qb14

I'm occasionally having a scary issue with my '13 RC450h. There are a couple of parking lots where the transition from the parking lot to the road is not particularly smooth and the speed of the other cars on the road require that you get up to 50mph pretty quickly.

When I hit the gas then then hit the bumps in the transition, the TRAC light turns on and power to the wheels is lost for a couple of seconds (exactly the opposite of what I want to happen). Is this happening to other people or is this something that needs to be looked at? Is this just a result of traction control and I need to remember to turn it off when leaving a parking lot and entering a busy road?

Cruiter

It's normal. As you go over uneven roads like that there is a very minor and brief moment on occasion where one wheel rotates slower than the other, especially if braking. The computer senses it and takes over braking control until both wheels are turning the same rate. I have a 2010h and I know one particular road that's rough like that where I make a left hand turn about 20mph which is just enough to make it happen. I get a kick noticing how quickly the computer takes over. Sometimes I even get a tighter (more pressure) brake pedal. It's perfectly normal.

Bert, if you read this I'm sure you can provide a more technical explanation than what I just experience.

Droid13

Completely normal. Traction control is ABS in reverse. Just like ABS is designed to prevent skidding while braking, traction control prevents excessive wheel spin while accelerating. These systems help the typical driver stay in control during situations of low traction or aggressive driving. If you want maximum power to the wheels regardless of the outcome, then as you say simply turn off the traction control. Keep a firm grip on the wheel though, under full acceleration unexpected changes in traction of either tire may result in unexpected vehicle direction.

PS What sounds even more scary is having to drive somewhere that it takes 295HP full acceleration to safely manage a turn. What do the poor people do?

BertL

Jim and Andy did a great job on explanation. OP, for me the greatest learning curve with my RX450h, as well as my new MBZ is remembering the things the car will do to help improve my safety. What can be almost as strange, especially as these vehicle systems hopefully don't have to kick in often, is when they do ... as the driver, it makes you wonder "What the heck just happened?". As others have said, the computer kicks in faster than our reflexes, so what happens is generally a whole lot better than if it wasn't there. ...anyway, for me, the trick is to become acquainted with the safety systems in each of my vehicles by reading and re-reading those sections of the manuals so I have a sense of what the car will do if it needs to... If you've not done that recently, it may be worth your while.

TRAC coming on is one thing and wasn't as startling to me the couple of times I'm aware it's happened to me. My RX450h also has the optional Pre-Collission Assist, and if the truck thought I was going to hit something, more things would occur, pre tensioning seatbelts, etc, etc that could be startling -- I've not encountered that situation to-date (thank goodness). My new MBZ goes even further than that and would literally try to bring the car to a complete stop in the same situation -- even if I didn't put my foot on the brake. There are bunches of other systems as well that go just a little further than what more conservative Lexus does. E.g. I was in my MBZ yesterday and a €££<#^< didn't stop while he was making a right turn when a bunch of cars including me were already going through the green light. Accident avoided as lots of people applied their brakes and swerved, but let me tell you, those MBZ systems went off -- brakes were being applied even harder than I was pressing (felt like when ABS kicks in), seat belts tensioned for impact as if I were in a straight jacket, alarm went off on dash and audibly. The guy stopped, and as I and the others kept going, my car went back to normal as if nothing happened, and my mind started to check through the things I had read about that my car just did to take care of me. THAT was my latest introduction to safety systems at work. I love 'um.

oohpapi44

iTrader: (1)

Before you try accelerating into traffic without traction control, might be worth to drive to the parking lot on an off day and seeing what your comfort level is like over the bumps without the safety net.

But before you choose that route, make sure you are getting max power with safety gear on (not in ECO mode, using Sport mode, etc). I would exhaust those options first to see if you can get more of a jump off the line before you forgo traction control. Losing the safety net and adding in a rough road could make for a volatile combination.

vlad_a

Let's start with the fact that 450h has VDIM, which is a well-integrated VSC and TRAC systems, rather than 2 separate units. Loosing throttle response is normal when traction is lost. The car is "keeping you safe".
FWD vehicles are more prone to slip the wheels. Even if you got AWD, it is still FWD for the most part.
You can learn how to deal with the nannies your car has by getting on the gas a little later so Trac would not trigger. You can certainly turn it off. With FWD, just hold on to the steering wheel. Release throttle slightly if you're spinning wheel(s) and need to turn.

I keep trac off most of the time on my IS300. And that's RWD, which requires much more control.

CometVR4

This happens to my 335i quite often if I happen to run over some broken pavement while accelerating. You have to imagine what's going on under the wheels. Same thing could happen when applying braking while on a bumpy road. Less weight on a given tire as is lifts across the bumps. My advice would leave TCS on and just try applying less power until you can get on a smoother section of road.

Last thing we want to tell someone to turn off TCS/VSC that doesn't know what they're doing end up in a bad situation.