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Tire pressure with non-stock wheels


DakarDoug

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I know tire pressure is critical in maintaining life of your tires and proper handling. My question is, should I use the original tire pressure specs provided by BMW even though I am running 15" wheels on my 2002? Does wheel size even matter in this case? I have heard different theories but want to get everyone's opinion. Thanks.

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Guest Anonymous
I know tire pressure is critical in maintaining life of your tires and proper handling. My question is, should I use the original tire pressure specs provided by BMW even though I am running 15" wheels on my 2002? Does wheel size even matter in this case? I have heard different theories but want to get everyone's opinion. Thanks.

Your question is one of common sense.

Much has changed since BMW made air pressure recommendations for 13" rims and tires (some of which were equipped with inner tubes). Tire pressure is mostly dependent upon tire design and not unlike bicycles, some small (very low profile) tires require higher than normal air pressure while the larger fatter (balloon) tires may require lower pressures, especially to the extent they provide much shock absorption. Tire manufacturers are not going to recommend pressures that deviate far from the auto manufacturers' factory recommendations for liability considerations and some cars have handling characteristics that may be unforgiving if dramatic changes in tire pressure and tire/wheel combinations are added (Early 911). Stock 02's handling are fairly neutral and hard to seriously mess up.

It is common knowledge that use may dictate tire pressures anyways so that high speed or competition usually indicates much higher pressures than street driving. For starters I would consider the top of the BMW recommendation and work up to a point that does not exceed the max sidewall pressures, balancing that with passenger discomfort (rough ride) and even-tire wear.

If worse comes to worse, contact either Toby or the Tire Rack people who get their information from him! lol

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In my limited experience finding the right tire pressure for a given set-up is all about experimentation. And it heavily depends on how you drive as Bodie mentioned above. Different tires of the same size also vary in the amount of pressure used. I play with a cheap longacher(sp) tire temperature meter and it definitly gives info that is useful in terms of optimising tire and suspension set-up for given loads.

What kind of tires and what kind if driving are you doing?

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Over many years, and several different tire mfg., I've had good handling, and even wear across the width of the tread, by using 30# rear and 32# front. This for street driving with 195/60 x 14s on 6" rims, 19mm bars front and rear, Bilstein HDs, lowered springs (1½"), all on a ' 75 2002A. I drive fairly agressively, and have many, many years of racing, autocrossing, time-trialing. and driver's schools experience behind me.

This is just one example for you to begin with.

Bob Napier

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Guest Anonymous

Those tires and rims are hardly the best choice for rough roads. The lack of extra sidewall as found in the original equipment makes for lots of boneshaking.

It is hard to tell exactly how rough your roads are. If its as close to off-roading on the road as you may be implying, it sounds as though you want enough air pressure to keep the sidewalls from deflecting too much and allowing your rims to kiss some potholes. What pressure that is is hard to say, but I wouldn't be surprised to see some numbers in the high 30's (lb/in2). Notice what rally cars run. Hint: They are not built for comfort and transporting trunk babies.

hth

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I live in Sicily and the roads over here are poor at best...lots of potholes to say the least! Heck, I think the asphalt is even made from lava rock from Mt. Etna which breaks up easily when it rains. Anyway, just me in the car and if I happen to lose a few fillings, so be it. Will go for a pressure probably around 32 psi and see what that does.

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I run high 20's (28 front, 26 rear- ish)

with similar tires and that seems to work pretty well.

Unlike modern (E30's and up) BMW's,

I've found that even lower pressures work well

(even tire temps) on track.

Modern tires are hellaciously stout compared to

bias plies and the old radials. And stick a lot better.

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Chess, good to hear from you. Still in Sicily. Expected to return in June but back to the other coast. Received orders to Seal Beach, CA so will get to see the 02s running around So. Cal. My 2002 will be heading to Norfolk for a brief period until I can get it shipped to Ca. Drop me a note sometime to let me know how things are going.

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