Traction Control

The Prius "traction control" is not really traction control. It's CVT over-rev control. If the wheels were allowed to spin freely as in slipping on an icy surface, components of the transmission could go over 10,000 RPM, resulting in a steel/oil soup inside the transaxle.

Better tires help. I have Michelin MX4V 195-60-15. It still does it occasionally from a standstill on surfaces that are sandy.

 

No, it's really traction control. It just happens to be used to protect the HSD as well. For example, it functions as traction control in gravel and on snow, where it helps you to move when you may not be able to otherwise. Two days ago it prevented me from spinning out as I turned onto gravel with the throttle depressed (unseen oncoming car caused me to panic).

 

I'm trying to decide how big a risk it would be to disable traction control once in a while in tough spots if I am careful not to overspin the wheels. Of course, I have no idea what would constitute "overspinning". I assume a spin equal to the spin rate you have at highway speeds would be fine - but I'm not sure about that and I'm not sure how to know how fast I am spinning the wheels. Would a tach read out help? What do you all think? Should we stay away from disabling the TC under any circumstance, or just be real careful???

The problem is that in hilly snow country with steep drives and such it is at times impossible to keep adequate momentum up a long hill if you can't spin the wheels a bit. At least that has been my experience with "normal" vehicles. I do recognize though that it could be that I just need to learn a different approach to these driving situations and that maybe it will work out to back off on the accelerator. I know that in general even with normal vehicles a soft accelerator to avoid spinning is best, but not always. It seems though that sometimes a spinning tire is inevitable at a particular point in a climb but being able to keep spin going does apply some ongoing forward propulsion - often enough to make the crest of a steep slippery hill. This is going to be an interesting winter for me. Maybe I will learn a thing or two. I have been living in Vermont for 30 years and so I have a lot of experience driving in hilly snow country.

 

Pardon me if I disagree. True traction control would allow torque to be applied to the wheel that has traction while reducing traction to the wheel that wants to spin. I've had situations where one wheel was on dry pavement and the other was on ice - resulting in absolutely no movement by the "dry" wheel and a momentary spin by the "iced" wheel before the "traction control" shut everything down.

In the Prius system all traction shuts down if one wheel wants to spin. There is no limited slip differential in the system, which would be necessary to split the torque between the 2 drive wheels.

 

You're talking of limited slip, not traction control. In the Prius the traction control system actually does keep trying (better in model years 2005 1/2 and later), so it really is traction control. It is not limited slip, something that can function as traction control but isn't. You can still spin both wheels rapidly with limited slip diffs.

The problem with disabling traction control is MG2 puts out almost twice the torque of the ICE, and does so at 0 RPM. That is very hard to react to. Because the RPM of MG1 (the motor that can be destroyed) is proportional to wheel spin rate and inversely proportional to ICE RPM, if the ICE has stopped (because YOU are stopped), AND because it takes a finite time to spin it back up, you can very easily overspin MG1 before the ICE spins up.

Let's talk about the benefits of "spinning a wheel" to propulsion. Really the ONLY time it helps is if the tire is throwing something back, giving you propulsion, or digging to a higher traction surface. If there is pavement below, a spinning tire will simply ice it up. That's less traction than snow.
In ice and snow you really don't want the tires to spin very fast because they heat up and that creates a water film. That equals almost NO traction.
With the Prius, you want to apply -some- throttle, but not a lot. You apply it and hold the pedal there, letting the system keep retrying. If the car won't move then the only way forward is to use momentum. Stop, reverse, and try again at a higher speed. The Prius WILL NOT plow through deep snow. Snow deeper than 6 inches will stop this car, unless it's really light powder. Just from the ground clearance.

Good winter tires will make a big difference. Disabling traction control will get you a destroyed HSD eventually.

