NSX NC1 - Track Review Laguna Seca - Randy Pobst

[Valkyrie Pilot]

I wonder if what Randy was experiencing at the track had more to do with the brake bias rather than just an alignment issue, it took Porsche forever to get the brake bias sorted out on the 918.

Under trail braking conditions the electronic nannies will be working overtime trying to get regenerative braking applied at the same time as modulating the hydraulic brakes to give the sensation as well as the expected pedal feel for a standard hydraulic only braking system.

If the brake bias distribution is not right, it is possible that the front end will experience substantially higher deceleration rates than the rear end of the car, thus causing the rear end to be unstable under braking (think super aggressive front pad and mild rear pad scenario for those who have tracked).

The opposite also causes instability as well when the rear end has higher deceleration rates than the front, (like using a pad with higher operating range on the rear of the car vs the front, while the front end provides sufficient deceleration compared to the rear everything is fine, once the front pads start fading and the rear keeps biting the car becomes unstable under braking/trail braking)

It could also be the way that the rear e-diff has been implemented, a traditional clutch based LSD is supposed to help quite a bit during trail braking. Folks use different ramps/percentage lockup under acceleration/deceleration depending on the types of tires that are been used. I don't know the internals of the e-diff on the NSX2.0 so can't guess if it provides an extra layer of stability under braking.

Not been able to pinpoint the root cause of problems is not something that I would like to have to deal with as a track enthusiast.

Very Interesting point. Could this be an issue on one NSX and not another? I would think it could be since this is a brake by wire system as you reference and the electronics or sensors might be more susceptible to a glitch especially on a pre-production car. It sure would explain the dramatic difference between how busy Randy is vs. the calm that Aaron experience. Would you agree 2Slow2Speed?

FastAussie, care to comment on this hypothesis?

One question, wouldn't a rear brake bias be a good thing for stability vs. just an equal brake distribution? Or would that contribute to understeer?

 

[docjohn]

rear brake bias is used when fronts are getting too hot as in F1 but the rears grabbing before the fronts or with more mu is like down shifting with too little rev match and what happens next ? loosey goosy

 

[2slow2speed]

Very Interesting point. Could this be an issue on one NSX and not another? I would think it could be since this is a brake by wire system as you reference and the electronics or sensors might be more susceptible to a glitch especially on a pre-production car. It sure would explain the dramatic difference between how busy Randy is vs. the calm that Aaron experience. Would you agree 2Slow2Speed?

FastAussie, care to comment on this hypothesis?

One question, wouldn't a rear brake bias be a good thing for stability vs. just an equal brake distribution? Or would that contribute to understeer?

FWIW, I have no idea who Aaron is so can't comment. Randy is a pro-driver and knows what he is doing, he is also well known in the P-car community for his involvement in various development programs as well as his involvement in the general community.

I have been to LS many times, as anyone who has spent serious track time at LS, the track is really hard on brakes (brutal to be honest) due to the nature of the layout of the track stickier tires results on higher rotor temps as well. Even P-cars equipped with 3rd gen PCCB's experience wear, LS was known to destroy the first gen PCCB's on P-cars.

Grip levels at LS can vary quite a bit due to the types of events that are held there. I have been on the track after pro race weekends and the rubber laid out by the slicks used by the pro's make the track feel like a different track due to the extra grip that was available.

Braking on modern cars is not as simple as it seems, there are many vehicles that use Electronic Brake Distribution to vary the amount of force that a caliper applies to keep a car stable during braking, various sensors are used to determine the correct distribution.

Depending on grip levels even non-hybrid vehicles braking systems can get confused if the programmed software is fed information that has not been accounted for.

Professional and experienced drivers will use advanced driving techniques that casual and inexperienced drivers will not use. Trail braking, left foot braking, lift throttle oversteer to rotate the car etc, etc.

If the programming of the various modules have not been calibrated/tuned properly it is always possible to end up in a corner case that has not been tested. If that is the case most complex systems are designed to get into a pre-set mode, that probably will depend on the various inputs that are been fed.

Given the system complexity on a vehicle like the NSX2.0, there are other factors as well that might affect the way that the vehicle behaves under braking.

Ideally you want stiffness on the front axle of the car to prevent the car from nosediving and allowing weight to be present on the rear axle to assist on braking. Given that the NSX2.0 uses magnetorheological shocks/dampers it would not surprise me that the front shocks/dampers copmression rates go up during braking, at the same time you want the rear end to be planted so the rear dampers might end up in slightly less stiff mode.

Then you get into the actual cornering at that point the requirements might be a bit different, might want a more compliant font end so that the car doesn't understeer and the rear to be stiffer so that the car can rotate.

