Traction control TRAC

[kkayser]

Does anyone know if the traction control on 2004 Prius' transfers torque to the non-spinning wheel? My understanding is that when one wheel spins, the ABS system is supposed to cause drag on the spinning wheel so that torque is transferred to the other wheel through the differential. On my BMW, it works. If I have one wheel on ice and the other on pavement, when I accelerate the car simply goes forward. If I do the same thing In my Prius, however, all that happens is the engine stops running. If I do not let up on the gas, the car will inch forward until both wheels are on pavement then lurch forward.

Is it really supposed to work this way, just kill the engine, no torque transfer?

[Tideland Prius]

it doesn't "transfer" torque. Rather, the ABS system simply brakes the spinning wheel in hopes that it can get traction. If all else fails, it'll also retard the engine output and reduce power such that the wheels can get grip without spinning.

[priusenvy]

[Deleted due to initially posting information not applicable to Prius and not having new information to share]

[kkayser]

The differential can only apply torque to both wheels equally. Let's say one wheel is on dry pavement and one on ice. Little if any torque can be applied to the wheel on ice. Therefore, litttle, if any torque can be applied to the wheel with traction, and the car stands still. Now, if the wheel with no traction gets to dry pavement, torque can be applied to that wheel and to the other wheel as well, and the car moves. But what if, instead of the spinning wheel getting to dry pavement, we apply the brake lightly to the spinning wheel? Torque can now be applied to the braked wheel AND the wheel on pavement, and the car moves.

In short, braking the spinning wheel allows the differential to transfer torque to the non-spinning wheel.

[Pinto Girl]

<div class='quotetop'>QUOTE(wauwis @ Dec 21 2006, 09:37 AM) [snapback]365037[/snapback]</div>

The differential can only apply torque to both wheels equally. Let's say one wheel is on dry pavement and one on ice. Little if any torque can be applied to the wheel on ice. Therefore, litttle, if any torque can be applied to the wheel with traction, and the car stands still. Now, if the wheel with no traction gets to dry pavement, torque can be applied to that wheel and to the other wheel as well, and the car moves. But what if, instead of the spinning wheel getting to dry pavement, we apply the brake lightly to the spinning wheel? Torque can now be applied to the braked wheel AND the wheel on pavement, and the car moves.

In short, braking the spinning wheel allows the differential to transfer torque to the non-spinning wheel.
[/b]

Right; this is true on any car without a locking differential, not just a Prius.

[dandeman]

<div class='quotetop'>QUOTE(Pinto Girl @ Dec 21 2006, 05:32 PM) [snapback]365404[/snapback]</div>

Right; this is true on any car without a locking differential, not just a Prius.
[/b]

Correct... I used this trick in my 4Runner 4x4 (that doesn't have lockers) to get up hills with one wheel hanging in air and the opposite corner wheel having very little weight on it..

With it in 4Lo and loading the brakes a bit, it applies enough torque to other wheels firmly on the ground to move it forward...

[jayman]

Last winter we had an unusually warm spell, which resulted in the edges of intersections being icy but the centre part being bare. Even with my studless winter tires - Yokohama Ice Guard 10 - my Prius was pretty slow getting off the line. Other cars didn't seem to be having any trouble.

If the car had "real" traction control, the computer would briefly apply the brake to the spinning wheel, allowing torque transfer to the wheel on dry pavement. My 2004 Prius is clearly not like that, it just kills the power. The "Traction Control" should be renamed "PSD and chain protection device."

I don't mind using studded snow tires, and with my new Goodyear Nordic tires I finally have a good winter car. Have had several blizzards so far and I easily have better traction and stability than almost any other car, pickup, or SUV.

As far as the parking brake trick, a million years ago in college I had a 1976 Chevy Monte Carlo with a factory limited slip. It was already four years old and the clutch plates were probably cooked already, but on ice I had to use the parking brake all the time to get torque transfer to happen. Unless I floored it and got the four barrel to really open up.