 

Well, I do accept everything you are saying - but I still think there are times on a long hill climb in gravel or hard pack snow for example where this car will kill all your momentum the moment the tires loose traction and spin even just a little bit - if they would just let you spin a bit you would not have the loss of momentum issue. Also, I hate to sound like a complainer, but if you sell a car in Vermont and you don't disclose that it simply will not drive in 6 inches of snow you are going to have a lot of very angry customers on your hands. We often get 6 inch storm - it is a regular thing. What the heck do you do if you come out of a meeting at 5PM and you can't move out of the parking lot because we've gotten 6 inches of show. Ugh. Its wierd though because I have read some posts - one guy in Maine, which is a lot like Vermont - in which the posters claim that with good tires and the right technique this car is actually excellent in snow. If it can't drive in 6 inches of snow its hard to call it excellent.

I guess I just have to make the best of the situation. I'll put some high end snow tires on for the winter and get some practice staying off the accelerator pedal. But I don't think I'm going to fool around disabling the traction control - too risky.

 

Noticed the slip on a wet gravel road last night and have been wondering about how the car is going to or not going to get around come winter.

Some one had mention tires. Is that going to be the only option for us northern drivers and or use another vehicle.

And if the answer is tires are they regular snow style tires? Or will mud and snow work?

I have run all season mud and snow on all my vehicles up here year round. BF Goodrich Touring, but I suppose it will kill the mpg.

 

Okay, I can't sit on the sideline any longer, so let me wade into the discussion.

Issue #1: Is it traction control or is it not?
The traction control system on the Prius works by reducing power when wheel spin is detected. The main purpose of this system is to avoid over-reving the hybrid drive system. The extremely high low-end torque of the electric motors would make this very easy to do, even on dry pavement. As a side benefit, the traction control also helps maintain traction in slippery conditions by avoiding wheel spin.

In this respect it is traction control, but not the most sophisticated kind. Some traction control systems will selectively brake individual wheels to force power to non-slipping wheels. This is a much better form of traction control (in respect to slippage), and is used on Toyota's FJ Cruiser.

Any of the newer Prius (2006 and on) have an improved traction control algorithm. It is still the simple power limiting system, but it is not as aggressive as it was on the earlier Prius. With this new system you can force some wheel spin by holding down the accelerator.

Issue #2: Would disabling the traction control system improve hill climbing in slippery conditions, such as snow or loose gravel?
In one word, no. I agree that some wheel spin is helpful in these conditions, but no human driver will be able to produce limited wheel spin with the Prius without traction control. The low-end torque is just to high. You would end up digging a smoking hole and going nowhere, while possibly destroying your hybrid drive system.

What would be ideal is a speed limiter, which would allow controlled slip in these conditions, much like the limited slip used with diesel electric locomotives.

Tom

 

I think also that those of you who haven't driven in winter are over reacting. Pearl did just fine last winter (all six months of it). I did plow out the back alley once, when we had about 8" of snow. It was powder. Funny, because my plow marks between the wheels lasted three weeks. No neighbors wanted to drive that month I guess.

As with ANY new vehicle, good winter tires on all four wheels are necessary. The tires that come on just about any new car are NOT winter capable. The touring tires are better than the 15" Goodyear Integrities, but are still not winter tires. I didn't want to be changing wheels/tires twice a year so I put on Nokian WR tires and threw away the Goodyears. The current version of the Nokian is the WR G2, though I think you can still buy the WR. They worked very well. They also worked very well all summer with no excessive wear. Excellent rain tire too. There is no mileage hit with these tires.

 

I hope you are right about that. Keep in mind though that driving in snow on a daily basis in the mountains might be quite a bit different than driving in snow in Edmonton. We'll see. I have an open mind. Its just that I had a heck of a time recently driving on a steep gravel driveway so its hard to imagine that snow/ice isn't going to be 10 times worse. There sure are a lot of Pri'i around here so I won't be alone.

 

The most trouble I've ever had with my Prius and traction control was on a steep gravel drive with the OEM Goodyear Integrity tires. It was not a happy combination.

