I bet it's so marginal that you'd never notice it though.
It's definitely there. More noticeable in open wheelers. If you really want to test it, take one out with a setup & on a trak you're very familiar with & crank the wind to full speed.
Hmm, you sound like you mean it affects downforce (since you mention setup and track familiarity) but I meant tyre cooling. If wind affects tyre cooling wouldn't you prove that by just leaving the car stationary on a windy day and see how long it takes for tyres to cool?
I'm sure wind must affect the handling somehow (or why have it?) but I've actually never tried high wind
Indeed. I agree worn=lighter tyres should make almost no diff to the car but a smaller rolling radius should be trivial to spot. But I think this effect is definitively absent or I'd (surely!) have noticed it by now...
Must have a play with Tweak. Where did you find it? Don't suppose source code is available?
Hmm, that explanation seems a bit fuzzy to me. For a given heat input, thinner tyres should actually overheat *more* quickly (and cool down more quickly), no? So perhaps the point is that the heating *is* less on a thinner tyre (hence we observe it's harder to keep it hot) and therefore you can drive it at a higher slip angle for the same equilibrium tyre temperature and get more grip out of it as a result.... ??
Wow. Had NEVER spotted that the tread bars get thinner with time. Sheesh. Could have sworn I'd read that Wiki page properly before; in fact the text mentions "Wear" in the section title but nowhere else... And that pic makes it seem like the Wiki authors are (like me) unaware of the wheel rim temperature being part of the tyre-temp info
And double-wow. Those graphs are superb. Something I've been wanting to find/make for ages now. Thanks a mil. Will have to have a proper look when I get home in a few days. I've been pondering how to try and automate a procedure for generating stuff like this (maybe there's a way to write an AI for LFS to drive a car in controlled circles...?). OR, WAY easier, Scawen could just make the tyre models (and other stuff like torque curves) public... (Big hint there Scawen, if you ever read this )
cmon, it doesnt make the car significantly lighter, I wonder if those few grams in revolving mass of the tyre make a difference really?
btw. Android - I reckon you took maximum points of grip vs. slip. Do you maybe have bundle of graphs for the type of tyre - grip vs. lateral force at given temp to see not the optimum tyre temp but the characteristic of the tyre at given temp? Just curious.
well, it is not symmetrical - lots of heat in couple of seconds in the corners and cooling down on straights. So the shorter transition the easier optimum equlibrium to achieve. And I will have to do this test to see if my feeling that tyres cool down too long has some points.
Now that I think about it I'm not so sure about the weight reduction anymore, since as you've all pointed out the difference would be minuscule.
However the radius of the tyre changes and that is even quite easy to verify. Simply make a setup with ridiculous brake strength, get some speed on a straight and mash the brakes to create an enormous flatspot. Instead of being a real flatspot, LFS simulates this (rather poorly if you think about it) by wearing down the affected tyre pads. If you then drive very slowly - preferably in wheel-only view - you'll see the tyre bounce up and down as it rolls over the worn-down pads/section. Actually, this is what I'm talking about:
No idea about Tweak though, I haven't been keeping up with LFS for quite some time now. Heh, two seconds later I find this.
@AndRand: I don't have the source graphs for that anymore, no, though I don't believe the heat changes the grip characteristics much at all. It seems to be more of a static grip modifier scaling the grip/slip curve up and down the G-force axis.
What makes quite a difference is tyre air pressure relative to the weight of the car. At low weight/high pressure the rising grip line to the peak/plateau is steep and the transition sharp, whereas a high weight/low pressure the grip rise is flatter and the transition much more gradual and smooth.
- This is how a grip/slip curve looks in LFS in general. Note that these are all lateral grip curves - the longitudinal grip curve looks pretty much like the pre-U lateral curve to the right.
- Here I found an old tyre pressure grip curve comparison, see that on a high pressure the grip peaks at about 6° slip whereas on the lowest pressure it reaches the maximum at about 10°. The difference visually doesn't look too great here mainly because the line was probably taken with the FOX, which is pretty lightweight so the tyre pressure had less of an effect.
I know you meant cooling. I suggested the open wheeler because there is more exposure to ambient air, and the velocity thereof is not shielded by a wheel well. I suggested the setup/track familiarity because if you are real comfortable with it you'll notice that your heating/cooling cycles are noticably modified by a high wind setting.
Wow, never noticed that. But I guess it doesn't modify the circumference? In other words, what I'd have expected to notice already if it's actually happening is that tyre wear would then raise the RPM for top speed on the straights. Since I've not noticed it (many of my sets would redline with only a modest increase in revs) I had assumed it was absent, but come to think of it I'm notoriously good at *not* noticing things
Nice. Look forward to trying that when I am reunited with my wheel... (I'm so bad with a mouse it's pointless!)
Wow, more lovely data to digest! (Btw, does the RAF file give you access to the tyre wear data?)
