All that is great, but I don't agree that that much accuracy and consistency is significant at the level of anyone reading this. 2 lbs? Let's be realistic.
All that is great, but I don't agree that that much accuracy and consistency is significant at the level of anyone reading this. 2 lbs? Let's be realistic.
I am. Just because someone at a certain level of capability cannot feel the handling differences and the race-long changes in the handling that this sort of inconsistency brings about, does not mean that the changes are not there and don't make a difference.Originally Posted by starkejt
Well, okay. But taking a step back, I also will not believe you can verify that your scales are within .001" of each other with just a .0005/ft level.
Verify? No, since that would take a second and maybe a third set of measuring equipment, and each one would have to be set up and re-calibrated every time you move it.
There are also scales available that are graduated to .0001" per foot.
The whole idea is to use instruments that have a high enough degree of accuracy so that any built-in inconsistencies are minimized to as small a window as possible.
If your equipment will only give you an inconsistency window of, say, 5 pounds, and your car responds (in a handling change) to 2-3 pounds, then every time you set the car up you will be chasing your tail to figure out why the handling difference.
This sort of attention to detail is part of the reason why the guys at the pointy end of the grid are there, and others whom are just as good drivers are not.
As an example - years ago with a certain driver we found that the best setup at a particular track was to add 12 pounds of weight to the right front so that as the left front tire grew, the car would come back to even across the front, making the car to be at its best at the end of the race when everyone else's cars were starting to drop off.
But we found that adding 14-15 pounds instead of the 12 aggravated the growth difference between the 2 front tires, making the car worse.
If the scales had not been consistent to within a very tiny window every time we set them up, there is no way we could have confidently made that 12 pound crossweight change and know that the car would respond correctly.
Last edited by R. Pare; 04.02.12 at 12:42 AM.
The most accurate "racing scales" don't have load cells accurate enough to detect a 2# difference in cross weights (1#/corner) on a car that weighs more than 1000#. Nor are their surfaces machined flatter than .0005"/ft.
I understand the more accurate and more repeatable the better you can tune...but way too many variables out of our control, in my opinion, to be sweating details that small.
How much does the scale pad deflect with a 400# load on it, how about a 150# load on it? Now your platform that was level to .004" might be perfectly level, might be off .008" now.
Which grid are we talking about? I haven't seen anyone working to that level of consistency at any event where I've been. I've seen plenty of people turning adjustments on the car until the weights on the scale are that close, but that does not mean the car is actually that close with any kind of repeatability. Unless you have someone who is really good with lots of expensive measuring equipment setting up the scales and checking them throughout the day. Which I have not seen anyone doing. If you are speaking somewhat hypothetically of a high end professional environment, then okay, that's different.
I guess I am saying there is a difference between thinking you are at a certain level of precision because your instrument is that precise vs. actually being at that level. Not to mention, as Daryl brings up, how many of us have scales good enough to work to such a standard?
For some people, good enough is just not good enough.
My suggestion is to listen and learn from the resident experts. Talking smart about engineering to RP is analgous to Truman Capote trying to sucker punch ‘Smokin’ Joe Frazier. Not a very good idea.
VR
Iverson
Rick, good advice and I certainly wouldn't attempt to tell Richard Pare how to engineer anything. That doesn't make my points any less valid. There is no use in measuring to a standard that is more precise than the tools utilized to obtain said measurements.
No one is trying to teach Richard anything. He is certainly smarter and more knowledgeable than most (probably all) of us. That doesn't make you an idiot if you don't agree with him on something.
Daryl, I will yield to your point my friend. Sort of like working with significant figures in chem and physics.
However, I am powerless over trying to achieve the best and most repeatable data I can. From my chair here, accuracy and absolute precision is of the bottom line.
Besides, I could set up my platen and level it fore-aft and laterally with my Starrett in less than thirty minutes. If nothing else, it made me feel as thought I was contributing to the effort.
Last edited by Rick Iverson; 04.19.14 at 10:03 AM.
Hoo boy - last post on the subject.
What is at issue is that you want to make the window of error as small as possible, therefore making the errors induced into the setup as small as possible, giving you a more consistent and more predictable car - there will always be some degree of error simply because none of the equipment is perfect and the tolerances add up, but the ability and need to minimize it is crucial in making a car handle consistently.
In that vein, it makes zero sense to use less accurate equipment than what is readily available, unless of course you just flat cannot afford said equipment.
I agree, Smokin' Richard.
...or unless you are already winning without it
However, I understand where you are coming from.
I believe for 99.99% of the club racers there is other lower hanging fruit.
I believe for 99.99% of the club racers there is other lower hanging fruit.[/quote]
At the level of detail we are discussing now I would probably start questioning the repeatability of the tire pressure gage and its effect on cross weight.
So what are the best people in set up using for pressure gages?
Even with a good set of setup tires, how accurate can they be? How to fix that part short of setup steel wheel "tire" devices?
As a proud graduate (and post graduate) of multiple ICP seminars, i'm in with Richard.
Go to any F2kCS or F1600CS event and walk through the paddock watching what the front of the field is doing. A lot of attention is paid to dialing in their pads, then using them every session, and rechecking them every day.
