Thank you for this first hand information. That is great.

And they are both LSD's (Limited Slip Differential). ATB (Automatic Torque Biasing) or "Geared, torque-sensitive mechanical limited slip differential" to be more clear.
http://en.wikipedia.org/wiki/Limited_slip_differential

 

Torque biasing does not necessarily limit slip. Example: when the biasing is so strong the outer wheel slips

 

I fixed my link above.

A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.

An LSD is in between a standard differential (aka open diff) and a locked diff (no difference in rotational speeds). A locker style differential is better than a spool in some situations as it acts like an open diff when very little torque is applied to the pinion gear, allowing the inside wheel to spin slower around corners. When torque is applied, it 'locks' both axles together. This isn't very good for road going performance applications. We want the lockup to be more predictable. Automatic Torque Biasing and Clutch Style Limited Slip Differentials are here to save the day. They both have their pros and cons.

If I weld the diff in my focus, or install a spool (or any differential for that matter), I guarantee I can spin BOTH front tires. That is not how the terms are defined.

 

If you want to make the rotational speed argument (which is just another way of saying slip) then you should be able to understand that the Torsen design does not control rotational speed at all.

 

I will not make any more arguments. I'll just point you to the manufacturer's websites and you can read for yourself what they market.

Quaife

Torsen (link was down)

Wiki link for torsen


No more arguments from me. Again, thank you so much for the primary source information. Good stuff. Good night.

 

Quaife sells it on their own website as a "Helical LSD".

Personally, I think it is a pointless bit of semantics to argue.

 

it really is i suppose

the fact of the matter is, limited slips limit slip (slip = difference in rotational speed)

torque biasing diffs... bias torque. they do not necessarily limit slip, that is a byproduct of torque biasing.

 

I think it is more important for people to understand the basics behind what they're buying and what the resultant driving behavior is once they're on the road.

Beyond that, the diff is more or less a "black box" sort of a device for most people... and that isn't always a bad thing.

While the engineer in me is fascinated with how it works, I'm much more interested in how it drives once installed.

I definitely appreciate the info you've brought back from the vendors. :thumbup:

 

do they have the same bias then?

 

It appears that under throttle they do. Off throttle.... could be up to interpretation.

This lines up well with some research I did a few years ago where it pointed to a Quaife being "greater than" the typical accepted value of 2:1, and a Torsen being "less than" the typical accepted value of 3:1. I always figured they were both around 2.5:1, but without data to back it up.

 

Since the forward bias is the same or nearly the same that means the helical angles are the same or nearly the same

since the helical angles are the same, the coast bias will also be the same.

so yes, same bias. straight from the horses' mouths.


and to reiterate, 2.1:1 is not the amount of bias. It is the amount of torque ratio at which point the differentials start to bias torque to the more grippy wheel.

 

how it drives once installed comparison (I will use an autocross situation of pulling out of a tight turn for this example):

LSD: attempts to maintain the same rotational speed for the inner and outer tire. Therefore the inner tire is still going to be overloaded and you will spin both wheels, causing understeer.

ATB/TBD: Attempts to bias torque to the wheel with greater torque capacity. The outer wheel will get more torque applied, "pulling" you around the corner and getting you on your way to the next straight.

In my experience the Torsen is VERY useful when I go into a corner too hot. Pedal to the metal and im out of it.


Now, for a straight line situation:

LSD: Attempts to maintain the same rotational speed for both wheels. this will provide great traction since if one wheel starts to slip, the differential will effectively apply (not bias, APPLY) torque to the other wheel which usually has more torque capacity.

ATB/TBD: The differential may never see enough torque difference to bias torque (remember, the Torsen is an open differential until 2.1:1 torque ratio). If one wheel gets started spinning it may already be too late, since you cannot bias 0 torque to the other wheel.

 

the Torsen design does not control rotational speed at all.

I need to correct myself here. The torsen design does control rotational speed by changing the overall gear ratio to each wheel. In my car you can hear the engine change rpm when the torsen is working.

It does not, however, attempt to reduce the rotational speed difference between the wheels. This happens as a result of torque biasing.

 

So if I waded through the jargon well enough, what you're saying is that the Torsen is a better unit for Road courses/autocross and the Quaife is better for Drag. If that's the case, I made the wrong decision, which explains why I still sometimes only see one patch when launching.

 

What he is saying is that the units function identically... Which would be my experience as well.

There are two helical-equipped Foci in my driveway... one with a Quaife, and one with a Torsen.

The downside to detailed information about a bias ratio or a torque ratio is that it is truly meaningless beyond a white paper. I'm sure that Torsen and Quaife are rather tired of internet bench racers hounding them for a single piece of info that doesn't help anybody in the real world.

When you fly into a corner, and begin to apply throttle at the exit, are you calculating how much torque you have running to your inside wheel and at what point will it begin to bias? No, not exactly.

You're waiting for or predicting the classic feelings of understeer, oversteer, wheelspin, and everything else that makes a good driver operate by the seat of his pants. It is a remarkable device, and time is much better spent flogging it around the track than sitting in front of a computer worrying about where it adjusts.

*If* we had access to an adjustable one or we were spending cubic dollars designing a new one to suit a particular application, *then* we might be concerned with the angles of the helixes. Until then, it is a black box.

I applaud anybody who wants to learn the contents of a black box. That's fine... but they shouldn't choose to use the information for the sole purpose of calling out an entire community who isn't up on the black box.

 

So if I waded through the jargon well enough, what you're saying is that the Torsen is a better unit for Road courses/autocross and the Quaife is better for Drag. If that's the case, I made the wrong decision, which explains why I still sometimes only see one patch when launching.

nope they are the same exact thing.

you only see one patch sometimes because the diff hasnt seen enough torque to bias to the grippy wheel. The torsen design "acts" open when it is not biasing. Open diffs send equal torque to both wheels.

