Scale question

I bought a set of Intercomp scales used. Level everything. even put slide turn plates under the front tires so they don't bind. Zero the scales. I stand on each scale, 200+/-1. So here's what I can't figure out. I weigh the car w/o driver, 3161. Then I get in the car with my suit and helmet, 3345. Raise the car rezero everything. Lower the car down on scales, bounce it, 3307 w/suited driver. The left rear is now light. other 3 read the same. Disconnected the front shocks to check for bind, no difference. the rear (ladder bar) doesn't appear to be bound up either.Even had my wife bounce the car with me in it. Readings returned to the same incorrect readingsafter it settled. so either the LR scale is goofy. something is bound up in the suspension. However it drives snd leaves perfect. The only thing I can think of is to build a platform and roll it onto the scales.
Doug

Move the LR scale to a different position?

Doug: I worked at a research center for a major automobile manufacture. I built numerous proto type vehicles. They had a set of scales built into the floor. I tried telling the big wheel that it wasn't correct. He ask me to prove it so I weighed the car then spun it around. The floor pockets were not level. So I was tasked with leveling everything so it weighed the same, try and see if the readings are identical. Birdtracker

Preload

Temperature ? This can effect the load cells on the scales, Did they come out of a cold garage into bright sunlight and the car weight was checked first when the pads were cold ? It could also be a bad connection on that pad, you could try swapping the pads / leads around as mentioned, to see if the problem follows the lead or the pad. I don't think there is suspension bind, the total weight would not alter it would just be in a different place. The difference is just over 1% error, well within the specs of most corner scales it's just odd it's on one scale in particular

I wa careful to level them the best I could. Set up a tripod in the center. Put a laser level on it. Leveled the laser. Then rotated it towards each scale. Measured down from the laser line to the scale itself. Yhen shimmed the scales to the same height with-in about 1/8". Temp about 65 degrees in the garage, no sun shining on them. I will try swapping the scale and cables. Along with double checking connections. Cant get back on it until monday. It does have preload. But on the scales it changes between around 50lbs to about 85lbs,
Doug

I find the best way to use scale to get them to work properly is to take two 2×12 or 2×14 about 36 inch long screw two of them to gather so you'll have 4 ramps raise car up set scales under each wheel then put ramps behind scale and roll the car back on ramps zero your scales push car back on scales that help take in binding out and if you want to bance the car up and down do on the ramps not the scales. Just how I do it and was taught to do who set up a lot of car

Built some risers so the car could be leveled with sliding turn plate on the front scales. Then acutual read the laser lever instructions on self leveling. Mounted the laser on a tripod. Checked each scale for exact height and being level. Checked all the connections as well. They were zeroed with the turnplates. They car was lowered ,then rocked. Rocking didn't affect the readings mire than a pound or two after it settled out. I'm surprised how heavy it is. My estimates pump it about 100 pounds lighter. Could the calibration be off? I don't know enough about them. I know that my weight compared to the bathroom scale is pretty close on each scale. So here it is. 5gallons of fuel. Weighed w/o me. And the with me including all my gear.
Doug

Did you empty the weight box?? weights looks pretty good on each wheel

The rear preload is perfect. It goes dead staright riding the wheelie bars past the 60ft clocks if you allow it to do that. The only extra weight is the brackets for holding ballast. They weigh 10lbs. I can pull them, the pass seat (21lbs), and run 3 less gallons of fuel (20lbs). So if needed to run index it can lose 50lbs. Here's the strange thing. this is an old weigh slip from different scales 10 years ago. The front weights are similar. The rear is not. It now has the weight brackets +10, Holley carbs +7, tubes in the slicks +8, and cast Dana cover +6, fuel then vs now, +30,, I'm heavier +10, no suit or helmet, +8. sSo it should be +79Lbs. But now it only has one battery now though the 16v is heavier -29lbs. New wheels -30lbs. Carbon hood and scoop -19lbs so -78. So pretty darn close though the distribution is probably more nose heavy. Along with preload changes. I'm going to go out and swap cable and scale location and see what happens.
Doug

DVW I don't think you should be raising the car and setting it back down on the scales.

I always have rolled it off bounce it and roll it back on. Has to be in the same spot too to repeat.

Front steering geometry is what is making the weights wonky when you pick it up and set it back down I bet.

