Hi guys,
Just wanted to drop in with a bit of info. I saw today a user manual for a pretty serious formula car series meant for the engineers (can't say which cars, sorry). In it was a table of the hole patterns for front and rear wing flaps which looked much like one of the ones Hyperactive posted about half way through this thread. Note that this is adjusting the flaps only, which are the pivoting part at the trailing end of the wing. The wings themselves on this car are fixed and can not have their angle of attack altered other than by adjusting ride height difference front to rear.
There's a table in the manual showing every possible hole combination. Turns out they indeed were selected to give single degree precision throughout the range. I.e., 1 deg, 2 deg, 3 deg, etc..
It was also pointed out to me today that the wings on Indycars (at least at the time this gentleman was involved with them) the wings were infinitely adjustable via a screw. The downside is you're counting turns of the screw rather than knowing exactly what the wing angle really is without the help of a table to look at, so if you have 6.70 deg wing, then change it to 7.25, then want to change it back again to 6.70, you might wind up with 6.73 or 6.82 unless you adjust clear to the end of the screw and start over again, counting turns very precisely.
On the holey design, he also pointed out that (if the rules permit it, which in this case they don't) it would be very simple to rig up a spacer that put you half way between the holes or something like that, so instead of 1 deg, 2 deg, 3 deg, you now can choose from only 1.5 deg, 2.5 deg, 3.5 deg. So the increment would remain the same while you could choose a different spacer to offset everything by 0.5 or 0.3 degree or what have you.
I do support decimals in LFS though if folks want it, even though I don't personally need it at the moment. Both types of wings exist in real life, so this is a case where everybody is right
Just wanted to drop in with a bit of info. I saw today a user manual for a pretty serious formula car series meant for the engineers (can't say which cars, sorry). In it was a table of the hole patterns for front and rear wing flaps which looked much like one of the ones Hyperactive posted about half way through this thread. Note that this is adjusting the flaps only, which are the pivoting part at the trailing end of the wing. The wings themselves on this car are fixed and can not have their angle of attack altered other than by adjusting ride height difference front to rear.
There's a table in the manual showing every possible hole combination. Turns out they indeed were selected to give single degree precision throughout the range. I.e., 1 deg, 2 deg, 3 deg, etc..
It was also pointed out to me today that the wings on Indycars (at least at the time this gentleman was involved with them) the wings were infinitely adjustable via a screw. The downside is you're counting turns of the screw rather than knowing exactly what the wing angle really is without the help of a table to look at, so if you have 6.70 deg wing, then change it to 7.25, then want to change it back again to 6.70, you might wind up with 6.73 or 6.82 unless you adjust clear to the end of the screw and start over again, counting turns very precisely.
On the holey design, he also pointed out that (if the rules permit it, which in this case they don't) it would be very simple to rig up a spacer that put you half way between the holes or something like that, so instead of 1 deg, 2 deg, 3 deg, you now can choose from only 1.5 deg, 2.5 deg, 3.5 deg. So the increment would remain the same while you could choose a different spacer to offset everything by 0.5 or 0.3 degree or what have you.
I do support decimals in LFS though if folks want it, even though I don't personally need it at the moment. Both types of wings exist in real life, so this is a case where everybody is right
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Well, that's one more than I've posted
Relax, I'm just teasing you. I thought the slogan was pretty funny, actually Err... I don't understand what that means
Oh yes, he's very nice indeed. Much more patient and civil than I am for sure
I didn't misquote you. That was copy/pasted right from the link I popped in the post
Wouldn't suprise me in the least.
Anyway, there's no need to get defensive. I said it was clever and wished you the best of luck
Good points on both sides. On the one hand, many (most?) wings are adjustable in steps of probably a fair amount over one degree, while the screw type ones would be infinitely adjustable (dial in 1/100th of a turn if you want). On the other hand, many people want finer adjustment for the sake of better tuneability, where the handling is ruined if you go 1 degree either way.
