Post rigs

[Jersey Tom]

It's not that I think damper tuning is unimportant... everything is important and adds up. The question is significance and order of operations. (An an aside though.. yes.. taking a corner is ultimately a yaw response so I think of almost everything in terms of that.)

Of the myriad of chassis tuning options that exist, you have the sort out the low hanging fruit (big gains) from the smaller stuff, and tackle things from big to small. In my mind, the biggest stuff starts at quasi-steady state loads, cambers, and slip angles... and if your basic balance and handling are off, you're sunk at a racetrack.

[DaveW]

yes.. taking a corner is ultimately a yaw response so I think of almost everything in terms of that.

Undoubtedly true, but again being overly simplistic, getting into a corner does not give lap time (if a driver is being "honest"). There is much truth in the old chestnut "Slow in, fast out". A driver does not have many cues to judge corner exit speeds (which do affect lap time), which is one of the reasons (in my view) that a multi-post rig test is so worthwhile. I could rabbit on, but won't.

Incidentally, mixing with the golden a**es of this world (road car development drivers), I would observe that K&C data is fascinatingly impressive in its detail. Interpretation, however, would appear to be more of an art form than a science.

[Smokes]

[/quote="DaveW]
The process attempts to match rig vehicle responses to previously recorded track data. Normally, one lap of track data is selected for the purpose. Technically, making set-up changes that might result in a different driving line, or different sector times will make the drive files obsolescent, but it is probably realistic to ignore that fact.[/quote]

Therefore to make an accurate drive file you would have to scan the whole track and for every bump kurb corner and gradient change. Then run a temperature coeffient to take in to account of the track expanding and contract depenant of the soil meachnics etc. and the map the ideal line and run the car on the post rig.

I know "ideal line" is very dependant on the driver driving style and the car set up but that would be the best way to see how performs on each set up you use.

Probably simpler and easier to use and active suspension to do this as it can work in real time using active ride height and yaw sensors and accelormeters to cope with the track changes and keep the aero stable but that would be cheating..

Also the objective of set on a F1 car would be to keep the aero as stable as possible. I really hate this myopic veiw that aero is everything.

I think i will stick with racing off road rc buggy and 1/12th scale on road where driving and set up is everything.

[Belatti]

The process attempts to match rig vehicle responses to previously recorded track data. Normally, one lap of track data is selected for the purpose. Technically, making set-up changes that might result in a different driving line, or different sector times will make the drive files obsolescent, but it is probably realistic to ignore that fact .

There to make an accurate drive file you would have to scan the whole track and for every bump kurb corner and gradient change. Then run a temperature coeffient to take in to account of the track expanding and contract depenant of the soil meachnics etc. and the map the ideal line and run the car on the post rig.

Stop smoking that my friend!

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Great posts Tom, thanks a lot!

The same to you Dave!

If we stick to my case (modest small formula team) I guess that the info K&C test provides were replaced by rough estimations I made before working with the car.

7-post (or in my case 4 post) was something we did later to improve the car handling and overall grip.

The thing is that my "rough estimations" were based in, for example, measuring ARB rate + motion ratio locking one wheel and placing a scale and a jack in the other side (obviously without spring in place). Others are to represend geometry in a soft and with measured G forces calculate roll moments and stuff.

I think I know what Im doing (at leat at some extent) when I change ARB blade angle without any K&C test. What I do not know are many other factors you Tom listed and that I have not chance of knowing otherway.

[Belatti]

In my mind, the biggest stuff starts at quasi-steady state loads, cambers, and slip angles...

There is where we differ. Quasi-steady state is very nice and simple way of studying and understanding vehicle dynamics, but without the proper damper tunning there wont ever be a parallel between a quasi-steady state study case and reality.

[Jersey Tom]

In my mind, the biggest stuff starts at quasi-steady state loads, cambers, and slip angles...

There is where we differ. Quasi-steady state is very nice and simple way of studying and understanding vehicle dynamics, but without the proper damper tunning there wont ever be a parallel between a quasi-steady state study case and reality.

Callin big time BS on this. Just not true, even at the pro race level.

[Belatti]

So whats quasy-steady in a car thats jumpig all arround a track?

[Jersey Tom]

In-plane (x-y) cornering response ultimately drives a lot of lap time. You can figure out most of the basic balance of a car with steady state car (K&C) and tire (F&M) properties, without knowing much or anything about the vertical dynamics. I don't believe the same can be said of the inverse.

