Bouncing on powering out of wide corner
Discussion
Car:
MX5 ND2 (184bhp + LSD) + approved eibach sports springs on factory bilsteins. No mods.
Problem/example situation:
Having approached a large radius trunk road roundabout I will trail the throttle around to the third (right) exit where I will progressively apply the throttle as I unwind the steering as I leave the roundabout. Quick, but all very smooth and controlled.
I find that as I simultaneously unwind the steering and apply the power, the rear of the car will begin to bounce (or rather undulate) until I've straightened up.
This doesn't feel like a slip as the car is not sliding, nor are the rear wheels spinning. The closest explanation would be 'tramping' but with the rear of the car oscillating up and down (maybe three or four times) rather than the axle itself.
I'm not sure if this is a rebound issue on the standard dampers or maybe something to do with the way the LSD is working. The clever adjustable electronic M diff on my M2Comp will fairly slingshot me out of the corner in the same situation whereas the little MX5's bottom bounces up and down out of the corner.
Any thoughts?
ETA You can just pick out (see and hear) the Alfa doing it here, but it's more pronounced in my MX5 (less sliding obviously!): https://youtu.be/9BuZmJmpTdk?t=286
MX5 ND2 (184bhp + LSD) + approved eibach sports springs on factory bilsteins. No mods.
Problem/example situation:
Having approached a large radius trunk road roundabout I will trail the throttle around to the third (right) exit where I will progressively apply the throttle as I unwind the steering as I leave the roundabout. Quick, but all very smooth and controlled.
I find that as I simultaneously unwind the steering and apply the power, the rear of the car will begin to bounce (or rather undulate) until I've straightened up.
This doesn't feel like a slip as the car is not sliding, nor are the rear wheels spinning. The closest explanation would be 'tramping' but with the rear of the car oscillating up and down (maybe three or four times) rather than the axle itself.
I'm not sure if this is a rebound issue on the standard dampers or maybe something to do with the way the LSD is working. The clever adjustable electronic M diff on my M2Comp will fairly slingshot me out of the corner in the same situation whereas the little MX5's bottom bounces up and down out of the corner.
Any thoughts?
ETA You can just pick out (see and hear) the Alfa doing it here, but it's more pronounced in my MX5 (less sliding obviously!): https://youtu.be/9BuZmJmpTdk?t=286
Edited by ben5575 on Monday 20th May 23:18
Is that the one with the multi-link rear suspension? I haven't quite got my head around it, but it looks to me as if there's plenty of scope for hub flex. I suspect it's leading to some bump/roll/toe coupling which is leading to a sort of reverse 'wheel hop' where the car is orbiting in pitch/roll instead of settling to an average position - a bit like a dutch roll in aircraft.
I suppose the resolution would be to change one of the bump/roll frequencies so they can't drive each other, and/or reduce the amount of flex and/or increase the amount of damping. I'm sure the owners' club will include people who have worked this sort of thing out.
I suppose the resolution would be to change one of the bump/roll frequencies so they can't drive each other, and/or reduce the amount of flex and/or increase the amount of damping. I'm sure the owners' club will include people who have worked this sort of thing out.
That’s really interesting thanks, I’ll post on one of the mx5 forums.
It happens at speed under power.
Doh. Just had a thought. I trail the throttle through the roundabout so the car is sat down. It squats more as I accelerate out of the junction. Perhaps the oscillation is the t/c kicking in which reduces the power which means the rear lifts slightly then stops as a potential slip is caught, the car beds down again, then reapplies, then stops on a loop as I ‘teeter on the edge of adhesion’ (for full Sniff points
)
The M2’s diff electronically sorts out the power across the driven wheels in a similar situation without applying t/c. The mx5 mech lsd isn’t as clever so the t/c kicks in. Maybe
Might have to don big boy pants and try it with t/c turned off. Will post picture of the results!
It happens at speed under power.
Doh. Just had a thought. I trail the throttle through the roundabout so the car is sat down. It squats more as I accelerate out of the junction. Perhaps the oscillation is the t/c kicking in which reduces the power which means the rear lifts slightly then stops as a potential slip is caught, the car beds down again, then reapplies, then stops on a loop as I ‘teeter on the edge of adhesion’ (for full Sniff points
)The M2’s diff electronically sorts out the power across the driven wheels in a similar situation without applying t/c. The mx5 mech lsd isn’t as clever so the t/c kicks in. Maybe
Might have to don big boy pants and try it with t/c turned off. Will post picture of the results!
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