PSM issue, Any input ???
06-19-2014, 05:01 AM
#31
Sumitomo HTRZII and PSM
mikeros1 -The PSM only engages based on rotational speed. Now if you were to put new N spec tires on the rear, with the fronts n spec having only 10% life, the chance of the PSM kicking in is pretty good. The problem here is even though he has Hankooks, the new tires in themselves have a lot of tread, yet the fronts are worn. The ecu sees the different rotation speeds, hence the ecu kicking in PSM. The problem is the rears when new 295-30-18 have a diameter of 26, the fronts when new have a diameter of 25.1. When run as a new set, there is not enough difference for the ecu to kick in, now take 40% or 50% away from the fronts now you have a much larger differential, and this in itself shows enough in rotational speeds to engage PSM. You will probably see this more while cornering. You are correct that Ps2 tires are much closer in diameter hence the reason some are able to get 2 rear changes to one front with no PSM interaction. In this case the rears will need to be run in before the differences are no longer a factor.
FWIW, Sumitomo HTRZIIIs are 25.1" front, 24.9 rear new BTW, which is pretty closely matched as well. I believe their sidewalls are softer than N spec ones though so maybe that may feed into PSM perhaps triggering more often from the effective diameter changes when accelerating or braking hard (under acceleration the rears have more effective weight on them and hence a lower effective rolling diameter, the fronts less weight and a higher effective diameter. Under braking it reverses of course, and in very hard cornering it could be that there is enough of a difference across each axle and diagonally too to have PSM freak out.
I ran Sumis on road and track and any spirited driving would soon have PSM fail completely and turn itself off on my car. Same car with some 245 and 315 Nittos, PSM is tending to stay up much longer. Not a big fan of PSM anyway so wasn't too disappointed at the time.
Last edited by 996tnz; 06-20-2014 at 07:22 AM. Reason: Fly2Low spotted the mistake - thanks
06-20-2014, 02:59 AM
#32
Rennlist Member
Join Date: May 2007
Location: Gig Harbor, WA
Posts: 791
Likes: 0
Received 0 Likes
on
0 Posts
under braking the rears have more effective weight on them and hence a lower effective rolling diameter, the fronts less weight and a higher effective diameter. Under acceleration it reverses
