In my experience I always drive harder and heat the tyres more in a race then when testing, just because there is so much more going on and you are thinking about an awful lot more things that when testing alone.
I tend to find you do a lot more little lockups, more small losses of traction etc. even though you dont really notice it.
If your R3's lasted 21 before a blow out in testing then banking on doing 20 laps stints in race conditions was a pretty risky strategy.

Just a little something for my fellow physics geeks who are into this stuff.

We've suspected for a while now that something was a bit hinky with the clutchpack diffs, and also that the locked diffs can work out faster.
I always thought it was funny that there was no pre-load adjustment on the diffs, and my suspicion was that preload wasnt modelled, as generally if there is an adjustable parameter modelled, we can adjust it.

I did the following test and it seems like there is indeed no preload on the clutchpack diffs at all, which means that as you pass through the neutral torque zone between power and coast, there is no locking and the diff is effectively open. Its possible that this contributes to some of the difficulties people have with car behaviour on corner entry because as you come of the brakes and start to turn in, you have an open diff for a moment.

Anyway, the experiment went like this for those that are interested.
Run up to full speed at the oval, then put the car into neutral and drive a turn just coasting. This should meant that the diff is under a no-torque condition and so the only torque transfer should be as a result of the preload in a clutchpack diff.
With an open diff, this experiment saw a very small difference in longitundinal force between the rear wheels, probably just as a result of the outer loaded wheel having more rolling resistance (60N difference fact fans).
With a locked diff, as you would expect there was a big torque transfer.
But with a clutchpack diff with full coast and power locking, only the exact same tiny difference of 60N was observed, which effectively means that when not subjected to torque the clutchpack diffs act as open diff.
Ergo, preload is not modelled.

I think.

Yah, it was an obvious setup gag. The acting was really bad, the l33t machine was just a big old beige box that probably had a 486 in it.

Oh yep, August 2003 just after S1 came out.

Heh, 'bout time dan. Its funny because I hadn't even fired LFS up for more than a few minutes practically since the last season of ESL finished, but the other night I thought I'd give it a crack, so I found a nice full UFR/XFR server at Krautracing and joined in.

And what did I see, only 'N1 Danowat' leading the race to the end, and I confess I thought that either you'd improved a lot, or it was a slow night. Turned out it was the former though, so nice one.

Quote from w126 :

Sprung mass distribution may be obtained from raf (vertical loads) provided that there is a moment when the car is standing still on a flat surface. Total mass distribution may be taken from garage view (with driver and fuel). I hope the two distributions are not equal. The calculation from the first post seems reasonable, though I'll check it one more time.

Ah, good point, I hadnt thought it all the way through. So what you need to do is park up on a guaranteed flat surface during the run (not sure whether one exists though to be honest), take the spring deflection readings from that point, and you should be good to go.
Although the flatness issue is a problem, if the surface isnt dead level it will mess up your sprung distribution and be a waste of time. I suppose that the garages at kyoto are probably as near dead flat as anywhere.

Just to clarify, raf file data includes the total sprung mass, and the total overall mass (both including driver), from which you can accurately derive the total unsprung mass.

It also includes dimensions from the individual wheels to the centre of gravity of the whole car (including driver). From this you can accurately derive the overall weight distribution at the contact patch.

However, from that data alone, I dont see how you can derive the individual unsprung masses.

If it weren't for a long standing bug in the raf output, we'd be able to easily derive it by comparing the vertical tyre load with the suspension deflection*spring stiffness, and working out the difference in load.

Unfortunately, the values that the raf output reports as being vertical tyre load are actually vertical spring load, so you cant do that.

Sorry about this, but you've been wasting your time. There is no way from the data we have to determine the unsprung mass distributions or the sprung mass distributions.

I needed to have some kind of figure for sprung mass distributions to do any kind of calcs for the suspension analyser (ie you need a figure for what mass is on your spring) so I just had to take the unsprung mass distribution as being 50:50 in the absense of any other data to derive some usable sprung masses.

So unfortunately, because you've taken the sprung mass figures as gospel, all thats happened is that you've proved to within 0.1% that I'd assumed an unsprung mass dis of 50:50. Which I had.

