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      10-20-2011, 06:39 AM   #1
baz57
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Tyre pressures - not as you would expect!

My post LCI E90 330d SE runs on Bridgestone 225 45 R17 91W Run flats. Same tyres front and rear. Maybe its me, but the pressure plate on the car tells me pressures should be 2.5 bar front, 3.0 bar rear.
On all previous cars, the pressure was always greater for the front tyres than the rear, presumably to take into account the extra weight of the engine.
So why are the rears on mine greater than the front?
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      10-20-2011, 06:54 AM   #2
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      10-20-2011, 07:07 AM   #3
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Simply that, RWD? But you can see my logic.....extra weight at the front seems to dictate a firmer pressure. I just checked by tyre pressures (my car is a recent second-hand purchase) and the pressures were about 30psi all round perhaps this is why the rears seem to have worn a little more than I expected. rears down to about 3mm tread, with 10k miles.
Off to inflate them!
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      10-20-2011, 07:18 AM   #4
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50/50 weight distribution on the BMW.
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      10-20-2011, 07:52 AM   #5
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In all my previous BMW's, I've always adjusted the tyre pressures in accordance to personal preference but ensured that its still fairly close to BMW's recommended ones. I've never got on with the recommended ones - my E92 felt rather dangerous to drive with the pressures at the recommended door jam ones. Took 0.1/0.2 bar off and it feels nice - even on the Bridgestone runflats. Been running them like this for a while now and tyre wear is also more even
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      10-20-2011, 08:11 AM   #6
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Now, having re-energised my tyres, im getting conflicting information - between the petrol stations air machine, and my trusty hand held pressure gauge! Which is more likely to be accurate? I was thinking of buying a digital gauge to replace my analogue one - anyone had experience of this type??
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      10-20-2011, 08:32 AM   #7
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A piston-type hand held is what you need.
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      10-20-2011, 08:38 AM   #8
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Quote:
Originally Posted by baz57 View Post
Now, having re-energised my tyres, im getting conflicting information - between the petrol stations air machine, and my trusty hand held pressure gauge! Which is more likely to be accurate? I was thinking of buying a digital gauge to replace my analogue one - anyone had experience of this type??
Petrol station pressure gauges are notoriously inaccurate. I use a good fashioned 'bourdon tube' type, but I'm considering a Michelin digital one which has a quoted accuracy of 1psi and that's as good as you'll get for 25. What's equally as important as the actual pressure, is balanced figures from side to side.
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      10-20-2011, 08:47 AM   #9
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I just use my local new-ish petrol station that has a paid for machine - meaning less people use it as there is a freebie a couple of roads down lol

I then check it against my digital tyre pressure gauge to confirm it - simples!
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      10-20-2011, 09:22 AM   #10
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Quote:
Originally Posted by baz57 View Post
My post LCI E90 330d SE runs on Bridgestone 225 45 R17 91W Run flats. Same tyres front and rear.
Congratulations on driving such a fine German automobile, with reasonably sized wheels, economically priced tyres and a compliant yet still sporty suspension.

Welcome to the club of people who don't like paying £3000 for a body kit and an explosion of fabric as grey as a British winter!
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      10-20-2011, 10:09 AM   #11
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Quote:
Originally Posted by bmwak View Post
In all my previous BMW's, I've always adjusted the tyre pressures in accordance to personal preference but ensured that its still fairly close to BMW's recommended ones. I've never got on with the recommended ones - my E92 felt rather dangerous to drive with the pressures at the recommended door jam ones. Took 0.1/0.2 bar off and it feels nice - even on the Bridgestone runflats. Been running them like this for a while now and tyre wear is also more even
I'd agree with this for my old 2006 330d. I ran it about 5 PSI lower on each tyre and found the handling improved. Although the downside was a more crashier ride.



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Congratulations on driving such a fine German automobile, with reasonably sized wheels, economically priced tyres and a compliant yet still sporty suspension.

Welcome to the club of people who don't like paying £3000 for a body kit and an explosion of fabric as grey as a British winter!
Its not only a body kit you get for 3000.






You get badges too.
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      10-20-2011, 10:11 AM   #12
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Look out, he'll be back if you're not careful.
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      10-20-2011, 10:36 AM   #13
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Quote:
Originally Posted by kaishang View Post
Congratulations on driving such a fine German automobile, with reasonably sized wheels, economically priced tyres and a compliant yet still sporty suspension.

Welcome to the club of people who don't like paying £3000 for a body kit and an explosion of fabric as grey as a British winter!
I admit, im loving the ride...as compared to my pre LCI E90 330d M Sport!
Oh and the economy too.... Having my cake AND eating it!!
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      10-20-2011, 10:39 AM   #14
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Quote:
Originally Posted by Jon D View Post
Petrol station pressure gauges are notoriously inaccurate. I use a good fashioned 'bourdon tube' type, but I'm considering a Michelin digital one which has a quoted accuracy of 1psi and that's as good as you'll get for 25. What's equally as important as the actual pressure, is balanced figures from side to side.
I reckon this is the one to go for.....My gauge is old, nearly worthless. The car cost zillions. Time to check out Mr Michelin.... Thanks!!
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      10-20-2011, 11:45 AM   #15
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I have about eight different gauges including a Michelin digital, my favorite is a Race-x analogue which I suspect is a little more accurate, certainly it is nice use, bought mine off Amazon. I think it is very important to check pressures. The handling was out when I recently bought my approved used BMW (brand new Michelin RFTs)... turns out pressures were variably out by up to seven psi! Assume nothing when buying from even main dealers. Even 1-2psi difference can make significant handling differences, particularly at speed. That's why I check pressures at least once a month, the ambient temperature is worth noting too.
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      10-20-2011, 12:33 PM   #16
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The Race X looks pretty good and I see it gets a 5 star rating from Auto Express. Also it's half the price of the Michelin; I might have a rethink.
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      10-20-2011, 01:57 PM   #17
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Quote:
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The Race X looks pretty good and I see it gets a 5 star rating from Auto Express. Also it's half the price of the Michelin; I might have a rethink.
I have ordered the Race X - It comes highly recommended.
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