Again, add on top of this the fact that you have active torque vectoring happening on both the front and the rear axle of the vehicle, then you have the added complexity of braking in the case of trail braking, or having both the brakes and the throttle been applied when left foot braking is applied.

The engineers from Honda have all the necessary data from their various modules to determine which case/situation resulted in Randy's experience at the track. It could have been due to a bad sensor, glitch in the signal (not sure how many levels of redundancy have been designed for the NSX2.0), programming, unexpected scenario due to Randy's driving style or condition of the track etc, etc.

As I had mentioned in some of my previous posts, a complex car requires a level of knowledge that is not accessible for us "mere" mortals.


Rear brake bias is useful on vehicles like the 911 where the weight of the motor is on top of the rear axle, one of the reasons why the 911's are so good at straight line braking. At the same time the reason why 911's require a good LSD to keep the rear end planted under hard braking.

A mid engine vehicle can also benefit from more rear brake bias as well, but not as much. Given that the NSX2.0 uses brake by wire they can implement whichever scheme is effective and change settings on the fly, maybe that is why the NSX2.0 has such great straight line braking numbers.

 

[Valkyrie Pilot]

FWIW, I have no idea who Aaron is so can't comment. Randy is a pro-driver and knows what he is doing, he is also well known in the P-car community for his involvement in various development programs as well as his involvement in the general community.

I have been to LS many times, as anyone who has spent serious track time at LS, the track is really hard on brakes (brutal to be honest) due to the nature of the layout of the track stickier tires results on higher rotor temps as well. Even P-cars equipped with 3rd gen PCCB's experience wear, LS was known to destroy the first gen PCCB's on P-cars.

Grip levels at LS can vary quite a bit due to the types of events that are held there. I have been on the track after pro race weekends and the rubber laid out by the slicks used by the pro's make the track feel like a different track due to the extra grip that was available.

Braking on modern cars is not as simple as it seems, there are many vehicles that use Electronic Brake Distribution to vary the amount of force that a caliper applies to keep a car stable during braking, various sensors are used to determine the correct distribution.

Depending on grip levels even non-hybrid vehicles braking systems can get confused if the programmed software is fed information that has not been accounted for.

Professional and experienced drivers will use advanced driving techniques that casual and inexperienced drivers will not use. Trail braking, left foot braking, lift throttle oversteer to rotate the car etc, etc.

If the programming of the various modules have not been calibrated/tuned properly it is always possible to end up in a corner case that has not been tested. If that is the case most complex systems are designed to get into a pre-set mode, that probably will depend on the various inputs that are been fed.

Given the system complexity on a vehicle like the NSX2.0, there are other factors as well that might affect the way that the vehicle behaves under braking.

Ideally you want stiffness on the front axle of the car to prevent the car from nosediving and allowing weight to be present on the rear axle to assist on braking. Given that the NSX2.0 uses magnetorheological shocks/dampers it would not surprise me that the front shocks/dampers copmression rates go up during braking, at the same time you want the rear end to be planted so the rear dampers might end up in slightly less stiff mode.

Then you get into the actual cornering at that point the requirements might be a bit different, might want a more compliant font end so that the car doesn't understeer and the rear to be stiffer so that the car can rotate.

Again, add on top of this the fact that you have active torque vectoring happening on both the front and the rear axle of the vehicle, then you have the added complexity of braking in the case of trail braking, or having both the brakes and the throttle been applied when left foot braking is applied.

The engineers from Honda have all the necessary data from their various modules to determine which case/situation resulted in Randy's experience at the track. It could have been due to a bad sensor, glitch in the signal (not sure how many levels of redundancy have been designed for the NSX2.0), programming, unexpected scenario due to Randy's driving style or condition of the track etc, etc.

As I had mentioned in some of my previous posts, a complex car requires a level of knowledge that is not accessible for us "mere" mortals.


Rear brake bias is useful on vehicles like the 911 where the weight of the motor is on top of the rear axle, one of the reasons why the 911's are so good at straight line braking. At the same time the reason why 911's require a good LSD to keep the rear end planted under hard braking.

A mid engine vehicle can also benefit from more rear brake bias as well, but not as much. Given that the NSX2.0 uses brake by wire they can implement whichever scheme is effective and change settings on the fly, maybe that is why the NSX2.0 has such great straight line braking numbers.

Good stuff. Thanks for sharing your insight. It is quite a bit more complex than I imagined and I had imagined quite a bit. So it sounds like they would have needed Acura to hook up to the car to understand the details. I know Car and Driver had the Acura engineers there but Motor Trend does not make any reference to them. I guess we know enough to know that the MT track time has some room for improvement.