Yeah, you may as well leave it on fella.. If you have a 70hz monitor refresh there is no earthly reason to have your fps any higher. This isnt quake where the physics bugs are fps dependent.

Quote from Bruce Saltzman :

We at AUTOSIMSPORT have felt for some time that the LFS community has not been adequately represented in our magazine...

Its funny, as i've always thought the same thing. So its great that you are looking to rectifiy it.

Quote from Vain :

Like every other driver: With sense and feel.
I thought about using the analyser, but it removes the magic from the setups. It's just "the best" * values everywhere and no more. That's why I make my setups without the analyser. I'm propably slower that way, but I don't think I need to be the fastest to have fun .

* Of course the setups out of the analyser aren't personalized, but the setting the analyser offers has this "It's mathematically correct, it hasto be good"-effect on it.

Vain

Just to correct you, the setup analyser spreadsheets dont give you the 'best' values, they dont propose any solution, they dont work out the mathematically perfect setup. There is no such thing.
All they do enable people to make comparative judgements about the effect of changes. You still have to know what you are doing to make any use of them, and you still have to know what effect you are trying to acheive. I'm not sure if you are talking about the same analyser to be honest, because the only place mine even begins to 'propose' a value for something is the critical damping values, and they are just really for guidance and comparison.

Of course, if people prefer to do there setups entirely through intuition, testing and telemetry I completely respect that, I just wanted to correct a misrepresentation of what the analyser actually does.

For anyone that wants them the analyser spreadsheets are over at the old RSC forum, in the 'Unofficial Add-ons' section, and there is also a table of S2 car values that you can paste in to get an approximate analyser for S2 cars, although there are greater innacuracies for S2 due to the new suspension modelling.

Quote from thisnameistaken :

I couldn't see any way to get the car to understeer less while trail braking, but oversteer more when adding throttle on exit

But understeer less and oversteer more are the same thing, and the reason you cant do that is because those two transients are the direct opposite of each other. So whatever effect your damping setup has on one transient, it has the opposite effect on the other transient, so the best you can do is set it to be balanced during both and add your oversteer that you want with a spring/arb setup.

I suspect the behaviour you describe as a problem is more do with brake balance and driving technique during trail braking (the only way you really understeer during trail braking is if you are locking or near locking the fronts), and diff setup or basic balance under power. I wouldnt try and solve it with dampers.

This might be a bit complicated but if you know how to set up a local working version of apache web server and php (google easyphp, winLAMP or XXAMP), you could download the unofficial hotlap chart source, set it up then just upload each SPR.
Because that was written before S2, it will use the screen name rather than licensed name.
Downside is you'd have to get people to run in hotlap mode, and do HLVC laps, so maybe its not really a goer.

I think its a good idea as an option. I'd probably turn it off myself though as its pretty easy in LFS to check your damage. Just one button that I have mapped to my wheel anyway.
ISI sims could really do with this though, cycling through that bloody LCD display to find it is highly distracting (although no doubt someone will tell me you can bind a key to each screen).

Havent read the whole thread so I'm not sure if this is useful, but RAF gives you X, Y and Z position at 0.01s intervals so velocity vector is pretty easy to calculate for each timestep.

Keep up the good work guys, Its a shame I dont have much time for this stuff these days.

I have a PHP script which extracts everything out of raf files and can be edited to work out any custom extrapolations of data from the basic raf data. Its not public because obviously it would enable easy reading of the setup data in a raf file, but if you would find it useful, PM me and I'll chuck it over.

Just a note about the unsprung mass calcs, I doubt that the total unsprung mass/4 = unsprung mass at each wheel, as unprung mass tends to be different at each end, depening on the drive train of the car. Scawen has never confirmed it this is modelled or not, but its on the big-old-list-o-cardata we asked him for a while back.

Also, me and bob have got tables of raf extracted car data for S2 cars, so you shouldnt need to go rummaging through all the raf files too much.

http://forum.rscnet.org/showpo ... =2747487&postcount=79

That post has a zip with a spreadsheet with everything we've got so far, might be of some use.

Last edited by colcob, Fri, 13 Jan 2006 09:36.

Yeah, ISI sims generally seem to be set up by default with major plough on understeer, even in RWD race cars.

