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Thread: [Magic inside!] Need Help With Differentials

  1. #131
    GT5 Pilot Jezza819's Avatar
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    I tried to adjust engine braking on one of my most troublesome cars last night, the BMW 320TC, but the settings only went from 1 to 5 and I guess the default was already at 4. It didn't seem to help it much. At the shorter Hockenheim course where I was running it it spun out at turn 1 and also that medium speed right hander as you enter the arena. It's like whichever direction the turn is, the outside tire speeds up and pushes it further in the direction you're turning. Now if I'm going way too fast for the turn and spin it out, that's on me. And at least with me this car doesn't like kerbs because I've spun it out at turn 1 Hockenheim by clipping that left hand kerb, Long Beach on the second right after you go around the fountain, and numerous other places.

    The V8 Supercar is the same way except more extreme I'm guessing because of all that torque it's very touchy on corner exit but I haven't looked at it's engine braking yet.
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  2. #132
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    For me lowering preload to minimum really fixed it. No sudden spin-outs anymore and a way more predictable behaviour. Have you tried to switch off all diffs completely in order to see whether this changes your car's disadvantageous attitude towards cornering?

  3. #133
    GT5 Pilot Jezza819's Avatar
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    Quote Originally Posted by El_Tim View Post
    For me lowering preload to minimum really fixed it. No sudden spin-outs anymore and a way more predictable behaviour. Have you tried to switch off all diffs completely in order to see whether this changes your car's disadvantageous attitude towards cornering?
    No not really. Since I've just started messing around with those settings I haven't done much. I didn't even know you could switch them off.
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  4. #134
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    Quote Originally Posted by Jezza819 View Post
    I tried to adjust engine braking on one of my most troublesome cars last night, the BMW 320TC, but the settings only went from 1 to 5 and I guess the default was already at 4. It didn't seem to help it much. At the shorter Hockenheim course where I was running it it spun out at turn 1 and also that medium speed right hander as you enter the arena. It's like whichever direction the turn is, the outside tire speeds up and pushes it further in the direction you're turning. Now if I'm going way too fast for the turn and spin it out, that's on me. And at least with me this car doesn't like kerbs because I've spun it out at turn 1 Hockenheim by clipping that left hand kerb, Long Beach on the second right after you go around the fountain, and numerous other places.

    The V8 Supercar is the same way except more extreme I'm guessing because of all that torque it's very touchy on corner exit but I haven't looked at it's engine braking yet.

    Hi,
    In regards to these two cars, try using the clutch + heel and toe if you are up for it, especially with the 320TC. I was having serious rear end lock ups as you are having and with a little patience these start to work well. i am actually using the H-gate and clutch instead of sequential with both these cars. i can also pm you my setups if you like.

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  5. #135
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    Jussi - I've been investigating the Clio Cup limited slip diff and found that when you enter the power side ramp angle and number of clutches you end up with more than 100% locking. This isn't possible. Is there an error in your spreadsheet?
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  6. #136
    Handling QA Lead Jussi Karjalainen's Avatar
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    Quote Originally Posted by David Wright View Post
    Jussi - I've been investigating the Clio Cup limited slip diff and found that when you enter the power side ramp angle and number of clutches you end up with more than 100% locking. This isn't possible. Is there an error in your spreadsheet?
    It is possible, nothing says you can't have more than 100% locking, and 100% locking doesn't mean that the two sides are "totally solidly locked together".

    What the locking percentage means is that if there's for example 500 Nm of torque coming into the diff, the locking torque between the left and right side will be XX% of that. So 50% locking would be 250 Nm in that case. With suitable materials it's not tough to achieve a higher locking torque than that. As an EXTREME example, you could have something like this:

    Click image for larger version. 

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    When you put those two faces together you don't need to push them together hard at all to create a huge amount of locking force (force required to make them rotate at different speeds). With enough clutch plates that have enough friction, and aggressive ramp angles, you can get a diff that has over 100% locking force, which basically means that you need more torque than what the driveline is transmitting to make the left and right sides rotate at different speeds. 150% locking percentage would mean that with 500 Nm of torque going in to the diff, you'd need 750 Nm of torque difference. You wouldn't be able to get one side to rotate faster than the other side with engine power in that case, but theoretically you could still use external forces to create differentiation.
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  7. #137
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    Thanks for your reply. I think we must be using different definitions of locking %. In post 2 you include a diagram which shows how locking % relates to torque bias.

    locking % = (torque to high grip side - torque to low grip side)/input torque

    so for example with a torque bias of 3:1 = (3-1)/4 = 50%

    using this definition you can't get more than 100% locking.

    The problem is I think the above definition is used by limited slip diff manufacturers, so its not possible to use your spreadsheet to convert manufacturers figures to ramp angles and clutches.
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  8. #138
    Handling QA Lead Jussi Karjalainen's Avatar
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    Good point there, but after conversing with others we think the calculations for both should be very comparable where locking percentage/effect is concerned. It's more of a difference of how do you approach the situation, do you try to measure the torque differences at the wheels and then work backwards to the input torque, or do you take the input torque and use the diff specs to calculate how much extra torque could be sent to one side. You should get very close to the same results either way, it's just approaching it from another direction in a manner of speaking.

    Don't worry too much about the over 100% locking though, it's mostly theoretical. In practice, since the engine can't put out more than 100% of its torque it basically means that from the driveline's point of view 100% locking behaves the same as over 100% locking. It's more of a theoretical question of "would this amount of input torque also be able to fight off external causes for slip as well, like the torque caused by the two sides trying to roll at different rates?" Feel free to limit the top end to 100% in your mind. =)

    EDIT: One reason why I like the "over 100% possible locking" is that it kind of reminds me every time that 100% locking percentage/effect is not the same thing as "fully locked" or the same effect as having a spooled diff. A spooled diff will never allow the two sides to rotate at different rates, beyond the material flexing at least, while even a 100% locking percentage clutch based diff is only just pushing friction faces together and doesn't solidly lock the two sides to one. It basically just means that the engine torque can never make one side rotate faster than the other.

  9. #139
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    Quote Originally Posted by Jussi Karjalainen View Post
    clutch based diff is only just pushing friction faces together and doesn't solidly lock the two sides to one
    I think the statement above summarize the distinction quite well.
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  10. #140
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    Here is some data taken with PC2Tuner to demonstrate what happens when adjust the power ramp, the signals are wheel slip, the rear axle are green and orange, notice how too high of power ramp, the inside tire slips first and more than the outside wheel, as you go down in power ramp, they slip the same amount, but if you go too low the spin % of the outside wheel spins more and sooner. From the graphs below I'd probally set my power ramp somewhere between 70 and 50 degs.

    Click image for larger version. 

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    Last edited by Zeratall; 25-07-2018 at 14:21.
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