Torsen Diffs

[Sailor]

I understand that with a Torsen, IF you lift a wheel then all traction is lost.
I noticed today when I was trying to get into an odd driveway that I lifted a wheel completely off the deck and that wheel spun..I went nowhere.
Is that correct (I'm a ZF sorta guy) or have I managed to break my diff?

[hks_kansei]

it is correct.

The diff shouldn't be broken.


a trick apparently (according to google) is to pull the handbrake on a few clicks so taht it causes drag on the wheel, this can help mimic traction so it can send some to the other wheel.

[NitroDann]

Thats correct. The torsen has a torque bias differential of up to 40% by memory, the difference is 100% when one wheel is off the ground, in that case it open diffs.

Thats why they are slow across ripple strips and bumps compared to a regular one.

Dann

[Sailor]

Cheers guys..confirmed my suspicion on the torque bias aspect.

So I don't have to race out and buy that OS Gikken....I'm almost disappointed

[hks_kansei]

Thats correct. The torsen has a torque bias differential of up to 40% by memory, the difference is 100% when one wheel is off the ground, in that case it open diffs.

Thats why they are slow across ripple strips and bumps compared to a regular one.

Dann

I think the bias differed between Type 1 and Type 2, as well as the actual mechanism that operates it.

[Matty]

it is correct.

The diff shouldn't be broken.


a trick apparently (according to google) is to pull the handbrake on a few clicks so taht it causes drag on the wheel, this can help mimic traction so it can send some to the other wheel.

Yep, I have heard this too - I believe it's in the owner's manual for the Hummer that traction can be regained by gently squeezing the brake pedal.

The Torsen design is based around the concept of a "bias ratio", that is, the torque can be distributed to the side with grip on a proportional basis up to the bias ratio. eg if the bias ratio is 2:1, and the inside wheel breaks traction at 100Nm of torque, the outside wheel will be fed up to 200Nm (limited by the power output of the car). But if the inside wheel is off the ground, it has 0Nm resistance, and 2 x 0 = 0 to the outside wheel.

Nerds look here

[Steampunk]

http://www.torsen.com/home.htm

[honki3rider]

What happens when I have a wheel in the air?
As mentioned above, the Torsen differential is a torque multiplier. The Torsen requires some type of resistance or friction in the system to function properly. A wheel in the air provides zero torque or friction on the system and as the Torsen multiplies the available torque, zero, by its TBR, the end result is still zero. In response to this, we developed the Torsen T-2R with pre-load to combat those wheel in the air situations.

Would it be safe to say that if you are sure you have a Torsen system in your car, you have the type 1 if your wheel lifts and you don't go anywhere and a type 2 if your wheel lifts but you are still able to move forward with a jab of the throttle? Torsens confuse me.

[hks_kansei]

Nope, type 1 and type 2 act the same, the only difference is the torque bias and the way they do it (t1 and t2 look completely different on the inside)

the only one that would do what you said is the T2R

[flycasta]

A torsen is just another kind of LSD. Like all plate LSD's they will allow a certain amount of slip. All LSD's have to allow slip otherwise they may as well be called ESD's Eliminates Slip Diff or commonly called a Locker. The amount of slip they allow is dependant on how the car should handle. Most cars have open diffs and the reason for that is to allow cars to turn corners and change direction easily in wet and dry conditions by allowing each wheel to turn at different speeds, plus they are also very cheap to manufacture and keep the costs of vehicles down.

Plate LSD's wear over time and when new will stop a wheel spinning up on wet painted lines, oil/slippery spots or when weight transfer of the car allows one wheel to become unloaded enough that that wheel can break traction, it doesn't have to be in the air, but over time they will slowly allow that to happen, given the same amount of torque transfer applied, more torque will lock them up but the amount of torque over time will reach its limit. Clutch plate LSD's have preload put on the clutch plates inside which gives instant lock up upon torque transfer and that preload will slowly loosen with wear and that it is why they wont lock up as easily. The amount of preload will depend on the manufacturer and the amount of friction surfaces inside the LSD. Too loose and you're wasting your time, too tight and you may as well have a locked diff. I had a standard Mazda plate LSD in my last B2600 and it would still lock boths wheels at 150,000kms no problems but it would require more acceleration/revs to get that to happen. Feathering the clutch will get it to happen because you are removing the torque for a split second and then reapplying it.

Torsens will allow more slip to an unloaded wheel because they are generally not as highly preloaded as the clutch pack LSD's. There is some preload inside the Mazda Type 2 Torsen and that also loosens over time but it is less noticeable because the LSD is torque biasing via gears and gears dont wear any where near as quickly as plates. The Type 2R and Guru Torsens have much more preload that lasts longer but they can also create problems of understeer in the wet because they are so tightly preloaded. Even on gravel surfaces the Torsen will allow 1 wheel to spin if the gravel on one side of the road is looser packed than the other side. Generally it is very hard to get an IRS car to lift a wheel at low speeds so the loss of traction can be put down to the surface the 2 wheels are on. Lifting a wheel at high speeds is more a possibility but at speed the car would very quickly see the wheel back on the ground again and time loss due to traction loss would be minimal. Most traction loss for torsens is on accel through cornering again when 1 wheel becomes unloaded enough to break traction, the trick then is to adjust suspension, if possible, to keep weight transfer to a minimum and stop that wheel from breaking traction.

Torsens are better if you want to put your diff together and forget it, they will give you pretty much the same feel from the start to the end of the diffs life. They have their little problems but overall are an excellent option over an open diff. The clutch pack LSD's are excellent but require more attention which is ok if you are racing and have the diff in and out of the car for different tracks or if you like to pull things apart to check them every so often. MX5's have a lot of different brands and types of LSD available to them so choice is a little harder to work out, most of the early RX's and Mazdas only had the plate type LSD's until the Gurus came along so their choice is limited unfortunately.


Duane