Car handling issue - Massive understeer

Discussion in 'Car Modding' started by Outl@w, Apr 26, 2020.

  1. Outl@w

    Outl@w Registered

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    Hoping someone can help as ive had this issue for a while and havent been able to solve it.

    Ive modded a few cars into the game now and I keep getting the same issue, and im not sure if its tyre, aero, or chassis related. My cars seem to have massive understeer issues which doesnt seem to go once the car/tyres have warmed up. There must be something Im doing wrong. Is this an issue anyone else has had and how is it fixed?

    The cars at GT cars, only weighing between 900-1200 so shouldnt be handling this bad. Ive been using the new tyres from the S397 database and a rough base from the Nissan GT1 for most other files, but most have been changed. HDV values have been updated from RF1 using the online tools, Ive tried different tyres, different aero settings and I seem to have made little difference.

    Thanks and any help appreciated.
     
  2. Lazza

    Lazza Registered

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    If you press Ctrl-D once or twice do the tyre loads look ok? (in line with the weight distribution)

    You can also see front and rear downforce on that same display, so check that at speed as well to make sure you don't have an imbalance.

    *further edit: there are really many many things that could cause issues, if you're modifying from the same base each time then obviously that suggests something is being missed or isn't suitable for the type of cars you're doing. Though generally I'd expect understeer more when modifying from an open-wheeler base, because the front wing downforce is often height sensitive and GT ride heights are much higher. But you want to make sure TGM and .tbc tyre sizes match (the loads should confirm that), the suspension isn't somehow broken (again loads will confirm), and then make sure aero makes sense - front wing and diffuser would be the main trouble areas there.

    If you're doing multiple cars, and especially if they're similar, I would strongly recommend using the physics spreadsheet as a base. It takes quite a lot of work to set it up the first time (and it starts with the FISI2012 physics, so definitely some values not suitable for tintops) but it prevents file link or math problems once it's done. The online tools look convenient but it puts the onus on you to make sure everything still makes sense as a package.
     
    Last edited: Apr 26, 2020
  3. mantasisg

    mantasisg Registered

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    It shouldn't be very difficult to find potential cause by looking at physics files, if it really is massive unrealistic understeer.

    If its tires, then could be too low friction, or some real time section value super off, such as super weak bristle spring. If it is Aero, then it is either front end lift, or massively higher rear downforce than front. Could be crazy CG weight distribution. Could be locked differential combined with other things. In general things can get combined and create an effect. It could be that your suspension is crazy stiff at front compared to rear. Could be that something is wrong with suspension travel. Could be that something is messed up with steering. Could be somethign wrong with chassis.ini, inertia stuff.. then it is more tricky.

    My first guess is to check steering wheel rotation setting vs wheel lock to lock angle. Perhaps it just turns in like mad.
     
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  4. TheBigDawg

    TheBigDawg Registered

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    Hey dude if you wanna package them up if they are driveable and send them my way through pm I'll drive em and see what the issue is better for ya
     
  5. Outl@w

    Outl@w Registered

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    Thanks for the replies. The issue I have with the cars is that when you take corners they just feel like they dont respond well and understeer. Even when your in the pits, if you turn side to side like your warming the tyres, the car scrubs and doesnt turn immediately, like a car should at low speed and like most if not all cars on RF2 should.

    The main issue I have is that Im not sure what the values should be or what are good values. I did Ctrl+D on one of the cars and stationary, and the loads on the suspension work out to the weight of the car, and are spread between all four corners. The aero is a lower value on the front then on the rear, as I would expect, but they are fairly close in value, different by 1500N. I believe that the inertia of the car is correct as I had it at the wrong value a while ago and its since been changed.

    @mantasisg - Is that the steering values in the control section of the HDV? Below are the settings if you can see anything obvious.
    NominalMaxSteeringTorque=10
    TurnsLockToLock=2
    SteeringShaftBaseLeft=(0,0.172778,-0.6725)
    SteeringShaftBaseRight=(0,0.172778,-0.6725)
    SteeringShaftAxis=(0,0,-1)
    SteeringInnerTable=(0.36429,0.160,-0.6725):(-0.20371,0.160,-0.6725)
    SteeringInnerTable=(0.20371,0.160,-0.6725):(-0.36429,0.160,-0.6725)
    SteerLockCaption="WHEEL RANGE (LOCK)"
    SteerLockRange=(23,0,9)
    SteerLockSpecial=(0,"240","(7.7) deg","TurnsLockToLock=0.66667;SteeringFraction=0.333333")
    SteerLockSpecial=(1,"270","(8.6) deg","TurnsLockToLock=0.75;SteeringFraction=0.375")
    SteerLockSpecial=(2,"310","(9.9) deg","TurnsLockToLock=0.86111;SteeringFraction=0.430556")
    SteerLockSpecial=(3,"360","(11.5) deg","TurnsLockToLock=1;SteeringFraction=0.5")
    SteerLockSpecial=(4,"380","(12.1) deg","TurnsLockToLock=1.05556;SteeringFraction=0.527778")
    SteerLockSpecial=(5,"450","(14.4) deg","TurnsLockToLock=1.25;SteeringFraction=0.625")
    SteerLockSpecial=(6,"540","(17.3) deg","TurnsLockToLock=1.5;SteeringFraction=0.75")
    SteerLockSpecial=(7,"630","(20.1) deg","TurnsLockToLock=1.75;SteeringFraction=0.875")
    SteerLockSpecial=(8,"720","(23) deg","TurnsLockToLock=2;SteeringFraction=1")
    SteerLockSetting=8

    Ive had a look at the physics spreadsheet before and its very confusing and im not sure if I have all the values to enter to change enough on the sheets, especially as the car is from GTR2 and bits I converted over to RF1 before.
     
  6. Lazza

    Lazza Registered

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    @Outl@w do the wheel toe angles (also in devmode) look correct? The HDV steering entries need to match the suspension, if they don't you can end up with strange steering angles and behaviour. So make sure the toe is correct (each wheel should be about half the setup 'toe' value).

    1500N difference between front and rear downforce? How much total? That could be quite a significant difference...

    Are you sure the tyres are scrubbing at low speed? Do the tyre displays show them heating up?

    Finally, are you sure the .tbc radius matches the TGM effective radius (middle node Y position, multiplied by the [Realtime] SizeMultiplier)? (Ctrl-T [I think] switches between TGM and .tbc when in the car in devmode. When you press it the car shouldn't move. Check from an external cam)
     
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  7. Outl@w

    Outl@w Registered

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    @Lazza I havent had chance to look at the tyre ingame yet but....

    At 168mph the front downforce was 5078.93N and the rear was 6567.14N, so that was the 1500N difference between them.

    The wheel toe angles in dev mode were FL 0.00 FR -0.06 RL 0.11 RR -0.11
    Caster FL -3.49 FR -3.44 RL -2.80 RR -2.74
    HDV entries
    FrontToeInRange=(-0.4, 0.05, 11)
    FrontToeInSetting=6
    RearToeInRange=(-0.1, 0.05, 11)
    RearToeInSetting=3
    LeftCasterRange=( 3.75, 0.25, 17) // front-left caster
    LeftCasterSetting=8
    RightCasterRange=(3.75, 0.25, 17) // front-right caster
    RightCasterSetting=8

    And when you say "The HDV steering entries need to match the suspension," matching values in the chassis file? Or values in the suspension section of the HDV? As theres no suspension file. Or values that are produced ingame? As one of the other cars has both front wheels pointing inwards at the moment which im sure was caused by the steering HDV but I cant remember how to solve it (last time I did it was a year or so ago)

    Thanks
     
  8. Lazza

    Lazza Registered

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    Is that in line with your design goal? If the car is front-heavy, that extra rear downforce will help produce understeer, but it might be correct - depends on the car. Presumably you have some guide figures you can check against.

    Fronts look ok there, steering obviously not quite centered but main thing is they aren't both -2.50 or something :p

    'Suspension' these days means chassis file. It used to be a .pm file. That chassis file defines where the steering arms end (at the steering rack) and that needs to agree with the HDV steering entries. When you get those wrong you end up with a pigeon-toed car or worse, as you say. If doing things completely manually I'd consider using the old steering entries as a placeholder (so you basically just define the amount of steering rotation) and let the game make a basic steering rack until the geometry is sorted, then you can do the proper new steering system - but if you're happy to do it manually or have a spreadsheet or similar to help, that's fine too.

    The other link there is making sure the inner ends of the pushrods in the chassis file (relative to the relevant subbody) agree with the HDV pushrod entries for each wheel (relative to the wheel), but your toe values look ok.

    As you mentioned low speed steering as well (which largely negates aero effects) I would definitely be double checking the tyre size between TGM and .tbc. After that I'm out of ideas :)
     
  9. Outl@w

    Outl@w Registered

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    @Lazza Thanks for all your help so far really appreciate it.

    Right so after much trial and error and changing the bits that youve said, the problem with the car is the aero. Ive tried the tyres, chassis file, susp and steering (control section) on other cars and they all work and feel fine. However I tried the aero and I get the massive understeer and general bad handling issues.

    Currently I have the RF2 Nissan GTR aero as a base on the car and it handles really well, much more feeling, moves about a bit and no understeer. The issue with that is it is obviously not the proper aero for the car. Ive tried entering the values manually in the HDV file, changed the values that I have from the RF1/GTR2 files and I get the same understeery issue. Ive even tried just changing the main wing base, and range values and then I have barely any aero at all. So..... what should I be looking for to change, and I suppose whats the main difference between the RF1 values and RF2 values that would cause this issue? (Apart from the many more entries)
     
  10. Lazza

    Lazza Registered

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    If you basically copy values from rF1 I think most of them should transfer directly. This would mean leaving the newer rF2 parameters on zero so they don't do anything weird.

    From a modding standpoint the two main trouble areas for understeer are the FWHeight parameter and the diffuser values - the first because it can create a very sensitive response to ride height (which can vary even between otherwise similar cars) and the second because it's not always clear what it's doing. But if you're transferring values this shouldn't be so much of an issue.

    Start simple. Zero everything, transfer a bit at a time, see what downforce you get. You should have some sort of target figures (even if that's from telemetry data gathered in rF1) so if the front or rear goes wrong you should be able to correct them - either by multiplying the base and per-setting values (FWLiftParams) by 1.x for the front wing (so increase those values by the same proportion, keeping the settings intact) or by multiplying all the diffuserbaseplus values by some constant.

    On the diffuser I think rF1/GTR only has base and 1st/2nd order downforce for the diffuser, rF2 does base/half/1st/2nd. So for a transfer you want that 2nd rF2 value to be 0 (FWLiftHeight might be the same; you should notice a difference in parameter names). If you're unsure of any values you should be fine to make them zero for now - that's better than leaving in figures that create strange behaviour (diffuserrake comes to mind). Also be aware of the force distribution parameters in rF2 - these allow you to define how much aero goes to which subbodies, check the skipbarber hdv for examples. If you end up with wrong values there you can have strange things like the front wing giving downforce to the rear of the car, for example.

    And since all aero (well, front wing and diffuser) is sensitive to ride height, make sure your operating ride height is correct - if not that might indicate an issue with travel, motion ratio, or stiffness.
     
    Last edited: Apr 30, 2020
  11. Outl@w

    Outl@w Registered

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    Changed all the values and left the ones I havent got at zero and car feels much better, thanks for your help. Found that it helps making sure that the FWSetting needs to sit inbetween the FWRange as well which it doesnt seem to be in most GTR2 mods. There is a massive different between the downforce produced on the front wing and the downforce on the rear wing, but adjusting the FWLiftParams has solved that too.

    Are there any of the RF2 settings for the aero that are important or that help improve the feel of the car? If so as I dont have any of the values for them are they able to be produced in the physics spreadsheet or do I need to have the values avaliable?
     
  12. mantasisg

    mantasisg Registered

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    There are various aero forces that you can adjust for various directions of motion for every "device" - front, rear, body, diffuser - there are more iiric. Also there are these interesting values for inertia added up with aero. Also all the aero stalling parameters for yaw, sideways, rideheight... all of that is incredibly meaningful for handling, and definitely affects the feel. Of course downforce or lift is probably making most feel difference, as you get different wheel loads and grip with that. Also changing aero balance is meaningful thing. But I suppose only good drivers are able to feel aero.
     
  13. Outl@w

    Outl@w Registered

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    Yeh thats good ill try have a look at those sort of things once ive sorting the other bits and pieces with the graphics for the mod. Be a bit of trial and error I think with those values.
     
  14. Chris Lesperance

    Chris Lesperance Registered

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    I was having similar issues with the DP01. I did a lot of physics things to midigate it, but was still getting some scraping. I finally figured it out last night. In rF1 and rF2, the origin of the 3d model is 0,0,0. The bottom of the car lines up with that. Well the base models for the DP01 was at -0.04. Raising that up to 0, made all the difference in the world.

    I'm not sure if this is your case, but something to confirm, as over the last 2-3 months of looking at the DP01 everyday, it was something I just noticed.
     
  15. Outl@w

    Outl@w Registered

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    Thats kl thanks ill have a look just in case. Just been doing so much trial and error with different extreme value changes just to see what things affect what. Worked out how to do twin turbos now so thats the next thing to do.
     

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