Very loose rear end (Handling)

[Tcoat]

Originally Posted by nextcar

A low bar indeed! But like killing time on a layover, I am killing time on a flight... so I cannot stop watching even though I know how this will end.

Edit: I would not say it stayed on topic the whole time unless @Cole works inside a Torsten and we actually witnessed him heating up due to resistance...

Well he does get pretty heated if you twist him enough so...

Still a pretty good record since we didn't start talking about blue dinasours or something.

[Ultramaroon]

How many times do I have to say it? They weren't blue. They had a bluish hue.

[Tcoat]

Originally Posted by Ultramaroon

How many times do I have to say it? They weren't blue. They had a bluish hue.

Well only Hum would know for sure.

[humfrz]

Originally Posted by Tcoat

Well only Hum would know for sure.

Well, the one that I do remember had a blueish streak on it .....


humfrz

[Tcoat]

Originally Posted by humfrz

Well, the one that I do remember had a blueish streak on it .....


humfrz

Must have been a special edition.

[Gforce]

Originally Posted by Edibrac

Okay, this might get long.

A space saver tire on one axle of a torsen differential will rotate at a higher RPM than the larger one on the other side of the differential. We all know this.

A torsen allows the axles of the car to rotate at different speeds through the use of a set of worm gears for each axle. These worm gears are also meshed together with spur gears. So when one axle is spinning faster than the other, like in a corner or different sized tires, the worm gear of the faster axle causes the worm gear of the slow axle to spin and therefore spin the slow axle.

Now the worm gears and the helical gear on the axles have a certain ratio. There is a limit to how much the faster axle can make the slower axle rotate due to this ratio.

In our example there is a speed difference between the axles due to tire size. If the spare is of a slightly smaller size than normal, the torsen acts as if the car is constantly cornering. This is not good for the torsen because the worm gears are rotating constantly, because we have a speed difference in the axles. The worm gears have bearings that are not sized for constant use like the bearings for the axles are. They are small bearings. Rotation in bearings cause friction, which causes heat, regardless of lubrication there is still friction. A couple of corners is not enough to cause enough damage from heat since it is intermittent. However we are talking about constantly having one axle rotate faster than the other for a long time.

So if they can be ran for a short time like this, why do manufacturers advise against it? Simple. People are idiots. The average person might not see issue with running the spare on the drive axle and put off replacing the tire while they continue to drive every day. So instead of saying it might be okay if a bunch of specific conditions are met, they tell the owner to not do it at all.

Simple.

The BRZ does not use the T1. It uses the T2 which fits parallel helical gears and no spur gears. The operating principle is similar. All the other helical torque sensing diffs use the T 2 style solution, more compact but not as robust.

Have you figured out how different the rolling circumference of the tires would have to be to cause a problem in the manner you describe?

Even if the space saver were to be that small (and it would have to be very small) the Torsen or any patent infringement avoiding variation of the Torsen would not wear any more than an open differential would in the same situation. That is to say, the supposed "limited slip" function you suppose would generate heat just wouldn't and reveals a lack of understanding about how Torsen type diffs work. They generate less heat when they are transferring torque than they would just differentiating. They are not relative wheel speed activated. Genius design actually. Bombproof enough for a Hummer.

Differentials are stronger than the axles they drive. You only find differential oil coolers on competition cars.

Your theory is well expressed, and courteous, but isn't correct.

Anybody else care to take a crack at it?

Most of the posts since my challenge are sufficiently infantile as to warrant ignorance, consistent with that displayed.

[Tcoat]

Originally Posted by Edibrac

Okay, this might get long.

A space saver tire on one axle of a torsen differential will rotate at a higher RPM than the larger one on the other side of the differential. We all know this.

A torsen allows the axles of the car to rotate at different speeds through the use of a set of worm gears for each axle. These worm gears are also meshed together with spur gears. So when one axle is spinning faster than the other, like in a corner or different sized tires, the worm gear of the faster axle causes the worm gear of the slow axle to spin and therefore spin the slow axle.

Now the worm gears and the helical gear on the axles have a certain ratio. There is a limit to how much the faster axle can make the slower axle rotate due to this ratio.

In our example there is a speed difference between the axles due to tire size. If the spare is of a slightly smaller size than normal, the torsen acts as if the car is constantly cornering. This is not good for the torsen because the worm gears are rotating constantly, because we have a speed difference in the axles. The worm gears have bearings that are not sized for constant use like the bearings for the axles are. They are small bearings. Rotation in bearings cause friction, which causes heat, regardless of lubrication there is still friction. A couple of corners is not enough to cause enough damage from heat since it is intermittent. However we are talking about constantly having one axle rotate faster than the other for a long time.