Yeah, this is all true. But as for the Top Gear test, firstly I doubt that the GT4 time is all that close to reality anyway, I know it reckons its a simulator but its not that close.
Also, Laguna Seca has to be one of the Biggest Balls Required tracks out there. Approaching the crest and braking for the corkscrew was pretty terrifying in SCGT 5 years ago, I cant imagine how much nerve it takes to go in there on the limit in real life.

http://www.autosimsport.com/poll.php

Lets get LFS up there folks. Then maybe FILSCA will start taking LFS a bit more seriously.

God guys lets just stop feeding the troll (yeah, yeah, I'm just as guilty). Dethred just gets off on being an internet troll and winding people up. He's been doing the same thing on these forums and RSC for years now. Maybe its time for the silent treatment.

Okay Deth, lets do this nice and simple seeing as you obviously have difficulty with basic maths and logic.

The logic first then:
Is a person racing the demo a racer? Yes. Is a person racing in a private server a racer? Yes. Is a person racing S1 a racer? Yes.

And now for the maths:
Number of S2 racers + Number of S1 Racers + Number of Demo racers = Number of racers.

If you have an S2 license, can you go and race with any of those people (except private servers obv.) ? Yes.

So how exactly have you been misled? Anyone is free to go to LFSworld and see exactly who is online at all times and what versions and servers are online.

Okay. I think I get you. You obviously know substantially more about this kind of thing than me.

Quote from Shotglass :

for a valuable spectral analysis the ideal road would be one that has bumps at all frequencies (or at least at all frequencies up to half the sample rate at which you measure spring deflection) in essence a white noise road surface

I dont necessarily agree with that, as a real road almost certainly doesnt have uniformly distributed bump frequencies up to 50hz, but probably has certain characteristic bump frequencies that might be worth taking account of. Only guessing though.

Quote from Bogey Jammer :

edit: your post frozen me colcob :melting:

Um, I'm not sure what you mean, but I'll try and explain it a bit better, I was in a rush last night.

Firstly, I dont think its a waste of time what you've done, I'm sure that this kind of analysis can be useful, but filtering and interpreting the data is probably something that only gets taught in third or fourth year of a auto engineering degree course, so its going to take us a while to work it out from scratch.

To try and explain a bit better what I meant, imagine the following:
A car is driving a course on a perfectly flat level surface, so the unsprung mass, ie the wheels and some suspension components, do not move vertically at all.
The Sprung mass, ie the chassis, moves around on the suspension and induces changes in the suspension travel.

In this situation, an FFT analysis of the suspension velocity will show you something about the natural frequency of the suspension and any harmonics.

But in the real world, the road surface has small high frequency bumps, large low frequency changes in elevation and everything in between, which all induce changes in the suspension travel, even if the car is driving in a straight line at constant speed. So all of those oscillations feed into the suspension travel data, and add frequencies to the resulting FFT plot.

But thats not necessarily a bad thing, because we only really care about how the car drives in the real world, and handling those bumps and elevation changes is one of the main problems behind suspension setup.

It would be interesting to see plots from a short section of straight from 3 different tracks, in the same car with the same setup, to see if this picks up noticeable differences in the dominant frequency of bumps on the different tracks.

This could actually be useful data for car setup, as say you know that South City has predominant bumps of about 5hz in a braking zone, it might be a bad idea to have a front suspension frequency of 2.5hz for example.

Thats all getting pretty hypothetical, particularly as the bump frequency depends entirely on how fast you drive over them, but you get the idea.

Just a few quick contributions from me, its past my bedtime.

Firstly, Spring frequency doesnt change with load transfer as I understand it, its certainly not the case that weight transfer changes the MASS resting on a spring, it just changes its current load, therefore should not influence frequency.

Also, I presume your input data was suspension travel. Now what we call 'suspension frequency' is actually the frequency of the sprung mass resting on the suspension under gravity.
But a measurement of suspension travel doesnt just contain data about the movement of the sprung mass, it also contains data for the movement of the unsprung masses, and without incorporating data about the absolute z-position of the two masses, its impossible to separate the two in the suspension travel data alone.

So your graphs are a bastard child of spring mass frequency and unsprung mass frequency, and probably tell us as much about the bumps on the track as they do about the suspension. Although even that data is distorted by the fact that all the bumps will have been run over at different speeds.