Snow driving has been good. Granted, we don't have mountains, but we do have big hills. We do have a fair amount of snow, sometimes 20 feet in a season. I've also taken the Prius ice climbing in Canada, and it did just fine.

Get some good tires.

Tom

 

The traction control works as designed but does not work as needed, that is, it is poor design. I guess if you live where it doesn't snow, that's fine. But I got stuck for the first time in my life last winter trying to move from a stop. Luckily, I could back up since there was no traffic but got stuck in another place, backed up from there, got stuck in another place and finally had to find a shovel to dig myself out. What a pain. This year I've got brand new tires and will watch the road better to avoid the deep snow in the first place, sticking to plowed roads or staying home!

 

It has to do with the tires. Since I switched to Nokia all weather tires I have not had any problems with the traction control. On occasion it will slip but this is very rare. I live in the Boston area where we get snow and ice in the Winter. Change your tires and the problem will disappear. FYI my mileage has also improved with the Nokia tires. FishHawk

 

I agree with both of these posts, which is to say that with good tires the traction control is manageable in most cases. It has trouble uphill on anything slippery or loose. Driving technique goes a long way in mitigating the problem, but technique alone cannot overcome physics.

On another note for both of these posters: please update your profiles so readers know what kind of car you are driving.

Tom

 

First, I'll mention something I was told years ago -- had my first car in Syracuse NY (has two over-lapping storm belts). A trucker said that he and his fellow truckers kept chicken wire in their own cars ... put some down wedged into the front of each drive wheel when stuck ... and carefully pulled out by gaining traction on it. Unfortunately, they left the wire there and drove off ... not sure other drivers appreciated it.

Second, I traded in a Taurus when I bought my 2009 Prius Touring. The Taurus had traction control, and it worked to perfection for my needs. But, interestingly, there was a switch on the dash which would disable it (of course, it had no electric generator/motor problems to contend with). Using all-season tires here in SE Michigan, it never got stuck in several years of driving, and I could tell that the traction control was a good help to me.

Which brings up the question in my mind about whether Toyota should have engineered in a way for the traction control to close down the electric motor when traction control was needed, but allow power from the ICE to be available. Just theoretical, but I wonder if that would provide the kind of vehicle control we're used to from our non-Prius vehicles.

 

Toyota's HSD 'transmission' cannot function in an ICE-only mode. If the electric MGs are off, then no power can get to the wheels.

However, this does not necessarily preclude other control algorithms for applying or turning off TC while still protecting the electric motors.

 

I have an 08. I love the vehicle in general. But living in Vermont in the winter - or any hilly or mountainous area with poor road conditions - is an adventure to saw the least. I have excellent snow tires and yes it does help. I have adjusted my driving technique which previously had been honed over a lifetime of winter driving in Vermont. Still, this vehicle is extremely poor in hilly snow and ice covered terrain - and even on steep terrain with loose gravel or wet leaves which we see all the time. One particularly dangerous situation is when you are trying to accelerate into traffic on a main road from a stop sign on a secondary road in slippery conditions. Another is when you are trying a ascend a steep slippery hill.

I cannot imagine that Toyota will not have a lot of claims related to accidents and personal injuries related to the extremely poor performance of the vehicle in these conditions. I live with it and make the best of it. But it is a huge design flaw that has significant safety implications. Toyota should deal with this. For now - be aware of the problem, practice in controlled situations, avoid putting yourself in a situation that the vehicle cannot handle, carry a shovel and sand, carry a cell phone, install the best snow tires (not all season) you can afford - make the best of a bad situation.

 

As previously mentioned, the ICE cannot power the Prius without MG1. Setting that aside, it is much easier to control the electric motors than the gas engine. If you were going to shut down one or the other, you would shut off the gas engine.

Tom

 

Just for clarification,
When you say excellent snow tires, can you elaborate?
Which tires, what rating, kinda thing.

Thanks kindly.

 

Toyota is not responsible for the weather and road condition.