New Tyres=Worse Driving

Going back to the tyre pressures, obviously the Michelins are still runflats. Alot of people on here seem to run 36/34psi. However on the door the stickers says 2.6 for the rears and 2.4 in the fronts so x14 equals 36psi in rear and 32 in front.
I currently have 36/34 is it worth me dropping to 32 in the front?
 
Book it's 33/36, but if running a lighter load 32/34 is probably ok... I ran 32/34 today and it was pretty nice on Bridgestone RFT's.

You could maybe drop another 1-2psi on the rear, as the high pressures seem to be there to support high luggage loads, and there is no variance on book figures for all that extra load in the boot (ie, my partners car has +3psi for rears iirc, for sustained high speed high load work on the rears)

Experimentation is always key imho. I rekon running less rear camber would settle it down lots as it's always the rear shimmying left-right from the back that puts me off the most on bumpy roads, not the front end.

Dave
 
On the way home tonight I was giving this a thought as well. A few things came to mind, I don't know if any are anywhere near the correct answer, but here goes:

--wide, low profile tires react much faster than higher profile tires on your "standard" coupe or sedan
--our tires are summer, high performance tires and they don't like to be driven at anywhere near freezing temps (rft or not)
--these are true sports cars and the steering reacts quickly
--sitting low near the ground intensifies the feeling of speed and movement
 
I still think its an alignment problem.

I never had this problem until I drove back from Connecticut and their bad roads.

The car at ANY speed was near perfect. Even 135mph.. :evil: Now it is twitchy at anything from about 40mph and up...

Like I said further up in the thread, I am having the car aligned tomorrow morning. Will post the results tomorrow night.
 
Wow - for all the alarm about tire pressure I am surprised no one has brought up what the recommended pressures are for the ///M with the non RFT Conti's. 30psi all the way around.

The tire pressures on the doors of the RFT cars are not applicable as a guideline once you take the RFTs off. Form my own experience on my local track last year I found that running at about 31-32psi hot (Michelin PS2s) was just about right for a good solid feel of the tires through the course of a 20 minute run session. Any higher than that and the traction had a very greasy feel in the turns from over inflation. The shoulder tread wear also seems to bear this pressure out as I had no evidence of the sidewall rolling over at all at 32psi hot. Underinflation will almost always allow too much sidewall flex and will show tread wear that goes farther into the sidewall than the little wear triangles you can note just beyond the tread on your tires.

RFT tire pressures on non RFT rubber is almost extreme over inflation. There is a reason why BMW is not using those kinds of numbers on the ///M.
 
In my limited experience I'd say it's worth consider ing the pressures too.

I have F1 Asymmetrics 18" now and they seem best on the RFT pressures but the 120D I had did feel sloppy after I changed to Sportcontact2s (though not as bad as your description) until I put an extra 0.2 bar in.

Wouldn't do any harm to try it with a couple extra psi and see how it feels.
 
This rings true - when I've had tyres done at BMW on the old Mini CooperS, I found they had pumped them up to 38PSI!!!

I generally pump RFTs to 32 all round and don't have any of the issues you mention.
 
Running my FK452's 32psi all round now. Will see how they wear in. Feel a bit slippy right now but generally nice ride :)
 
AlanL, good point, but the original poster said he had Michelin PS2 ZPs fitted-run flats.

Waiting on shipkiller's post--cars go out of alignment so gradually, that when you first drive them after having the alignment reset, they feel a bit strange. Couple that with new tires, and it might just feel twitchy.
 
OK.

This morning I checked my tire pressures. It was 30'F at 0730. Tire pressures all around were a bit low @29psi. but that is do to the cold temps. I do not have runflats... :thumbsup:

The car was still twitchy on they way to my indy....


He put it up on the machine. The front left toe was out of tolerance, and the rear right toe was out of tolerance. Caster and Camber were all good.

After adjustments, everything now good.

