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Thread: [Magic inside!] Need Help With Differentials

  1. #101
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    Thanks..... good to know......!!!! So..... when tuning better start with the preload ang then with the rest of the differential.... possiblly....

  2. #102
    GTE Pilot hkraft300's Avatar
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    Quote Originally Posted by sillib View Post
    Thanks..... good to know......!!!! So..... when tuning better start with the preload ang then with the rest of the differential.... possiblly....
    I’d done it backwards so far.
    Adjusted the ramps, then clutches, then preload.
    I might reverse that
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  3. #103
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    Well.... i think it is a situation where you start from the ramps and the clutches after all but you must have preload in mind in some off input situations to control oversteer or understeer that might come up.

    Also another question if one might know...... :
    Using the calculator if for instance i have lets say 40% for decell lock using different values for differrent combination of ramp or clutces that means i have the same results for both scenarios ex.. dec ramp 40 and clutch packs 4 gives 38% decel lock and dec ramp 50 and clutch packs 6 gives 40% decel lock... but lets assume that i had two cases with the exact same result lets say 40%..... does the car behave exactly the same or is there some hidden info in those different values.....?

    I hope things wont get more complicated and the car behaves the same becsuse it sure feels very close.....

  4. #104
    Handling QA Lead Jussi Karjalainen's Avatar
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    Heya guys, been busy at work, sorry for no responding sooner.

    Preload is indeed always active, and power/coast locking adds on top of that. When you're using the calculator you can see that in the graph. Whether you adjust the preload or the ramps first/last is up to personal preference.

    Preload the vast majority of the time won't affect your total locking amount that much (low torque engines excepted) but it will affect the behavior when you're feathering the throttle, i.e. the behavior between engine braking and power on.

    Quote Originally Posted by sillib View Post
    Well.... i think it is a situation where you start from the ramps and the clutches after all but you must have preload in mind in some off input situations to control oversteer or understeer that might come up.

    Also another question if one might know...... :
    Using the calculator if for instance i have lets say 40% for decell lock using different values for differrent combination of ramp or clutces that means i have the same results for both scenarios ex.. dec ramp 40 and clutch packs 4 gives 38% decel lock and dec ramp 50 and clutch packs 6 gives 40% decel lock... but lets assume that i had two cases with the exact same result lets say 40%..... does the car behave exactly the same or is there some hidden info in those different values.....?

    I hope things wont get more complicated and the car behaves the same becsuse it sure feels very close.....
    The calculator is somewhat of a simplification of what really happens in the physics (I try but it's complicated), but different angles and clutch counts resulting in the same percentage should be pretty much the same end result.
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  5. #105
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    I've just accessed the Diff calculator and Google told me it's in the trash! Don't delete it!
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  6. #106
    GT4 Pilot blinkngone's Avatar
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    I almost hate to ask this question. I have seen many setups with all the differential switched to off. They are running very fast times. How/why does turning all differentials to off work?
    Here is an example of one guys front wheel drive LSD, he does the same on rwd, there are many Indy cars using the all diffs off LSD.
    Click image for larger version. 

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    Last edited by blinkngone; 30-01-2018 at 19:48.
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  7. #107
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    Hey Jussi, great information on this post. I need a quick tip on your guide.

    Ok so I understand how different numbers affect locking and in what way. My question would be, if there is a general rule of thumb on the locking percentage we should be generally go after when tuning a car?

    An example, I tried driving the La Ferrari and noticed that when releasing throttle entering a corner the car would throw it's tail out and the same when pressing throttle to exit the corner. Generally the driving felt very unstable. Also by default, I would even get spinning on a straight line with full throttle. Does this car need a 50% locking, 100% or maybe 75%? If the "ideal" (I understand that there can be a matter of preference here) is for example a 75% lock for the perfect balance, then would inducing a 100% create a very understeery car with opposite results?

    So would it be correct if we said

    25% = Oversteer generally
    50% = Balanced Steering
    75% = Understeer generally

    This is the point I can't get out of this post, what is the percentage I should aim for when tuning?
    Last edited by lotzik; 01-02-2018 at 03:28.

