DSC light comes on way to easily

[RFieler]

I've been dealing with this problem for a while now. I have a '13 E70 x-drive N55. I had all 4 corners of the brakes replaced and the rear tires then I started getting the DSC light coming on very easily. It happens while going over moderate bumps and during hard acceleration and severely cutting engine power. The valvetronic actuator was bad and after it was replaced the problem did get a lot better but it is still there. The rear tires were replaced with the identical size pirelli p zero (315 35 20s) tires but they have a different tread pattern. I measured the circumference today and the rear tires are about 1/4" larger than the fronts. Can anyone tell me if this is the culprit?

[ard]

what are the 'revs per mile' on the front and rear tires???? tirerack should list this spec, although not all are listed. You want that within single digits front and rear.


Not only can it cause DSC issues, it can damage your differential.

[pshovest]

Make that transfer case......

[ard]

yeah, the transfer case is where the differential function exists....

[ard]

Originally Posted by RFieler

I measured the circumference today and the rear tires are about 1/4" larger than the fronts.

Also, this isnt the whole story.


When you set the car down, loaded in the front on smaller tires... relatively less weight in the back on those fat tires.... the 'rotating radius' maybe be MUCH larger than your circumference measurement indicates.


In other words, the unladen circumference may not really tell you how the front and rear truly differ when weighted and rolling....



revs/mile is based on the tire being loaded, as I recall. it is a much more direct measure of the impact on the ...transfer case/differential.

[RFieler]

Upon reading my original post I realized that i made a mistake. I said the circumference was off by a 1/4" but I actually meant the overall height was 1/4" higher in the back tires as opposed to the fronts. Considerably more severe.

[pshovest]

Originally Posted by ard

yeah, the transfer case is where the differential function exists....

As long as the OP understands a F/R tire diameter difference wears out the transfer case, not the differential(s).

[ard]

Sure, agreed.

OP what brand, specific model and size tires on your front and rear?

[RFieler]

They are Pirelli p zeros on both front and back (275 40 20 / 315 35 20) but the fronts are the older model and the rears are the newer model. I've ordered two new front tires to match the same model as the rears. I'll update my findings upon installation of the new tires this coming week.

[ard]

Looking those up on tiresize.com, both the 245/40 and 315/35 come in at 724 revs per mile


GL