Enlighten me on diffs

[slngsht]

I've always thought that for our apps, a torque sensing diff is the way to go...



I see 2 players in the market: Quaife, and TrueTrac.



I haven't done an exhaustive price search, but it seems like Quaife is substantially more expensive. Is it an improvement over the TrueTrac design?



Any reason not to go with a torque sensing diff?

[scannon]

Any reason not to go with a torque sensing diff?



If one rear wheel has zero traction, the torsen will act like an open diff. So if you get rear inside wheel lift or are on snow, you are going to be spinning one rear wheel.



As a data point, I got in on a group buy of Quaiffe diffs in England. What would have cost about $1,250 here cost less than $800 shipped to the USA. This was the diff only, did not include the ring and pinion or the housing nor the installation. It was for the Sierra diff in my Caterham.



Skip

[slngsht]

skip, thanks...



Both of those conditions (lifting a rear wheel, or ice/snow) will be very unlikely in the seven.



I'm looking for one for a 9" ford rear. Quaife = 1300, TrueTrac= 500. Big difference.

[rv-4mike]

Did you consider going 8.8" instead of 9"? With the boom in Factory Five Cobras there is huge aftermarket support for the 8.8 and they are dime a dozen. It would be bulletproof in your car.

[slngsht]

Did you consider going 8.8" instead of 9"? With the boom in Factory Five Cobras there is huge aftermarket support for the 8.8 and they are dime a dozen. It would be bulletproof in your car.



LocostV8 set me up with a nice deal on a 9" with disc brakes http://www.usa7s.com/aspnetforum/images/emoticons/yesnod.gif

[rv-4mike]

Cant argue with a good deal on a 9"! http://www.usa7s.com/aspnetforum/images/emoticons/smile5.gif

[xromad]

I'm running torsen and quite happy with the results.



Couple of notes:

1. Given good traction on both tires, nothing beats an open diff. It has the fewest faults and the best power distribution characteristics of any configuration.



2. Another advantage of an open diff is that you don't completely loose cornering traction on the rear of your car just because you applied too much power.



3. Most torsen setups do have a limit on how much actual power they can handle. The good news is that those power limits usually assume a car that weighs at least twice that of an average 7.



4. There are different types of torsen that have more or less pre-load. I.E. Not all torsen's fail to transfer power when one tire has 0 traction.



5. A realy good traction control system that applies braking power to the spinning wheel can give you all the fantastic benefits of and open diff with all the traction of a torsen. But I think a system like that kind of misses the point of a 7 type car....   http://www.usa7s.com/aspnetforum/images/emoticons/lol.gif

[slngsht]

2. Another advantage of an open diff is that you don't completely loose cornering traction on the rear of your car just because you applied too much power.





That's one thing I have enjoyed with the existing rear... when I step on it in a corner, it is VERY easy to control.

[solder_guy]

I enjoyed reading this basic article about diffs .. this morning .. lots of animations! :)

How Stuff Works: Differentials (http://auto.howstuffworks.com/differential.htm)

Rob

[Ian7]

Mr. "scannon"

what torsen acts like an open diff with the inside wheel off the ground, and why?

thx

[scannon]

Mr. "scannon"

what torsen acts like an open diff with the inside wheel off the ground, and why?

thx
I can't tell you why because I don't understand just how a torsen diff works. Someone on here probably can explain it for us.

I've had several torsens and they all would spin the inside wheel if I lifted a rear wheel in a hard corner. I had to go to softer sway bars to keep the wheels in contact with the ground.

If you are on ice, you can gently apply the parking brake and the torsen will transfer the load to the other wheel. Both wheels have to have a minimum amount of traction.

Several times when I have parked on a friend's weird driveway, one wheel was off the ground and the car would not move. Until I learned about the parking brake trick, I had to push it a bit to where both rear tires were in contact with the ground.

I have heard that some torsens are biased such that this is not a problem but IIRC there is a compromise in how well the torsen performs otherwise.

Skip

[slngsht]

agree with Mr. "scannon" :)

Torsen's need a small amount of torque to work, otherwise they act as an open diff, so lifting a driven wheel is a bad thing.

