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      03-17-2007, 01:18 AM   #1
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Tyre pressures

Hi Guys,

Since i got my car 3 weeks ago, I thought the ride to be a bit bumpy so this morning I checked my trye pressures. Stone cold, they were 40psi. The door card says 200 - 220 KPI which is around 30psi. This I thought was low so I droped it to 36psi. I later went out and checked them when hot and they were 39psi. I droped this to 36psi hot. I'll check them tomorrow morning again before I go out.

For those with the M-Sport staggered tyres 225/45/17 + 255/40/17, I'm interested to see what pressures you are running (cold or hot).

Why on earth would the "wally dealer" set them to 40psi in the first place contridicting the official settings.
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      03-17-2007, 07:04 AM   #2
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Hi Guys,

Why on earth would the "wally dealer" set them to 40psi in the first place contridicting the official settings.
Which dealer?
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      03-17-2007, 09:20 AM   #3
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Well I don't want to shame the dealer publicly but you can see my location and I'm sure your assumption would be right.
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      03-18-2007, 02:40 AM   #4
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There are very few subjects around that seem to attract as much BS as tyre pressures. IMHO for normal road use, the "right" tyre pressure - if indeed there is one - is the pressure which provides the most even wear across the width of the tyre. That signifies that the contact patch is doing what it should.

Excess pressure will wear the centre, enhance steering feel, enhance wet grip ( slightly - as the tread grooves are forced a liittle wider) and compromise ride. Insufficient pressure will wear the edges, diminish steering feel, marginally reduce wet grip, improve ride.

After a lot of stuffing around with pressures with many different cars and many performance tyres, I've come to the conclusion that somewhere between 34-35psi all round seems to yield the most even tread wear, almost regardless of the vehicle/tyre combination. Of course you should bump it up if you are fully laden on a long trip, or at a track day track day. But I never run any car below 34psi, regardless of what is on the placard.

Try it out and I'll bet your tyres wear optimally across the width of the tread
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      03-18-2007, 04:33 AM   #5
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I'm running the 18" M sport wheels at no higher than the recommended pressures listed on the tyre placard in order to get some sort of ride quality.

Also, don't forget that you need to reset your OBC tire pressure monitor each time you change tyre pressures in order not to get false low pressure readings.

I drove a 323i touring recently with 18" wheels and no M technic sports suspension and the ride quality was pretty good compared with my vehicle.

I'm thinking next time around I will probably go with this combination as the 18" wheels and M technic suspension on Sydney's poor roads is a little too firm and will create more rattles as the car gets older.
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      03-18-2007, 04:40 AM   #6
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Thanks NickG .... I agree with your comments and I also tend to think 34psi is a good number to be at. I've reset mine to 34psi (cold) and the car deffinitly doesn't bounce as much now.
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      03-18-2007, 04:53 PM   #7
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Quote:
Originally Posted by 9c1 View Post
I'm running the 18" M sport wheels at no higher than the recommended pressures listed on the tyre placard in order to get some sort of ride quality.

Also, don't forget that you need to reset your OBC tire pressure monitor each time you change tyre pressures in order not to get false low pressure readings.

I drove a 323i touring recently with 18" wheels and no M technic sports suspension and the ride quality was pretty good compared with my vehicle.

I'm thinking next time around I will probably go with this combination as the 18" wheels and M technic suspension on Sydney's poor roads is a little too firm and will create more rattles as the car gets older.
Is your car running RFT Pirelli Euforias' by any chance?
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      03-18-2007, 09:30 PM   #8
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Is your car running RFT Pirelli Euforias' by any chance?
Any reason you asked about Euforias? The reason I asked is I bought 4 euforias (with 50% tread left) and 17" alloy 158 from ebay about a month ago for only $350. I wander why they sell them so cheap. Maybe they are not good? I havent put them on the car yet, as I am still waiting for the car.
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      03-19-2007, 12:35 AM   #9
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Tyre pressures will vary quite a bit depending on whether it's hot outside or not and also when you've just driven the car. Always take the pressures in a semi-controlled environment - e.g. inside a garage where the temp may be similar.

I'd always go for manufacturer's figures but how fast you go round corners will make a bigger different to your tyre wear over the long term than a few PSI here or there.
 