I'm most surprised that the lateral grip doesn't drop at high slip angles - I guess this is what Scawen meant about the grip being too high at high slip? Much more pronounced than I had imagined - it really doesn't drop at all. Weird that it was "better" in the older patch (by which I mean that I believe the more physically realistic one to be the one that falls beyond the peak, rather than having a plateau). [Edit: but the longdit. grip does fall at high slip you say? Scratches head....]
And I'm intrigued about the high pressure effect. Modest drop in grip at high pressure, big drop in slip angle required to get it. This should presumably make the car more driveable too? (Not to mention shorter time constant, thus more crisp anyway...)
Aha. Well, I will give it a whirl, but I would have thought that even a high wind will pale into insignificance compared to a race car's average speed around just about any track. The downforce will be affected as it scales with the square of the total air speed on the wing, but the cooling effect (he says confidently ) should I think just be linear with speed.
Errr, the bumping is a direct result of one section having a smaller radius than the others. Of course if all sections are worn the wheel diameter and with that also the circumference decreases.
Theoretically, if you have a tyre with a radius of 30cm (23.62'' diameter) it needs to rotate at 884.19 RPM to achieve a wheelspeed of 100 km/h. If you wear down this tyre by half a centimetre to 29.5cm radius, the required RPM increase to 899.18, or if you rotate the worn wheel at the same RPM required for a non-worn one, the wheelspeed will be 98.33 km/h.
However, do note that the speedo in LFS works by measuring the speed at the differential / wheels and simply assumes a certain tyre circumference to calculate the actual speed (like real cars do). If you drive a car in 5th gear at 5000 RPM the speedo will always display the same speed regardless of how worn or inflated the tyres are. Now if you had a GPS like system that showed your actual velocity, it would be clear that you're actually moving at a different speed than the speedo displays with worn or differently inflated tyres.
I am a bit surprised. First, I thought grip curve is symmetrical in both directions (3d chart with grip circle would be interesting ), second, I will try to do the tests - with temperature rise the grip curve should not only move higher but also shoud get less steep, so the transitions are softer, similar to lower pressure effect but with less deformation, thus better control, right?
so to simulate this could two people hop on a server, and get the xrg, and the xrt (so the xrt can definately keep up and check speed) set a quite low ratio for both, test top speed of the XRG, let the tires cool down, then do a burnout until the tires are about to explode let them cool, do it again, let them cool once more, then test the same speed?
The smaller circumference certainly doesn't help you achieve better laptimes.
However when the tyres are worn down likely following things happened:
1) You drove for a quite long time and are more likely to be "in the zone"
2) The tyres have less heat capacity, cooling down from the usual overheat phase thus enabling you to go faster after having to drive careful
3) Your fuel level is lower than on race start
4) The tyres behave differently somehow (???)
Er, yup, I know that I'm just saying that LFS isn't necessarily going to model both a height change AND a circumference change due to the thinner piece of rubber. My best guess (but it IS just a guess) is that LFS does not model the circumference change.
A useful reminder - I think I had probably forgotten that LFS uses the axle/diff speed.
However, it wasn't what I was getting at anyway - I didn't say I expected to see a higher top speed come up on the speedo, but that the revs for top speed should be different.
The real top speed (if the limiter doesn't kick in) would be approximately the same with a smaller rolling radius, as it's decided almost entirely by aero drag, with the main thing causing a slight change in speed being the modest change in engine power at the new, higher engine speed.
But in a setup which has max speed sufficiently close to redline revs, I was thinking that the car might actually hit the limiter... But in fact maybe you'd need to use an analyser to see the difference, if it is only a couple of percent or so (2% means only 140 RPM at 7k RPM).
I think I'm going to check this out next time I wear my tyres down a lot
FWIW, my money's on number 4, if the "worn tyres are better" hypothesis is correct at all.
AND, I've just realised that your super-cool tyre data-gathering technique could actually help prove what's going on here
All one would have to do would be to test a tyre when fresh and then again when worn down almost to the canvas and compare the grip/slip data.
Now this won't necessarily reveal the effect I mentioned earlier - that a tyre may get heated less for a given cornering force (due to less mechanical work being done in the thinner rubber layer, due to less distortion). But it should certainly show up any "magical" extra grip which is appearing at a given slip angle.
(It might even reveal the reduced heating too though, I guess.)
You can always change FinalDriveRatio I think it is neglectable... maybe the mass of the tyre changes, which placed at the end of the tyre radius (we are talking about less than 1cm change) can make a slight difference, but... very very slightly
Of course doing a RAF extract of the worn tyres could bring some light into that, but... the problem is to acquire worn tyres in the first place. Heating them or changing pressure is something that can be done in a minute, but wearing them down is a far more daunting task.
The easiest way is probably to let the AI drive lots and lots of laps on a balanced and not too difficult track, though if the AI pits for refuelling or crashes (doing a reset) all the wait would've been for naught. Even if it succeeds and wears down the tyres, it could happen that it simply doesn't use the tyres in a way that provides useful data.