One thing to keep in mind is that on the wings designed for a specific real car, it's probable that the available settings were given much more careful design consideration than simply allowing 7,8,9 degrees (or 7, 10, 12 for that matter). Suppose a real wing was tried with 7,8,9 degree adjustments. The crews might have found that usually 7 wasn't enough, but 8 was too much. The aero folks might provide a newly redesigned wing with 7.5, 8.5, and 9 degree adjustments.
Perhaps the guys that want the finer adjustability are really the engineers in the LFS world. Why not allow the finer adjustments for awhile, then later on pick out the fastest set of 5 or 6 or whatever settings and keep those as the only available options? Might that eventually lead to the best of both worlds?
One thing to keep in mind is that on the wings designed for a specific real car, it's probable that the available settings were given much more careful design consideration than simply allowing 7,8,9 degrees (or 7, 10, 12 for that matter). Suppose a real wing was tried with 7,8,9 degree adjustments. The crews might have found that usually 7 wasn't enough, but 8 was too much. The aero folks might provide a newly redesigned wing with 7.5, 8.5, and 9 degree adjustments.
Perhaps the guys that want the finer adjustability are really the engineers in the LFS world. Why not allow the finer adjustments for awhile, then later on pick out the fastest set of 5 or 6 or whatever settings and keep those as the only available options? Might that eventually lead to the best of both worlds?
Wow! Guess they can be that loud indeed
Thanks 
Oh, and I agree that if the car isn't supposed to be blown, it ought not to have the sound. Maybe if/when some new cars get put in they could be supercharged. I must admit that would be kind of cool
Oh, come on, rice factor?
http://videos.streetfire.net/s ... 904-b5f9-f3d0275dc7d8.htm
(Off topic here, but are the blowers really that loud from outside the car? I've heard some cruising down the street before, but not something like this at full throttle
)Oh my, the hypocrisy
http://www.lfsforum.net/showthread.php?p=289811#post289811
Funny and creative bit there though, I wish you the best
I can't say I've needed or wanted it yet, but +1 on the suggestion.
Lemme rephrase that. "A bit more"
True, although they generate a lot more in the corners. Once heated up they ought to cool off a bit down the straights.
I had dinner with the author of that book, Paul Haney, and Doug Milliken not too long ago, and Mr. Haney attended our tire presentation at the Motorsports Engineering Conference at the beginning of December (granted, this was just on our RC tire research, somewhat intended as comic relief in comparison to some of the other things going on
). Not everything in the book, including what is on that page, is entirely correct, however. Even Caroll Smith got graphs like this wrong in his "... To Win" series. (Tangent: One of the things that came up was how one might go about modelling loose surfaces for rallying and the like. Just having to do games, I got off easy with my reply )In another post I commented :
Figure 6.7 from the link above is exactly the one I had in mind when writing the above. A quick search didn't turn up that graph, so I didn't include a link to a copy of it. Anyway, I haven't seen a real force curve that looks remotely like that, ever, in any direction. Both curves there are artist's renditions rather than actual data and are the same ones shown in many vehicle dynamics texts aside from Mr. Haney's (a lot of these graphs come from old papers and you see the same ones reprinted with author's permission in all the books). The braking curves are much closer to reality (I've posted real (yet very old) data here on braking curves), but the tractive one is nonsense, at least compared to anything I've seen.
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Awesome, I had no idea and never heard this before... Thanks.
Learning
Carry on Right, Jeff. As you've experienced in your own time on the track in your racing experiences, the torque you feel on the steering wheel is not the same thing as the the corrnering force you get. There's probably a sort of middle ground there where the steering gets just ever so slightly lighter where you actually turn the hardest, no?
For others, this whole fiasco is just called aligning torque. Somebody else posted earlier (sorry, I forgot who
) that it can reverse. Yes, this sure happens. Anyway, this is all a force feedback thing :P When I'm running a sim I'm not judging anything on that at all. It is important though to differentiate between those who are and aren't... Feel..
