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RE: quattro-digest V3 #333

From: 	Dave Eaton[SMTP:dave.eaton@minedu.govt.nz]
Sent: 	Friday, April 12, 1996 5:18 AM
To: 	quattro@coimbra.ans.net
Subject: 	Re: quattro-digest V3 #333

nope, don't agree.  my ur-q with open diffs could be a real handful when punting hard.  locking the centre diff solved the problem but didn't make the car nearly as responsive as my s2 with it's torsen (less understeer).

Well, not sure what 'punting hard' is.......(when I think of 'punting' it's relative to getting 'punted in the weeds' - something to be avoided, IMFO!).....but, yes, you will get more understeer with both diffs locked on dry pavement and especially at low speeds and with low/no power, BTDT.....*but*, that's not what I suggested! I only suggested locking both diffs if the going is real tough - due to lack of traction - under these conditions the effect of any additional understeer is really a moot point - the point is moving forward under conditions that would leave you walking (stuck) with open diffs - or in the rain on the highway at highway speeds (locked center diff ONLY) where the effect of any additional understeer won't matter much due to the radically large turn radius of highway 'turns' or in snow/ice/mud where understeer won't matter at all.....and if you want power-on oversteer then lock only the rear diff, STAND on that loud pedal and STEER!      :)

in addition the speed that the torsen reacts to changing surface conditions is much quicker than your ability to turn the diff lock!

This is true! It is important to lock those diffs when the going gets tough and BEFORE you get stuck. One can typically anticipate deepening snow, mud, Real Steep (Tm) hills, etc, and lock the diffs well in advance of the anticipated obstacle(s). (obstacle is often a '4X4' stuck 1/2 way up the hill in front of you, -- PLEASE! remeber to beep and wave as you go by that stuck '4X4', or stop, beep, get their attention, wave, dump the clutch and press on -- my personal FAVORITE!  :)

in addition, the torsen puts more torque to the driven wheels (up to 75%) versus 50% with a locked centre diff.

NOT TRUE! Locked diffs put up to 100% torque to the wheel with the traction, automatically, instantly and as required, and up to 0% to the spinning wheel, instantly, and by defintion, with a '100% locked' diff. If both wheels have equal traction then torque split is 50/50 and will vary from 0/100 to 100/0 *instantly* depending on the relative traction of the two diff outputs.....

Both '100% locking diffs' and 'torsen diffs' have their advantages and disadvantages, neither a perfect or 'best' in all possible cases.