My 1984 Ford F-150 has no trouble at all if one wheel is on ice and the other wheel is on dry pavement. A locking rear end is the best modification you can make to a pickup. If one wheel is on ice and the other is on dry pavement, and I floor it, the wheel on dry pavement squeals and I leave behind a nice black streak.

[priusenvy]

<div class='quotetop'>QUOTE(jayman @ Dec 27 2006, 10:15 AM) [snapback]367230[/snapback]</div>

My 1984 Ford F-150 has no trouble at all if one wheel is on ice and the other wheel is on dry pavement. A locking rear end is the best modification you can make to a pickup. If one wheel is on ice and the other is on dry pavement, and I floor it, the wheel on dry pavement squeals and I leave behind a nice black streak.
[/b]

I've actually read where some people think a limited slip differential is dangerous on icy roads due to the amount of fishtailing it can induce. Without a limited slip differential, the stationary tire at least has some traction and can prevent the back of the car from moving sideways. But with a limited slip differential, both tires will spin, both tires will lose traction, and the car is more likely to fishtail.

[jayman]

<div class='quotetop'>QUOTE(priusenvy @ Dec 27 2006, 04:41 PM) [snapback]367368[/snapback]</div>

I've actually read where some people think a limited slip differential is dangerous on icy roads due to the amount of fishtailing it can induce.
[/b]

Happy New Year, just got in.

My 1984 Ford doesn't have a limited slip in the rear axle. A limited slip has clutch plates and a preload spring(s) to bias the clutches. They react to input torque, not wheel speed difference/delta. Hence at a stop or slow speeds, a regular limited slip is worthless.

Floor it and the plates firmly hold. But most of us don't try to drive on snow/ice with the gas pedal to the mat.

I had ordered that truck with the TrakLok option, and it was worthless. In the mid nineties I took apart my Ford 8.8 inch differential, and got a new 3.54 case with spider/side gears or "open" differential. In 2002 I put in a PowerTrax LockRite. It was very simple: take out the pinion cross shaft, the spider gears, and the side gears, and put in the new "couplers."

http://www.powertrax.com/lockright.html

This design drives both axle shafts equally, so it's like a Detroit Locker and is considered "locked" all the time. The only time it disengages is when you go around a sharp corner at low speed, then the outer wheel overruns the coupler, which is spring loaded. The inner wheel then has power around the turn and the overrunning coupler makes a "clickclickclickclickclick" sound.

You're absolutely correct that an EMPTY pickup truck with a locking rear end should NOT be driven in snow and especially on ice. With both rear wheels locked together, the rear end will step to the side. The best way to overcome that is to put 400-600 lbs of sandbags in the box.

With weight in my truck, it's very controllable in deep snow and even on ice. For winter I run dedicated snow tires, as I use the truck to plow out the driveway and yard at my hobby farm. Last winter I had to get new winter tires, I run studded Cooper Discoverer M+S.

From Dec 30 - Jan 1 we had a raging blizzard and received 22 inches of snow at the hobby farm. A neighbor invited me over Dec 31 and I managed to get my Prius stuck at the stop sign on the highway. Wheels wouldn't turn, Trac light bllinking, etc.

I called that neighbor for help and he came over in his wife's 2003 Ford Focus wagon. She's a nurse and has to get to work no matter what, this fall they put on studded Goodyear Nordic based on my review. No problems.

This neighbor is a long haul trucker and his tractor has an Eaton ABS and traction control system. He has learned the hard way what it can and cannot do. Rather than poke the Defeat button, he tried a different trick.

He told me to rapidly pump the gas pedal, trying different cycles of flooring the pedal. At around a 2 second period with my Prius the wheels actually will turn a bit, enough to rock and get going anyway.

This isn't a perfect solution. If you run studded tires like I do, a very slight amount of wheelspin helps the tire "bite" in and move you. I'll admit it feels totally unnatural to drive a car through deep snow by constantly flooring and releasing the gas pedal.