Not really. What you're doing with a graph like this is saying, "ok, right now the slip ratio is 0.2 (20% slip), so what's the force?" Now apply that to the tire or car and off you go. The transitional area is just the part that is rolling off into the peak after the initial climb. That's modelled just fine by measuring the tire forces and duplicating them with such a graph (or more typically, creating or using a math function that reproduces all those force data points on it given slip ratio).
When measuring a real tire there is indeed some high frequency noise, but as covered in an earlier post, you won't really gain anything from including it. It might actually make the car feel a little floaty and detached.
By using more than one curve, I meant that the curve at 10 mph might look very different from the one at 50mph in reality. Really though the issue people seem to bring up most nowadays is the "hey, I can spin the wheels like crazy and don't lose any acceleration" bit. That's good that people are now focusing on this. It means the rest of everything is very good and has come a long way!
Nah, it's fun to discuss such things
As a fellow geek, I love it too
I see where you're coming from of course. Getting it proper might really take more than one curve. Also, I don't know if that longitudinal slip curve there is for braking or traction. If it's traction, what does it look like at slip ratios of 2-3 or higher? For braking, that curve looks very close to other data I've posted here and at rsc in the past, much more so than in any other sim I've seen data plotted from.
The curves that end up being spit out in my model will look different at different speeds. This will be done at a pretty low level so I can't be sure just yet what they'll look like, but they'll come about as a result of other parameters specific to the type of rubber itself and a couple other things. I haven't checked to see what a slip ratio of 3 at 5mph versus one at at 100mph will look like yet, though. And data like that is quite rare. I don't recall seeing any myself yet either
The curves that end up being spit out in my model will look different at different speeds. This will be done at a pretty low level so I can't be sure just yet what they'll look like, but they'll come about as a result of other parameters specific to the type of rubber itself and a couple other things. I haven't checked to see what a slip ratio of 3 at 5mph versus one at at 100mph will look like yet, though. And data like that is quite rare. I don't recall seeing any myself yet either
There is a drop in grip at high slip ratio. Said that a few times now. My point there was that the shape of the curve is not like what you see shown in many places where at 10% slip you have grip of 1, then at 20% or 30% you have something like 1/2 or 2/3 of that at low (or any) speeds. What about at 1000% slip? Sure, there's likely to be a big drop there.
"Dropping back significantly." Yes, of course. But how much grip have they lost there? Are they at 50% the normal grip? 70%? 90%?
I agree that in LFS the wheelspin off the start should probably give less grip than what you currently get. Depends on the tire and especially the rubber compound though. Some don't change a whole lot at high slips unless they're getting really, really hot in the process.
"Dropping back significantly." Yes, of course. But how much grip have they lost there? Are they at 50% the normal grip? 70%? 90%?
I agree that in LFS the wheelspin off the start should probably give less grip than what you currently get. Depends on the tire and especially the rubber compound though. Some don't change a whole lot at high slips unless they're getting really, really hot in the process.
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The deal with starting a race is that the slip ratio curves are not really fixed. They're quite speed sensitive and vary with time and temperature. When you're nearly at rest and spin the wheels you may very well have a slip ratio of 10 or 20. While it's tempting to try to extrapolate out a longitudinal force graph measured at 60mph from a slip ratio of 1 out to 10 or 20 and say "this is about what the force must be at 5 mph with a slip ratio of 10 or 20," it doesn't really hold true. If the measurements were really made at that very low speed at extreme slip ratios, that would be another story.
I don't recall ever seeing any data out to slip ratios of 10 or 20 or anywhere even close to that. Usually that's not an interesting thing for whomever is paying big bucks for the tire testing so it just doesn't ever probably get investigated. Additionally it's rather difficult to really test things in slip ratio much past the peak on acceleration.
