be this Winter food for thought and project. Last year the biggie was the huge front sway bar project, that took nearly a year of thinking. Hoping i don't run out of brain cells by next Spring.
Bob

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Hi Bob!

About RCH, I know I've said forever that it's about 18", but that depends on ride height, among the other usual suspects.

Speaking of a software model versus a physical model, I'll take the physical model every time. Having to convey everything through a computer screen has certain insurmountable drawbacks.

Any chance you'd tolerate the exhaust pipes exiting the car ahead of the rear axle? To minimize the impact on ground clearance, you could create an exhaust tip that's short in height but very wide to conserve exit area; you know, something like an inch tall but ten inches wide.

Exiting ahead of the rear axle normally makes it a few dB louder for the driver relative to a full rear exit, but there are ways to reduce noise to make up for the difference. Doing this, however, would add to the weight and complexity of the exhaust system. Or, you could attack the noise problem by using passive methods inside the cabin with heavy, lossy IIR rubber sheets that you'd apply to the cabin sheet metal. Expect to add about 30-50lb to the car (as usual, the eternal weight-gain issue.) Continuing on the weight angle, you would at least reduce weight by eliminating roughly four feet of tubing for each side of the exhaust system relative to the full rear exit which is, what, 15 lb?

But the upside is that you may be able to avoid that packaging nightmare with the rear axle...
_______________________________________________________________________

About determining the car's COM location: I never tried it but always wanted to. I haven't looked at the stated procedure in many years, but it involves four-cornering the car with it horizontal and then tilted in roll a considerable amount (the more the better, to a certain point.) BUT, when you do this, the tires and the suspension move around in ways that are difficult to control. Even the exhaust system tends to shift a bit. Plus, the gas in the tank moves. All of this slop tends to give a falsely high estimate for COM height, maybe something like 5-10 percent (??) In other words, if you wanted to get the true COM position within an inch or so, you'd be hosed.

Me, I'd remove everything that can move from the car prior to this measurement. Then, knowing the total weight of the car in this state and the determined location of its COM, I'd measure the weights of all the removed components, along with each component's COM location relative to the car, and then calculate a final revised COM location for the entire car (mathematically, it's trivial.)

As a compromise, you might be able to chock/clamp the car under the frame in a way that immobilizes it, yet without changing the scale weights (harder to do than it sounds.) Empty the car of gas. Calculate your COM position. Calculate an adjustment for about 55lb of gas in the tank. Or, do the opposite: fill the tank completely, then adjust for about a 55lb weight reduction. Done this way, you might be able to hit about 1% of accuracy for the COM height.

This is a lot of work but I'd do it!

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Some states do allow the exhaust to exit in front of the rear axle due to safety reasons with carbon monoxide entering the cabin. Not sure if PA is one of them.


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Didn't think of that - thanks for pointing that out.

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This RC and CG thing has been something smoldering on a back burner for many years for me, 100s of hours surfing, reading peoples thoughts and ideas looking for that light bulb to turn on and have that revelation. Unfortunately I've never found that and as a result you move onto something else that bugs you, and back on the back burner that rear RC problem, thinking goes.
As the candle in the wind gets dimmer, time to make another go around at that damn lousy rear RC on these cars.

Being I'm retired, surfing, as in the web type, I'm pretty good at. The patience needed I learned back in the last millennium dial-up days. Didn't take long to find the technique for locating CG using the four corner scales. Also found several plugin calculators to quickly spit out a CG height. Simple you need wheelbase length in inches, weight at each corner at ride height entered in the calculator. Next raise the rear suspension as high as conveniently possible with an equal height stand and scale under each tire and check the corner weights at all four corner again, enter info into calculator. Enter the height the rear was raised and press "enter". A roll center height is produced. Sounds easy.

But as Mark said there are couple things that can effect the CG accuracy. Fuel level in the tank. Will insure that it is near 100% full so slosh is not an issue. About the only advantage I could ever give having the fuel tank filler being behind the license plate is this time. With the xxxx end of the car raised 12" or more no fuel will be at the cap. All the air in the tank will end up there.
A requirement of all my weight measuring is full tank of fuel. All my racing starts with a full tank. The car benefits running a full tank,

Had to laugh a couple years ago at an autox safety inspection they asked why I didn't take the spare tire out for the event. All i could think of as an answer was, WHY? Everything the car does is with a spare tire in the truck, it get weighed with a spare, it had a 4 lb difference rear side to side with the tire, WHY would I remove it.

