best tyre pressures for 225/45/18 conti?
 

I'm aware of lots of discussion about wearing edges and centres with the bigger MGR wheels. Has anyone concluded that changing the manufacturers tyre pressures has any value for longevity?

From my side of the fence, 32psi all round on the 18" wheels gives the best of everything. The only time that you need to change the pressures would be at extreme high speeds, a track environment or on a high speed track with bankings where IIRC, the pressures can end up something like 42 front 26 rear to compensate for the running round a bank and the higher loads on the front tyres.

I keep mine at 32psi and the length of wear has been very good on my current set of rubber. My fronts have done 12k and they've got 5mm of tread left on them and that a high % of country roads at 60mph and also motorway work. My last set of fronts coverd over 20K before needing changing and I'm in me squiesel so heavy up front.

Nic

Pondweed,

I usually keep my tyre pressures at 32 psi (the same 225/45 R18 tyres as you) in accordance with the handbook. However, I thought I'd pump them up to 34 (as they currently are) to see if there was any improvement in fuel economy and I'm sure there's slightly more tyre rumble than before - oh, and no noticeable improvement in fuel consumption.

I'll be returning to 32 psi all round before I head for my skiing holiday in France mid-Feb. 1,600 miles or so in 8 days, mostly on the autoroutes at 130 kmh (80 ish mph).

Steve

thanks - that's just what i needed confirmed to save me going through the same palaver.

Hmmm! Had a rethink on tyre pressures with my 225/45 18s. The outer edges of the front tyres are beginning to look worn (have done 11,500 miles of mixed driving) and have mentioned this to a trusted mechanic.

He was astonished that 32 psi is recommended, informed me that many BMWs with the same size tyres run at 35-39psi, so I'm going to follow suit! I've experimented already and have run the car at 40 psi all round with no increase in road noise (strange, as there was a slight increase at 34 psi!). Only detrimental effect was that the inside tyre lost grip more easily than normal when accelerating out from a junction.

I'm going to run the car at 38 and report back. Pondweed, I'll send you a PM.

Steve

I'm amazed. I've never ever seen tyre pressues like that in any BMW not even the 19" M wheels.

32 sometimes even less is recommended for the 18" M Sport II wheels currently seen on most Sport model BMs (5er and 3er).

Sticking the pressures up that high is IMO asking for trouble.

any one else got any other thoughts?
I must admit, the bit about the inside tyre losing grip out of junctions makes me question sanity... and wont the centre of the tyre tread be at risk of wear?

My tyres are at 34 PSI, they are 17's and are of a soft compound, 2 PSI over but they ride fine.

I can usually get 85-90 miles urban for a tenner (don't know if thats good) I'm happy as that gets me to work.....I tend to fill up a little more for the day trips....lol

I check my tyres for wear every week, what with the high risk of punctures, the wear has been even all round. So hopefully I have got it right. ;)

I only fill to the brim when I need to, as I have always thought fuel can go stagnant like water if it sits in the tank too long.

Follow the advised PSI on the tyre wall, never over inflate by too many PSI though.

Absolutely - I can confirm the 'high' tyre pressures for BMWs - I've had 4 on the trot...including M3, 540i and M5...
All the 'normal' tyres pressures for these are around 34/38 F/R and for fully loaded or high speed 42/46 F/R.
I tended to keep mine somewhere between..or maybe nearer the higher end...people at the pumps thought I was mad!! I did a shedload of miles in them like this and never suffered any problems...I think if you keep your pressures between normal and fast use figure given in the handbook youll be fine.
The worst thing you can do is run too low on pressure (for motorway journeys) as that is when excess heat will build up and you risk total failure in the sidewall.

I have a R75 CDT now and run it at about 34 all round - no issues thus far - and I have varied the pressure slightly over the past week or so - to my mind this feels the best - for my 'skinny tall' tyres...195/65/15's and gives the sidewall slightly less flex.

With that in mind, I would think the 225s would be fine at 32 all round.

bit confused now - you've just said bmw (fronts quoted here) run between 34 and 42 ideally... and then agreed with the 32 all round for the 75/ZT 225 tyres right at the end??

If 32 allround is "manufacturer recommmended", can you envisage why bmw are specciing so high on similar tyres? I realise they are rwd, but...