So if they can be ran for a short time like this, why do manufacturers advise against it? Simple. People are idiots. The average person might not see issue with running the spare on the drive axle and put off replacing the tire while they continue to drive every day. So instead of saying it might be okay if a bunch of specific conditions are met, they tell the owner to not do it at all.

Simple.

Originally Posted by Tcoat

Exactly! Although you wasted your time writing it out since the response will be more misunderstood, plagiarized first year apprentice text book excerpts saying how you are wrong. There will be not one solid shred of evidence produced to prove you wrong though.

Originally Posted by Gforce

The BRZ does not use the T1. It uses the T2 which fits parallel helical gears and no spur gears. The operating principle is similar. All the other helical torque sensing diffs use the T 2 style solution, more compact but not as robust.

Have you figured out how different the rolling circumference of the tires would have to be to cause a problem in the manner you describe?

Even if the space saver were to be that small (and it would have to be very small) the Torsen or any patent infringement avoiding variation of the Torsen would not wear any more than an open differential would in the same situation. That is to say, the supposed "limited slip" function you suppose would generate heat just wouldn't and reveals a lack of understanding about how Torsen type diffs work. They generate less heat when they are transferring torque than they would just differentiating. They are not relative wheel speed activated. Genius design actually. Bombproof enough for a Hummer.

Differentials are stronger than the axles they drive. You only find differential oil coolers on competition cars.

Your theory is well expressed, and courteous, but isn't correct.

Anybody else care to take a crack at it?

Most of the posts since my challenge are sufficiently infantile as to warrant ignorance, consistent with that displayed.

Called it!

[Gforce]

Originally Posted by Tcoat

Called it!

Since you are also wrong no surprises there.

The description is accurate until it gets into limits on wheel speeds.

Torsen type diffs are not speed sensitive nor are they speed actuated.

From a differentiation perspective a Torsen is a completely open diff.

Going straight down the road or through the sharpest bend there is no limit to the differentiation a Torsen can accomodate.

The "gear ratio" concept is half right. The limit on torque bias, the bias ratio, is imposed by the angle of the gear teeth on the helical planetary gear. Obviously, this is a fixed limit both as to a specific application and in an absolute sense.

Torsen work by axial thrust on the helical planetary gear. The gear is pushed endways into a specially machined "pocket" or in some types against a specially designed thrust washer, usually hardened steel. Interesting is the fact that the thrust reverses on overrun allowing for the possibility of a different bias ratio under braking. ABS overrides Torsen effects most if the time but without ABS Torsen can improve braking performance also. The key to understanding why wheel size makes no difference is to understand that the torque bias requires different thrust on the left and right axle shafts. Wheel speed has no effect on this. It is also easy to see that the friction is largely static friction anyway if full torque bias is engaged. Torsen in theory would run cooler when torque biasing than when differentiating.

The one exception is a pre loaded Torsen such as the T2R type or some Quaife types. They have a spring loaded thrust washer which provides slightly more than zero torque resistance.

[Tcoat]

Originally Posted by Gforce

Since you are also wrong no surprises there.

The description is accurate until it gets into limits on wheel speeds.

Torsen type diffs are not speed sensitive nor are they speed actuated.

From a differentiation perspective a Torsen is a completely open diff.

Going straight down the road or through the sharpest bend there is no limit to the differentiation a Torsen can accomodate.

The "gear ratio" concept is half right. The limit on torque bias, the bias ratio, is imposed by the angle of the gear teeth on the helical planetary gear. Obviously, this is a fixed limit both as to a specific application and in an absolute sense.

Torsen work by axial thrust on the helical planetary gear. The gear is pushed endways into a specially machined "pocket" or in some types against a specially designed thrust washer, usually hardened steel. The key to understanding why wheel size makes no difference is to understand that the torque bias requires different thrust on the left and right axle shafts. Wheel speed has no effect on this.

The one exception is a pre loaded Torsen such as the T2R type or some Quaife types. They have a spring loaded thrust washer which provides slightly more than zero torque resistance.

How many times are you going to just say the same thing? just repeating the same thing plagiarized from the Torsen site is not supporting your statements with other documentation. Show us something that says it can not be damaged that you didn't write. I have met all your requests for proof yet you still have provided nothing beyond you own assertion. If what you say is accurate it should be easy for you to prove it.

[Gforce]

For the record this thread first described the problem accurately in post #15, new tires of different and inferior spec put on the rear axle which is a no no. I answered that question correctly in post #29. Immediately challenged incorrectly by one of the less knowledgable posters to this forum, admittedly in a crowded field of contenders. Any doubt about that issue was neatly resolved by the poster himself in post #33, possibly in a misguided attempt at sarcasm so inadvertent in that respect. Accurate nonetheless.