I used to calibrate weigh scales back in the day working for a testing lab and we had about 40 tons of calibrated weights and a crane truck - we would increase the calibrated weight onto a set of scales - then graph out the delta - you had to be within 1% to be considered calibrated for a scale up to 100K LBS

You could probably check your scales if you had some known weights - but it sounds like all your individual scale pads are weighing the same if you weigh the same on each scale - that's how I check them -

This is the results; I put each scale on the floor and zerod them. Then stood on each scale. all 4 read the same 201. When i was using the hoist it had alignment turn plates on the front scales. So when it was set done the tires could slide ourward and find their center. Additionally it was bounced front, rear, side to side. The last test was to roll the car back with the scales on the floor using 2"x10"s to roll it off. Was a litlle tough to get it back up as the scales are taller than the 2"x10"'s. Additional the garage dor is ptched towards the door. Using th elaser level this time the scales were all level side to side, but the rear scales were 3/4" lower than the fronts. Ther was no 3/4" material handy so I went with it as is. As you can see the results are very similar.
Doug

You have to take one bolt off the back of ladder bars, top bottom no matter. You can’t get the car balanced right without doing that, all four corners have to move, I would do all the shocks too.

Thy I did pull the front shocks on case there was an issue. Didn't think there would be since they just came back from Afco. Removing the ladder bar bolt would remove all preload. I wanted to know how much it had just for reference. It'll never make a pass with the bars neutral. So what it scales with no preload really doesnt give me any info. It launches straight and level.
Doug

I like ladder bars
Both cars I've own and race with them on worked very well Hook up in a mud puddle during a rain storm

That discrepancy is caused by the bind in the ladders bars. To get any kind of reference of how much weight is on each wheel bolt has to be out. Weight jacks corner to corner, diagonally. Put 80 pounds on right rear hook up bolt and go racing. Ladder bars are the same as rear attached to frame no amount of jacking will change anything in the back unless the whole frame flexes. Your weight has to be in the chair to set up properly, like it will be raced. Tried and true procedures

Ah I see. I don't have plates so I have to roll it on and off.

Its all just for reference anyway. If the car is launching straight the weights are right.

Maybe I haven't been clear. Post #1; The results were inaccurate. I used the laser incorectly. No slip plates.The pictures in post #8 are; Pic #1 car without driver Pic #2 with me, suit, helmet as raced sitting at the line. These weights were taken after post #1 in which the results were incorrect. The 2nd time around weights were taken with slip plates for the front wheels. Scales leveled with in 1/16" all the way around. The car was lowered from the hoist. Then jounced front, back, and side to side. Post #13 This compares the readings taken when lowering the car using the hoist vs rolling the car onto the scales. As you can see the results are within a few lbs. This may be due to the fact that the rear scales were 3/4" low using this method. Yes I could've removed the ladder bar bolt and removed the pre load. And if the front torsion bars could be loaded equally. Then, yes I understand that would give a true weight distribution without bias. Moving the torsion bar with the driver in the seat to level the car induces preload itself. And trust me that preload disappears with the front wheels in the air. I don't understand put 80'bs on the right rear? Add 80lbs ballast? Add preload until the previous right rear reading is 80lbs heavier? Why 80lbs? What if one car has more left to right bias to start with. Or one driver is 150lbs and another is 350lbs? I can't see how one set amount of weight fits all applications. When I built my car the prevailing theory was to add a few flats of preload. Then add or subtract preload until the car went straight. This is how it's been for 10 years. Only a flat or so change ever. And that was when the rear shocks and springs were upgraded. Since I'll be setting up a new car simiilar to mine, I was curious on my weights. Figured to start out with his with the same rear weight bias as mine and go from there.
Doug

Ok

Interesting info on your scales I suppose. But possible the previous set of scales was lite? Have you ever weighed it at the track, not that it is a be all end all as we vary 5-15lbs on different scales running NMCA stuff. But it gives you an idea of where you are total wise. And those scales are open at all the events. One thing folks miss frequently is tire pressure it can and will affect corner weights if not correct as raced. Fun experiment to see how much weight you can move around by just changing air pressure on a corner a tad. As for lift on and off the scales, not ideal but it works as long as you are bouncing on the car after they settle. But it is preferred to roll them on and off for sure..

I really dont understand the disconnecting the bolt and adding weight to a corner. The entire point of preload is to be able to "move" weight around as needed to get the car to work. As for initial set up we always start at neutral. We will ad preload to a point but at some point you need to look at rear steer rather than pre load. If you car needs a full turn of preload to work you might consider adding rear steel to make it work. I have found over the years most cars set up correctly really should not need TURNS of preload, only a few flats unless they are making really good power, then adding rear steer is a better option.

