[GMTRB5]

Just wondering what other people do with their tyre pressures?!

I've got the 19's as part of the M Sport Plus pack .. I tried inflating them to the amount recommended for a full load, which was 2.6 bar at the front and 3.1 at the rear .. was fine with the wife and 3 kids in it, but today going to work with just me the ride was really bumpy ...

Have put the tyres back down to the standard 2.2 at the front and 2.3 at the rear ..

Does everyone else leave at 2.2 / 2.3?

[SpeedTrip]

I run my F11 530d M-Sport @ 2.4F & 2.8R after experimenting ... typically only me and a 66Kg dog on board ....

[AP]

I run mine as per the label near the B pillar. 2.2 bar front and back (or is it 2.3 front and back, can't remember to be honest)
530d saloon with 19" wheels
didn't want to make them any higher given the ride is firm enough as it is!

[HighlandPete]

I've experimented with pressures over the years and find RFTs (for my use) need to be above the lower range on door placard, even for lighter use.

I run my F11 535i on 18" wheels at 2.4 (F) and 2.7 bar (R). Increase if I'm driving loaded over distance. Run 17" winter RFTs much the same pressure.

Key reasons for my choice, ride and handling balance and most even and balanced wear rate. Steering precision also deteriorates with less or more pressure in normal use.

One thing I quickly learned when first running RFTs back in 2006, they are slow to warm up, particularly in colder seasons and when wet, so BMW's lower door placard figures don't get you up to ideal working pressure if you make shorter trips. Fine if you are working the tyres hard enough to heat up, but if your trips don't allow for that, tyres really need a bit more cold setting pressure to compensate. For me that is + 0.2 - 0.25 bar (3 psi) for normal use.

HighlandPete

[AP]

I always thought that you needed to check tyre pressures when the tyre was cold, or at least it not warmed up by driving?

[HighlandPete]

Originally Posted by AP

I always thought that you needed to check tyre pressures when the tyre was cold, or at least it not warmed up by driving?

Absolutely, that is what I'm referring to, cold setting pressures. 'Setting' and 'working' pressures are two different values.

The problem is, if the tyres don't warm up to the working pressure, the value that really matters, (the one we don't check with a tyre pressure gauge) we can be running on too low a pressure.

A hot tyre can increase pressure by up to 0.3 bar, (4 psi) it is possible to be running in conditions, where the ideal working pressure (the one BMW allow for) is never achieved in our driving. Lower than ideal working tyre pressure is a reason for corrupted steering, excess tramlining and odd tyre wear. RFTs just make the situation worse, as low working pressures causes us to partially run on the side walls, making for even more odd tyre wear.

I've personally experimented with the variations of tyre pressure over varied conditions, when I was trying to understand why with RFTs the 330d road feel and steering was so erratic over different trips on the same roads.

HighlandPete

[AP]

interesting thanks
So the next question I have is how long does it take a tyre to reach its "operating temperature". (I know how long is a piece of string..)
Ambient temperature would be a big factor but are we talking 5 minutes , 30 minutes?

[HighlandPete]

Originally Posted by AP

interesting thanks
So the next question I have is how long does it take a tyre to reach its "operating temperature". (I know how long is a piece of string..)
Ambient temperature would be a big factor but are we talking 5 minutes , 30 minutes?

You are right, it isn't a simple answer. I noticed the issue of RF tyre pressure as I drive a lot of trips around the 12 mile mark. Driving feel would be so different, a sort of "how will the car steer today?" I recall one trip where after driving about 15 miles in the dry, I hit a cold storm, the temperature dropped out to 3C with heavy rain. The car just changed its feel in less than half a mile, tyres chilled and the ride firmed up, the steering corrupted, tugging and following any road imperfections or cambers.

We get away with being too concerned with the finer detail of pressure on non run-flats, but my own experiences got me checking out the working pressures.

Here are a couple of my first experiments from my E91 330d. I even got into taking tyre temperatures with an infrared thermometer, lower ambient temperatures and RFTs hardly warm at all if the road is damp, even worse if really wet.

Examples on Bridgestone Potenza RFT’s.

3°C ambient, damp conditions.
Pressure 2.3 bar
Trip 12-miles.
Tyre temperature, difference hardly noticeable.
New pressure 2.35 bar
Ride/steering, awful.

6°C ambient, dry conditions.
Pressure 2.3 bar.
Trip 12-miles.
Tyre temperature, feeling warm to touch on the inside, outside just noticeable.
New pressure 2.5 bar
Ride/steering, improving as you drive.


Examples on Goodyear GS-D3 F1’s.

3°C ambient, damp conditions.
Pressure 2.25 bar
Trip 12-miles.
Tyre temperature, feeling warm to touch. Both sides of the tyre
New pressure 2.45 bar
Ride/steering, good at beginning and excellent at end of trip.

6 - 8°C ambient, dry conditions.
Pressure 2.3 bar
Trip 12-miles.
Tyre temperature, feeling warm to touch across the tyre.
New pressure 2.5 bar
Ride/steering, very good at beginning and excellent at end of trip.

Note the changes in setting to running pressures, after 12 miles.

HighlandPete