The one PITA of this scaling the car method is as you shift the weight, load, to the front because of raising the rear the ride height is changed on both ends, this skews the results. So to negate ride height change you remove all four shocks and replace them with a solid shock of fixed lengths. The length is set to mimic ride height when the car is set back on the ground and sitting just on the scales. Now when you do the jack the rear of the car up and set on the 12" stands both the front and rear heights don't move and you get a more accurate CG height.
If you spend time in a chassis shop notice a fixed length of steel rod duplicating suspension geometry ride height will be substituted for springs and shocks during chassis construction.
Tonight dug out some 3/8 x 1 1/4" flat stock, a couple lengths of 1/2" threaded rod and think I have what I need to make the two front solid "shock". Using threaded rod I will be able to tweak the ride height at the top using nuts. Being the Viking front shocks have tie wraps on the shock shaft to show max compression traveled I can use the tiewrap to indicate the position of the shaft at ride height. Just jack the front suspension into droop, slid the tiewrap down all the way. Drop the car back to ride height and the tie wrap will slide on the shaft, now indication the ride height. Removing the shock, compress so the tie wrap touches the lower tube and measure the length needed for a solid shock. Sounds pretty easy.
For the rear I have a set of Comp Eng shocks that I may weld the shaft to the bottom tube so it doesn't compress or rebound. Same method using a tie wrap as the indicator on the shaft to find ride height length of solid shock. Those Comp shocks are near brand new, hate to destroy them with a welder, but tried to give them away and no one bit on them. They may be donated to the cause and end up in the scrap pile afterwards.

As far as the exhaust, tailpipe thing goes. On the car is an ATR 2 1/2" stainless exhaust system made for the GN, installed in 2000, and still very nice condition, it doesn't rust, wear, corrode, it's a near forever exhaust. Cutting them up may require and act of god. Tailpipe exits are GN, behind the rear tires . Noisier that the stock SS bumper exit but tolerable. All my custom exhaust vehicles had behind the tire exits. It is very important for me to continue dumping the exhaust, behind the tires.
I believe here in PA exhaust legally can not dump under the car and needs to exit behind the cabin.
The law reads thus:
"An exhaust system shall extend and discharge completely to the outside edge of the vehicle body, including a truck bed, or as originally designed."
But along with window tint, tires outside the body lines, cambering, illegal lights, exhaust is just another violator of the law often done.

Tomorrow have a few hours to spare in the morning. If this week I want to borrow the four corner scales for a few days I need to produce four fixed length shock substitutes quickly. Shouldn't be a big deal, just, more thinking.
Bob

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Your best bet for a 3-link and exhaust is probably to emulate as much of the S197 mustang 05-13 as possible. That's what I run, with the right amount of work I'm sure I could make tailpipes work and behind the tire would be easier than out the back due to the PHB.


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Locking out the suspension seems like a good idea, I'd be curious how much it affects it either way? Also, do you have to weight the rear in the lifted position? I'm seeing that you need front and rear weights when level, but only front weight (and height) when lifted. That should make the process a little quicker.
Do you plan on doing the measurements at multiple heights? The higher the lift, the less sensitive your measurements will be, but if there is any shifting happening, the lower height would be more realistic for real world use. Maybe a matching pair of jack stands on each axle tube, then take a reading at each notch? I'm sure you'll have something nailed down for that.

Anyway, looks like another fun, practical science experiment. Hope it goes well!


Shawn

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We measure CG height just about every day in our lab. For passenger vehicles, we have a cradle that you drive an axle onto and lift the cradle with an overhead crane.

