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Old 03-13-2018, 10:31 AM   #1
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Tow Vehicle Front Tire Pressure with Load Leveling Hitch

I'm towing a 2013 23D with a 2001 BMW X5 4.4i

I've got unusual front tire wear, especially the out edges as if the car has been cornered hard. The tire pressures are accurately maintained.

I've been thinking about this and I wonder if I should be increasing the tire pressure on the front tires when towing. The normal pressure for all 4 is 32#, the owners manual says the rears should be 40# if the load on the rear axel is above a certain value.

But it occurs to me that with a load leveling hitch the front tires are sharing the extra weight and perhaps they should be increased also... maybe to 40#?

What are the thoughts of others with experience in this area?

Thanks
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Old 03-13-2018, 10:57 AM   #2
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low pressure will increase wear outside, high will increase wear middle of tire.
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Old 03-13-2018, 08:21 PM   #3
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This is usually a sign that the front of the vehicle is being lifted due to heavy loaded rear.
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Old 03-13-2018, 11:16 PM   #4
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A PSI of 45 rear and 40 front is standard for us. The D likely has a heavier tonge weight, so a review of correct pressure for the load the TV axles are seeing is appropriate. That suggests a trip over the CAT scales to establish loading and how much tongue weight you are shifting forward. It may be necessary to give the alignment a check. You likely need to do that anyway, because if you are showing much wear, it's time to move on to a new set of tires. Pat

Edit Note - ask your tire shop or check the internet for a load vs tire pressure chart to get you started.
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Old 03-13-2018, 11:45 PM   #5
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Hi, on my tow vehicle I leave my front tires at factory specs. I add ten pounds of pressure to my rear tires. In your situation I think you might be transferring too much weight back to your front tires.
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Old 03-14-2018, 12:05 AM   #6
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I agree with weighing axles to establish what loads you are applying front and rear.

I ran my 2003 X5 (with 32 psi door placard recommendation) at 35 psi, with good results over multiple sets of tires. With a full load I didn't ever need to go above 35. Check your BMW placard, because on some of my BMWs there was a psi recommendation, and one for full vehicle at sustained high speeds. It didn't need the highest pressure even if fully loaded, unless one was driving at speeds not legal in North America.

What I have seen quite a bit on the X5 is edge tire wear due to toe settings. The vehicle was sensitive to toe. The published toe spec was a range and the best tire life results were achieved with the minimum toe setting of the published acceptable range. The sensitivity (IMO) was due to the tire width. The vehicle was designed for a 17" tire on the six cylinder model (the base tire) and as time went by and fashion changed there were optional 18", 19", and 20" from the factory (and more from the dealer). With that wide a tire, if toe was set too high, the tire was essentially scrubbing. It wore the inner edge or outer edge depending on the axle loading.

Worth checking before doing a full alignment, as a diagnosis, but I would get an alignment anyway.
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Old 03-14-2018, 06:50 AM   #7
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I think you need to weigh it hitched and go from there on the tire pressures.
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Old 03-14-2018, 09:18 AM   #8
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Tundra CrewMax and Classic 30 towing 8 years and 3 sets of tires-
No unusual tire wear at all, but tires rotated every 5,000 miles to account for weight of the trailer on the rear-
33 psi per the tire placard inside the door jamb-
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Old 03-14-2018, 11:08 AM   #9
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I grew up rotating tires regularly, and did it for customers many times in the shop. The OP has an X5, and BMW specifically warns against rotating tires. I was doubtful on my first BMW, and so watched tire wear closely. Six BMWs later, I have never had uneven tire wear. The two X models that I towed with got about 75 - 80,000 km on a set of tires, and those were performance tires, changed about 10 k early due to winter weather conditions.
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Old 03-14-2018, 11:13 AM   #10
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I wouldn’t go above manufacturers recommendation and surely not to 40. I Check the pressure on my Fiat500 every trip. I have a Roadmaster system and have had no unusual wear. It would surely be worth having the alignment checked by knowledgeable shop. Good luck.
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Old 03-14-2018, 01:15 PM   #11
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Thank you everyone for your thoughts

Additional notes and replies:

The front isn't lifting, the load leveling hitch has been carefully setup so that all 4 tires are bearing the tongue weight. This is what led me to start thinking about adding air not only to the rear (as recomended by the door jamb decal) but also to thr front.

The 23D does have a heavy tongue at 720#. The tires are 255/55 ZR18 with onoy 10k miles on them (the rears don't shoe wear). The door jamb decal says 32# all around and 40# when carring a heavy load. I agree an alignment check is on the list. Weighing sounds like it should be on my list also.

The X5 has 100k miles, this is the 3rd set of tires with only 10k miles on them. I have never had uneven wear and never rotated the tires before.

I'll update the thread when I have more information regarding the solution.

Thanks again, Steve
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Old 03-14-2018, 01:38 PM   #12
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Good additional information.

The 18" tires will have the best life of any of the options for the 4.4

A couple of thoughts on an alignment.

1) You don't just want it reset, you want to know where it was, to determine if it could have been part of the problem. Front toe-in would be the first thing I would look at. You could do that in your driveway with a tape measure to see if it is out much, just as a starting point.

2) BMW alignment service procedures require that weights be added to the vehicle before aligning, to simulate a typical driver/passenger load. Recommend you talk to whoever does your alignment about this, and ask what the effects could be with your additional load. I wouldn't go outside the recommended alignment spec for any one item, but I would consider setting it to the positive or negative limit of the published range for any one item, depending on the effect of additional vehicle load.
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Old 03-14-2018, 01:39 PM   #13
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Manufacturers specs are for normal loads. If I ran Mfr specs on my Dakota the tires would run too hot under full load...I know this from experience. So I run full 44 psi on rears and 35 front. Even if you can't get to a scale to weigh the loads, just look at the tire shape at road contact and pressurize tires to at least approximate the contact profile and side wall bulge in unloaded conditions.
If you are not showing wear under normal conditions, and wear under load then one of two things might be happening.Under inflation results in wear on the outside edges....both inside and outside. If the excess load is changing the alignment then you might only get wear on the outside. This would indicate that perhaps you are transferring too much weight to the front, and at the same time more pressure in the front is needed. You can only verify by doing the weight distribution; front and rear on a scale. Split weight differential/ratio F/R should be about the same loaded as unloaded. i.e. roughly equal additional weight should be added to both front and rear axles.
I would think if you are overloading the front axles you would feel the steering to be a bit heavy and the vehicle would lean excessively into the turn. If under-loaded the steering is light and the vehicle is twitchy when steering is applied.
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Post Script . Op has just added new info, so I won't change my answer, but it looks like getting Air pressures up to max rear and somewhere in between on front is likely to fix a lot of the problem. I walk the full circle every stop and touch each tire and hub every time. That way I can assess individual temps and determine if I have a problem that needs addressing. Certainly running in hot weather raises the tire temps but they should all be about the same if pressures are correct.
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Old 03-14-2018, 01:52 PM   #14
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Outer edge could be not enough load on the front...check the alignment with a load..would be the best way
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