Out of Control Traction Control??

[MikeM.]

Traction control trying to slow you down, cruise trying to speed up, what would happen? Does one system override the other? Just curious how the computer determines what to do?

AFAIK, cruise control is over-ridden by anything else.


Touch the brake? CC goes into standby mode.


Lose grip under acceleration? A power reduction request is sent to the engine control module. Would cruise control override that and throttle up? No, of course not! Cruise control will onlythrottle up when appropriate.

The programming of the CX-5 is very sophisticated and, from what I've seen by putting the car in a huge variety of challenges, it's very robust/reliable.

 

[craigo]

AFAIK, cruise control is over-ridden by anything else.


Touch the brake? CC goes into standby mode.


Lose grip under acceleration? A power reduction request is sent to the engine control module. Would cruise control override that and throttle up? No, of course not! Cruise control will onlythrottle up when appropriate.

The programming of the CX-5 is very sophisticated and, from what I've seen by putting the car in a huge variety of challenges, it's very robust/reliable.

CC and TCS have been under the same umbrella for many years now...probably since the development of TCS as the two need to work in concert. I just found a video from 1973 for Buick that introduced them together: https://www.youtube.com/watch?v=SKozAIgESPw (with delightful funky bass line). Interestingly, maxtrac failed to catch on because it was an emissions beast.

 

[craigo]

Tom95 "In looking back I probably shouldn't have been using Speed Control but my other car is a Prius (2005) which has 100% Traction Control and I have been in similar conditions using Speed Control."

Your heaver Prius has narrow tires that press the water out of the tire/road interface better than the lighter CX5 that has wider tires. What is the tire pressure in your Prius?

So many variables to account for. 'Similar' wet road conditions are anything but if studied closely.

It's mild rain here today. Easy to make the Toyos spin with even mild acceleration. If he engaged the CC and it accelerated, it would immediately sense the slip, disable CC, drop a couple of gears which induces engine braking and slow down quickly.

 

[yrwei52]

Let me say, THIS IS NOT ACCEPTABLE and I hesitate to think what might have happened if I had been an inexperienced driver in this situation.

As I've posted in another thread, you can file a safety complaint to NHTSA and report this incident to Mazda North American Operations' Customer Experience Center. Every system has its limitations. But this may force Mazda to look into the issue and make some safty improvement hence save some lives later.

 

[Tom 6-6]

Just need to slow down and not use cruise control in the rain. The government doesn't need to get involved in a situation where it is driver error.

 

[MikeM.]

Just need to slow down and not use cruise control in the rain. The government doesn't need to get involved in a situation where it is driver error.

Agreed. Hydroplaning can be like hitting a wall of water once the tires lose contact with the road. The water between the tire and road surface has huge friction compared to a tire planted on the road surface.

Filing a NHTSA safety complaint about hydroplaning would be almost as laughable as filing a complaint about icy roads. I can see it now:

I was just minding my business, cruising along at 60 mph. It had been raining but as evening approached the rain stopped and the temperature dropped to 28 degrees. My tires had at least 5,000 miles before the wear bars were flush. I applied my cruise control about the same time I went to change lanes and without warning my car started sliding and the brakes were pumping on/off but my foot was not on the brakes. Then it downshifted and started accelerating like it had a brain of it's own! My foot was not even on the gas. I didn't go very far sideways but t was real scary nevertheless. I pulled over to the shoulder and gathered my wits. Everything appeared back to normal so I drove off more slowly this time and didn't turn the CC back on. This is a safety defect!

 

[vroom]

Agreed. Hydroplaning can be like hitting a wall of water once the tires lose contact with the road. The water between the tire and road surface has huge friction compared to a tire planted on the road surface.

Water between the tire and road lowers the friction compared to being planted on a dry surface, which is why you can end up sideways in a hydroplaning situation, but it increases rolling resistance a lot (which is probably what you meant, just making this more clear for others). In that situation, the CC might try to compensate the increased resistance by downshifting. Perfectly normal.

But yeah, any competent driver should recognize a potential hydroplaning situation and drive accordingly. Manufacturers can only be expected to compensate for incompetence to a certain degree (I'm thinking BSM for people who don't do shoulder checks for example)...

 

[piotrek91]

but it increases rolling resistance a lot. In that situation, the CC might try to compensate the increased resistance by downshifting. Perfectly normal.