We put a load cell in the rigging and zero it out with the cradle suspended. Then pull the front of the vehicle on to it and lift as high as we can before the rear bumper hits the ground. Then we take a laser line level on a rolling cart that rides on a rail and get it shooting a vertical plane perpendicular to the vehicle centerline. Then roll it along the track to shoot the center of the crane hook and the shackles on the cradle, mark the floor, and measure the distance from the axle that's on the ground to the laser. That, combined with the load on the load cell tells you how much moment there is about the reaction point on the ground. That load is reacting the weight of the vehicle acting at the CG. Knowing the weight of the vehicle, we can calculate how far the CG is from the reaction point on the ground and draw a vertical line on the vehicle (using a poster board usually to mark on). Then when you let the vehicle down, that line is no longer vertical. Repeat the process with a rear lift and you have an X at the CG. Some of my colleagues did a similar exercise using wheel scales (you only need one pair if you know the total weight of the vehicle) on their nitrous pro-mod. The trouble is getting enough inclination on a low vehicle to get an accurate number. Using the wooden block wheel stands would improve the lift, but you'd have to be really careful.

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Glad to see some input on this CG project, and much appreciated .

Bernie did you ever have you car CG done at work?

Today a trip to the hardware store and 6' of 1/2" threaded and a 10 nuts and flat washer procured. Decided 3/8 x 1 1/4" steel was overkill for the project and went with 1/4 x 1". This material to make the solid shock replacements rods.
For the rear rod welded one end of an 18" piece of 1/2" threaded rod to a 1/2"-13 bolt at a 90 degree. That end will bolt into the rear lower shock mount just like a shock would. At the top a 1/4 x 1 x 3 1/2" flat stock got drilled 1/2" in the center and 3/8" at each end. The piece will get bolted into the top shock mount location and nuts and flats on each side. I will we able to install that rod setup, one each side and adjust the nuts at the top to lock the rear suspension at ride height.
At the front similar setup except made a 1/4 x 1 x 3 1/4" plate to mimic the lower end of the shock mounting. A 1/2" rod 14" long is welded to a 1/2" hole in that plate's center. At the top nuts and flats to lock that threaded rod at ride height.
With this threaded rod setup I will be able to adjust all four corner to my known ride height before the scaling procedure.
So that is done.

The car will be scaled at ride height twice before removing the shocks and installing the threaded rod at four corners. Once with me in the driver's seat and the second time no driver. The no driver weight will be used in the calculation to find CG.

The threaded rod as shock replacements will now not allow the suspension to move, compression and rebound negated, which should allow more accurate info.

The plan is to raise the rear suspension as high as I can safely. My minimum is 12" under the tires and will try to get higher if possible. My understanding is the higher the more accurate the numbers are.
Found these calculators:
https://robrobinette.com/cg_height_calc.htm

https://brakepower.com/center-of-gravity-calculator.htm
Bob

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Hi Bob,

(SSM - thanks.)

As much fun as it's going to be to know the exact location of the COM, what, may I ask, are you going to do with that information? (With limited resources, I always skip getting information that serves no practical purpose, no matter how fascinating.) Anyway...

So to summarize, COM in x,y can be gotten in a single measurement set with the car horizontal. To get z, you have to create two different directions of the car's weight vector relative to the car, which is where tilting enters the picture. So you wind up taking two sets of weight measurements: one horizontal and the other tilted. I always heard of the tilting happening in roll, but I generally like pitch better provided the car's suspension and tires have higher pitch stiffness than roll stiffness (Bob, with your massive sway bar, I wouldn't immediately assume that's the case!). If we immobilize the suspension, then tire stiffness still counts, but that strongly favors the pitch method. And yes, the greater the tilt, the more accurate the z calculation.

Either way, you're faced with the challenge of completely immobilizing the car during tilting and preventing stuff from shifting around. If you don't do that, you'll always get a falsely high estimate for the COM height.


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Mark have been busy reading my new book and how back in the 60s before we had all this software based knowledge it was modeling that won the day. Amazingly for a large part of the handling research done back in the day was driven by the Corvair, and Chaparral. More later as I wonder through the 800 pages of that book.

Yes I know that finding the CG of my car is just an experiment in wasting time as it may be. But unless someone does the actual foot work and spits out the CG from their foot work I will pursue my own testing. I know the variables on the testing procedure can influence the results and will try minimizing them with the goal of getting a good number. Would think anything + or - 1/4" would be good info.

Something i need to be aware of during testing is the Longacre 4 corner scales I'm using are borrowed, not mine and damaging them is not going to happen, i hope.

