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Thread: [Magic inside!] Need Help With Differentials

  1. #121
    WMD Member M4MKey's Avatar
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    what ? So by less locking on the accel diff, you have less powersteering ? That' doesn't make any sense. I agree with the first and final part of your post. Higher angle = less locking. But then Higher angles on the accel diff makes more powersteering
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  2. #122
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    Quote Originally Posted by M4MKey View Post
    what ? So by less locking on the accel diff, you have less powersteering ? That' doesn't make any sense. I agree with the first and final part of your post. Higher angle = less locking. But then Higher angles on the accel diff makes more powersteering
    less locking = less power over is actually very logical, because the axle "locks" it self later, allowing for more power being sent to the unloaded wheel.
    Power steering is an altogether different thing.
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  3. #123
    Kart Driver 2010 Synergy Camaro's Avatar
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    Quote Originally Posted by Jussi Karjalainen View Post
    Also good to know is that higher ramp angle = less locking, as the help text denotes. So in a very very simplified form if you want to avoid power oversteer, increase the power ramp angle, and if you want to avoid lift off oversteer, decrease coast ramp angle.
    Thank You Jussi. I also appreciate your suspension calculator very much. I am able to use and understand it just fine. Hopefully, after playing around with the differential calculator I will get the hang of it in time also.
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  4. #124
    Handling QA Lead Jussi Karjalainen's Avatar
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    Quote Originally Posted by M4MKey View Post
    what ? So by less locking on the accel diff, you have less powersteering ? That' doesn't make any sense. I agree with the first and final part of your post. Higher angle = less locking. But then Higher angles on the accel diff makes more powersteering
    More accel locking increases power oversteer for the same reason why drift cars use aggressive accel locking (or even spooled diffs) instead of open diffs. =)

    If your diff is open, the torque distribution is 50:50, so the amount of power/torque you can put down is limited by the tyre with the lowest grip. If one tyre has only enough grip to manage 100 Nm of torque without slipping, you can't send more than 100 Nm to the other tyre either, for a total of 200 Nm going to the ground and doing useful work, even if it could handle 1000 Nm of torque.

    What locking does is effectively increase the amount of torque you can send to the side with more grip. If you were in the situation above but had 100 Nm of preload, you could send 100 Nm to the tyre with less grip and 100 Nm to the tyre with more grip due to the 50:50 torque split, but also 100 Nm extra on the tyre with more grip due to the preload, for a total of 300 Nm of torque going to the ground. Accel locking works in the same way basically, the main difference between it and preload is that preload is always the same, whereas accel (and decel) locking varies by how much torque is coming to the diff (so on 100% throttle you get more locking than on 50% throttle, in low gears you get more locking than in high gears, etc.).

    So, locking allows you to put extra torque/power on the tyre with more grip. Before you were limited by the tyre with less grip, but locking enables you to overpower both tyres at the same time. This causes oversteer. =)

    And on top of that there's the potential for a yawing torque to be applied on the car with more locking. If you have lots of accel locking, maybe even a spooled diff, and you're cornering hard, your outside tyre will have way higher grip potential than your inside tyre. If you mash the throttle, most of the thrust pushing the car forwards will be coming from the outside rear tyre. That tyre is not in the center of the car, so as it pushes the car it will also try to rotate it (just like if you push a box forwards near it's edge it'll spin, but if you push it in the center it'll go straight). That can add an extra tendency towards oversteer. =)

    Here's a showcase of a car with 90 degree accel ramp and no other locking, vs. the same car with 20 degree accel ramp:



    EDIT: At low loads where you're not really straining against the limitations of the tyres (for example turning into a parking spot, which requires lots of differentiation but isn't really putting the tyres at their limits of grip under normal conditions) lots of locking can indeed cause understeer, but when pushing to the edge it becomes about the difference between spinning one wheel vs. spinning both. With locking you'll always want to rotate both wheels, one can't turn independently, so if you're going to get wheelspin, you'll get it on both driven wheels.
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  5. #125
    WMD Member PostBox981's Avatar
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    Thanks Jussi for spending so much time in this thread. I am sure I still donīt get all my diff settings right but with every single post of yours the technology is getting a little clearer for me. Without all your help I guess some 95% of us would be completely lost in the dark.
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  6. #126
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    So I need low values to prevent over/understeer? Thought it was the other way around.

  7. #127
    Handling QA Lead Jussi Karjalainen's Avatar
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    Quote Originally Posted by Max Torque View Post
    So I need low values to prevent over/understeer? Thought it was the other way around.
    Low coast ramp angle = more deceleration locking = more understeer

    Low power ramp angle = more acceleration locking = more power oversteer (when a car is capable of breaking traction at least)
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  8. #128
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    Quote Originally Posted by Jussi Karjalainen View Post
    Low coast ramp angle = more deceleration locking = more understeer

    Low power ramp angle = more acceleration locking = more power oversteer (when a car is capable of breaking traction at least)
    Ah, ok, I confused "more lock" with "higher value". But "higher value" means less lock.
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  9. #129
    GT5 Pilot Jezza819's Avatar
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    I've just started to try and see if I can make diff changes to fix the cars that I'm having trouble with spinouts either off throttle or on. It doesn't seem to matter. I actually think I could spin one out if it were sitting totally still. But in looking at the diff settings the power and coast doesn't seem to have as big of a range as preload does. Does it make sense to see what the range of power and coast are and set them right in the middle, see what that does, then start going up or down on each and see what happens? I forget which car I was looking at but the low end of preload was -100 and it went all the way up to 400. Needless to say I put it right back where it started and didn't touch it.
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