Anyway, did a "quick" test with one FZR AI on KY Nat, letting it drive 2hrs on R3 slicks. The maximum tyre wear was reached at about lap 35, in which it did a pitstop to refuel where it also changed the tyres. From looking at the wear of the F9 view, it seemed like it was worn about 30-35% - it was definitely over 30% though, as the AI set its pitstop strategy to change when worn > 30%.
Looking at both left and right rear tyre data (lateral grip vs. slip angle) and comparing lap 6 to lap 35 shows that there's definitely NO change in tyre behaviour by wear (as I suspected, to be honest). The curves looked pretty much 99% identical and the tiny difference can most likely be attributed to a difference in tyre temperature, air pressure and/or car weight.
Hey - nice one And the negative result isn't a bad thing - it actually simplifies matters, because I just remembered another thing (which we could call number 5 ):
The "less heat while cornering" effect I've been mentioning (or at least hypothesising, but like many people I've personally observed that worn tyres run cooler) almost certainly comes with another effect if physical realism is preserved: lower rolling resistance. Perhaps THIS could be the magic ingredient to explain why worn tyres are "quicker"?
(I should have remembered this sooner, ouch.)
How to verify it? Well, I guess it should mean that the real top speed would be higher - that might be the simplest place to look. So if you review the (actual, not speedo) straight-line speed for your AI at low/high tyre wear...
Impossible. Reading the speed would be a piece of cake, but there's no way to do a useful speed comparison on an almost full and empty fuel tank. Also there's no track on LFS where you can reach air-resistance limited top speed. The oval comes close, but not quite - even there it depends on how well you exit the last corner. Besides that, the AI absolutely sucks at the oval (it was actually braking there on the KY Nat run :doh:)
Larger tyres generally exhibit lower rolling resistance, so I'm not sure your reduced rolling resistance hypothesis necessarily holds true. Most rolling resistance comes from rubber hysteresis in the sidewalls, which should be unaffected by tread wear.
OK, scratch the terminal velocity approach - maybe it's possible to get at it a little more indirectly by checking the axle torque and car acceleration at the same speed for both tyre states?
You will also know the mass of the car (which will differ due to fuel loadings) and thus I *think* (hey, it's late ) that all the required ingredients will be available to allow us to calculate the power dissipated into the tyres?
The power to the axles (call it axlepower) is proportional to axle torque * axle speed (more precisely, it's 2 * pi * torque * axle-turns-per-second, which will give you a result in Watts if torque is in Nm). If it's the same in both cases (due to the rolling radius being identical, which might be the case) then so much the easier but it's not actually a requirement.
The power soaked up by the rate of change of kinetic energy of the whole vehicle mass (call it accelpower) is easy to calculate from the mass, velocity and acceleration. The kinetic energy is 0.5 * m * v^2, so accelpower will be
m * v * dv/dt or just m * v * a (with kg and m/s and m/s^2 for units, this will also be in Watts).
The power soaked up by the aero drag will be the same for both cases (cos same speed) and thus we don't need to know it (but the RAF file may have enough info to allow it to be calculated directly? I've not yet used a RAF analyser.) The missing piece of power is presumably being used up by the rolling resistance (if I've not forgotten anything), most of which is probably heating up the rubber. (I think??)
So if (axlepower - accelpower) differs between new tyres and worn tyres, we have our smoking gun, provided of course I've not been too hasty and missed something major (!).
Goshdarnit Bob, your objection is disgustingly plausible Not sure why a larger tyre should have less resistance, but certainly the sidewall argument seems sound.
But, maybe the sidewall distorts more with a thicker tread layer because of the extra effective leverage? (Reaching a bit here )
OK, recalling that what I'm chasing here is "if and why worn tyres are quicker *in LFS*" (i.e. not in real life), maybe another place to look hard is cornering. (This may be a lost cause! But read on if you want to indulge me...) I've watched a replay where worn tyres *may* have been the secret to carrying a lot of speed through a high-speed complex of corners. If the worn-down tyre is scrubbing less speed off, then a test for this might involve monitoring the axle torque required to maintain steady speed while cornering at a given acceleration. I'll maybe have a go at this...
(I must admit I'm doubting somewhat that worn tyres are actually quicker! But if they do turn out to be quicker, it doesn't have to be physically realistic - it can just be an (accidental) artefact of the way LFS models those rather complex lumps of rubber...)
)
), second, I will try to do the tests - with temperature rise the grip curve should not only move higher but also shoud get less steep, so the transitions are softer, similar to lower pressure effect but with less deformation, thus better control, right?
I think it is neglectable... maybe the mass of the tyre changes, which placed at the end of the tyre radius (we are talking about less than 1cm change) can make a slight difference, but... very very slightly
Not sure why a larger tyre should have less resistance, but certainly the sidewall argument seems sound.