Bob

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Hi Bob - well, +/- 1/4" is about +/- 1%, so yes, you need to be careful about the immobilization aspect. And I can also appreciate pursuing information just for the fun of it. Sometimes apparently useless information I got later became useful in ways I didn't foresee.

Also, before I forget, to get an accurate rear RCH, you'll need to know the front RCH too. The coupling between the two is weak but not negligible.

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About ^^^ sorry, I was thinking ahead to the whole roll axis deal - for the rear RCH, you only need data from the rear suspension.

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Yes, mapping all the rear suspension pickup points and angles is just down the road in this project. Actually easier than mapping all the front points when i did them.

Yesterday my safety inspection was canceled by my shop guy, he was swamped and no time for setting up the computer rack for the 86's rack time. Also didn't pickup the Intercomp scales yesterday. But, made a trip there today and hauled his scales back to the shop. We scaled the car a couple years ago, maybe 5, and I thought they were Longacre, nope Intercomp.
https://www.intercompracing.com/sw500-e-z-weigh-deluxe-scale-system-p-7.html
New 3000 bucks when he bought them.

One of his young workers loaded the scale box in the van, I wonder why. When I unloaded it in the shop i found out why, it weighs 100 lbs, each scale weighs 23lb.

When reading the instruction book on the scales they show how to set up the program to measure side to side CG and also vertical CG. You just do the setup, program in the needed numbers and bingo the digital display tells you the answer. Cool.

Never had a set of wood cribbing to put under the wheels of the car. In the shop was several old wood custom sized 2 x 4 x 8' which were dimensional 1 3/4" x 4" x 98". My brother gave them to me and they were laying around for several year in the shop. Made two 16 x 16 x 10 1/2" high cribs. Have several large pieces of 1" thick 17 ply plywood, again a donation from my brother. It's the material they use in railroad pass car seats, awesome stuff. I cut two 17 1/2 x 17 1/2 " pieces to top the cribs so the 16x16" wheels scales sit nicely on the cribs. So the rear tires can now be safely, comfortably sit on 11 1/2" high cribs. DONE.
If needed and can be done could add another 1 3/4" height to the cribs easily.

The Intercomp is battery powered, it's charging now, tomorrow looks like a play day with scales.
I don't mind borrowing expensive tools, always return them in cleaner condition and don't keep them long. Goal is to get them back by Tues.

Have a good idea how to go through the whole CG process, not difficult but will do it a couple times to insure accuracy.
Finished making the four adjustable 1/2" threaded rod shock replacement the other day, Once the car is scaled with me in the car, with no driver in the car, both at ride height I will pull the shocks and install the threaded rod "shocks" and then adjust then to my non driver ride heights at both ends. The threaded rod allows that easily.
Then it on to the CG testing phase. Is 11 1/2" high enough to get an accurate number, time will tell.

Years ago the car was scales with me in it on these same scales. It showed a 58.75% weight on the front end, OUCH. Yesterday I measured the wheelbase again and verified it at 108 7/8", yep, not factory 108". Moving the front balljoints forward 3/4" to obtain 9 3/4 degree caster along with moving the rear axle rearward 1/8" to add endply to the driveshaft and bingo, 108 7/8" wheelbase.

On the concrete floor you can do the layout of the horizontal CG of the car as scaled at 58 3/4%. You can also measure, layout what a 50%-50% horizontal CG would be. There is 9 1/2" difference, again OUCH. Transferring those measurements to the driver's door and it gives you the prospective relative to the driver's seat. My knee caps are at the 58 3/4 and my navel is near the 50. So most of my mass is located rearward of that 58 3/4. When scaling the car with no driver I expect that 58 3/45 will be even higher, oh boy.

Moving right along.
Bob

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With that amount of lift, I'd guess about 82- ish lb increase at the front axle and the same amount decrease at the rear axle (assuming you lift the rear.) You can't increase the lift? The accuracy of the scales will be the big determinant of your COM height calculation. To hit 1% COM height tolerance, your weight tolerance will need to be better than about +/- 0.6 lb per scale - that might not be possible with your scales. Do the usual corner jouncing prior to each measurement to minimize any stiction effects.