I have plans for a way to model all this and got a thumbs up on the ideas from a couple of guys that do a lot of tire testing, but am not prepared to describe how that will work publically any time soon. Sorry to be a poo about it, but this one is where folks will have to do their own research.
Some curves you see in books or online under tractive, positive slip ratio (acceleration rather than braking) show a curve that climbs up to a peak, then suddenly and very quickly swoops down to 60-70% of the peak value and flattens out. You'll see something similar in some sims and folks will emphatically insist that that's how the tires really work. They don't. Real curves look a lot more like the LFS ones than some of these other ones floating around.
Case in point: Have you seen the super slow motion tire video that's been floating around showing drag racing tires? At very low forward speed right at the start there is actually quite a significant amount of slip. Those big drag tires may not be the same animal as others, but it's probably not unreasonable to say that there is a period of time there in at least one of those clips where the slip ratio was as high as 3 or more. If they were losing grip they wouldn't be operating the tires that way. However, at much higher speeds they do indeed lose a lot of grip if the slip ratio goes up that high.
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Tires do generate quite a bit of noise during these tests. The graphs that you see published are processed to average/cancel out the noise. I can only recall one pure data sample that's online somewhere (no link handy atm, sorry), and the fluctuations were on the order of maybe 2-4% or so. However, they're very rapid so in the end for all intents and purposes you are essentially running the processed curves anyway.
A sim doesn't lose anything from leaving out this noise. I'm not aware of any vehicle dynamics simulations that make any attempt at duplicating it all. There are other unknowns with the tires, the chassis flex/compliances, etc., that are much more significant than tire force noise.
Ah, real research and test data found Carry on 
Edit: Interesting quote from your link:
"The authors in [5] develop a nonlinear estimator which consistently returns true parameter estimates in simulation to within 3%. The accuracy afforded by the new estimator structure motivated the experimental characterization of the relationship between tire inflation pressure and longitudinal stiffness estimates. This current work goes on to characterize the influence of tire inflation pressure, normal load, tread depth, frictional heating and surface lubrication on longitudinal stiffness and effective radius for two different types of tires. "
And this was freely available on the web, go figure Bet it took all of a couple minutes to find this little tidbit, eh?
Anyway, this is science. This is the difference between real data being used and folks adjusting and fudging and manipulating things to make them "feel right," which has no bearing whatsoever in determining what's realistic from an engineering point of view (and is really the mortal enemy of the real racing industry, where very often all anyone is trying to do is figure out why the car *doesn't* feel right or do what they thought it should be doing all along.)
Science doesn't work that way, and neither does your car. As perhaps illustrated above, there is some rather serious thought given to this sort of topic by folks that aren't quite the epitome of stupidity
Great find. Read it and then read some more and keep looking. The stuff you want to know is available out there online
Looking forward to reading the debates this generates and seeing more folks dig up food for thought!
Carry on Edit: Interesting quote from your link:
"The authors in [5] develop a nonlinear estimator which consistently returns true parameter estimates in simulation to within 3%. The accuracy afforded by the new estimator structure motivated the experimental characterization of the relationship between tire inflation pressure and longitudinal stiffness estimates. This current work goes on to characterize the influence of tire inflation pressure, normal load, tread depth, frictional heating and surface lubrication on longitudinal stiffness and effective radius for two different types of tires. "
And this was freely available on the web, go figure
Bet it took all of a couple minutes to find this little tidbit, eh? Anyway, this is science. This is the difference between real data being used and folks adjusting and fudging and manipulating things to make them "feel right," which has no bearing whatsoever in determining what's realistic from an engineering point of view (and is really the mortal enemy of the real racing industry, where very often all anyone is trying to do is figure out why the car *doesn't* feel right or do what they thought it should be doing all along.)
Science doesn't work that way, and neither does your car. As perhaps illustrated above, there is some rather serious thought given to this sort of topic by folks that aren't quite the epitome of stupidity
Great find. Read it and then read some more and keep looking. The stuff you want to know is available out there online
Looking forward to reading the debates this generates and seeing more folks dig up food for thought!
