Sticking to the road when going over uneven pavement

[tetsuos]

Are you absolutely certain about that? My understanding of anti-lock brake systems is that they only disengage the brake on the one wheel that is locked up, and only temporarily. If more than one wheel locks up, the system might disengage the brake on more than one wheel, but that could easily cause complete instability. I'm totally guessing, but I have a hunch that Tesla Motors would not be approved to sell a vehicle which engaged anti-lock on all wheels at the same time. I hope someone who is an expert can clarify here.

My experience with the Roadster suggests that the ABS engages in an all-or-nothing fashion. If one wheel locks up, due to hard braking on an uneven surface where a single wheel becomes airborne, all wheels go into the ABS pulsation mode. I can demonstrate this by going over a sunken manhole cover or a speed bump while braking hard. Braking efficiency is immediately reduced in a rather extreme way. The system seems to reset after about half a second of ABS mode, once it detects normal wheel rotation.

Regardless of how the individual wheel brakes operate, the brake pedal vibrates during anti-lock action, so perhaps you are reacting. I don't mean any disrespect, but do you have any experience with anti-lock brakes? I only have one other vehicle with anti-lock brakes, the 2000 S-2000, and it has only ever engaged the anti-lock system on uneven pavement - specifically, when driving over the "road turtles" that we have here in the U.S., combined with sand or grit on the paved surface to make things worse. So, from what is being described in this thread, nothing really seems any different with the Tesla Roadster than with other anti-lock systems. Granted, the interpretations here seem to include some wild theories, but the subjective reports don't seem that alarming to me.

I would say that I have moderate to high experience with ABS. I have driven 5 other cars with anti lock brakes on a regular basis, and many others (rentals) for short terms. My '05 Audi TT had much more intelligent ABS, and the transition between normal and anti lock mode resulted in much less variation in stopping distance. The same is true on my Audi Q5, which is not a small car. The Benz A class and M class also have much more granular applications of ABS compared to the Roadster.

Driving here in Hong Kong tends to be quite aggressive, so there are plenty of (daily) opportunities to test anti-lock brakes. Add to that the heavy seasonal rains, and you've got nearly perfect conditions to test all stability control systems on a vehicle.

 

[zack]

At any rate, I'm still curious about my experience detailed in the original post. Which will improve cornering performance over uneven surfaces... increasing or decreasing the adjustable shock settings?

 

[doug]

Sorry I'm late to mention it, but you might want to read through this thread, NHTSA Complaint wrt Regen and TC, which seems related to this topic.

 

[speedy99]

At any rate, I'm still curious about my experience detailed in the original post. Which will improve cornering performance over uneven surfaces... increasing or decreasing the adjustable shock settings?

Still waiting for my tesla to arrive, but my experience with PSS9 adjustables in a 911 was that the hardest setting was NOT the best. In fact, after having the system set up by a race shop, the street and track settings were this same - and the setting was near mid range. This was a real eye opener for me - and verified on the track. In your case, I would think softer is good, you want the wheels to maintain contact, not bounce off the bumpy pavement. For cornering, roll bar settings also come into play, so there isn't a simple answer, other than full firm is not always best for max traction.

In fact, in wet conditions (lowest traction), max SOFT (shocks and rollbars) is the best (track) setting, as it allows the suspension to absorb any unsmooth inputs by the driver before they cause loss of traction. Some people even disconnect their roll bars completely when racing in the wet.