  8. #108
    Handling QA Lead Jussi Karjalainen's Avatar
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    Hi guys, sorry for the silence. Not gonna sugarcoat it: I just kind of forgot about the whole forums (namely I forgot to read them personally, we do of course get information delivered to us regardless) for a while when I was sick over Dec and Jan, and didn't remember to come back after I got better. Trying to catch up with everything that I've missed now, better late than never I guess?
    Quote Originally Posted by poirqc View Post
    I've just accessed the Diff calculator and Google told me it's in the trash! Don't delete it!
    That's alarming, it shouldn't be! I'll look into it.
    Quote Originally Posted by blinkngone View Post
    I almost hate to ask this question. I have seen many setups with all the differential switched to off. They are running very fast times. How/why does turning all differentials to off work?
    Here is an example of one guys front wheel drive LSD, he does the same on rwd, there are many Indy cars using the all diffs off LSD.
    Click image for larger version. 

Name:	pCARS2 2018-01-30 15-45-34-09.jpg 
Views:	2 
Size:	245.4 KB 
ID:	249301
    Well, at least an open diff prevents any kind of power oversteer for the most part, but it does also limit the maximum amount of power you can effectively utilize. Also it'd tend to make cars pretty unstable, so you'd either need to be super smooth on the controls or work the setup to be more stable otherwise. Some cars these days have so much grip in their tyres though that even in real life they run very little accel locking, LMP cars are a good example of that. They have so much grip and great traction control systems, that they don't really need much locking to put down fast laps. The driver might want some extra to get the behavior they want out of the car though.

    None of us testing ever found that we were faster with an open diff than with a closed one, at least under the vast majority of conditions, but it's something to look into, definitely.

    Quote Originally Posted by lotzik View Post
    Hey Jussi, great information on this post. I need a quick tip on your guide.

    Ok so I understand how different numbers affect locking and in what way. My question would be, if there is a general rule of thumb on the locking percentage we should be generally go after when tuning a car?

    An example, I tried driving the La Ferrari and noticed that when releasing throttle entering a corner the car would throw it's tail out and the same when pressing throttle to exit the corner. Generally the driving felt very unstable. Also by default, I would even get spinning on a straight line with full throttle. Does this car need a 50% locking, 100% or maybe 75%? If the "ideal" (I understand that there can be a matter of preference here) is for example a 75% lock for the perfect balance, then would inducing a 100% create a very understeery car with opposite results?

    So would it be correct if we said

    25% = Oversteer generally
    50% = Balanced Steering
    75% = Understeer generally

    This is the point I can't get out of this post, what is the percentage I should aim for when tuning?
    Ah, this is an interesting question. Honestly, it all depends (yay). The percentage refers to how much locking force is being generated by the torque that's coming into the differential. So if your driveline is putting in 1000 Nm of torque (remember that gearing ratios will multiply torque) and you have 50% locking, the locking torque is 500 Nm. So if you have a hugely powerful/torquey engine engine, you can get a lot of locking force even with relatively low locking percentage. Conversely if you have a low powered engine like lets say the Ford Escort or the Nissan Fairlady, to get enough locking force you might have to run the diffs much stiffer. So on a high power Formula car 10-15% might be enough while a low powered racer might work well with 70% or more (one of the reasons why the decel locking is sometimes so high, engine braking doesn't give you nearly as much negative torque as the engine's power gives positive torque). And of course what gear you're in affects things as well, you get more locking in lower gears than you get in higher gears due to the torque multiplication of the transmission changing.

    As for the percentages you put out, are those for coast or power locking? 25% locking on coast would be very little and could lead to entry oversteer, while for acceleration locking it's not that much and might on some cars still have power understeer. And like I say above it's all quite dependent on the car anyway.

    The best rule of thumb I can give is that if you want to avoid power oversteer try to stay under 30% accel locking, maybe even under 20% on high powered cars, and for entry oversteer you'll generally want more than 40%, and 70% is a-OK.

  9. #109
    GT4 Pilot blinkngone's Avatar
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    Hi Jussi, thanks for the reply. I guess they are getting away with it with the oval track Indycars(Honda and Chevrolet), Formula A and Formula X at Monza Historic Oval and the Daytona Tri Oval. If you try and activate any other LSD even minimally you are going to be way off the pace. But they can do it with some FWD/RWD cars as well. Some people are also able to run with all the differentials(except ratcheting) turned on at other tracks. So, I think you are saying that all differential types "off" is the same as an "open" differential then what would be the description of all differentials "on"?
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  10. #110
    Handling QA Lead Jussi Karjalainen's Avatar
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    All of them on? That'd include spool, which trumps everything else (for hopefully obvious reasons), so that means it'd equal a spooled diff. =)

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