By post #18 the topic had already veered off into a discussion about use of the deadly space saver spare. I have done my best to correct the ignorance displayed by many on this thread as a public service. I acknowledge there are none so blind as those who will not see. Even the "cannot sees" can be forgiven for not understanding.

[Ultramaroon]

Originally Posted by Gforce

...From a differentiation perspective a Torsen is a completely open diff.

I think this is at the root of my disagreement with your position on the basic operation of the torsen and any variant.

Do we agree that when the outputs are being driven equally (no differentiation) that a component of the input thrust vector places an axial load on the worm gears? I think yes.

This is where the friction comes into play. Under load, at the onset of differentiation, those gear teeth do rub relative to each other. They are not involutes. (edit: They do have that component in their shape but they are somewhere in between worm and spur in operating principle.)

It is that very same friction on which the torsen relies. The only time a torsen truly behaves like an open diff is when there is zero torque applied to the input.

Without any statement to consequence of continuous operation, do we agree on these points academically?

[Tcoat]

Originally Posted by Gforce

For the record this thread first described the problem accurately in post #15, new tires of different and inferior spec put on the rear axle which is a no no. I answered that question correctly in post #29. Immediately challenged incorrectly by one of the less knowledgable posters to this forum, admittedly in a crowded field of contenders. Any doubt about that issue was neatly resolved by the poster himself in post #33, possibly in a misguided attempt at sarcasm so inadvertent in that respect. Accurate nonetheless.

By post #18 the topic had already veered off into a discussion about use of the deadly space saver spare. I have done my best to correct the ignorance displayed by many on this thread as a public service. I acknowledge there are none so blind as those who will not see. Even the "cannot sees" can be forgiven for not understanding.

Nobody is vilifying the spare. The whole message was follow the manual and don't use on the drive wheel. You have not proven that long term use will not damage the diff. In fact you have not proven any of your statements. Saying "I am smarter than you all" and repeating the same thing over and over is not proof. Telling people it is ok to have the spare on the drive wheel is not a public service.

[driftartist]

Originally Posted by Gforce

For the record this thread first described the problem accurately in post #15, new tires of different and inferior spec put on the rear axle which is a no no. I answered that question correctly in post #29. Immediately challenged incorrectly by one of the less knowledgable posters to this forum, admittedly in a crowded field of contenders. Any doubt about that issue was neatly resolved by the poster himself in post #33, possibly in a misguided attempt at sarcasm so inadvertent in that respect. Accurate nonetheless.

By post #18 the topic had already veered off into a discussion about use of the deadly space saver spare. I have done my best to correct the ignorance displayed by many on this thread as a public service. I acknowledge there are none so blind as those who will not see. Even the "cannot sees" can be forgiven for not understanding.

...You really seem like you need a hug...and a friend.....and a nice warm comforting drink like a hot coco or something. Follow your heart and don't give up on your dreams.

[Gforce]

Originally Posted by Ultramaroon

I think this is at the root of my disagreement with your position on the basic operation of the torsen and any variant.

Do we agree that when the outputs are being driven equally (no differentiation) that a component of the input thrust vector places an axial load on the worm gears? I think yes.

This is where the friction comes into play. Under load, at the onset of differentiation, those gear teeth do rub relative to each other. They are not involutes. (edit: They do have that component in their shape but they are somewhere in between worm and spur in operating principle.)

It is that very same friction on which the torsen relies. The only time a torsen truly behaves like an open diff is when there is zero torque applied to the input.

Without any statement to consequence of continuous operation, do we agree on these points academically?

I'm afraid not. I'm also disappointed that nobody has yet jumped on the error in my post. So, either nobody in this thread understands how their T 2 Torsen diff works or everyone who does isn't interested in clarifying it for others.

Torque biasing differentials are engineered to differentiate exactly as open bevel gear differentials do. They are not speed sensitive, they react only to torque. They bias torque by exploiting the internal frictional forces generated by helical worm gearsets and, more importantly, the frictional forces generated by the ends of (or faces of the side gears in the case of T1 and the new split gear types) the worm gears when they engage the diff case.

Torsen bias torque delivered at the crown and pinion, transferred through the "carrier" which is the Torsen part. They can only bias torque by reacting to uneven torque resistance at the output shafts. Furthermore, unlike an LSD they cannot limit slip to the output shaft experiencing the lesser reaction torque. Understanding why that is so allows one to understand how a Torsen works, that it isn't really an LSD and why using a space saver or other tire of even significantly different rolling circumference cannot wear the torque biasing components of the Torsen. Despite what the lawyers who write owner's manuals might say.

There are some good reasons not to run different sized tires on the drive axles of a car but differential wear isn't one of them.