The rear tires on our 2014 (base) GLK were on the wear markers, so made an appt to get two new tires.

I double-checked the fronts and they were dated Feb 2017, so decided to replace those also, so new all the way around.

I notice on the rears (before replacement) the center of the tire wears more than the outside, indicative of "over-inflation".
(wear markers on outer sides of tires not quite worn, but center wear markers were worn down to).

This GLK has 235 /45 R20, for all four tires. The GVW for front is 2535 and GVW for rear is 2888, so cant imagine 7 lbs more air is required for additional 300 GVW.


So, why the 7 pounds more air for rears?

What are other folks doing - maybe dropping to 42psi for rear? Anything else I'm missing?

 

I think it’s a load issue, when you load it up inflate the rear more, tires handle a greater load when inflated more. It’s more necessary with highway driving. Yes if your wearing out the center of the tire you are over inflated. I just leave them all the same at about 35 and mainly drive empty. I think 45 might be above or at the limit for the tire.

 

Where are you getting your tire pressure specs? The sticker on the inside of the fuel door shows what you should use. For a GLK250 the normal load spec is 35F 38R, full load is 39F 46R. A GLK250 is about 200lbs heavier than a GLK350 2WD and 120lbs heavier than a GLK350 4matic so your pressures should be the same or slightly less. Looks as if you are using the full load pressures. Your wear patterns are bound to reflect this.

 

Fuel Door ?

Our sticker is on the inside door jam on the driver's door... photo below shows it ... if I'm reading it incorrectly, please let me know

 

Thanks ... it's rare we ever carry anything in the back ... heck, it's rare there's four people in it ... it's mostly just one driving or the two of us !

I'll adjust the rear psi down - thanks !!

 

Our 2010 GLK350 has 35F and 39R on the sticker which I thought was high. Did you read the "additional information" in the manual?

 

Running a tire at maximum cold pressure can be dangerous if you set pressure when cold and on a hot day on highway you exceed maximum pressure. I blew out belts on a Michelin doing that and going around corners fast. 35-38 cold, all around all the time works well. Over 38 and the ride gets rougher. Remember you can increase pressure 5-6 lb on a hot day on highway.

 

fyi none of the discussed tire pressures are the tires max rating. I have never seen an instance where anyone would suggest running a tire at its recommended max rating.

 

You are correct !! Never ever noticed the sticker on the fuel door ... Thanks !!

So I got the manual out and numerous pages mention "refer to the placard on the driver's door B-pillar". One page mentioned (see below) to also check the fuel door, which I did ... and as @karmikan already suggested👍

So the sticker on the B-pillar is showing maximum load pressure, while the fuel filler flap shows Normal and Max pressures

So thanks to all who provided hints to the solution ... I shall readjust the pressures to 35F and 38R.

 

Having been down this road many times with a slightly bumpy ride, I elected to go 36 psi cold all-around.

I've used this number on many cars and SUVs that ride on 16-19" wheel/tire combos and have found it to be the best ride AND tire wear pattern (as long as alignment checks out).

Drive more (if you can afford the gas), worry less.

 

You cant just pick a tire pressure and go with it for all cars, wheels and conditions. You should always consult the manufactures suggestions. There are so many factors such as conditions tire choice and driving style that there is no one size fits all solution. there are some very interesting vids on this subject as well as tire wear as a result of improper tire pressure.

 

That's true.

Gonna throw in my two cents. For quite some years now, on my GLK and other cars, I measure tread depth. On my GLK, specifically, I have measured the tread depth around each tire approximately every 90 degrees. I measure the outside of the tread, the middle and the inside and record them. Then I average the four readings from the outside and do the same for the middle tread and inside measurements.

I measure carefully using a high quality tread depth dial indicator. I also use a very high quality analog racing tire tire pressure guage for accurate and repeatable readings. I have the ORIGINAL Pirelli standard size tires on my OEM 20 inch wheels and the recommended size on 17 inch rims for winter. Each set of wheels/tires are on the car for about six months. Essentially, the 20 inch for Spring and Summer and the 17 inch for Autumn and Winter. Every time each set go on they go to the other end of the vehicle. One year the tires are up front and the next time they are in back (always on the same side of the vehicle).

