If I lower my Tyre pressures, will it mess with my VC?


Si

 

Possibly. VC works based off the differential of speeds. Lowering tire pressure on one axle would change the radius and how many revolutions to cover a unit of distance.

 

you have to keep the diameter of whatever you do close to 26 inches rear 25 front for total tire diameter. so adjust accordingly ......

 

You've got this the wrong way around, fronts need to be a fraction taller than the rears.

 

No.

Exactly.

 

maybe, but only if you overinflated the larger diameter tire, and under inflate the smaller diameter tire. It would tend to increase the shear forces of the silicone fluid within the VC.

djcooper@rennkit.com

 

I've had the warning lights pop on from a mix of incorrectly and worn tires, so it is likely a yes for the physical impact as the electronics are even noticing.

 

AFAIK there is no warning that the viscous coupling is being abused or mistreated. A number of owners run the wrong tires and even some get the front and rear diameters mixed up and get no warning lights.

In your case what is going on is the warning light is coming on because the system is detecting a wheel speed mis-match due to different tire diameters which can happen if one replaces just one tire on an axle and the tire tread depths differ by more then 30%.

(This might cause a premature failure of the differential but does not affect the viscous coupling.)

Or the lights come on because one is causing the PSM to kick in because the tires are worn out.

Over the 147K miles I've run a combination of new tires at all 4 corners, new rear tires and nearly worn out front tires and new front tires with worn rear tires and have never had the warning light come on. But I run 4 matched and N-rated tires and in the cases where one tire gets a puncture and I have to replace the punctured tire I replace both tires on the axle if the undamaged tire is worn too much.

 

yes to all of the above... fronts taller than rear........... ny bad whoops my bad computer dyslexia...........

 

yes is completely possible, the VC "doesn't care" re:visuals, but ABS does..

 

If you use the right tire combinations i doubt that the pressure will throw a code. maybe if you use some weird tire pressure.

 

was responding to splitime about worn tires/off sizing...

 

The systems are fairly sensitive (which is kind of impressive considering the tech dates back to 2000/2001.) Even switching to ****ty Hankook Ventus tires with weak sidewalls made my PSM go crazy in turns. But if you're running the right sized tires, a difference in tire pressure shouldn't make enough of a difference unless you're basically running one set overinflated, and the other two basically flat.

 

ok using 235/40 or 245/40 in th front combined wirh 315/30 in the back does not do anything. Thats about 6 mm more tire up front. How could tire pressure ever create such a hugh difference?!

 

As a data point, with 245/335 after mounting new tires and still at shop inflated 50psi, PSM cut in during a mid-speed corner I was just casually driving through. Never had an issue after lowering pressures to 36/40.