Tyre pressures / steering wheel position

[Calypso-E34]

My car is a 2016 F10 520d Sport, fitted with the 18" wheels.  When the tyres were last changed, non run flat tyres were fitted about 14000 miles ago.

What pressures would be right for these?  Should it just be the same as if it had run flats?  Current pressures are 1.9 bar all round according to the on board monitor.

I have noticed that the steering wheel isn't quite straight when driving in a straight line, and the steering wheel doesn't self centre quite as quickly as I feel it used to. 

[neil.o]

1.9bar is too low - below pic is from 2011 F10.  I have 18inch non-runflats and have landed on 2.2bar front 2.4bar rear. 

To your other question : As far as I know runflats/non-runflats should use the same pressure so long as size/ratings are the same.  But I have also found tweaking is required within the recommended pressures depending on tyre manuf/model, just like tyres on cars that were never designed to run runflats, IMO.

Steering wheel not straight ahead and self-centering could be separate or related issues,  I guess checking tyre pressures is worth the effort before getting in deeper !

Edited November 9, 2022 by neil.o

[Matthew]

Yes... 
The tyre pressures are the same irrespective of RFT/non-RFT. 

[Calypso-E34]

So.  Pumped up the tyres using an Arnold Clark compressor.  Put 32 psi in all four tyres - or so I thought.  When I drove the car again, the indicated pressures were all over the place.  I visited a local filling station and did the same there.  I got closer to all four being even, but no cigar.  How can this be?

Steering wheel still slightly off centre, so I guess I'll need to book it in somewhere to have that looked at.  Pity the tyres don't need changing yet.  I don't like these Road X things at all - would like to get back to run flats it should have.  I got a fright recently driving down to Cairnryan to catch a boat.  Big bang, metallic noise, and I thought shite - I've hit a pothole and had a blowout.

Turns out I hit a big lump of steel something that had fallen off a HGV I'm guessing, and the noise was me dragging it along - surprisingly little damage.  BUT - If that had been a blowout, I couldn't have continued my journey as I have no spare.

Not cool.

 

[Matthew]

15 minutes ago, Calypso-E34 said:

So.  Pumped up the tyres using an Arnold Clark compressor.  Put 32 psi in all four tyres - or so I thought.  When I drove the car again, the indicated pressures were all over the place.  I visited a local filling station and did the same there.  I got closer to all four being even, but no cigar.  How can this be?

Steering wheel still slightly off centre, so I guess I'll need to book it in somewhere to have that looked at.  Pity the tyres don't need changing yet.  I don't like these Road X things at all - would like to get back to run flats it should have.  I got a fright recently driving down to Cairnryan to catch a boat.  Big bang, metallic noise, and I thought shite - I've hit a pothole and had a blowout.

Turns out I hit a big lump of steel something that had fallen off a HGV I'm guessing, and the noise was me dragging it along - surprisingly little damage.  BUT - If that had been a blowout, I couldn't have continued my journey as I have no spare.

Not cool.

 

It is all about the pressure gauge attached to the compressor. I have a Ring RAC635 tyre inflator to get the tyre pressures somewhere near where they need to be and then one of these to get the pressure spot on, iDrive and pressure gauge always match:

PCL Digital Tyre Pressure Gauge Self Calibrating DTPG8 Twin Hold On Connector 5014875121529 | eBay

Steering wheel off centre is down to alignment rather than tyre pressures, unless in an extreme underinflation of one tyre on the axle

[neil.o]

another vote for separate pressure gauge,  second option linked below, approx 10pounds.

https://www.amazon.co.uk/RACE-RX0014-Tyre-Pressure-Gauge/dp/B000VZ8S26/ref=sr_1_1?crid=8BBRR3MAB9&keywords=pressure%2Brace%2Bx%2BRX0014&qid=1668512790&sprefix=pressure%2Brace%2Bx%2Brx0014%2Caps%2C40&sr=8-1&th=1

I use a 12V compressor which lives in the boot with the tyre gunk and the prayer that I never have to use in it anger.  The digital gauge on the compressor often seems flaky,  so I bought the separate gauge to figure out what was going on.  The separate analogue gauge makes more sense and matches the iDrive TPMS readout. 

Agree that runflats will prove their worth in a scenario like the one you describe,  I guess the missus and I are lucky we haven't needed it in either car.  Up to a few years ago I was convinced non-runflat was the way to go, but I think modern runflat tech is far improved comfort-wise versus the E90 E60 and early F10 era.

With tyre pressures adjusted and steering wheel still off-center or pulling to L/R,  I'd agree with Matthew that alignment is a probable cause. Also worth keeping in mind a wheel bearing  - my 2011 F10 pulling slightly to left, and with alignment in spec and no sticky caliper, I think I have an 11 year old bearing to replace.

[AndrewToo]

Interested in the comparison between digital read out and analogue accuracy. I’ve never considered a lack of accuracy. I’ve just today bought a Michelin digital one after my 10yr old Ring one gave up the ghost a few months back. Oh well.

[neil.o]

I suppose I saw differences between the readout on the same tyre when using:

• 12V compressor built-in digital gauge, (reads all over the shop)
• the local petrol station compressed air analogue gauge, (which may never be calibrated or cared-for)
• and the missus' idrive TPMS readout,  (which may be quite accurate, I think it has temp-pressure correction, but is a faff to adjust pressure and then reset and re-read)

and I thought a dedicated half-decent pressure gauge was worth a tenner, and its seems to agree tightly with TPMS.  It was just chance that I got an analogue one, I googled reviews and went by that, I'm sure digital ones are as good or superior if decent quality