Quote:
Originally Posted by mojo1
My M Sport tire pressure at "b" pillar states 35/41 PSI. When I took delivery the pressures were set at 28/33. The ride was compliant at the lower pressures but gave some tire squeal at semi hard cornering. I bumped the pressures to manufacturer recommendations but the ride changed drastically to the worse. Currently I have the set at 32/35 seems about right to me. What have you set your tire pressure at.
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I don't know exactly, but take a look at the B pillar specs again and take notice of the standard tire pressure psi, and the "high speed" psi.
There will be a difference of a few pounds between the 2.
If you tend to drive at higher sustained speed, such as a lot of highway driving, or carry heavier loads like a lot of people, then the higher pressure is recommended.
If 35/41 is the standard psi, then I would NOT go lower than that.
The reason is that the tire pressure has been determined to work with the X1's weight and suspension to give you best handling and ride.
If you go under that pressure your handling will not be as good as it is designed to be, because your tires sidewalls won't have the pressure needed to maintain proper sidewall stiffness that is calibrated to work with the suspension tuning.
Also, with under inflation you run a greater risk of damaging the tire and the wheel. The tire can be damaged due to increased sidewall flexing that will increase the tires temperature at speed. The sidewall can become much hotter than intended and that will weaken the tire compound. Couple that with the additional flexing and it can lead to sidewall structure fatigue and potential failure with a sidewall failure.
With RFT's the car will keep you safer as it can maintain adequate structure to let you safely stop or get to a repair center.
Still, not a good thing to allow to happen.
The other negatives are quicker and excessive tread edge wear as the tires contact patch is distorted, along with greater tread wear in general.
Your MPG can also drop as the tires shape is flatter causing more friction than is intended or needed.
This might seem like a good idea as one may think there is more tread contact with the road for increased traction. But the opposite happens due to the other factors at play like the softer sidewall and greater flex that allows the tire to "roll" on itself increasing wear and heat in the sidewall.
That's why you're hearing more tire "squeal" as there isn't really more usable tread contact as low sidewall stiffness is allowing the tire to lose it's functional shape and it can't maintain proper traction. You're hearing the tire squirming and squealing cause it's in distress, and it's telling you to feed it more air.
RFT's by design have a very firm sidewall structure and don't as much "give" as non RFT's to soften the impacts from road imperfections.
That's what causes the more jarring impacts that get transferred through the tire, through the suspension mounts and steering components and then through the body structure and steering wheel, to you.
I would put the pressures where they need to be for the safest handling, and best tire wear, and best MPG.
Running under inflated will simply wear the tires out faster, and RFT's are not low cost.
If you really can't stand the ride, then try a set of non RFT's.
That's what I did with my 135i and current '13 335i Msport.
Within 3 months from new I had tire rack install a set of ultra high performance all season Conti DWS tires.
Fantastic tire on both cars, resulting in a much nicer ride especially when hitting bumps or road imperfections.
Handling, traction, and braking still great compared to the stock max performance summer only tire, Bridgestone S001 RFT.
Both cars had the higher "highway" tire pressures.
Great wear, great MPG.
335i with staggered set up, I get between 27-28 MPG, calculated by hand in the traditional way.
Sorry to be so long winded.
I have a tendency to do that.