Driving to work, :D :D :D Not twitchy now. Then I noticed that before, the car, while drove in a straight line, would steer easier (?) to the left than to the right. Did I say that right? Now it is perfect. Even blasted up to 95MPH. :thumbsup:
 
I'm sure that was a typo and he meant 95kph :rofl:

Thanks for the update on the alignment. :thumbsup: I'm going to have mine done by a different shop once I switch tires. Hopefully that's all it is. Oh, I'm also going to drop my pressure to 30psi on all 4 and see how that feels since it's the standard setting for the M.
 
I've been reading this thread with interest, hoping it was the alignment. I had mine done by a really knowledgable specialist as mine felt twitchy after i had new tyres fitted. It turned out 2 of my wheels were quite a bit out, after the alignment mine now feels very stable at high speed.

I would deffinately say to anyone wanting to get alignment checked to go to a good specialist with the latest equipment and knowledgeable people as there are alot of garages that don't really know their stuff.
 
I've heard that those that use Hunter alignment gear are generally very good, as the equipment itself is very very good.

It is a shame that so many people sell their services in this regard but actually know very little. It really is a case of doing your homework as most places out there are no better than you sat at home with a spanner and a ruler (honestly)

Dave
 
AlanL said:
Wow - for all the alarm about tire pressure I am surprised no one has brought up what the recommended pressures are for the ///M with the non RFT Conti's. 30psi all the way around.

The tire pressures on the doors of the RFT cars are not applicable as a guideline once you take the RFTs off. Form my own experience on my local track last year I found that running at about 31-32psi hot (Michelin PS2s) was just about right for a good solid feel of the tires through the course of a 20 minute run session. Any higher than that and the traction had a very greasy feel in the turns from over inflation. The shoulder tread wear also seems to bear this pressure out as I had no evidence of the sidewall rolling over at all at 32psi hot. Underinflation will almost always allow too much sidewall flex and will show tread wear that goes farther into the sidewall than the little wear triangles you can note just beyond the tread on your tires.

RFT tire pressures on non RFT rubber is almost extreme over inflation. There is a reason why BMW is not using those kinds of numbers on the ///M.
Click to expand...

You make a great point about RFT vs Non RFT tires. I too am running Michelin PS2's but my question is why the difference 33psi front 36psi rear with RFT? I understand the higher pressures on the RFT, but why the difference front to rear? Shouldn't we run the same differential ,3psi front to rear albeit at a lower psi with our PS2's? Geez I just read my post and confused myself :rofl: Just trying to find a proper PSI for everyday driving. Thanks. :thumbsup:
 
Z4good said:
You make a great point about RFT vs Non RFT tires. I too am running Michelin PS2's but my question is why the difference 33psi front 36psi rear with RFT? I understand the higher pressures on the RFT, but why the difference front to rear? Shouldn't we run the same differential ,3psi front to rear albeit at a lower psi with our PS2's? Geez I just read my post and confused myself :rofl: Just trying to find a proper PSI for everyday driving. Thanks. :thumbsup:
Click to expand...

I actually found the same numbers by feel out on the track and found that the best stability and tire wear patterns with my coupe came out of equal front/rear tire pressures far below the recommended RFT numbers. I was pleasantly surprised to read the door numbers for a ///M roadster owned by one of my students after I had already done several events on the PS2s in my 3.0si.

My take is that the oddball unequal numbers imprinted on our door tags is what it takes to make our cars feel normal in spite of the RFTs. :smart:
 
AlanL said:
My take is that the oddball unequal numbers imprinted on our door tags is what it takes to make our cars feel normal in spite of the RFTs. :smart:
Click to expand...

Also, again, because there is no differential for luggage loads I would imagine.

The Z4 standard doesn't really have a very large gross vehicle weight, a few hundred kilo's in the boot pretty much loads the car to the maximum with two passengers, while a lone driver with no fuel or luggage probably needs nowhere near 36psi, it is there because people simply wouldn't change it when loading the car with luggage etc, so they just advise pressures for the full load situation.

High load/speed pressures are very common, most other cars I've had have them, the Z4 doesn't.


I'm running 31psi all round on FK452's right now and it feels super stable but still agile. Did some left right jinking down the motorway at ~ 90mph and solid as a car would be at that speed imho... no pulling, just went where I pointed it.

Dave
 
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