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As I mentioned the shocks will be replaced by sold constraints that will allow no suspension compression or rebound, so no need to account for springs, or shocks, while measuring. And there is no rubber, all delrin, at any point in the suspension, zero stickion.
Yes much higher elevation of the rear axle would be good, starting at 11 1/2" to see how that works out and if i can safely go higher. I have the necessary stuff to go higher. Lifting the rear of that car, done under the centersection is a little tedious. The sway bar on the car limits where the floor jack can be placed to raise the rear, safely.

If you ever had a vehicle move, slide, while jacking the safely thing become the primary goal. Having put jackstands under the car numerous times to get the rocker panels 24" off the ground the safely thing is always the concern. Even to the point of now owning 10 ton stands used for HD trucks.
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Hi Bob - Forgot at the time I posted that you were locking the suspension - good deal. So no jouncing. Delrin - you can still get some stiction, but again, thankfully, you're bypassing the issue. Safety - of course.

Also, you're locking the front and rear axles from rolling during this test, right? And, the surfaces that the tires are resting on will tilt along with the car as you raise it? It will be very important to lock the car from moving longitudinally during the test. A shift of more than about 0.026" will introduce more than 1% of error in your height calculation, and that's on top of scale accuracy issues.

If you just rest the tires on horizontal surfaces throughout the test and don't lock the axles nor the chassis, so the car is free to roll forward and backward, then your COM height measurement will be relative to the heights of the rolling centers of the front and rear axles. Of course, that's quite doable and legitimate as well, and might actually be preferable because it's easier.

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Today had a few hours to play with the car and the scales. It was a day to work on CG technique and just get a feel of doing the whole weigh in thing.

Once you set the four scales on the floor, attach the leads and then zero the scales. The first thing you find is the rechargeable battery in the digital box is dead, won't take a charge anymore despite having it plug in for 24 hours. To operate the scales you need to leave the charger plugged in and fly that way. Battery is one of those antique 9 vdc NiCad from a decade ago. I'll deal with a replacement before the scales are returned.

Once zeroed jack up the car, place the scales under each tire, physically settle the car back to near ride height and look at the results. Yesterday a trip to the Sunoco pumps and 50 bucks squeezing in as much gas as possible, everything out of the trunk except the spare and jack, now time to turn on the scales.
OH MY!!!! Just sitting, no driver this fat turd put on almost a 100 lbs from the scaling several years ago. 3710 lbs today, I just can't believe that.
Last time was 3610. I know i have maybe 4 more gallons of fuel in the tank from last time, 35 lb, a catch can installed, four 17" wheels and tires that are a little heavier than the old 16", a cup holder, an A/F gauge, a couple other things that added a few pounds but, 3710!!!!!

Next is jump in the seat and scale, 3880, when we two driver the car it then becomes 4055, OH MY!!!

Next is jack up the rear and put 11.5" under the rear scales. That transferred 29 lbs from the rear to the front. This was just a see what happens test, shocks are still on the car. And I didn't follow the procedure correctly when allowing the computer to do the math and it was skewed. Couldn't get the vertical CG answer from the scales readout.
Will pull it all down again soon and go through the whole procedure correctly again beginning at the zeroing. As mentioned it's a procedure.
Will then remove and replace the shocks locking the suspension travel at ride height and test again.
Yes it's all fun and games with probably no real useful info except I know the car is a fat pig.

I did bring the numbers from the testing today and plugged them into one of the calculators on line and it said 20.4" vertical CG from my inputs. I really do hope that is not true, that's terrible. Doing the weight transfer math 1.9% moved forward with the 11.5" cribs. Some say 10" or more is good, some say a lot more height is more accurate. My Lincoln floor jack is near it full extension. Next would be putting the jack on a 6" solid crib and also adding 6" to my wheel cribbing, 17 1/2" would then be possible.
We'll see how all that plays out over the next couple days.

I forget what that saying is about insanity? Something like this, "Insanity is doing the same thing, over and over again, but expecting different results.”
I'll keep playing that the scales until I get less than 20" height.

Bob

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4 gallons of gas: 25.0lb.

Bob, some of those numbers just plain don't make sense. How exactly were the tires and car supported during the test?

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Weights I feel are 100 % correct from the scales. Fixed measurements accurate. Yes i was generous on the 35 lb gas weight, brain fart was thinking 8.4. That 3710 number threw me for a loop.

