Just remembered - a warning to everyone picking up new cars...my tires were set at 49 PSI by the dealer

It rides a little better with 33 in there...

Does anyone actually run the pressure that high, or was it a mistake?

 

I've been experimenting recently with different tire pressures - currently running 34 front and 31 rear (205/45-R17 Bridgestone RE050A). Since I'm an old fart with greatly diminished sensitivity I'd like to hear what others have found to be the optimum pressures to use for somewhat aggressive diving in the twisties.

 

i'm sure it was a mistake, or more like an oversite. i learned a long time ago to always get the thing aligned and balanced before i leave the dealer with a new car. apparently this stuff is just set when being built and not really checked. the dealer also does not check it before putting it out on the lot, so you've got to check all this stuff there or at least as soon as you get it home.

 

I checked the torque of wheels at the dealer before I took delivery and the lugs were all real close to 90 ft.lbs. However, when I checked the tire pressures, they were all 52 lbs. I have been running 34 lbs. front and rear. 7k Miles on 205x45x17s with one rotation. All 4 tread wear looks great.

 

If you tweak the tire air presure,do you need to re-set the low pressure
warning,or does it activate at a low pressure,and not just a change in pressure?

 

I believe that the low pressure warning is given when wheel speeds do not match.

If three of your wheels are turning at a certain RPM, and the forth wheel is turning a faster RPM, then logic says the forth wheel is low on air. Low air pressure causes a smaller tire diameter and therefore a faster wheel speed RPM for a given road speed. All of the wheel speeds are continously monitored by the sensors used for ABS braking and DCS.

This is my simplified understanding of how the pressure warning works on the MINI.

 

The low pressure warning does not sense tire pressure. It senses the difference in wheel rotation speed. If a tire is low, the wheel rotation speed changes and is sensed by this system.

So.... The key is to have similar pressure in all four wheels.

Good luck,

 

So then you don't know you have a bad tire till you are going how fast

 

and what is the pressure difference ,how low is the bad tire when this would
trigger the sensor,and thank you for reminding me this is how it works,forgot

 

The one time my tire sensor flashed its warning during 6,500 miles, I found one tire with a screw in it causing a slow leak. It had 4 lb. less air than the other three.

Joe

 

4 pounds ,thats good ,not to flat yet.

 

I have the factory 16" Dunlop SP5000 RF tires with V-spoke wheels. I have tried varied cold PSI pressures and currently I am running all 4 corners on 37PSI cold. Love the ride quality and best of all the razor sharp handling!

I have found that anything below 35PSI is not worth in terms of handling so I highly recommend setting your cold tire pressures at 35PSI or well above.

 

Here’s my semi-informed W.A.G. on how the Flat Tire Monitoring System works:

When you press the button to start system re-initialization the wheel rotation counter are zeroed out. As you drive off each counter counts the revolutions of its associated wheel. After an unknown (to me) distance has been covered the system can now turns ratio of each wheel. It then starts to monitor each wheel, and if a wheel starts to exceed its stored ratio of revolutions to the other wheels by some unknown (to me) amount, then it assumes that it has lost air and trips the warning lamp.

This allows for sloppy inflation as well as intentionally carrying differing pressures.

Here is a way to verify: Air up all tires to 36 psi and re-initialize the system. Stop the car and bleed one tire down to 28 psi. I’ll bet that you’ll get a warning light when you drive off. Stop and shut down again, re-initialize the system with one tire at 28 at the others at 36. Drive to a compressor and bring the 28 psi wheel up to 36 psi. I’ll bet that you’ll again get a warning light when you drive off.

I’m presently running 35 psi on the fronts and 33 on the rears with Bridgestone Potenza RE050A tires. It is better in the twisties than the somewhat lower pressures that I had been using before.

 

You really should have MORE pressure in the rear if you are going for optimum handling. More air in the rear will help the car rotate better and reduce understeer (push) in corners. I have done a lot of experimenting on the track this month running Yokohama AVS ES 100's. Pyrometer readings (three places across the tread. Inside, center, outside.) after each run helped me determine that 34 front and 36 rear was perfect for my situation. (remember that pressures go UP as the tire gets hot.) It should be noted that I run an H-Sport Rear Competition sway bar on the middle setting. This also reduces understeer inherent in the MINI.

Pyrometer checks after a drive will tell you if your tires are inflated properly for the track or street. You want the heat readings to be as identical as possible across the width of the entire tread.