Working for a few seasons with DaveW i learned to be more precise as to recording tire circumferences after each session, and calculating what it would take to adjust the car quickly on pit lane in a switch from drys to rains.
Repeatibility is very important.
Back in the day Champ car teams had a set of setup wheels and tires that were used only for that. We then had data on every set of tires in use and could understand any deltas for things like cross weight due to stagger changes. But then we also had driver adjustable cross weight systems so didn't worry too much about it on the setup pad, only to measure where we started and where the driver took it to.
Tim
------------------
'Stay Hungry'
JK 1964-1996 #25
Am I wrong in assuming that the FM crowd chose this class to avoid having to worry about the precision that it takes to make FF and FC cars go fast? Or are they looking for the unfair advantage by doing the setups with the same precision that the development classes use?
The last I heard, FM could use bump rubbers and packers. Now if that is still true, then the precision required to achieve maximum performance may exceed that required for other cars.
Years ago I asked a FM driver what I would change about his car if I added a .125 packer under each bump rubber and then lowered the car .125 in. He did not have a clue. On a good day it might make the car a lot faster or un-drivable.
My preferred method for setting an alignment pad is to use a transit level and a precision level. The transit level I use (and it is not an expensive unit) can resolve the height of each pad to the edge of the scribed lines on a 64th inch machinist scale. I then use the machinist level each pads. Again, the precision is only required to make the setups repeatable and consistent. You can do a very good job with a carpenters level and a extruded bar, or a water level, if you have good technique.
Bias ply tires have so much variance in diameters that I do all my setups without tires and then use the scales to set balance and tune ride height. Each set of tires needs to be checked on the scales before and after every run. Sad but true.
I once met a very competitive roundy-round guy. Because of the pace of their Saturday night events, there is no time for scales at the track, so he did all his careful setups in his shop. Then when he got home he would go back on the scales to see what his adjustments on the track did to the car. I understood that part.
One evening i visited his "shop" because i didn't own scales at that time and wanted to borrow his. OMG! His shop had a dirt floor that had 50+ years of oil spilled on it and was packed as hard as concrete, and... sloped about 5 degrees diagonally towards one back corner. The guy would jack up his car and slide his scales under each wheel, uneven floor and all. After he saw me turning pale, he explained that he put the scales on the same spots each time (he had little carved out lines in the packed floor). He had been setting up the same place for about 25 years, and it was all about repeatability, 5 degree slope and all. He admitted his "baseline" could not be used if he put the car on a level pad.
I asked why didn't he at least dig out level pads in the floor for the scales. He said then he would be tripping all the time in the holes, and his creeper would get stuck in the holes. Too much hassle.
He would openly tell guys that asked at the track what his cross-weights were, knowing full well if they copied it on a level pad, their new setup would be way off his.
Needless to say, I never unloaded my car.
I am very lucky in that we have an old cast iron surface plate in our shop. Using this plate for the last 5 years has been a MAJOR eye opener in learning how to setup cars. The main result of this use and the learning experience is that I can now get a car within 5lbs of cross weight without scales. Of course I measure EVERYTHING and keep the records. It really pays dividends when you are in a hurry and do not have the time to get on the scales. You had better know what each flat of adjustment does to the car and of course your had better understand what tire stagger does to the car too.
You also have to know that some cars simply are not repeatable (imho) and there are others that are really great.
BTW, it is hard work to get them right.
Thanks ... Jay Novak
@ Steve, I personally think that packers/rubbers make FM's unpredictable and many times that is why they slide around so much. Thats just my opinion, packers make fm's devilish at times, I never used them long enough. I learned to set up these cars from guys who prepped cars when the pro series existed. I can assure that "precision" and repeatability when prepping an FM does make a difference. FYI You could drive an FM with 3 mm rear toe out where the FF wishbone would probably snap, very different cars. The FM driver who is fast would probably over drive the FF and vice versa. With a little bit of practice both can be rewarding depending of how much work you put into it. I can't wait to drive my FB one of these days, it felt way more precise than the best FM out there and my fb is very crappy.
Here a pic of it in the corner of my shop, i better get used to it sitting there while I go prep some FM's and put bread on the table
Last edited by JRMarchand; 06.18.13 at 4:28 PM.
ditto on what Frog said:
Get the front weights close, and then just drive the pig.
Options ...........
some accurate scales:
http://gizmodo.com/5898264/scientist...-single-proton
or
Last edited by Swift17; 01.29.14 at 4:46 AM.
Juan; I posed the packer question to a guy who insisted that you did not need to think as an engineer to run a FM.
Packers and bump stops are a very tricky aid to handling. Get them right and they are very useful. I do use them at times. But use the wrong type with the wrong setup and you get the results you have experienced or worse.
In rig testing ( 7 post) I have seen improved grip with bump rubbers but it is tricky and takes testing to get it right.
The FB may resemble a FC but the performance is in another ball park very close to FA. It is amazing to see the differences that 30 hp and -200 lbs. can make (FB v. FC). The difference in speed gives a big increase in down force with very similar aero packages.
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