New to the Cooper S. Just got it a couple of weeks ago.

If I change out the 17 inch runflats for 16's are there any necessary changes to the air pressure sensor system? Also, what if I get standard instead of runflat tires?

 

You don't have to make any changes to the air system at all. And everyone reccomends ditching the runflats. The ride gets better, and regular tires are cheaper. Plus, there are many different kinds out there that grip better than the runflats.

 

:smile: I'm sure that I'm in the minority, but I like the OEM 16-inch Dunlop Performance runflats! I'm on my second set (about 44k miles on my odo), and they are wearing well, with plenty of grip! With all the cross-country trips I make, I feel safe using runflats.


Clover

 

No need to worry about affecting the MINI's tire pressure warning system by switching tire/wheel sizes, or switching to non-runflats. Here's the verbose explanation:

There are two basic pressure monitoring techniques I have seen in use in passenger cars. The first operates by direct pressure measurement from inside each wheel. This is accomplished by strapping small pressure sensor/transmitter units installed inside the wheels, with the tires mounted over them. As the wheels rotate while driving, a small generator (like "shake to charge" emergency LED flashlights use) in each transmitter keeps a battery (or storage capacitor?) in the unit charged. The stored charge is used to transmit a signal which corresponds to the current pressure inside the tire (sort of like a MAP sensor does for engine management) back to the car's body control module. The body control module can then alert the driver if the pressure reading of any tire falls outside of a specified range.

The advantage of this system is that it is very accurate. It also offers the capability to provide the driver with a display of real-time pressure readings from each wheel while the car is in operation.

The disadvantage is that it is expensive, due to the cost of the four sensors, and it requires extra care during tire changes to avoid damaging components of the system. In addition, retaining the pressure monitoring system when converting to aftermarket wheels is a PITA, since the sensors must either be removed from the stock wheels and somehow mounted to the new wheels, or a spare set of sensors must be bought and fitted to the new wheels.

An example of this type of system can be found on late 1990's Corvettes (and possibly newer ones, as well- I haven't kept up on this since when I was a line tech.) One amusing "feature" of the Corvette system is that there were only 4 frequencies or "channels" used for the sensors- one for each corner of the car. Every Corvette of a given model year used the same 4 signals. The result of this could be quite amusing, or disturbing, depending on your point of view... if a Corvette with a misinflated tire got close enough to another Corvette, the sensor on the misinflated wheel could trigger a warning alert in the other car!

The second method used to monitor tire pressure is indirect. This method uses the ABS wheel speed sensors to compare relative rotational speeds of all 4 wheels while the car is in motion. Here's how it works: if a tire loses pressure, the tire's sidewalls flex to a greater extent than normal, thus reducing the radius of the wheel/tire assembly as measured from the wheel hub center to the tire's contact patch at the road. This change in radius is accompanied by a corresponding change in effective circumference of the tire. This, in turn, causes the affected wheel to rotate at a different rate than the other wheels. If a wheel speed difference beyond a certain threshold is detected, the tire pressure warning indicator lamp is triggered. This is the system implemented in the MINI, and many other cars.

The main engineering benefit of this "indirect" method of monitoring tire pressure is that it utilizes an existing sensor data from another vehicle system (ABS), and thus costs little to implement, compared to the direct-measurement type system. In addition, converting to aftermarket wheels, or even changing wheel/tire sizes, is not a problem. This is because there are no sensors to mount inside the wheels, and since the system relies on detecting relative speed differences between wheels, as long as the circumference of all 4 wheels/tires remain proprtionally equal, the system will still function properly.

The disadvantage of this system is that if all 4 tires are improperly inflated, the system might not detect the problem, if they are all misinflated in matching fashion.

:. In short, the MINI's tire monitoring system is quite "mod-tolerant." Just make sure all 4 corners match, and you should do well.

 

That feeling of security is a wonderful thing. I still have my non-runflat winter shoes on, so every time we go out for a motoring day trip, part of our paranoia check is making sure we have a charged cell phone along, just in case. That's in addition to the emergency tire repair kit that lives in the boot! It's sort of like packing an umbrella to go the amusement park on a sunny morning, just to make sure it stays that way.

Now that a 19% pulley is on our car, a spare belt and the belt tensioner tool will also be packed alongside the tire repair kit for long trips. Can't be too safe out there- the funnest roads are often far from help, so it's best to be ready to help one's self!

Oh yes-- there is also a towel in the boot. And I usually have some pocket fluff about my person.

 

I never leave home without my towel with an embroidered 42!