Hi Brian,
I am surprised that no AWD afficionados have replied, so let me give you my two cents worth.

I do not think that wheel spin will be a factor on winter tsd rallies.

I used to compete in a rwd car (with a welded diff mind you) running the odo off the transmission and found that odo error was minimal. I assume that brake lockage cancelled out wheel spin. (I used to run with more rear brake bias in the winter to help get the rear end out.) In the early days I ran the odo off a front (non-driven) wheel and on occasion, I found odo slow down due to brake lockage, but again it was minimal.

Secondly, as I recall, most rally sections average thirty km in length (when you can zero the odo), not fifty or sixty. But that may have changed these days.

What you will need however is a navigator who can correct the odo error using a calculator. Chances are your stock odo will not match the organizers odo, and based on the initial route odo check, the navigator will have to correct distances during the entire event.

Dave

Alright...I'll jump in.

I run an Audi 90 quattro.  I've mounted the sensor for our ODO on the rear diff housing.  

We do notice the odo being off by .1 or .2 km, usually near the end of a section, when we've done a fair number of Km's already.

My navvie is usually pretty quick to realize that the ODO settings have begun to slip, and he just compensates for it.  If he notices one reading is off, he checks it against the next...and can figure out how off we are.

We've only ever made one wrong turn because of it...it was a section where you had to turn at an unmarked road at XXkm.  Problem was, there were 3 roads within about 300m.  Truth be told though,  we were a little confused at that point anyways...so even if we were dead on, we would have had to check it.

I don't find I lock up the brakes much...if I do, it's for what maybe 3 feet at a time?  I do, however, spin the rear wheels more...and that accounts for more 'distance' in the ODO.  I will probably swap my sensor to the front tranny to see if I notice a difference.

HTH,

-Dave

I don't know about "well qualified", but I'll try to relate our experience.

The answers so far cover off most of the points about adjusting as you go along.  You're really never going very far without a reference point with an official distance, so your navi can correct as you go along - sometimes running it all through the calculator, mentally adding the .05 or whatever.  Just make sure you're communicating about the same readings - car odo as is or "adjusted" car odo, or the route instructions.  You may find that you are adjusting it for awhile while the navi catches up on calculations. ie you are given 24.5 and you know it will read .1 high and be 24.6.  After you navi catches up, remember to stop adjusting. In the heat of an event or after 8 hours or motoring you have to keep  on talking !!

We do use a TerraTrip, which takes care of the official to car odo factors.  However, it also is affected by drivetrain/wheelspin - in winter or summer.  As tempting and as much fun as it looks, I don't you have to throw the car around that much in winter or get a great deal of wheelspin....maybe not more than hard driving on gravel.

AS for the ABS - I have a cut-off switch for it.  I turn it off for gravel, but in the winter I like leaving it on in the slippy stuff.  I like the feedback it gives as an indicator of  how slippy it really is.  When I get a little of the pumping I know I'm pushing; and I'll back off "a little".

Hope this helps.  See you out there.

Alan

By stock I assume you mean the odo on the dashboard. They are always hooked up to the transmission. Either mechanically connected to a gear running off the final driveline shaft or electronically to a sensor mounted on the final drive.

So, in relation to the above questions, the dashborad odo will always experience wheelspin error regardless of whether they're front, read or AWD. With AWD, there will be much less spin in general, there's too much grip.