The official 991.2 GT3 owners pictures thread...
#692
Not sure about formulas, but...
Over simplifying I’d say that more lockup helps at higher speeds but hurts at lower speeds. To understand why:
Consider the extreme case where you’ve locked the rear wheels together with a spool (100% lockup). This is bad particularly around tight radius bends: the rear always wants to track straight and you need to drag/ slip the tires relative to one another to overcome this. This results in extreme understeer at lower speeds, with the front always fighting to overcome the rear. Bad at an autocross, which is why the advice is often to ditch a clutch type LSD entirely and go to a torque biasing diff, which does not induce understeer.
At high speeds things change. As corner radius increases the difference between the inside and outside wheel-speed decreases, so the dragging/ understeer is dramatically reduced. Second and more importantly the car’s overall handling balance shifts towards oversteer, so you actually want some understeer in the mix to stabilize it. Hence the advice that track cars get clutch type LSD with plenty of lockup to add stability.
Hence the simplification that the R’s LSD is biased towards tighter bends/ lower speeds and the GT3’s biased towards larger bends and higher speeds.
Over simplifying I’d say that more lockup helps at higher speeds but hurts at lower speeds. To understand why:
Consider the extreme case where you’ve locked the rear wheels together with a spool (100% lockup). This is bad particularly around tight radius bends: the rear always wants to track straight and you need to drag/ slip the tires relative to one another to overcome this. This results in extreme understeer at lower speeds, with the front always fighting to overcome the rear. Bad at an autocross, which is why the advice is often to ditch a clutch type LSD entirely and go to a torque biasing diff, which does not induce understeer.
At high speeds things change. As corner radius increases the difference between the inside and outside wheel-speed decreases, so the dragging/ understeer is dramatically reduced. Second and more importantly the car’s overall handling balance shifts towards oversteer, so you actually want some understeer in the mix to stabilize it. Hence the advice that track cars get clutch type LSD with plenty of lockup to add stability.
Hence the simplification that the R’s LSD is biased towards tighter bends/ lower speeds and the GT3’s biased towards larger bends and higher speeds.
#693
Rennlist Member
Thread Starter
#694
Rennlist Member
A couple from this morning.
#695
Great looking cars gang, hope you guys are enjoying driving them. Miami Blue looks really good and would have been a great non-PTS back-up color for me. Any of you guys got through break-in and rev'ed the cars near 9k RPM yet?
#697
First BR Parkway run
#699
Rennlist Member
Finally got a chance to drive the new arrival (45 degrees and clear in SW Ohio). Certainly lightyears ahead of its stablemate in refinement but may be missing a bit of the steering feel/feedback which I love in the 6GT3. Only put about 75 miles on it today and am wondering how anyone can possibly keep the engine below 4000rpm for the initial 2000 mi break in period...
#700
Race Car
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Not sure about formulas, but...
Over simplifying I’d say that more lockup helps at higher speeds but hurts at lower speeds. To understand why:
Consider the extreme case where you’ve locked the rear wheels together with a spool (100% lockup). This is bad particularly around tight radius bends: the rear always wants to track straight and you need to drag/ slip the tires relative to one another to overcome this. This results in extreme understeer at lower speeds, with the front always fighting to overcome the rear. Bad at an autocross, which is why the advice is often to ditch a clutch type LSD entirely and go to a torque biasing diff, which does not induce understeer.
At high speeds things change. As corner radius increases the difference between the inside and outside wheel-speed decreases, so the dragging/ understeer is dramatically reduced. Second and more importantly the car’s overall handling balance shifts towards oversteer, so you actually want some understeer in the mix to stabilize it. Hence the advice that track cars get clutch type LSD with plenty of lockup to add stability.
Hence the simplification that the R’s LSD is biased towards tighter bends/ lower speeds and the GT3’s biased towards larger bends and higher speeds.
Last edited by fxz; 12-17-2017 at 04:34 AM.
#701
Rennlist Member
#702
The torsion diff is particularly interesting in that rather than lock the wheels together it directs more thrust to the wheel with more traction (outside). Thus unlike a traditional LSD which increases understeer it actually uses the engine’s power on the outside wheel to help rotate the car, great for tight corners. Unfortunately it doesn’t do a thing under braking, so it’s no help on high speed corner entry. Little wonder that the industry is moving towards electronic control to get the best of all worlds.
#705
White on black always looks very Porsche like.