 

what works best in an AutoX/road course setup is highly dependant on the car, drive train layout and speeds at which the car will reach.

for EG:
Any Porsche we build for track purposes, Solo1 or any type of racing where high speed corners in higher gears are encountered, we run plate-type LSDs. on say an AutoX or street driven Porsche we'll suggest or run a ATB(Torsen/Quaife).

again, depending on the driving you are doing one dif will always be limited in a certain area.
if you look at a lot of the drift guys, cornering speeds are not that high but most of them use a plate-type dif to get lockup so they can break both wheels away equally. some may even run Spools but that's beside the point.

with plate type difs you can alter the dif-action under things like accel, coast and i think decel(i'm not the guy who handles dif setup here) again to suit the type of driving you are doing.

in the focus world, simply because there are no serious plate-type difs on the market as an option, everyone just defaults between the quaife and the torsen. imho, neither is better nor worse than the other. like everything, people try ONE thing and then preach that it's the "bee's Knee's". the people who have driven both in a high performance situation may not but usually can tell there is little difference between the 2 all testing being equal which is why a lot of people opt for the "cheaper price or lifetime warranty" angle.

having built and driven Focus' with both quaifes and torsens, i really don't see a difference in how they work between the 2, just in how they allow cars to power out of corners vs a stock diff. i'll install which ever the customer wants but wont suggest one over the other... i opt-out for the "cheaper price, lifetime warranty" angle, and let the customer choose!
i know some places push one over the other but usually that's simply a profit margin reason or they don't carry the other and want you to buy a LSD from THEM!

 

So if you do have a torsen or quaife and you're still getting one wheel to break free constantly, you'd be best suited to invest in some sticky tires. That way, the torque required to break the tire free would be greater, and hopefully greater than the torque required for the differential to operate differently than an open diff. Correct?

And Mitch, thanks for clarifying that in an unbiased sense. I have the Torsen and have been happy with it 90% of the time, and now that I know switching to the quaife wouldn't make a bit of difference that helps.

As a side note, wasn't f2 or someone selling a clutch(plate)-type diff for a while? Did anyone get that, if so, opinions?

 

i think F2 was trying to get Kaaz to start making and selling their plate dif again... don't know if it's reality or not, yet....

 

all i can say is ive driven both the ford torsen and the quiafe in high powered foci, and i personally like the feel of the ford torsen better

 

what difference was there?

 

what works best in an AutoX/road course setup is highly dependant on the car, drive train layout and speeds at which the car will reach.

for EG:
Any Porsche we build for track purposes, Solo1 or any type of racing where high speed corners in higher gears are encountered, we run plate-type LSDs. on say an AutoX or street driven Porsche we'll suggest or run a ATB(Torsen/Quaife).

again, depending on the driving you are doing one dif will always be limited in a certain area.
if you look at a lot of the drift guys, cornering speeds are not that high but most of them use a plate-type dif to get lockup so they can break both wheels away equally. some may even run Spools but that's beside the point.

with plate type difs you can alter the dif-action under things like accel, coast and i think decel(i'm not the guy who handles dif setup here) again to suit the type of driving you are doing.

in the focus world, simply because there are no serious plate-type difs on the market as an option, everyone just defaults between the quaife and the torsen. imho, neither is better nor worse than the other. like everything, people try ONE thing and then preach that it's the "bee's Knee's". the people who have driven both in a high performance situation may not but usually can tell there is little difference between the 2 all testing being equal which is why a lot of people opt for the "cheaper price or lifetime warranty" angle.

having built and driven Focus' with both quaifes and torsens, i really don't see a difference in how they work between the 2, just in how they allow cars to power out of corners vs a stock diff. i'll install which ever the customer wants but wont suggest one over the other... i opt-out for the "cheaper price, lifetime warranty" angle, and let the customer choose!
i know some places push one over the other but usually that's simply a profit margin reason or they don't carry the other and want you to buy a LSD from THEM!

AWESOME post. thank you.

So if you do have a torsen or quaife and you're still getting one wheel to break free constantly, you'd be best suited to invest in some sticky tires. That way, the torque required to break the tire free would be greater, and hopefully greater than the torque required for the differential to operate differently than an open diff. Correct?

yeah basically. More torque capacity isnt really 100% of the technical answer but you get the jist of it.

At an estimated 160wtq, in first gear my torsen works great in straight lines most of the time. You can hear the engine reach peak torque around 5000, sit there while the diff catches up and the car goes faster, and then off I go. But when I have my summer tires on and its really cold (aka i get more power/torque and my tires are rock hard) I get some one tire fire, usually the passenger side. So sticky tires would certainly help.

 

You can hear the engine reach peak torque around 5000, sit there while the diff catches up and the car goes faster, and then off I go.

That's.... really odd. Sounds broken.

Sounds like some sort of engine or clutch issue, because I've never had one do anything like that.

It is a differential, not a CVT. It can't mechanically decouple BOTH drive axles from the engine at the same time. The power has to go somewhere, and if both wheels have grip, it will result in smooth acceleration. If they don't have grip, engine RPM will increase as one or more of them begins to spin.

 

Yeah that's not a diff that's your clutch not fully engaging. You've got a hydraulic system issue somewhere IMO. And yes Mitch, Kaaz was the company I was thinking of. Don't know what happened to that, unfortunately.

 

it happens in 1st gear only so it is NOT the clutch. Ive been over this with focussport a few times.

It also only happens when i have more power/torque due to cold weather. I happen to have JUST the right amount of torque to break one wheel loose.

it is the differential dynamically changing the overall gear ratio. If you take a look at an exploded diagram of a torsen it will make sense.

its wheelspin... without the spin.