Strange brake assistance

[albertw]

I encountered an annoying brake assistance in my '24 4BW while cornering at a brisk pace (well below the traction limit - roughly twice the posted advisory speed for the corners). When I tried to brush off a bit of speed mid-corner with gentle brake application the car took over and hammered down the brakes hard enough to engage ABS. The ABS engagement wasn't quick enough to prevent the hard braking from locking up the rear wheels and rotating the car about 10 degrees before one of the nannies (probably ABS catching up) snapped it back into line.

I repeated it several times and it always happened in my usual mode for brisk driving - Sport, but not if I reduced my corner speed by about 20%. Out of curiosity I tried it in Tour and in Competitive Driving and it never happened, even at higher speeds approaching the traction limit.

I can't find anything in the Manual that would explain this. Brake Assist "detects rapid brake pedal applications due to emergency braking situations and provides additional braking" which doesn't apply since I was applying the brakes gently and gradually. Automatic Emergency Braking and Intelligent Brake Assist appear to be ruled out for several reasons. Both work only when a collision is imminent, which was never the case during my testing. AEB works up to 80 km/hr and all my testing was done at speeds above that. IBA requires quick application of the brakes which I didn't do.

The fact that it happened only in one of the three driving modes I tested makes me think it might be a glitch. Has anyone noticed this in their cars?

 

[albertw]

How about if I rephrase the question. Has anyone tested braking mid-corner in Sport and not had brake assistance activate?

I'd like to know if my experience was normal. I'm concerned that if I have to make an emergency stop while cornering close the the traction limit this excessive braking might really upset the car, so I've switched from Sport to Competitive Driving in the twisties. I would rather use Sport for the more aggressive stability control, but I don't want to go through the hassle of trying to convince the dealer to reprogram the electronics only to find out it is normal behaviour that the engineers somehow thought was appropriate.

 

[rdollie]

I simply drive in Track on the street and on the track for a very consistent experience. It's even fine in chillier rain periods since I know better than to push the car hard in those scenarios. Once it dips below the low 40s I drive something else and I know my track season is over here in the PNW.

 

[Sergio]

I’m going to the track Nov 5 for the first time in the BW, I’ll see if it does anything like your’s does.

Maybe the stability control module needs to be calibrated. If it thinks the car has a little bit of yaw, when you push it in a corner it thinks the rear is hanging out more than it really is and wants to straighten the car out.

My Mazdaspeed3 with R compound tires will apply the brakes taking a turn aggressively, it brakes so much that it kills the corner speed. The stability control has to be turned off to run quick laps. It only has one setting, not like the Cadillac.

 

[ngoni]

Do you have some level of PTM on? It's purpose is to allow some amount (depending on the setting) of wheel spin in the corners. The default setting without any PTM engaged has all the nannies ready to clamp down on any fun you might be getting up to.

 

[rdollie]

I had a chart from Spring Mountain that shows the differences in stability control by PTM mode but I can't find it. Does anybody have a version they can post?

 

[albertw]

Do you have some level of PTM on? It's purpose is to allow some amount (depending on the setting) of wheel spin in the corners. The default setting without any PTM engaged has all the nannies ready to clamp down on any fun you might be getting up to.

No, I haven't used any PTM mode for at least a year. The manual says all PTM modes revert to Tour when the car is restarted ( but stays in Sport, Tour or My Mode when restarted). So I'm sure the car is in the mode I set it to.

 

[albertw]

I simply drive in Track on the street and on the track for a very consistent experience. It's even fine in chillier rain periods since I know better than to push the car hard in those scenarios. Once it dips below the low 40s I drive something else and I know my track season is over here in the PNW.

My interpretation of the many discussions here of what the various modes do (necessitated by the absurdly vague and contradictory descriptions in the manual) was that PTM progressively reduces and eventually eliminates ESC while retaining more of TC, whereas Tour - Sport - Competitive Driving do the opposite. I want to retain some ESC and don't care at all about TC, so the Tour - Sport - Competitive Driving series is what I use.

A bit of explanation in case someone is interested: Here in BC there is an oppressive Excessive Speed regulation. 40 km/hr or more over the posted limit gets your car impounded for a week and no help getting home, plus thousands of dollars in fines and surcharges on your insurance. So I stay below that threshold. My favourite interesting roads have speed limits of 80 km/hr (roughly 50 mph), so my absolute limit is 120. That is at or a bit above the traction limit for corners with advisory speeds of 50 with my Michelin AS4 tires. (Advisory speeds here are noticeably lower than for the same corner in the western US.) I can't accelerate hard out of corners without exceeding my limit instantly. So, no use for the PTM modes.

I suppose the reason I'm not getting any replies with actual experience with braking while cornering in Sport is that most serious drivers use a PTM mode when driving aggressively.

 

[beamon]

I have experimented on the same tight turn with different ptm modes and noticed the car braking and cutting off power when ptm inactive and slippage detected and then increasing degrees of rear end tail wagging with dry ptm and then sport ptm (need to be careful as rear will come out a bit to the side in case there is a car next to you), but it is fun for sure. I’ve also learned to use race 2 ptm only if looking to take off from a standstill while laying some rubber down on the pavement…car manages to stay relatively straight if road is dry.

 

[jwolf99]

I had a chart from Spring Mountain that shows the differences in stability control by PTM mode but I can't find it. Does anybody have a version they can post?

I don't think this is from SM and apologies to whoever came up with this for not giving cred, but I find this chart a huge help.