I can't imagine the resistance of a hydroplaning tire being higher than that of a wheel rolling on pavement.
An un-driven wheel will spin down, but a wheel actively driven by the engine should spin faster when hydroplaning.

What I think happened to OP:

1. He started hydroplaning
2. cruise control closed the throttle
3. the front tires spun down to a low speed, so the car downshifted to 3rd and added lots of gas
4. the wheels are floating on water so they quickly spun up to high speed, so the TC kicked in and shut off cruise.
5. Now OP's car is in 3rd gear at 60MPH with no cruise control
6. OP is frightened and he doesn't get on the gas enough to overcome the engine braking of 3rd gear at 60MPH

The only thing I don't get is why the gear display showed 3 instated of D.. maybe OP bumped the shift lever in to manual mode during the ordeal?

 

[vroom]

I can't imagine the resistance of a hydroplaning tire being higher than that of a wheel rolling on pavement.
An un-driven wheel will spin down, but a wheel actively driven by the engine should spin faster when hydroplaning.

That is exactly why I make a difference in my post between friction and resistance. To displace all that water takes a lot of power (water is heavy and incompressible). This will slow you down a lot, and the car will need to work harder to keep up speed. Agree though that all that newly injected power might cause the tires to spin-out a bit.

 

[piotrek91]

That is exactly why I make a difference in my post between friction and resistance. To displace all that water takes a lot of power (water is heavy and incompressible). This will slow you down a lot, and the car will need to work harder to keep up speed. Agree though that all that newly injected power might cause the tires to spin-out a bit.

reading your posts I get the impression that you think that a hydroplaning wheel will somehow require more engine power to spin than a non hydroplaning wheel.
I don't think this is the case.

 

[MikeM.]

I can't imagine the resistance of a hydroplaning tire being higher than that of a wheel rolling on pavement.

It's true, the hydroplaning wheel has a lot more resistance than a rolling wheel. The mechanism is called hydrodynamic friction (or drag).

For example, say you're driving 70 mph in a straight line (in a car without DSC) and there is a puddle in the left wheel path (but not the right). The car will spin-out counter-clockwise, not clockwise. This proves the hydrodynamic drag is slowing the left side more than the rolling resistance on the right side. A car equipped with DSC will apply the right rear brake to prevent a spin-out.

 

[vroom]

reading your posts I get the impression that you think that a hydroplaning wheel will somehow require more engine power to spin than a non hydroplaning wheel.
I don't think this is the case.

No, a hydroplaning wheel takes less power to spin up (increase its rate of rotation when more power is applied), you are correct, that is not what I am saying.

Initially, the wheel is spinning at the same speed the car is moving because the tire is coupled to the road. A deep puddle is encountered, and a lot of water needs to be displaced. The car looses a lot of speed in that process, and so do the wheels because more power is not being applied yet. This fools the CC in thinking that a lot more power needs to be applied to keep up speed, but all that does is spin the wheels faster than the system expects because there is now a low friction film of water between tires and road. This makes for a very confusing situation for the system, leading to strange behavior as noted by the OP.

Am I making any sense here?

 

[piotrek91]

It's true, the hydroplaning wheel has a lot more resistance than a rolling wheel. The mechanism is called hydrodynamic friction (or drag).

For example, say you're driving 70 mph in a straight line (in a car without DSC) and there is a puddle in the left wheel path (but not the right). The car will spin-out counter-clockwise, not clockwise. This proves the hydrodynamic drag is slowing the left side more than the rolling resistance on the right side. A car equipped with DSC will apply the right rear brake to prevent a spin-out.

I agree that there is more resistance to forward motion when going though water or hydroplaning.. but as you can see in that old NASA video, when hydroplaning actually occurs it takes very little force to spin the hydroplaning tire.
https://youtu.be/HekD4jhepSs?t=7m20s

 

[piotrek91]

Am I making any sense here?

yes you are.
We're on the same page.

 

[vroom]

Another situation where low fiction and high rolling resistance can coexist is deep snow. Apply too much power too fast and you spin out (low friction). You need to apply power more gradually. But when you get up to speed you need to apply more power than on a dry road to maintain your speed (high rolling resistance).

Snow drifts on the road could probably cause similar CC erratic behavior.