OK, I noticed this in the UFR, braking at the chicane at AS North with the Race_S set when S/T/U came out. Now I've had it happen again in the XRR at KY Nat, again with its Race_S set, braking hard in 3rd gear for one of the infield corners: It seems that with heavy brake application, the revs just suddenly drop off rapidly while still at a sensible speed for that gear, then the auto-clutch kicks in and when I try to get back on the power I slide.

I've noticed if I back off the brake a bit it doesn't happen, and the car can be held on the edge of this behaviour with the brake pedal until it's time to open the throttle again, but given that a downshift isn't necessary so long as you're gentle on the brake then why does it look like stalling when the brake is fully depressed?

It's happening to me in the attached .mpr (sorry, 2Mb-ish) on most laps at the left-hand corner in the infield towards the end of the lap.

This is probably because the front wheels are locking up while they are still connected to the engine. Its like putting the engine into 4th from 0 mph.

Yeah, locking up. Also looks like your outside rear wheel is bottoming out a lot.

This has been an issue with the LSD since it came out. It was especially a problem with the XRR, but happens on all cars. The drive axel basically gets locked by the brakes. Your tire might not be locked up, but the axel. is. The rev's will drop just like you say, and it usually results in a spin. I have even had this happen with the UF1.

Try moving your brake bias further to the rear if possible. If not, lower the brake force some. The other thing to do us to use the locked diff. For some reason, using the locked diff removes the issue.

Quote from Hallen :

The other thing to do us to use the locked diff. For some reason, using the locked diff removes the issue.

my best guess is that it had something to do with the clutchpack not being preloaded which colcob confirmed
while the clutch is engaed the diff is completely open

Quote from Shotglass :

my best guess is that it had something to do with the clutchpack not being preloaded which colcob confirmed
while the clutch is engaed the diff is completely open

People keep bringing that up but I don't understand why that would cause the problem as described above.

Also I don't think I've ever had it happen to me... perhaps the problem goes away on superior sets.

Quote from Bob Smith :

People keep bringing that up but I don't understand why that would cause the problem as described above.

could either be some weird effect with how the engine braking kicks in and out when the diff switches from coast lock to open and back again or one wheel getting less torque from the road (maybe by lifting a little) causing it to lock up with no additional torque being transfered to it from the other one that could keep it rolling

from what i've seen reducing braking power to a reasonable value during turn in fixes the problem and ofc it depends on diff setup too

Quote from Bob Smith :

People keep bringing that up but I don't understand why that would cause the problem as described above.

Also I don't think I've ever had it happen to me... perhaps the problem goes away on superior sets.

Go try braking into T1 on BLGP with an XRR and you'll notice (and if you really don't, try race_S set)...

Quote from Bob Smith :

People keep bringing that up but I don't understand why that would cause the problem as described above.

Also I don't think I've ever had it happen to me... perhaps the problem goes away on superior sets.

I must be missing something, it seems logical that this happens -> it should happen MORE with more coast lock and it should still happen with a locked diff with enough brake pressure. Lock up your driven wheels IRL and see what happens with the clutch engaged

I can only get this to happen in LFS by appying WAY too much brake... I also use a manual clutch, maybe that has something to do with it - I saw some sort of autoclutch behaviour mentioned earlier.

Probably locking the wheels indeed, or one of them at least. Why not run it through one of the LFS lap analyzing programs and check the slip ratios in the areas and times where it occurs?