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Put a tire on the ground facing forwards so it will roll away from you if you push it. Now, drag it sideways to the right. The tire is operating at a 90 degree slip angle. There will most certainly be a force to the left
The confusion here in the thread seems to be because some are talking about slip angle in the car's reference frame, while others are speaking of it in the tire's.
Tire lateral force curves like the ones the OP posted are lateral force in the tire's plane, not the car's. In the car's reference frame of course increasing slip angle beyond a point will reduce lateral force on the car right down to 0 at 90 degrees slip angle. However, the tire is indeed producing full lateral force in its own reference frame (the tire plane), only now it's acting to slow the car down in a real hurry.
Here's a fancy version of what you posted from some real tire data:
http:/performancesimulations.com/files/tire2.JPG
When I talk about lateral force, I'm talking about it in the tire plane.
It should look very much like the LFS curves in general. The only tires I've ever seen with any significant drop off after the peak in lateral force are big truck tires (even in the dry) and other tires on the wet. Even a street or racing tire in the wet doesn't drop off as much as the curves that were posted originally as an update. Big truck tires from semi trucks and so on do though.
Try googling "tire lateral force curves" or something similar. There are plenty of examples out there. Just make sure you know for sure whether you're looking at a real set of tire data or an artist's rendition of what they think tire data looks like. Unfortunately most text books are chock full of bogus curves which is probably what led to all this misunderstanding in the first place. Also, make sure you know whether you're looking at dry or wet test data when you find it.
Longitudinal curves generally do indeed drop off somewhat at high slip ratios. It's highly speed sensitive though so it's tough to say, and this sort of data is even more rare than lateral force data is. However, it's fairly predictable how it will vary, but I'm not going into that aspect of tire modelling here. :shhh: Sorry
The LFS curves look quite good though in longitudinal as well as lateral. I wouldn't change much, and if I did, you'd barely notice it in sim anyway. It's that close
They don't change with chassis adjustments other than camber. When you change the springs or something like that you change the loads on the tires, but the 1000 lb load 0 camber curve still looks the same. Only now maybe you're at 750 lb load instead of 1000 because the ARB has been tweaked.
In reality, yes, they change with tire pressure. They do in LFS too, although I don't know exactly how they do so. In general it seems to be in the right direction. Increasing pressure seems to increase cornering stiffness (the curves rise more quickly at the beginning and peak at a lower slip angle), at least that's how it seems to me to work in LFS.
They'll change a bit from lap to lap too, yes, but my point was the curves in LFS look much, much more like real tire curves than in any other sim I've seen curves plotted from.
If the tire is in contact with the road there is friction, always. 100% slip (slip ratio = 1) means that if the tire's free rolling speed was 30kph, it's rotational speed is 60kph. I.e., it's spinning at twice the speed of free rolling. There is most certainly plenty of force being produced. It doesn't vanish to 0 in any case except when it is no longer in contact with the ground.
LFS tire force curves are much closer to everything I've seen in reality than the OP's suggested curves, which as axus pointed out, look very much like Simbin/Blimey's curves. LFS curves are the closest thing to reality I've seen in a sim. Granted, I haven't seen what Papy's curves looked like with their Nascar stuff, but in the rFactor/GTR/GTR2 vs LFS debate, LFS wins hands down. Their curves actually look like somebody bothered to do some research into tire operation
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Yeah, it's kind of a shame, really. There were a lot of servers running it when it came out, but not so much now. I love the car
Awesome, Tristan, thanks for sharing that. I love watching your videos.
One question: Is the diff whine really as loud as it sounds there or is that a microphone placement thing perhaps? If it's a microphone thing, where was the mic?
Thanks. Looking forward to more vids of you running around in anything for sure
FGED GREDG RDFGDR GSFDG