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I purchased Rial 17-inch wheels, here in Germany, for winter use with dedicated snow tires. Had a hard time finding the tire pressure on-line. What I did end up with is from the Continental web site. See attachment.
Run the tires hard 38 or above. This puts a smaller patch on the the snow so the lugs have a higher pounds per square inch of patch to bite through the snow. It's not like sand where you want to float on the top. The Blizzak hygroscopic layer will take care of the water film on any ice and are great for icy conditions. Just remember that the hygroscopic layer will probably wear away in 12000 miles and although the tire is still good, you will lose its water absorbing ability.
OK - a linear curve, so determining pressure per tire load is straightforward, right?
Curb weight - 1925kg or 4244lb
Payload - 575kg, or 1268lb
Total load - 5512lb
Front:rear weight distribution - 53:47
therefore - single front tire load - 1461lb, single rear tire load - 1295
This equates to pressures in the 19psi range and less. That can't be right.
Every tire reseller recommends this tire, at this load rating, for the GLK 250. What am I doing wrong here?
Last edited by whiskywizard; 11-16-2015 at 03:45 PM.
OK - a linear curve, so determining pressure per tire load is straightforward, right?
Curb weight - 1925kg or 4244lb
Payload - 575kg, or 1268lb
Total load - 5512lb
Front:rear weight distribution - 53:47
therefore - single front tire load - 1461lb, single rear tire load - 1295
This equates to pressures in the 19psi range and less. That can't be right.
Every tire reseller recommends this tire, at this load rating, for the GLK 250. What am I doing wrong here?
Bridgestone is basing the load rating on the maximum sidewall deflection and patch size. With more air in the tire, the same load will generate less sidewall deflection and a smaller contact patch. So for a given deflection/patch size as the internal pressure goes up, the amount of weight it can support also goes up. Since friction is dependent on µ x N, where µ is the coefficient of friction for the two materials in contact, and N is the Normal force (weight), the size of the contact patch will not change the grip the tire has on the road under normal conditions. More square inches does not create more traction because the load per square inch goes down.
With rain or ice there is a small layer of water which changes µ. This is what the Blizzak's have a hygroscopic layer to remove.
With snow, unless you punch through to the asphalt, µ is very low. So you want as small a patch as you can, within reason, to generate the highest pounds per square inch on the tire tread lugs. If you have 1 lugs per square inch, a patch of 10" W x 5" long, (50 lugs) and you have a weight of 1400 pounds on the tire, each lug is pressing down with 28 pounds. If you increase the tire pressure to reduce the patch by 25% so it is now 10"w x 3.75 long, you only have 37.5 lugs in contact but the same weight, so now each is pressing through the snow with a downward force of 37.3 pounds. Actually increased force by 33% The more downward force, the more likely to contact the pavement.
You can figure your patch size by taking your vehicle weight on that wheel and dividing it by the tire width time the inflation pressure.
Patch length = weight on the wheel/(tire width x psi)
I moved up to Canada (from America) and I'm thinking of not installing TPMS for my winter tires on my GLK since that is an option in Canada. Has anyone else tried this? Does the light keep flashing? Is it just a warning when you start the car? Can you click "ok" and it'll disappear for the rest of your trip?
2011 Porsche 997.2, 2015 GLK250, 2009 Sierra 2500HD Diesel
Originally Posted by hiker007
Do you get the TPMS on them?
No. Canadian GLKs use rotational speed difference to infer pressures and do not use TPMS sensors in the wheels. Each wheel has a regular old-fashioned valve stem instead.
I moved up to Canada (from America) and I'm thinking of not installing TPMS for my winter tires on my GLK since that is an option in Canada. Has anyone else tried this? Does the light keep flashing? Is it just a warning when you start the car? Can you click "ok" and it'll disappear for the rest of your trip?
After you clear the message that indicates there are no sensors (comes on maybe after 10 minutes driving) that you will get a small symbol that blinks on and off rather slowly in the bottom right-hand corner of the guage. I don't find it annoying. It does not go away. It's always there.
In other words the written message disappears with pushing the "okay" button and in its place is the small symbol. Looks like part of a tire with an exclamation mark in the middle.
Called Costco Canada earlier this morning. They don't even carry TPMS for this car there. The guy on the phone said I could get approval from the manager to mount/install the tires without TPMS or I could bring my rims in and mount them to the tires, then install it on the car myself.
Noticed this morning that the tire symbol was blinking as soon as I started the car (after it sat overnight) and then I got the message after some minutes. Cleared it with the okay button and then got a steady illuminated tire symbol instead of blinking. Hadn't noticed that before.
Symbol is located on the bottom of the tachometer guage.
Originally Posted by MBKLUE
After you clear the message that indicates there are no sensors (comes on maybe after 10 minutes driving) that you will get a small symbol that blinks on and off rather slowly in the bottom right-hand corner of the guage. I don't find it annoying. It does not go away. It's always there.
In other words the written message disappears with pushing the "okay" button and in its place is the small symbol. Looks like part of a tire with an exclamation mark in the middle.
2011 Porsche 997.2, 2015 GLK250, 2009 Sierra 2500HD Diesel
Originally Posted by GLK350AMG
Called Costco Canada earlier this morning. They don't even carry TPMS for this car there. The guy on the phone said I could get approval from the manager to mount/install the tires without TPMS or I could bring my rims in and mount them to the tires, then install it on the car myself.
Hmm- so Costco staff seem to be unaware that the Canadian GLKs do not use in-tire pressure sensors. Oh well; I wouldn't consider Costco staff to be the technical authority on very many things. Except perhaps pushing oversized portions. They DO know that business pretty well.
Hmm- so Costco staff seem to be unaware that the Canadian GLKs do not use in-tire pressure sensors. Oh well; I wouldn't consider Costco staff to be the technical authority on very many things. Except perhaps pushing oversized portions. They DO know that business pretty well.
I moved from America. I told them my car has the American version of TPMS.
11-15-2015, 04:20 PM
LOL. Yes, 'every' gold bar I own is in that vehicle. 
