[ds968]

ok, since there were no replies to this "side comment" on the racing segment thread, I'll post it here:



how often do you guys ( 968 is a daily driver ) check your tire pressure ?

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[EEZATOY]

How about not often enough - generally I try and make sure I check them everytime I fill up (but not always) . Reality, my tire actually hold there pressure pretty well. Usually not down more than a pound or two.



Sam

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[flash]

just about every time i drive it - that sounds like a lot until you stop to think that it's only once or twice a month that i drive the car



as a reference only, shraeder valves leak in a standard tire at a rate of about a pound a month



also, tire pressures are more critical the lower profile you go

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[sasilverbullet]

Once a week.

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[ds968]

man, you guys are diligent ! I really must get my act together and stop neglecting this item ( MAY BE a three months interval... if I remember ! ) <img src="/forum/images/smilies/968/ohmy.gif" class="smilie" alt="" /> <img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" />



and yet, the tires still don't seem to lose more than 3 lbs...max.



but it's going to be on my Saturday morning checklist from now on



oil level - check !

coolant level - check !

brake and p.s. fluids - check !

beer bottles supply left - check !

new: tire pressure - check !

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[flash]

wow - if i let my tires go a pound out the car gets all weird



i end up going through pretty much a preflight check, since i rarely drive the car - i can see how things might get let go though for a daily driver

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[Lemming]

Everyday, but that's because I have a leaky rear tire, which gets replaced tomorrow morning. Normally I check the pressure weekly.

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[Larry Currie]

When I walk out to the car, and think, wow! That tire looks low.

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[Beachboy]

I'm running stock sized tires and I can feel a one pound difference. If I'm going on a long highway trip I find running two pounds low, 34 psi cold, makes it much more comfortable but I can't run the off ramps like I like to. I find 36 psi cold to be ideal for handling and that's where I run it.

Checking your pressure at fill-up is a mistake. The tires are warm and you will underinflate unless you know the change from cold to warm and inflate accordingly.

Climate is another factor. If the outside temps drop substantially from when you inflate you will lose pressure. Driving in the rain requires higher pressure if you want ideal running temp because they never get up to running temp on wet roads.

Lastly. If you are losing a pound a month you have a leak. Fully functioning schraders do not leak air.

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[flash]

when i was working in a bike shop we actually did some testing because i could swear that my prestas were holding and my buddies shraeders weren't - we tried a bunch of new tubes - they leaked



i've had a number of tire shops tell me the same thing



every tire i've ever had has lost about a pound a month



the nature of natural rubber also leaks, but i imagine that varies based upon tire construction



i'll be on the phone with bridgestone for an interview next week, and i'll bring that one up in the list of questions - that's a good one to find out - thanks for the inspiration

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[Beachboy]

My presta valved bike tires slowly leak but they start at 120 psi. and I inflate them for every ride. BTW it's good practice to deflate the tires for storage, even short term, it relieves the stress on the sidewalls and will prevent premature cracking. Some of the old type glue-up tires leaked very quickly.

The car tires may, in fact, leak small amounts over long periods of time. Some wheels leak. I would estimate that I check my tires on average once a month. My gauge is a fairly accurate mechanical type than reads 1/2 lb. minimum. It may be that my tires are only losing 1/2 lb. per month but I've never seen even that except at this time of year when we start getting cool nights, that's due to expansion/contraction issues.

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[flash]

interesting - now i am going to have to keep track and chart my tires on each car - oh great, another project - lol



this should actually be good - i have different sizes on all 3 vehicles:



275/55/17 on the jeep

245/40/17 and 225/45/17 on the bmw

285/30/18 and 255/35/18 on the 968



i see a spreadsheet happening with time and mileage

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[RPM]

After 5 years of 944S2 and 968 ownership I am with Beachboy on pressures for stock rims and tires. 34 around town and 36 when I am playing hard.



Don't forget that the 'quality' of the air you use can also have an effect. Little home compressors are not as efficient as larger gas station systems and neither are as good as the equipment at a good tire shop.



I just wish I could find an easy nitrogen source.

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[flash]

i run a touch less air when i am playing hard because the tires heat up more - that's what i've seen most of the guys on the track do as well



each tire reacts differently too - keep in mind the sidewall construction when working out your pressures - stiff sidewall tires need less pressure than soft sidewall tires - use the chalk method to work it out if you don't have a tire temp gauge



not sure what you mean about the home compressors - they generally don't have water traps, and that can be a problem, but air pressure is air pressure



i picked up one of the dual stage crafstman pro series compressors - very nice unit - quiet, fast, holds pressure forever



according to the local expert here, nitrogen dissapates in a matter of 8 hours in a tire, so it is really only useful on the track - we have a shop here that has the setup, but even the storage tank doesn't last that long - club racers here don't see any real difference in lap times or tire temps - the theory is sound, but frankly the application does not seem to result in any better lap times - this is probably due to inconsistent driving technique - the idea is to minimize temp change, but that presumes you drive very well and a little thing like a 10 degree shift in tire temp can make a difference for you



the going recommendation is don't waste your time and money - it's better spent in seat time

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[RPM]

nitrogen dissapates in a matter of 8 hours in a tire

Learn something every day.

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[sasilverbullet]

????

Nitrogen dissapates in a tire???

????



I used to be an aircraft mechanic - big jets - the AF has been using nitrogen in tires since the '50's. In all my courses/classes/ learning no-one ever said the nitrogen 'dissapates'. Keep in mind that these tires are filled orginally with pure nitrogen, and always aired up with pure nitrogen.

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[flash]

as i said, "according to the local expert" - i haven't actually checked this one - i imagine there could be an osmotic thing happening or something with the selectively permeable membrane of the tire - have to look at the molecule size to find out - that will have to wait for another day when i am done sorting my sock drawer



i am sure the theory is sound, and with the AF and its unlimited resources it makes a lot of sense



bottom line though, nobody here seems to see any advantage in real performance, and all seem to agree that you are better served by spending the money on instruction or seat time

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[rustech]

The principal constituents of the atmosphere of Earth are nitrogen (78 percent) and oxygen (21 percent). The atmospheric gases in the remaining 1 percent are argon (0.9 percent), carbon dioxide (0.03 percent), varying amounts of water vapor, and trace amounts of hydrogen, ozone, methane, carbon monoxide, helium, neon, krypton, and xenon.

I wonder if the nitrogen in regular air "dissipates"??



I check air pressure like Dan, once every 2-3 months, or when something feels "out".

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[Greimann]

[quote name='flash' date='Sep 9 2005, 12:32 PM'], "according to the local expert" -

[right][post="9692"]<{POST_SNAPBACK}>[/post][/right][/quote]

You need to find another expert. It is actually the opposite, nitrogen stays in the tire longer, doesnt support corrosion and consider this - it is 78% the major component of air.



http://www.automotive.com/features/90/auto-news/14858/

http://www.airliquide.com/en/medias/pdf/bu...res_filling.pdf

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[flash]

as i said, i never checked this claim out, and really made my decision based on the lack of results from the users



now thinking about it, even if the tires were inflated with 100% nitrogen, the 22% change is not likely to result in all that much of a difference anyway, and would likely only be noticed in the most extreme situations



glad somebody is up on this - sure seems to support my decision

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