Really to me all that matters now is good oil-line routing and it's corresponding flow/pressure to each part of an engine.

“I really dont understand the disconnecting the bolt and adding weight to a corner.“
More weight on that right rear corner to plant it (it wants to rise from torsional power) so pull bolt, crank on torsion bar or put more weight over that side. Install bolt so it just slides in, then turn the adjuster to tighten it up a little. Weight will very from car to car but not much. One reason Chrysler put more spring leaves on one side.

For sure I've weighed at NMCA. It's been a few years. But as I remember it was around 40lbs lighter. I've moved it back to neutral in the past just to see where it was at. It has less than 1 turn of preload. 3-4 flats at most. I've thought about rear steer as well. Right now the housing is dead square to the centerline. Maybe rear steer would be preferable? We'll talk about it at 131.
Doug

Cranking the torsion bar works fine as long as it doesn't wheelie. As soon as the front wheels are in the air that preload is lost. Been there, almost hit the guard rail. No need to add weight. Add preload by lengthening the RS ladder bar double adjuster. This will lift the the right rear adding weight to the RR and LF. The only potential downside is added LF weight. At 100lbs difference I've seen no difference in how it drives or stops. Over 850 passes at 145-150.
Doug

One thing to remember, every car rotates from torque and rear the opposite way. I’m done.

Well I think I have a pretty good handle on what it takes to make a ladder bar work. We have been 1.08 60' with a small block NA with a ladder bar. Ill stick to my way thank you. Worked on dozens of cars so far and no one is dissapointed..

Doug might be worth looking at to think about rear steer. My 64 like yours works fine with a couple flats. Mine is a bit heavier but we have been 1.25 60' so far, but Ill admit I have not really worked on it a lot. Just pulled it apart checked it all and started at neutral. I prefer the wheelies over getting ALL of the 60'. I am still pulling a bit of timing at the hit to calm the wheelies down some. I now with some better shocks and ride height adjustment and a less aggressive front pickup point we could make it much better. But might not be as fun,

One thing to remember, every car rotates from torque and rear the opposite way. I’m done. [/quote]

I agree. Thats why the right rear tire spins on a single track rear axle. Thats also the reason the right rear needs more load. Be it weight, preloaod, tighter shock settings, heavier spring. That is until the car has enough power that hit needs to be reduced with negative anti-squat, heavier springs reducing stored energy, stiffer rebound/loose compresion on the shocks. But that's a whole nother discussion.
Doug

I am happy you posted about this Doug as we are currently working with my buddies Roadrunner on rear steer and pre load to get the car to go straight, as you and Al are talking about. We are scaling his car tomorrow for similar reasons as you mentioned. Not so interested in the overall weight of the car as "it is what it is", but more interested in how the weight will move around when we start to throw preload at it so we know when we are at the track, if we make an adjustment, how much weight we just moved from the driver side slick to the passenger side slick, or vice versa. It will also be interesting to see what his scales say compared to Mason Dixon scale.

He has a ladder bar with housing floater and caltrac split mono leaf opposed to coil over springs. Good afco shocks valved by Yancy in Texas. We had a bunch of preload in it and still couldn't get it to go straight. We stopped, and decided to put some rear steer in it at the track with 1 1/2 flats of preload and made it better, actually started to push left a little bit. Tomorrow we are going to see how much rear steer we put in it at the track and hopefully get this squared away next weekend at 42.

If I understand the OP, you weighed it w/driver. Picked it up. Lowered it back down, and the weight was nearly 40# different?

The total weight of the car should always be the same regardless corner weights, unless the scales are junk.

Bound suspension, broken shocks, cranking springs and bolts will move corner weight, but will not change the total weight. Can't.

I suspect the scales were sold for this reason. Borrow another set to confirm. A single jammed up pad can do this.

And cranking weight into a corner will always make the diagonal corner heavier as well. i.e.crank weight into RR, LF gets heavier as a result. Conversely, jacking up the spring/T bar on the LF is one way to get the RR heavier without making the car sit high on that corner.

As power goes up, rear corner weights have to be moved to compensate for the "propeller" affect on the rear housing from the torque being applied by the driveshaft. But that's another conversation.


ETA Now I see you rezeroed the scales. Even after an extended session, I've never seen scales move more than a pound or two when the weigh is removed. Once zeroed and the car set on the pads, they should come back to zero, +/- 1 or 2 pounds, unless something is wrong.