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      12-18-2011, 11:57 PM   #1
Lotus7
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Tire Pressure Check Time

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Last edited by Lotus7; 02-05-2012 at 05:46 PM..
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      12-19-2011, 12:30 AM   #2
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Not to derail, but was looking at cigarette lighter volt meters and was like..woah, that's a photo inside an X3, perfect.. then noticed it was from you =D You think that's the best option to get?

http://www.amazon.com/Equus-3721-Bat...4276065&sr=1-2
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      12-19-2011, 01:25 AM   #3
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Thanks for posting Lotus. Comprehensive and very useful as always. Any thoughts on what pressure to store summer tyres at?
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      12-19-2011, 01:25 AM   #4
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Quote:
Originally Posted by Lotus7 View Post
sard,

I have a new Equus and an old Vector (which I've had for years), and the Equus is definitely the better one. It has higher resolution and the one I received was quite accurate. However, both work and either will indicate if your charging system and the BER system are working and what condition the battery is in, but the extra resolution of the Equus is frosting on the cake.

I think the current model (the one in my pic) looks a lot nicer than the old "sharp-cornered" version.

Now, back to tire pressure!!
ok =)
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      12-19-2011, 02:31 AM   #5
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Quote:
Originally Posted by Lotus7 View Post
I don't think it makes much difference, but I set them all to about 35 psi this time of year when it's about 35-40 deg F. in the garage.. I do stack them 4-high (with layers of plastic foam and cardboard between them), so want to be sure they're all inflated enough to eliminate any sidewall deformation of the bottom ones. Done it that way for years with plain street tires and lightweight (thin sidewall) race tires and never had any problems.

They are designed to withstand 45 psi at 150 mph speeds and 200 deg. temps., so sitting in a cool garage at "0" mph should be a welcome rest at 35 psi.
Thanks, mine are stacked 4-high too so the keeping the pressure at 35+ makes sense to aid the separation
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      12-19-2011, 04:33 AM   #6
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Sorry if I am repeating, but I'm on the iPhone app and it's harder to search old threads. My dealer is offering a special on nitrogen in tires. I had never heard of this and wondering if people here had done it and what would be the benefits. It live in Wisconsin, so my winters are quite cold. Thanks for the help.
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      12-19-2011, 09:58 PM   #7
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One caution. Set the tire pressure monitor to the expected running pressure and not at the garage pressure. It means first adjust the pressure to expected pressure in cold condition, set TPM and then inflate it to higher pressure.
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      12-19-2011, 10:50 PM   #8
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What I do is "Lotus7 Math" each week as the average daytime temperature drops. Once I adjust the pressure (typically adding more air) I then set the TPMS. Should I actually be resetting TPMS later, once the air in the tires has acclimated to outside temperatures?
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      12-20-2011, 09:27 AM   #9
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I'm planning to drive from 60 deg F to lake Tahoe where ambients are around 10 deg F, do you think I will get TPMS alarm as I had last set them when the temp here was 75deg?
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      12-21-2011, 01:03 AM   #10
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Quote:
Originally Posted by Lotus7 View Post
Going from 75 deg. to 10 deg. will drop your tire pressures by about 6 psi, which is about the amount the TPMS triggers at, so it's possible [to get an alarm]. The Lake Tahoe temps for next week look like the lowest night-time temp will be 10 deg. but more like 40 deg during the day. I wouldn't add any air before the trip, but certainly would once you arrive.

However, there is another factor that actually works to your advantage in that Lake Tahoe has an altitude of 7000 feet. The atmospheric pressure at 7000ft. is only 11.3 psi (absolute) vs. the pressure at sea level of 14.7 psi (absolute). That effectively raises the pressure that the TPMS transmitter "sees" by 3.4 psi and reduces the chances for an alarm. It also means that your tire pressure gauge will read 3.4 psi higher than the real (absolute) pressure that is required.

For more details about setting correct pressure at altitude see this article.

However, you still need the extra air in the tires to compensate for the lower temps. It gets complicated when you change both temperature and altitude.

Happy skiing- stay warm!
Wow, you added one more dimension, great!
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      12-21-2011, 09:12 AM   #11
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Quote:
Originally Posted by Lotus7 View Post
Sorry to complicate your life.

On the other hand, you could just ignore it like 99.99% of the population, and be perfectly OK. Driving a few miles at low speeds with pressures that are 5 or 6 psi "low" is not going to cause any problems at all other than giving the X3 slightly poorer steering response that may be hardly noticeable.

Only us "Type-A" engineers worry about such things!
No way, you didn't complicate my life, you gave us inputs to think more and plan and understand better.

Now my innovative senses are triggered and think that right way to generate TPMS alarm is :

If Ts1, Ts2, Ts3 and Ts4 are the tire pressures when TPMS is set and t1, t2, t3 and t4 are the actual tire pressures sensed by TPMS, then

Alarm shoul be generated if max{(Ts1-t1), (Ts2-t2), (Ts3-t3), (Ts4-t4)} -min{(Ts1-t1), (Ts2-t2), (Ts3-t3), (Ts4-t4)} > x amount of pressure.

A warning for low tire pressures can be generated if max{(Ts1-t1), (Ts2-t2), (Ts3-t3), (Ts4-t4)} > y amount of pressure.

This simple mathematical formulation can take care of variations in tire pressures of all tires due to temperatures, altitudes, storms etc.

Last edited by April1; 12-21-2011 at 09:31 AM..
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      12-21-2011, 09:57 AM   #12
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Quote:
Originally Posted by Lotus7 View Post
Knowing and programming the "alarm" pressure is one thing, but the real solution would be similar to what the HMMWV (Humvee) H-1 uses: An on-board central tire inflation/deflation system. However, might be a little "overkill" for the occasional trip to Lake Tahoe.
Last time you added one more dimension to the topic but this time you added one more angle / twist to the topic. Thanks Lotus7, more we discuss with you, more we get informed.

Anyway for my Lake Tahoe trip this weekend, I am carrying a crude system of hand held tire pressure monitor and 12V air compressor incase needed to improve my driving pleasures.
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