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post #1 of 7 (permalink) Old 05-26-2015, 05:43 PM Thread Starter
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Tire Inflation Question ?

I am wondering what the right tire inflation is on my W211, W123, W124, and W126 is?

More specifically, should I stick to the "max" pressure marked on the inside of the fuel door or pay more attention to the max pressure by the tire manufacturer?

Seems like the max pressure by MB back in the day is a little low.

I want max fuel economy and tire life.

Advice please.
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post #2 of 7 (permalink) Old 05-26-2015, 05:55 PM
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Quote:
Originally Posted by LostInTime View Post
I am wondering what the right tire inflation is on my W211, W123, W124, and W126 is?

More specifically, should I stick to the "max" pressure marked on the inside of the fuel door or pay more attention to the max pressure by the tire manufacturer?

Seems like the max pressure by MB back in the day is a little low.

I want max fuel economy and tire life.

Advice please.
Sorry, man, you can't have it both ways.

Max means max, as in "NEVER EXCEED." The difference between what MB says and what the tire manufacturer says is because MB is saying it based upon the car's weight and weight distribution, taking into account certain performance and safety considerations, and the tire manufacturer is stating it as a design principle. Exceeding the pressure marked on the tire is dealing with the devil and could have disastrous results.

Inflating your tires to the tire manufacturer's max pressure will generally result in better fuel economy. However, it will likely also increase ride harshness, reduce available traction and decrease tire life, since you're reducing the contact patch and wearing the center tread down more quickly than the rest of the tire.

You should stick to the MB recommended pressure for the best compromise of tire life and fuel economy. Start with the max for normal speeds stamped on the fuel door (assuming you are running stock tire sizes, too). Then monitor wear with a tire tread depth gauge. If it's wearing more on the edges, bump it up a couple of pounds. If the center is wearing more quickly, back off a pound or two. Check it at every tire rotation at least. Over time you'll know what you need to do when you buy the next set of tires.

Hope that helps.

Good luck and happy motoring.

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post #3 of 7 (permalink) Old 05-26-2015, 06:17 PM
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The rule of thumb is that you should have the same proportion of your pressure divided by max tire pressure what is the actual load on the tire divided by max load allowed.
In life you have pretty loose tolerances and for example when driving on beach you should have like 10-15 psi.
When you forget to inflate leaving the beach and start driving fast with this pressure, the tire will overheat and blow up.
I always like to drive with 3-5 psi above the recommendation what gives me less worry when I don't check the pressure for 6 months and also longer tire life as with my love for hard cornering I am always ending with bold edges and good tread on the center.

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post #4 of 7 (permalink) Old 05-26-2015, 06:28 PM
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It is noteworthy that MB's recommended tire pressures for one and the same model vary somewhat from country to country, and in the US they are typically lower than in Europe. For my car the US recommendations are 27/27 PSI (Front/Rear) for normal load, the German recommendations for the same model are 32/35 PSI for normal load (these values are for the same wheel/tire size). This is, of course, because in the US cars are not supposed to travel at high speeds, and are often equipped with tires with lower speed ratings. I run pressures closer to the German recommendations.

If you exceed the MB recommended tire pressure somewhat, you won't necessarily reduce tire life in the way in which Check Codes described it. Depending on your tire wear pattern, increasing pressure on the center patch might even be desirable, namely if your tires are wearing out on the sides first. But if you increase it only by some PSI, contact pressure might still remain pretty even across the tire profile. At any event, an increase in tire pressure means reducing the flexing work that the sidewall of the tire has to perform. This means that the tire will remain cooler while driving and will be less likely to develop sidewall cracks (this might only matter if you run tires with long tread life, like most Michelins or Continentals). Because of this, a moderate increase in tire pressure can actually extend the life of the tire. And of course it will save some fuel.

On the other hand, if you increase the tire pressure a lot, the ride will not only become harsher, but you will also put more stress on suspension components (shocks and bushings). These are, of course, designed to absorb shocks, but making them work harder will somewhat affect their life expectancy, just like driving on bumpier roads would.

Last edited by Simon_E; 05-26-2015 at 07:49 PM. Reason: Clarified the reference to Check Code's post, hopefully to his satisfaction.
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post #5 of 7 (permalink) Old 05-26-2015, 07:21 PM Thread Starter
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What makes me wonder is the "delta" between the MB max. and the tire manufacturers max.

On my 1980 240D, the MB label shows a max for the rear of 32 PSI.

The rear tires show a max of 44 PSI.

It is a stick shift, so I have a good feel for how far it will roll out of gear.

When I inflated to 32 PSI, the car rapidly slows.

Inflate to 37 PSI, not so much.
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post #6 of 7 (permalink) Old 05-26-2015, 07:24 PM
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You Simon made me going to the garage and check the fuel door on W211.
Our prelift W210s had note below pressure chart saying
"for speeds above 100 mph add 10 psi"
W211 has double chart with different pressure for low speeds and different for above 100 mph. The difference is like 4 psi on front and 5 psi on the rear in the wagon.

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post #7 of 7 (permalink) Old 05-26-2015, 07:32 PM
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Originally Posted by Simon_E View Post
If you exceed the MB recommended tire pressure somewhat, you won't necessarily reduce tire life as Check Codes wrote.
If you are going to reference someone, either quote them or restate directly what they said.

I didn't say anything about "somewhat." "Somewhat" in a thread like this is little more than gibberish. I believe I was very clear and precise about what I wrote. If you disagree with what I write, then so state and reference it exactly. Otherwise just leave me out of it and instead state your own opinion. There is no reason to garbage up the thread with misrepresenting what someone else said.

To be clear, I said
Quote:
Inflating your tires to the tire manufacturer's max pressure will generally result in better fuel economy. However, it will likely also increase ride harshness, reduce available traction and decrease tire life, since you're reducing the contact patch and wearing the center tread down more quickly than the rest of the tire.
While it varies, tire manufacturer's maximums may be 25-50% higher than MB's stated maximums (IIRC the tires on my car are rated by the manufacturer for 44 PSI). Running at that high a pressure will indeed have every one of the results I noted above. I'd also get a double increase in fuel economy, because the loss of contact patch would scare me enough that I'd drop my speed dramatically.

Happy motoring, folks.

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