The car is sitting with the front tires on the front scales, the scales are sitting on my concrete floor, where my alignment rack is setup when i need it. The turnplates for the alignment rack and the front scales are set up in the same location on the floor. I neglected to set the front scales up in the same manner as when the turnplates are set up for alignment. Each turnplates is leveled in two planes and then both turnplates into the same height plane. hope that makes sense. I learned that from shimming those turnplates dozens of times. Now each plate has specific shims and location on floor, Just makes all that easy.

When I do the second go around with the scales they will be leveled and in plane, doesn't take long to do once you know the drill. I think front corner weights will change a hair, but no big deal.

At the rear tires after zeroing and the front tires have scales under them next is the rear tires just set on the scales. Now all four corners are pushed down to measured ride height using the ride height gauge, the drywall T square, great toy with lots of uses. Gotta be 2 decades now with 24" to 30" inscribed markings on it.

Next press a couple buttons and corner weights, F-R % bias and total weight, stares you in the face. Ouch.

There's a process to input measurements for wheelbase, axle height and how high the stand is and I inputed that after the fact, not before, my bad, but was anxious to get a number and knew i was also running out of play time. But also knew today was just a run through.

As I mentioned using the Robineete calculator it said 20.4" CG. I'd love to hear ten other people say they know the CG on their car and they were surprised how high it was.

Ya know all this CG is just to know what the moment arm really looks like. I said to Bill in the shop the other day, it can be like a short breaker bar or a short breaker bar with a 12" pipe on it. It can get pretty serious torque wise quickly.

Bob

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OK. The fact that you have to enter axle height (front and rear; they should be slightly different,) tells me a lot.

1. So you start with the four scales in a common plane and exactly horizontal. Right?
2. You park the car on top of the scales. The car is free to roll, but because the scales are horizontal, the car stays put. Right?
3. You get in the car and press a button to get weight measurements at all four corners. Right?
4. After this, or maybe during this, you press another button and get the scales to read zero as a reference. Right?
5. You get out of the car and jack-up the rear. Right?
6. You set the two rear scales on a pair of 11.5" box-like stands with horizontal top faces, and set the scales down on those, directly beneath the rear tires. Right?
7. You lower the rear jack so the rear tires now rest on the scales. Right?
8. You get back in the car and press a button to get the weight changes at all four corners. Right?

Just curious what all the numbers were, and what is the accuracy of the scales? Thx.

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Mark once I've done the second go around and know I got good numbers from the second, more refined setup I'll post some numbers.
As said first go around was just to get familiar and see what would make the second, third or fourth number crunching the most accurate.

Intercomp claims .1% accuracy.


https://www.youtube.com/watch?v=1Yk3UFS6UX8

Andy won the 3rd UMI KOTM.
Bob

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0.1% of 2,200lb is +/- 2.2lb, which is 7.6% of 29lb. By the way, is that 29lb for the axle, or for each scale? I'd contact the manufacturer to get a more precise understanding of the kind of uncertainty involved. It may work differently when you're zeroing the scale to get a difference.

But that aside, I'd still strive for a higher inclination.

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Have you targeted a goal from where you are now?

Last edited by 1 Slow SS; 09/18/22 10:23 PM.

Enjoy life, family first!
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Bob, just jumping ahead a bit here, if you say you're actually going to do something about your COM position, I'd say two things: One - fantastic and good for you! The car needs it, at least in x. All you have to do is move the engine to the trunk. Two - I'd be dumbfounded. If back in the day at somewhere around post 1,432,986 of the sway bar thread where the idea of doing a chassis-stiffening experiment was proposed but ignored, if such low-hanging fruit was left on the tree there, then why strive to reach such high-hanging fruit here? (All said in good-natured humor - promise.)

One more thing about scale accuracy: you can duplicate the horizontal phase of the test and add a 20-ish lb weight known with high accuracy to each scale in succession while the car is parked on top of them, and see how accurately each scale reports the weight difference. This will tell far more than any commentary from the factory. If there isn't enough room on the scale for the weight, then divide the weight into parts and place the parts around the tire for a tighter grouping - you get the idea.

Last edited by MAP; 09/18/22 11:12 PM.
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