[ClubCrosstrek]

Here's an independent study of a few leading AWD systems, including Subaru's Symmetrical AWD.

The best Traction and Control AWD vehicle is from Subaru

Subaru blows the others out of the water.

 

[Errant Venture]

I was pretty skeptical, especially after absolutely no criticisms were leveled at the Subaru's, but after a semi-careful examination, the Subaru seems to be going the same speed, and seems to have followed the same path as all of the others. By my amateur measure, that's pretty impressive.

 

[ClubCrosstrek]

I don't know what technical differences Subaru offers, but from what I understand they really do have something special about their AWD system. Maybe someone who knows more can chime in.

 

[AWDfreak]

It's the symmetrical layout of the Subaru Symmetrical AWD. Having a symmetrical layout significantly reduces torque steer, which occurs mostly because of an asymmetrical layout (such as unqeual-length driveshafts from left-to-right).

Now do take note, there are 4 versions of Symmetrical AWD.

1) Continuous AWD, 50:50 F/R torque split, viscous center differential (all manual transmissions except WRX STI)
2) Active AWD, 60:40 F/R torque split, electronically-controlled multi-plate transfer clutch (all automatic transmissions except H6-equipped Subarus and a few other exceptions)
3) Variable Torque Distribution (VTD), 45:55 F/R torque split, multi-plate electronically-controlled transfer clutch (all H6-equipped Subarus and a few select ones, including some turbo models)
4) Driver Controlled Center Differential (DCCD), variable between 50:50 F/R to as much as 59:41 F/R [pre-MY2008 could go as much as 65:35 F/R], electromagnetic center LSD similar to VTD combined with a mechanical center differential similar to Continuous AWD (all STI models with DCCD)


Also, the VDC stability and traction control system is well-calibrated to redirect torque to tires with more grip by clamping on the wheels slipping.

Basically, it is attempting to substitute a real LSD by stopping the wheels that are slipping (it knows this through the wheel-speed sensors), which redirects torque to the tires with the best traction.

Other off-road oriented manufacturers such as Land Rover and Jeep have the same type of calibration with their traction control systems. Most other manufacturers don't take this off-road capability into account, sadly.

 

[Got One]

Thanks for that. I was following everything until I got to number 4. ???

 

[Poego]

Now do take note, there are 4 versions of Symmetrical AWD.

1) Continuous AWD, 50:50 F/R torque split, viscous center differential (all manual transmissions except WRX STI)
2) Active AWD, 60:40 F/R torque split, electronically-controlled multi-plate transfer clutch (all automatic transmissions except H6-equipped Subarus and a few other exceptions)
3) Variable Torque Distribution (VTD), 45:55 F/R torque split, multi-plate electronically-controlled transfer clutch (all H6-equipped Subarus and a few select ones)
4) Driver Controlled Center Differential (DCCD), variable between 50:50 F/R to as much as 59:41 F/R [pre-MY2008 could go as much as 65:35 F/R], electromagnetic center LSD similar to VTD combined with a mechanical center differential similar to Continuous AWD (all STI models with DCCD)

I was reading something similar to this when I was doing my research on the Crosstrek, the article I read stated the Manual Crosstrek was case 1) 50/50 like you said, but it said the CVT Crosstreks was variable up to 90% to the front wheels, I'll try to find the source if I can. Do you think our CVT crosstrecks are Active AWD 60/40 AWDfreak? Or could it be different with the CVT Transmission?

 

[AWDfreak]

Now do take note, there are 4 versions of Symmetrical AWD.

1) Continuous AWD, 50:50 F/R torque split, viscous center differential (all manual transmissions except WRX STI)
2) Active AWD, 60:40 F/R torque split, electronically-controlled multi-plate transfer clutch (all automatic transmissions except H6-equipped Subarus and a few other exceptions)
3) Variable Torque Distribution (VTD), 45:55 F/R torque split, multi-plate electronically-controlled transfer clutch (all H6-equipped Subarus and a few select ones)
4) Driver Controlled Center Differential (DCCD), variable between 50:50 F/R to as much as 59:41 F/R [pre-MY2008 could go as much as 65:35 F/R], electromagnetic center LSD similar to VTD combined with a mechanical center differential similar to Continuous AWD (all STI models with DCCD)

I was reading something similar to this when I was doing my research on the Crosstrek, the article I read stated the Manual Crosstrek was case 1) 50/50 like you said, but it said the CVT Crosstreks was variable up to 90% to the front wheels, I'll try to find the source if I can. Do you think our CVT crosstrecks are Active AWD 60/40 AWDfreak? Or could it be different with the CVT Transmission?

The CVT models still use the Active AWD that the old 4EAT used. I'm very confident of it.
The torque split F/R should still be 60:40 as far as I know.

Only specific Subaru turbo models equipped with a 4EAT/5EAT/CVT use the more-advanced VTD.

CVT listed as being mated to Active AWD
http://www.subaru-global.com/13xv_rr_spec.html

 

[ClubCrosstrek]

Wow, thanks for all the info AWDfreak. Can I ask how you know so much about car mechanics? You may have mentioned before but I forgot.

Thanks!

 

[AWDfreak]

Eh, I like to think that I know a little.

I read. A lot. Read everything Subaru I can possibly take in, in a day. And it helps that Subaru posts the specifications on Subaru Global.
I also frequent Subaru forums looking up random information.
And I contact Subaru of America for information as well.


Speaking of which, no XV Crosstrek, but a third generation Subaru Forester (SH) demonstrating the VDC and AWD system working together, along with many other vehicles failing the roller test. Do note this roller test is very difficult, as the rollers they use are not low-profile rollers.

Noteworthy portions in the video:
40:39, 41:07, 42:08, 42:50, 43:04, 43:18, 43:47, all examples where the VDC helps the Subaru AWD by redirecting torque to wheels with the best traction. For most AWD systems, it's not entirely the AWD system alone, but the stability (commonly known as ESC) and traction control (commonly known as TCS) have to work with the AWD system to make an AWD system (especially with open differentials) very effective.

AWD sistems wars (testing) on rollers

The reason why most of the vehicles were unable to move is because most vehicles, even AWD vehicles, are equipped with open differentials (with the exception of the center differential on AWD vehicles). A small amount have a rear LSD, and very few have an LSD on the front and rear (which the Subaru WRX STI has, LSD on both front and rear).

Turbocharged Subaru models usually, if not always, have a rear LSD.

It's best to contact Subaru of America to check if your vehicle has a rear LSD. Sadly, I still don't know if the XV has a rear LSD (and would GREATLY appreciate it if someone would find out, sometimes I feel Subaru of America gets very tired of contacting me!)


For anyone who wishes to get on serious off-road trails, but doesn't want to rely on the VDC alone, one can upgrade the front and rear differentials to a limited-slip differential. Locking differentials (also called lockers) often found on conventional off-road vehicles are highly impractical for Subarus because kits do not exist for Subarus as far as I know, necessitating a completely custom drivetrain build.

 

[Got One]

And another in a similar vein. http://subievideos.com/subaru-crosstrek-xv-versus-land-rover-defender

 

[AWDfreak]

And another in a similar vein. http://subievideos.com/subaru-crosstrek-xv-versus-land-rover-defender

Indeed. Note at 3:48, the right rear tire in the air isn't turning because the VDC (Vehicle Dynamics Control) is redirecting torque as necessary to the tires with more traction.

 

[Poego]

Sadly, I still don't know if the XV has a rear LSD (and would GREATLY appreciate it if someone would find out, sometimes I feel Subaru of America gets very tired of contacting me!)

According to this the manual transmissions have a viscous LSD. Is that what you were referring to AWDfreak?

 

[AWDfreak]

Sadly, I still don't know if the XV has a rear LSD (and would GREATLY appreciate it if someone would find out, sometimes I feel Subaru of America gets very tired of contacting me!)

According to this the manual transmissions have a viscous LSD. Is that what you were referring to AWDfreak?

It's an LSD built into the center differential, not the rear differential. So if the center differential experiences an excessive difference between the front and rear, it will attempt to maintain a 50:50 front-to-rear torque distribution.

It is different than a rear or front LSD that makes a difference in the side-to-side torque distribution.

 

[mklenk]

Question: is VDC available with the manual transmission version of the Crosstrek? Or is it only coupled with the CVT?

 

[Poego]

Question: is VDC available with the manual transmission version of the Crosstrek? Or is it only coupled with the CVT?

Yes it is, VDC is ABS/computer controlled and the same on both transmissions.

 

[AWDfreak]

Question: is VDC available with the manual transmission version of the Crosstrek? Or is it only coupled with the CVT?

Yes it is, VDC is ABS/computer controlled and the same on both transmissions.

Indeed.

In fact, I believe it was either model-year 2007, 2008, or later that all Subaru models came with VDC standard.