Just about every year I end up lowering the tire pressure a bit due to a lower tread depth measured in the middle versus the outside and inside tread measurements - this indicating over inflation.

I am now at the point where I see even tread wear across the outside tread, middle tread and inside tread of both the Summer and Winter tires. I am now using 31 psi for fronts and rears to have gotten to this point. Yes, 31 psi (2.1 Bar).

I am almost always alone when driving this particular vehicle. Never carry any load of significance. Never tow anything. Keep the fuel tank generally between half and full. A mix of city driving and high speed driving.

Yes, if you use quite a bit higher pressure it will SEEM better. Better fuel mileage, lighter steering etc. But, of course, there's a reason for that. Obviously if you carry heavier loads on average, you'll need a higher average tire pressure. Naturally you also have to check and readjust tire pressure to your target as average daily temperature goes up or down during the course of the season.

2014 350 4Matic.

 

Someone said we are not talking about maximum pressure , well we should be because my Michelin have a 44 psi Maximum pressure . If you fill a tire cold to 44 it could easily reach 50 on the highway on a hot day. That’s how you say blowout. Actually anything at or above max pressure is a risk.

 

The original Continental tires on my 2015 GLK350 were 51 psi maximum pressure. The Michelins on my C-Class are 50 psi max. This would avoid exceeding maximum pressure using full load pressures from the tire placard.

 

And your reply is much more than 2 cents
Great reply with feedback!!

So, I'm curious ... I adjusted the tire pressures to what's called for on the fuel door...

I used my longtime pen tire gauge (highly rated), but the TPMS disagrees with it (shows higher values)

Should I adjust tire pressure based on TPMS readings?

 

Well ... in my case, I never carry anything in the back (though once a month, a bail of alfalfa) ...
.
so it's just me in the SUV 99% of driving it.
So I don't need Max load rating tire pressure

 

Honestly, I've never heard good things about the pen type tire pressure guages. Probably not the best accuracy and repeatability of readings can be suspect. Gas station tire pressure guages should also usually be avoided as they get abused. Treated roughly, dropped etc. I would be inclined to go with the TPMI readings. On the other hand, you cannot get readings via the TPMI after the vehicle sits overnight and you can't even get a reading immediately when you start driving. It takes a bit of driving before the first readings show up on the display.

 

The least accurate tire gauge I’ve seen is the pen type. I have a good round analog gauge that I checked against a 110$ calibrated gauge.
My Tpms are accurate I’ve found. 36-38 all around by your Tpms is what I would set them at. If you do a highway trip loaded up, raise the rear. I wonder if raising the rear has an effect of emergency high speed handling, and that’s why it’s recommended. I don’t have the answer.

 

It is my understanding that the max pressure on the sidewall takes that in to consideration and all tire pressure references are to cold pressure.

 

If you look at a tire and read "Max pressure" then think that is a good idea and max it out. 1 you should not be doing anything to your car. Probably not even putting gas in it 2. are probably the reason shampoo has a "for external use only " warning on it.

 

Insame , that’s insane, I blew out a Michelins belts running MAX pressure as stated on the Tire, not the vehicle. When filling to Max pressure cold, it is going to be way over the Max when tire warms up. Read up on tire Max pressure and blowouts. your post is insane

 

I don't think you are comprehending what I am saying and the fact that you would put the max the tire pressure, like I said you should not EVER do, helps me understand why this concept is hard for you grasp. let me make this crystal clear for you. DO NOT EVER INFLATE A TIRE TO THE MAX PRESURE RATEING THAT IS LISTED ON THE TIRE. warm, cold, in a dream. just dont do it.

I think you need to read up on my post again.

 

Your right, I apologize I didn’t read it fully.

 

Read this.

 

All god. I also apologize. Just getting real tired of people not reading what is there then trying to "call me out".