Bimmer32

PLease don't shout at me. Doing so is very impolite. You need to read my posts and replies more carefully. You are struggling against a strawman.

I do agree that you also are talking about straight-lines at least some of the time (over generalized above--should have said that you appeared to be emphasizing curved lines in what I was replying to), but given my explicit or implicit assumptions, my straight-line solution is better all around IMO. It's fine with me if you like yours better than mine. As said above, let's let him choose at this point. Maybe he will let us know what he likes best.
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Hope you don't mind if I could intercede and summarize. Smcd is saying that high front/low rear is best for cornering and straight line acceleration. The original poster is saying that he is not understanding that since low front/high rear gives him a better feel on cornering and straight line acceleration as Vnod/BMW adviced.

I, too, think lower rear gives better straight line acceleration because you'll have more grip. As for high fronts, RWD don't need gripping in straightline accelerate and helps with better rolling if the pressure is higher.

Now for cornering, high front would mean (theoretically) lesser traction but no understeering. Low rear would sound logical since you'll need to fight inertia.

Now finally, for overall "street" performance, I think Vnod is right to use BMW recommedation. It offers better comfort (no high front=less bumps) and safety and slightly higher rear (2 psi). Really, 2 psi, in my opinion, reduces tire wear (less gripping) since the E60 is RWD.

A project manager at my work races motorcycles for about 10 years now. He has for racing (combining straightline and cornering), over all lower psi is best, but of course poor gas mileage. Who cares when you are racing anyway? I think he said for car tires, it's around 22 psi.

znod

PLease don't shout at me. Doing so is very impolite. You need to read my posts and replies more carefully. You are struggling against a strawman.

I do agree that you also are talking about straight-lines at least some of the time (note that I said "you are talking about taking frequent curved lines at speed"--which does not contradict the idea that you also are interested in straight lines--as acknowledged in my earlier posts), but given my explicit or implicit assumptions, my straight-line solution is better all around IMO. It's fine with me if you like yours better than mine. As said above, let's let him choose at this point. Maybe he will let us know what he likes best.
[/quote]

Hope you don't mind if I could intercede and summarize. Smcd is saying that high front/low rear is best for cornering and straight line acceleration. The original poster is saying that he is not understanding that since low front/high rear gives him a better feel on cornering and straight line acceleration as Vnod/BMW adviced.

I, too, think lower rear gives better straight line acceleration because you'll have more grip. As for high fronts, RWD don't need gripping in straightline accelerate and helps with better rolling if the pressure is higher.

Now for cornering, high front would mean (theoretically) lesser traction but no understeering. Low rear would sound logical since you'll need to fight inertia.

Now finally, for overall "street" performance, I think Vnod is right to use BMW recommedation. It offers better comfort (no high front=less bumps) and safety and slightly higher rear (2 psi). Really, 2 psi, in my opinion, reduces tire wear (less gripping) since the E60 is RWD.

A project manager at my work races motorcycles for about 10 years now. He has for racing (combining straightline and cornering), over all lower psi is best, but of course poor gas mileage. Who cares when you are racing anyway? I think he said for car tires, it's around 22 psi.
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HI B32:

I agree with what everyone is saying. Most importantly, I agree that lower in the rear is better for straight lines if one has a traction issue. But, higher in the rear is better if one does not have a traction problem for ride, mileage, and safety--and no loss in performance. The original poster sort of blew these factors off except performance. In this regard, I am saying why blow these factors off if one is like me--99% straight lines and slow curves and no traction problem. If the poster wants to get frisky and do so fast curves, then change the tire settings to more in the front. The only problem is that he appears to like more in the rear for friskiness--on both straight and curved line. So, what's likely to be better for him? Well, I wish he'd say what he has settled on. I know what's better for me.

The following is interesting to note in judging tires since they may perform differently with different pressures. It may be highly pertinent for those that like more in the rear--particularly those that approach BMW's front/rear recommendations. Here's an excerpt from the recent Road and Track tire test.

"The Tire Rack generously offered us the use of its BMWs for our test. The 325i is a wonderfully balanced car, and its handling is so consistently predictable that we felt sure we'd get a clear idea of what the tires were doing as we put them through the tests. The required tire size?225/45R-17?is made by the 11 brands we wanted to evaluate. We used BMW's recommended tire-pressure settings of 29-psi front and 35-psi rear for all our testing."

smcd

Thanks Bimmer. A good summary. No question there is personal choice here - no 100% right answer - just depends on what behavior the driver is looking for.

In this case, he asked for better straight line acceleration so I made the appropriate recommendation. If he asked for better tire wear, best balance, or most safe, I would have made a different recommendation.

I don't know motorbikes well but the optimal temperature for almost all car tires at the track is around 40psi hot. For example, Toyo recommends 38-42psi for their Toyo Proxes, a very popular high traction street & track tire. There would be a lot of unnecessary sidewall wear on a 22 psi tire. This may be more appropriate for a motorbike where there is less weight transfer to manage.

Ricracing

A really nice conversation, thank's guys, very instructive.

One matter that didn't come out was that, if you have rear seat passangers in your car, I suppose at least that the rear wheels should have higher psi then?

In these days I'm looking for the ultimate comfort, not racetrack handling, and I also see the safty matters important.

Therefore I go with the given psi's, but with the lower recommendations +2 psi.

znod

HI Rr:

You are very welcome for my part. And, I am sure that goes for the others as well. I think we did cover some issues pretty informatively.

smcd

Very welcome. Wouldn't be fun if we all enjoyed the same settings, now would it?

There are two recommendations by BMW typically - one for normal load (driver/passenger) and one for full load (4-5 people + luggage). Both of these are posted on the door frame of your BMW (and any car in the USA at least). I think they recommend about +4 PSI on the rear due to the increased weight they're supporting.

Ultimate comfort with safety for me is probably 34-36 psi all around. If I was in the city with a lot of potholes, I would keep it around 33 all around for a softer ride. Then boost the rear when you need it for extra load or are doing a lof of highway driving (don't need the soft ride - safety is more important).

I run with 40 at the rear when towing my M3 with the X5 for example but 36 at the rear for daily driving.