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      03-19-2007, 12:38 AM   #10
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just had a thought... if you get new rims and tyres, what would the pressure be? the same as manufactuers recomendation? or is it different from tyre to tyre?
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      03-19-2007, 12:45 AM   #11
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Tyre pressures will vary from car to car. Heavier cars will need different pressures to lighter cars. Different tyres do have different max limits, however.
 
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      03-19-2007, 01:46 AM   #12
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Originally Posted by JameB View Post
I'd always go for manufacturer's figures but how fast you go round corners will make a bigger different to your tyre wear over the long term than a few PSI here or there.
If I recall correctly, BMW's recommended pressures for my old E46 were something ridiculous like 28psi front 32 rear. I'd suggest these have a lot more to do with turning the car into an understeering pig to avoid lawsuits from inexperienced American RWDers than with providing an enjoyable motoring experience. Whatever, they certainly stuffed the steering feel and made it handle very much like my wife's 10 year old Saab 9000.
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      03-19-2007, 01:55 AM   #13
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Quote:
Originally Posted by ed-320d View Post
Any reason you asked about Euforias? The reason I asked is I bought 4 euforias (with 50% tread left) and 17" alloy 158 from ebay about a month ago for only $350. I wander why they sell them so cheap. Maybe they are not good? I havent put them on the car yet, as I am still waiting for the car.
I can't pretend to be an expert on this, but from what I have gathered:

1. Euforias are first generation RFT's, and may not have been the best of that generation. Plenty of people have dumped them ( and other early generation RFT's) because of ride and noise issues
2. RFT's have improved significantly with each new generation, but some people are still dumping the latest ones. I'm increasingly certain Bridgestone's latest RE050A RFT is at least partly to blame for the flawed ride in my e92 335i for example.
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      03-19-2007, 03:01 AM   #14
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Quote:
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Is your car running RFT Pirelli Euforias' by any chance?
No NickG, it's running Bridgestone RE050A RFT's which were the OEM tyres supplied with it. I actually think it's more the M technic suspension that's causing the firm(er) ride rather than the tyres alone.

I'm considering changing to Michelin tyres when it's time to replace them as I had a really good run with them on my E46 and I've always found Michelins to be quieter and longer lasting than any other brand. Not sure if they do "sports" RFT's though.
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      03-19-2007, 05:30 PM   #15
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The M technic suspension is very firm compared to the non sports model but the RFT also dont help the situation. I'm 99% sure I'll go for a good quality but non RFT when replacement time comes around. All you need is a can of sealant incase of a flat.
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      03-21-2007, 05:42 PM   #16
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mtech suspension is firm? since when?

or maybee mine has colapsed, lol... my m suspension (soon to change to aftermarket) is not hard at all when compared to other cars i ride in
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      03-22-2007, 02:36 AM   #17
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Quote:
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mtech suspension is firm? since when?

or maybee mine has colapsed, lol... my m suspension (soon to change to aftermarket) is not hard at all when compared to other cars i ride in
In my experiance, comparing M suspension in E90 to E46, the E90 is much firmer. The RFT don't help either.
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      03-22-2007, 05:15 PM   #18
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the ride firmness doesnt always determine the quality of the product. BMW m tech suspension is well refined and should be enough for normal roads and a bit of spirited driving. It will also survive track work but its sloppy handling can be seen
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      03-23-2007, 04:53 AM   #19
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Yeah, I agree it is pretty refined. I owned an STi for about a year and getting into an E90 with M-sport suspension felt wonderful!

The biggest benefit of the suspension is the road holding - it's sublime going round corners at speed...
 
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      03-23-2007, 09:38 PM   #20
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to enjoy bmw's suspension and a reason why its so good you must watch this

http://video.google.com.au/videoplay...x5+nurburgring
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      03-23-2007, 10:41 PM   #21
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Quote:
Originally Posted by vgr02 View Post
In my experiance, comparing M suspension in E90 to E46, the E90 is much firmer. The RFT don't help either.
ahh, the new suspension can not come soon enough!!!
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      03-24-2007, 03:34 AM   #22
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cant remember what i typed before chem0 edited it. just watch the clip


Last edited by Sephanite; 03-24-2007 at 09:19 PM.
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