[Stokked]

The link provided by solder_guy has a pretty good basic explanation. On the torsen...

"The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together. The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction.

These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.

However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero."

[Ian7]

mr. scannon

"Several times when I have parked on a friend's weird driveway, one wheel was off the ground and the car would not move. Until I learned about the parking brake trick, I had to push it a bit to where both rear tires were in contact with the ground."

I would have thought that out there in snowy Colorado (like we do here out east), you'd spend a lot of time gently touching the brake pedal when the wheels of your open-diff street car start spinning in the snow. Its a crude version of electronic traction control, with the drawback that its lightly braking all wheels, but always works to get unstuck.

Thanks for the Torsen explanation.

[scannon]

I would have thought that out there in snowy Colorado (like we do here out east), you'd spend a lot of time gently touching the brake pedal when the wheels of your open-diff street car start spinning in the snow. Its a crude version of electronic traction control, with the drawback that its lightly braking all wheels, but always works to get unstuck.

Thanks for the Torsen explanation.

Its been so long since I've had an open diff rear drive car in the snow that I can't remember what it was. I have an AWD Legacy GT with dedicated snow tires for the winter. I have to get it well into boost before it will spin the tires, even on ice. The Caterham and Miata both have LSD but neither gets driven in the snow.

Skip

[solder_guy]

All this discussion has convinved me that my Seven will perform just fine with an open diff. So I don't have to go with the LSD.

Rob

[slngsht]

All this discussion has convinved me that my Seven will perform just fine with an open diff. So I don't have to go with the LSD.

Rob


It's good to have LSD if you regularly overpower your rear wheels.

[Mandurath]

Though it might help ya learn more control unless you like buying tires :d

For the cost I think I would go with the domestic units. Cheaper, and for the 9", just as good as a Quaife. Best thing about a 9" is its pseudo quick change ability. Couple of chunks with different ratios for different plans and your set. Have a buddy that drag races a T-Bucket with a 9". Has different gear sets for different tracks, 1/8 or 1/4.

[scannon]

All this discussion has convinved me that my Seven will perform just fine with an open diff. So I don't have to go with the LSD.

Rob

A torsen will make a huge difference in your ability to get out of the corners if you are racing or doing track days.

Skip

[slomove]

http://www.usa7s.com/aspnetforum/upload/1061280621_Simpsons_Donuts-l.jpg
Better quality donuts with LSD!

[slomove]

Another minor disadvantage: while the LSD can give you a good advantage on the dry track the Quaiffe style can be a handful on a wet/muddy/oily track.

If you accelerate out of a corner already at the limit of adhesion and one rear wheel suddenly loses traction (mud on the track, oil slick etc.), the other wheel gets immediately double torque. This will cause an instant spin without any warning (been there, done that).

According to the previous posts the Torsen diff would not do that.

Gert

[Birkin42]

I am no expert on Torsen/Quaife LSD diff's, but having looked at both, they are designed very differently.
If I am not mistake, the Torsen uses 45 degree helical gears arranged with their axis 90 degrees to each other and uses the friciton in the gear mesh to create the torque bias. I believe this system has the problem of acting like an open diff if no traction is available from the other wheel.
I'm pretty sure a Quaife has shallower helical gears with their axis parallel to each other and uses the friction between the idler gear and the carrier to positively drive the wheel with the most traction. I believe a Quaife do not transfer all power to a wheel with no traction.

The negative I have heard about Torsen's is that they can create push or understeer when powering out of a corner since the internal friction in the gearsets causes the diff to acted locked and hence does not want to track a circle but wants to go straight. I am not sure if a Quaife has the same issue but I would suspect it would to some degree.
I think any LSD in the end will create some handling issues but in turn will provide much better drive out of corners. Whether this trade off is worth while depends on personal preference and how easily your car can light up an inside wheel.

Jack

[slngsht]

This is an old thread from before last year's upgrades. I ended up with a Camaro rear, which has a Torsen unit in it.

[Mandurath]

hehehe guess should read the whole thread sometimes....:leaving: