WRC now without the central differential. What changes?

[Federico]

With the new 2011 wrc regulations the central differential is banned so now the cars have only the front and rear completely mechanical.

What changes in the car and handling without the central differential? The transmission won't be overstressed on the tarmac?

[Arunas]

Do you have any source for this? Really doubt central diff can be banned, may be you meant limited slip diff?

[Federico]

Do you have any source for this? Really doubt central diff can be banned, may be you meant limited slip diff?

Nope. 100% sure the central differential is banned.

http://www.zercustoms.com/news/Citroen-DS3-WRC.html

Semi-automatic controls and the central differential are now prohibited

Now they also have a system that disconnect the rear axle when the handbrake is applied.

[Formula None]

No center diff, so the front and rear diffs are connected directly to the trans output shaft? 50:50 all the time then. I would expect more understeery cars on tarmac stages.

[Arunas]

That is really strange. May be it relies on some cluch (it is mentioned possibility to disconect rear drive during hand brake aplication)?

[Tim.Wright]

No center diff, so the front and rear diffs are connected directly to the trans output shaft? 50:50 all the time then. I would expect more understeery cars on tarmac stages.

That doesn't mean 50:50 torque split my friend. A locked axle means the torque bias ratio can be infinite. I.e. all the torque will go to one axle if the other looses all traction.

The torque split will depend heavily on the track conditions at each moment as well as the front and rear diff ratios. It will definately cause some un predicatabilites in the handling.

Tim

[Jersey Tom]

+1 to Tim.

It does seem like an odd rule change to me.

[747heavy]

If they have banned the center diff, they will probably use a clutch-pack to allow some slip between the front and rear axles.
This is not an uncommon solution in todays (small) SUV´s which are mainly driven in 2WD mode.
On loose/low CoF surfaces, such as gravel or snow&ice, it´s not such a big problem, as the difference in slip can be accounted for by the wheels.
On tarmac it would put some stress onto the drive train.
IMHO it would make the cars a little understeering.

The handbrake activated "cut off" of the rear axle, is not so new either.
Many cars had it back in the mid 90´s in the WRC.

In it´s simplest form it´s just a clutch which disconnects the torque/drive to the rear axle.
A clutch pack in between the output shaft of the center diff and the propshaft would do the job.

something along the lines of this/ but with a simple hydaulic input via a tandem or twin master cylinder in the hydraulic handbrake.



If you use a clutch pack anyway (like in the Nissan illustration above), you just use a "brake light switch" on your handbrake to open the clutch and then you have only front wheel drive.

[mep]

What is the reason for the ban?
I can't see anything wrong with a central diff.
Banning something is in principle never a good solution so why doing it without any need to?

[Formula None]

No center diff, so the front and rear diffs are connected directly to the trans output shaft? 50:50 all the time then. I would expect more understeery cars on tarmac stages.

That doesn't mean 50:50 torque split my friend. A locked axle means the torque bias ratio can be infinite. I.e. all the torque will go to one axle if the other looses all traction.

The torque split will depend heavily on the track conditions at each moment as well as the front and rear diff ratios. It will definately cause some un predicatabilites in the handling.

Tim

Oh right, 50:50 only under the most perfect conditions. Thanks for the correction. I was confusing myself by thinking of how the two axles would be locked together speed-wise (I imagine this has much less importance F-R than L-R). So each axle would have to cope with potential all engine torque, depending on traction available... Realistically, would this happen much?

Another stupid question: in an oversteer situation (where the front and rear axles are traveling along different arcs), would it be ideal for the rear axle to spin faster than the front, rather than have them tied together? In a RWD setup this obviously isn't an issue, so how do rally cars deal with this?

(Assuming all this is true, everything I've read so far seems to come from the same Citroen press release; FIA has yet to release 2011 docs)

Were WRC center diffs before typically LSD-type, Torsen, epicyclic, viscous...?

[747heavy]

X-trac mention a fixed 50/50% torque split for there new WRC/IRC g/box

http://www.xtrac.com/pdfs/532%20SUPER%2 ... EARBOX.pdf

[Formula None]

Thanks 747. It would seem center differentials were not banned, just rendered non-adjustable.

[Arunas]

X-trac mention a fixed 50/50% torque split for there new WRC/IRC g/box

http://www.xtrac.com/pdfs/532%20SUPER%2 ... EARBOX.pdf

This is about S2000, not WRC, so unfortunatelly nothing certain about centre diff from this source.

[Formula None]

WRC is adopting S2000 regs next year, including going to 1.6L engines.

[Arunas]

WRC is adopting S2000 regs next year, including going to 1.6L engines.

It will be similar. Just S2000 is not 1,6L, and WRC will have 360+ Nm torque. Anybody with more detail on tech regulations?