Tire Psi - Mercedes GLA Forum
 
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post #1 of 7 Old 10-01-2019, 11:16 PM Thread Starter
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Tire Psi

Hi Everyone,

Just throwing this out there to see if anyone experienced something similar.

I was driving today and got a service alert that I needed to correct my tired pressures. It told me the rear tires were a little low, so I set them all to 33 psi at the gas station. Later in the day I used the car again and the service symbol was still there but the message to correct my tire pressure was gone. Then as i started driving and it told me three tires were low. As I was driving they all gradually increased and fluctuated around 33 and 34 psi.

Just wondering if this is something I should take to get checked out.
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post #2 of 7 Old 10-02-2019, 01:30 AM
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Did you reset the tire pressure values on your system console? If not, it could be set to other values. Could also be your pressure was fluctuating with driving-sitting cycles. Or something else.

Seems like fall and spring are the traditional times for the TPL to activate as seasonal temperatures adjust...even in Hawaii.

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post #3 of 7 Old 10-02-2019, 02:33 AM
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When I suffered a blow out a few weeks ago the tire pressure warning stayed on for about 50 miles before resetting.

Pam's 45 has had messages frequently when the seasons change.

As I drive my 997.2 in spirited fashion I can see over 10 psi differences between cold (adjusted for 65F ... 32 front and 37 back) and hot (up to 40 front and 48 back).

Often if I'm driving north or south with the sun to one side I will find the tire pressures on the sun side will exceed the pressures on the other side by one or even two psi.
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post #4 of 7 Old 10-02-2019, 07:45 AM
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My local dealership routinely fills all tires to 35 psi even tho' that's incorrect according to the fuel door placard. And of course they reset the computer's alert threshold based on same. So as turbolink cites, if you properly fill you must also reset the threshold.

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post #5 of 7 Old 10-03-2019, 08:12 PM
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Actually I've been wondering about this lately. Does anyone else follow the manufacturer recommendations and inflate to 45? It seems awfully high to me. I've been meaning for a while to come check the board to see if there's a consensus, and suddenly my inbox mentions this thread....
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post #6 of 7 Old 10-03-2019, 09:18 PM
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Welcome to the GLA forum nashmercy. You've raised one of the most debated topics here with no clear answer, as everyone's operating style, requirements, and environment are unique, not to mention the many GLA derivatives around the globe. If you type "tire pressure" in our Search box (upper right of most browsers) you'll get a quick listing of all the discussion in our archives. Here's just the top one to help figure out which range fit you:

https://www.glaowners.com/forum/merc...-pressure.html

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post #7 of 7 Old 10-03-2019, 11:43 PM
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Beyond the concept of ideal handling there are a number of factors ...

Softer pressure equals softer ride. In the early days of steel belted radials Chevy and Ford had very low tire pressures listed. This created higher flexing in the sidewalls that created higher temperatures that added to belt separations. The tire shops recommended higher pressure to reduce flex and temperature and the risk of separations.

Higher pressures also yield higher mpg values.

The reduced temperature increase from higher pressures also reduces pressure increase during driving (from the ideal gas equation ... PV = nRT).

Higher pressures also crown the tread and can result in excessive center tread wear.

Low pressure will let the center of the tread bend inward resulting in wear on the outer edges.

Both low and high pressures lower the tires' contact patches resulting in reduced traction.

That being said, low pressures allow the tires to bend and if you find yourself stuck when off road (assuming adequate ground clearance) letting some air out may get you unstuck (or a piece of carpet under the drive wheels or a lot of other options).

So what's the right pressure? Start with the gas flap. Watch the tire wear. If wear is on one edge only worry about alignment. If the tire starts to scallop (indents at intervals around the edges of the tire) check balance (and shocks). If wear is on the center of the tread reduce pressure. Add pressure if wear is on both sides.

Wear takes time. Be patient. And realize there is a wide range of pressures that "work" (unless you're on a race track).
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