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post #1 of 12 (permalink) Old 06-24-2019, 11:39 AM Thread Starter
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The 3g 6MTX Under Extremes

Here's an interesting observation....

I'm property shopping right now, including in some areas with rather "extreme" access. As in on top of a ridge, with a switchback-laden and very steep driveway. Many of these, if not most, are gravel "roads" (if you can call them that.)

The 6MTX (I have a 2016 Sport) has an interesting limiting factor in these conditions. First, all front-drive vehicles have a nasty characteristic in that weight transfer is to the rear under acceleration and on a steep grade with loose substrate this is very bad to start with. In other words your ultimate climbing capacity in such, assuming no ruts that cause you to high center on something, is mostly about the traction loss from that effective weight shift. You do much better with rear-wheel drive in such conditions.

Anyway, the 6 MTX has a second limiting factor -- even with TCS intentionally selected OFF if you get into any sort of wheelspin event (even a light one) under such conditions the ECU will shut down power delivery even though you've told the system not to do that. Note that you CANNOT slip the clutch in such an extreme hill-climbing situation to try to get further into the torque band; you'll light the clutch on fire if you do that, so you have to make the climb in first gear with the clutch all the way out (and locked) and keep your vehicle speed high enough to remain reasonably within the torque band of the engine.

This was a quite-extreme situation but I wanted to know if I could get up that driveway in my "6." The answer was "no"; I was forced to back down from about halfway up one specific section. With an automatic I might have had different results due to the torque converter (if you don't overheat it, which you might), but in first gear with the MTX it just wasn't happening.

This was a ridiculously extreme set of conditions but it was a useful piece of knowledge to have -- I now know where to start worrying about that limit in this vehicle.
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post #2 of 12 (permalink) Old 06-24-2019, 01:13 PM
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"When in doubt, throttle out"


Seriously though, sounds like something more off-road capable would be needed for that property you're describing. You could look at reducing tire pressures but that would get cumbersome quickly. Interesting the traction control never full turns off though.
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post #3 of 12 (permalink) Old 06-24-2019, 02:20 PM Thread Starter
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Well yes. Generally it's ground-clearance that's the problem but not in this case; there wasn't any serious rutting or similar that got you into trouble there. If the drive had been PAVED it would have been ok too, but paving that would be prohibitively expensive (never mind the substrate requirements so it doesn't get washed out), so... no.

Essentially what appears to be the case is that there is ECU code that detects what it thinks is serious wheel hop sort of stuff and shuts down the power delivery. This might in fact be a reasonable protective measure, as that sort of thing has a habit, if pushed too hard, of doing really SEVERE damage to things.

I wasn't all that surprised to find the limit; what was surprising was exactly what it came from. I suspect a Miata would have made it without too much trouble simply because it's rear-drive.
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post #4 of 12 (permalink) Old 06-24-2019, 02:41 PM
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Time to put it in reverse and try again!

I'm curious as to what the gradient is for that driveway because there's a section of Mt Washington Auto Road that's around 18% (maximum allowed for public roads) and it, until recently, was all clay. My 6 got up it without issue, but it also wasn't winding switchbacks so I could keep momentum going.

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post #5 of 12 (permalink) Old 06-24-2019, 03:16 PM
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Funny this subject came up.

Went to Road America yesterday for Indycar. Staff was forcing the fan parking situation in that they point, you park. Case closed. As luck would have it they parked me in a glacial bowl covered in lovely spring grass and it was going to rain before I left. Despite my protestations, that's where I wound up (big crowd, no patience from the staff). Sure enough, it rained 10 minutes after the race ended, and my attempts at getting out of the bowl were further frustrated by non moving traffic. By the time I got far enough up the hill to make a run at the plateau and pavement, the wet grass and underlying gravel rendered my efforts useless as the traction control, on or off, essentially stalled the car (6spd manual). Further excitement was provided by the minivan next to me trying to cut the line, losing traction and having him slide sideways toward me front end first and a car far too close behind me to give me enough room for an alternate attempt. Cursing and finger pointing ensued. Eventually I was able to back up and realign myself for a better run and I escaped. But Damnit!

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post #6 of 12 (permalink) Old 06-24-2019, 06:22 PM Thread Starter
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By the time I got far enough up the hill to make a run at the plateau and pavement, the wet grass and underlying gravel rendered my efforts useless as the traction control, on or off, essentially stalled the car (6spd manual).
Yep.

TCS being deliberately off didn't matter in this instance, which REALLY pissed me off. I took a running start at that section too.

It wasn't the grade per-se; it was that the "gravel" they had used was best described as "small rocks"; common in mountainous and other seriously-hilly areas, but REALLY STUPID! A FAR better choice is pea gravel plus some sort of binder, even if only SOMEWHAT effective in reducing the frequency of having to come back out and lay more of it (e.g. tar); I have no idea if what they used to use in this regard as binder is even legal nowdays, but it used to be VERY effective. The other problem is that with any sort of "stable" driving surface on the side of a ridge like that you HAVE TO trench the high side and then every 100'-200' put a culvert pipe in UNDER the road from the high to the low side to keep runoff water from accelerating down the trench on the high side or the water that runs off WILL undermine a solid surface or rut a dirt one. Paying someone if you don't own (or don't know how to use) the earthmoving gear required is expensive and people don't want to fork it up.

In any event the problem is that until the "gravel" gets embedded into the underlying dirt it slips under load and once it starts slipping the car detects differential speeds on the drive wheels and TCS on or not it will deny you anything more than VERY LIMITED slip; if you try to force through it with the throttle it'll literally deny the engine fuel entirely and stall it (it did in my case.)

I HATE nannies and this car has one in this regard that you can't shut off. Most of the time they're fine but in this specific case I think I could have made it up the hill had the ECU not interfered with me.

Oh well.
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post #7 of 12 (permalink) Old 06-24-2019, 10:49 PM
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My case, as well. If I could have gotten good purchase on the gravel I could have kept momentum, but HAL had other ideas lol.

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post #8 of 12 (permalink) Old 06-25-2019, 07:49 AM
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Dang, @GerryB glad you made it out unscathed!

I've had my issues with HAL ( ) in the snow as well, but at least in those scenarios I've got dedicated snow tires to back me up.

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post #9 of 12 (permalink) Old 06-25-2019, 10:23 AM
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Precisely. My 2005 6s had (I believe) the most aggravating TCS in the world. It was so violent it would almost snap your head into the steering wheel. Or simply stall you in light snow. Blizzaks forever!

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post #10 of 12 (permalink) Old 06-25-2019, 10:52 AM
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Quote:
Originally Posted by GerryB View Post
Precisely. My 2005 6s had (I believe) the most aggravating TCS in the world. It was so violent it would almost snap your head into the steering wheel. Or simply stall you in light snow. Blizzaks forever!
Quoted for agreement. The 1st-gen TCS was the most maddening thing I ever had on any of my cars. Luckily, Mazda has steadily made improvements on it (at least IMHO). The 2nd-gen was much more forgiving, and even with all the torque from the turbo going to the front wheels, my 3rd-gen rarely kicks on the TCS light...

I'm tempted to try what tickerguy did on my 6, just to see if the TCS activates by itself...


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