Even the majority of transient yaw response of a car is driven by steady-state tire properties. Can and does have a much bigger effect on vehicle balance, response, and stability than low-speed damper tuning, roll stiffness, etc (which are all secondary to the allmighty tire).

But that's just my personal experience. I live in a world of tire data. So if it were me, I'd sort everything steady state first to get the basic balance and responses (off-throttle, on-throttle, turn in) right.. then get into vertical dynamics to bump the raw aero and mechanical grip levels up across the board.

[DaveW]

I can see that we are just not going to agree, JT, however long we throw the subject around. Hence I will close by suggesting that, whilst K&C data is undoubtedly useful, for most half decent race vehicles a driver will tell his race engineer about lateral balance, & a half decent race engineer will know what to do about it. On the other hand, a driver will not normally be aware of sub-optimal damper settings (a good car on a poor surface feels much like a bad car on a good surface) &, in my experience, even a good race engineer will struggle to optimise dampers settings unless he has history to fall back on, a validated vehicle model, or a multi-post rig to help him. Personally, I've lost count of the number of times I have been told categorically that "dampers do nothing", & discovered after one rig run that the comment was accurate - but only because the dampers were a factor of 2 away from where they should have been.

I would just add that the guys at the sharp end tend not to play around with bars & springs to find a lateral balance, but they do worry about tyre temperatures & diff. maps....

[Jersey Tom]

I would just add that the guys at the sharp end tend not to play around with bars & springs to find a lateral balance

Not in my experience...

In any event, this is all a good example that there is little that's fundamentally agreed upon when it comes to these things (which is fine). No one has it all figured out... some organizations are just 'less wrong, more often'.

[Belatti]

I would just add that the guys at the sharp end tend not to play around with bars & springs to find a lateral balance

That is in the same line of thought of our post rig "consultant".

In any event, this is all a good example that there is little that's fundamentally agreed upon when it comes to these things (which is fine). No one has it all figured out... some organizations are just 'less wrong, more often'.

Well, thats a nice conclusion. We have different approaches and the only way to compare them would be to have 1 car to work on, go to a track with the same car and the same driver the same day, and hope the driver "style" is as neutral as it can be regarding our different setups

[Smokes]

I would just add that the guys at the sharp end tend not to play around with bars & springs to find a lateral balance, but they do worry about tyre temperatures & diff. maps....

I agree with Dave W on this.
As i think bars tend to mask other problems with the car and further more induce tweak if not set up correctly

Changing spring means changing dampers to suit the new supension system frequency response and thus would mean going back to the 7 post rig.

You should only use bars when you are sure you have everything else set up correctly and the car is not "tweaked".

Diff maps are far better way of controlling lateral slide than tuning the suspension as you continuouly adjust the diff to not over load the cars suspensions lateraly coming of the apex when throttle is begining to be applied. Which mean the car can apply more power earlier in corner to increase exit speed.

Bellati I am not smoking anything Marlboro 100 are too expensive these day and are bad for the lungs.

Please note I am probably talking utter rubbish as I am not a race engineer.....

[Jersey Tom]

Diff maps are nice... except when your diff has no adjustment which is the case in many series.

Trying to play with tire temps to fix a problem of roll stiffness, camber, or steer imbalance... IMO is just putting a bandaid over an issue and not really solving the root problem. Tune the right thing with the right 'tools.'

Does changing spring rates impact your damping? Of course! That's again, why I say set your roll stiffness split and (most of) tire pressure first, to get the average corner loads right, then go to dampers to play with TLV.

It's one thing if you have designed and built the chassis (e.g. F1) and have a pretty good idea of where everything is set.. and you're just doing fine tuning. How often is that the case though? GP2, IRL, Indy Lights, NASCAR... all are supplied chassis. If I'm handed a chassis, I want to know as much about the car from a mechanical standpoint first off.

But again.. just my way of thinking about it. I live more in the K&C and F&M realm.

[Shrek]

Have anybody ever heard of a pull down rig, i was told it's better than a 7 post shake rig. i think Mittler Brothers made it.

[Jersey Tom]

Pull down rigs are for a completely different job than 7-posts. It's almost like a ghetto, poor man's K&C machine... except it's not really built to measure anything. It literally just grabs the chassis and pulls it down.

Good for looking at setting coil binds and bump stops on a stock car.. maybe some basic manual camber measurements or rough ride rates if you have spring load cells. Other than that, not exactly a fancy piece of equipment. K&C goes far far beyond what a pull-down can do.