Discussion in 'Wheels & Tires' started by ragnuoy, Dec 31, 2009.
Door tag indicates 33 psi front and 41 psi rear. Rear at 41 seems like a lot. Suggestions.
I'd start with those pressures and see how it handles.
Before you go following stock pressures, check your tires as well. Some tires have maximum pressure ratings and if you've modified the car in any way in the wheel/tire department, those pressures may not be correct.
I would go by what the tires dictate, not by the info on the door jamb.
I really wouldn't go higher than 35 psi for pressure, most tires have a maximum pressure of 40 psi and when the tire warms up the air pressure increases
I'm astounded at some of the advice here. Pressures listed on the tires themselves are maximums from the tire manufacturer. They have nothing to do with your car, your driving style, or conditions. They are maximum levels for that tire, regardless of the car they're on, and nothing else.
The top line on the placard on cars in North America reflects the car manufacturer's recommendation for a fully loaded vehicle, meaning full complement of passengers and luggage at the maximum carrying capacity of that vehicle. We call that "cover your a*s". If you look further down the placard you'll see what the rest of the world gets which is recommendations based on loading levels from one-or-two passengers up to fully loaded. You'll notice the fully loaded tire pressures listed at the bottom of the sticker are usually the same as what you see on the top line on the sticker as "recommended".
Start by using the car manufacturer's specification that coincides with the load you're carrying. Be sure to check them cold or when driven less than five miles or so, and invest $25 in a good tire gauge with a mechanical dial. All pressures listed are for "cold" measurement. Pressure will change with driving (particularly in hot weather) and ambient air temperature, too, so be sure to check and adjust tires at the onset of cold weather. Once you've established a base-line from the vehicle manufacturer's suggestions, adjust them to your own driving style and conditions. Adding more to the rear tires (or less to the front) will increase under-steer while less in the rear (or more in the front) will increase over-steer. Using the 33-front and 41-rear you mention will result in sluggish handling when the car is not fully loaded. I'd think 36 all the way around would offer a more reasonable place to start with your car.
If you notice, the pressure recommendations don't change from the stock 15" to the 17" used as options in Europe or on the same body-style M5 so take it as a starting point only. Another issue is your 530i likely came with a special-for-BMW 6-ply Michelin MXV tire that was never available as a replacement from your local tire store. Even if you bought a replacement Michelin MXV it would likely be a 4-ply and the sidewalls weren't anywhere as stiff as the original-equipment tire. In such a case, you'd need to add air pressure to restore the handling the car came with because you can't get the same tire.
So start with the factory recommendation on your car for the load you're carrying. Adjust one-or-two pounds at a time to suit the feedback the car gives you, the tires you're running, and the handling and tire wear you experience.
'95 525i 5-speed
17" 235/45 tires
Gee...I thought that's what I suggested.......
No, you suggested starting with the North American cover-your-a*s-so-we-don't-get-sued-for-not-having-enough-air recommendation on the TOP of the label which is for a car fully loaded with five passengers and a full load of luggage. You might want to back up and read what I wrote again.
I donned my flp-flops and ventured out in what's left of the snow: What the sticker actually says is "up to 4-persons" 26-psi front, 32-psi rear and (IMHO) that's really not enough for a "big" car. Setting the tires closer to similar front-to-rear pressure will make the handling a bit more neutral with less under-steer. But it's all relative to what feels best, what tires the OP is running, etc. That's why I suggested 36 all around as a good starting point. 33-33 would work, too. 32-41 is as silly as 26-32, in my mind. I once heard under-steer described as offering the advantage of letting you see through the windshield what you are going to hit-as your car leaves the road!
Happy New Year, everyone.
Rough night last night??
Actually, no, but thanks for asking!
But then I'm not the one exhibiting compromised reading-comprehension skills! (All in good fun!)
Have a Happy New Year Phil. May your run flats never need replacing.
Same to you, Steven. And may neither of us ever own a BMW with run-flats!
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