[Daytona_550]

Question related to towing...

What do you do for tire pressures when towing? My towing vehicle has 33psi cold pressures listed on the door decal. The tires are marked with max 44psi (cold).

Tire shop recommended I set all four tires to 40psi when towing.

If it matters, I am towing 6000lbs (auto transport and track car).

Do you follow std cold tire pressure from decal, or do you go higher when towing?

[MustGoFast]

Originally Posted by Daytona_550

Question related to towing...

What do you do for tire pressures when towing? My towing vehicle has 33psi cold pressures listed on the door decal. The tires are marked with max 44psi (cold).

Tire shop recommended I set all four tires to 40psi when towing.

If it matters, I am towing 6000lbs (auto transport and track car).

Do you follow std cold tire pressure from decal, or do you go higher when towing?

Tire pressure on this damn thing seems to be a loaded question as my manual, door plaque, and idrive all have different answers as to base pressure. I couldn't find anything in the manual about tow pressure for my ride either.
With my past SUVs and Trucks I used the same pressure to tow as I did to drive every day.
Note our vehicles do have a higher pressure for speeds over 100mph I wouldn't suggest using that pressure or speed while towing

[bono]

My standard pressure is the front and in the back is 32 psi. I inflate rear to max, i.e. 50 psi and front to 38-40 psi when towing. Obviously, you want more pressure in the tires with a higher load.

[jad03060]

FWIW, never exceed the max cold pressure listed on the tire.

If you do not try to exceed the load spelled out in the manual, you should be okay with the suggested pressures and not need to raise them. The tire's ultimate load factor will change with the cold pressure, but the vehicle should handle the max it was designed for when you have to listed pressure.

Note, if you've changed your tires to something other than stock, and did not match the load range, you could easily overload your tires and that can get dangerous quickly. It's not just the tire size that's important, it's the cord layout, material involved, and thickness.

If you're not using the OEM electrical interface, you won't get the built-in safety logic that is designed to help prevent sway. While it's not all that hard to make the trailer's lights function, it's a lot more difficult to activate the vehicle's safety logic, and on the latest BMWs, from what I can tell, nobody has a module that provides that functionality. On older models, there were two aftermarket companies that could duplicate the OEM functionality: Westphalia and RightConnections, but they do not currently make a module that offers that on the G05, and nobody else has tried or at least mentioned it.

[bono]

Find tire pressure chart for your tires. The load capacity on your tire is max capacity which is achieved at certain pressure. And that won't be the pressure you are using when going for groceries. Therefore, when towing, you have more load on the rear tires (and front, if you use weight distribution). You should increase pressure.

[Daytona_550]

Thanks for the feedback!

[jad03060]

The maximum load for the vehicle is taken into account with the tires selected and the recommended tire pressure. Raising it, does change the TIRE'S load rating (up to it's max, when at max pressure), but it won't do anything to the VEHICLE's (the axle, bearings, wheels, hubs, body, brakes, etc.). FWIW, when you add the OEM towing package, BMW also restricts your tire choices from the factory to ones that WILL meet the specifications for max load. IOW, some tire/wheel choices cannot be selected if you select the towing option.

[bono]

Yeah, obvious stuff. Not sure why you are making connection between tire pressue and bearings, wheels, etc. This is not what somebody asked about.

In the previous post you stated: "If you do not try to exceed the load spelled out in the manual, you should be okay with the suggested pressures and not need to raise them.". Even though I do not know this specific case you were commenting on, there is a good chance that your comments are not correct, given that suggested pressure is not suggested for towing.

Originally Posted by jad03060

The maximum load for the vehicle is taken into account with the tires selected and the recommended tire pressure. Raising it, does change the TIRE'S load rating (up to it's max, when at max pressure), but it won't do anything to the VEHICLE's (the axle, bearings, wheels, hubs, body, brakes, etc.). FWIW, when you add the OEM towing package, BMW also restricts your tire choices from the factory to ones that WILL meet the specifications for max load. IOW, some tire/wheel choices cannot be selected if you select the towing option.

[jad03060]

The tire pressure listed for the vehicle at its maximum load should work with any towing you can safely do. Towing is taken into the vehicle loading. IOW, the tires, when inflated to the suggested value SHOULD have all of the safety factor involved to safely carry that maximum load. Considering that they don't recommend anywhere near approaching the high speed values when towing, you should be fine, but bumping it up to those high speed values would give you a little more margin, but it should not be needed and may affect the ride and tire wear.

Everything in the vehicle that relates to weight and load factor is important. Exceeding the design parameters is not a good idea. The X5 was not designed to handle a weight distribution hitch, so adding one is making a vehicle modification that, without the engineering knowledge of the vehicle that only the manufacturer really has, is risky. You could be overloading a component by shifting the weight that was not designed into the platform. They list a max tongue weight for a reason...

[bono]

Tire pressure

Again, you said "If you do not try to exceed the load spelled out in the manual, you should be okay with the suggested pressures and not need to raise them.". Manual typically shows "standard" pressure (e.g. 32 psi) and "increased" pressure for high speed driving. I would not suggest anyone to tow with 32 psi, unless this is jetski. There is no "towing" pressure in the BMW manual. At least, not in the manual I've seen.

Other (random) stuff thrown in

Who is talking about exceeding design parameters? The recent discussion is about proper tire pressure for towing.

X5 not design to handle a weight distribution hitch? Please direct me to any document prepared by BMW that states that the vehicle cannot handle WDH. Unfortunately, you would waste your time if you tried to find it.

[jad03060]

A weight distribution hitch changes the axle loading by transferring some of the tongue weight from mostly the rear axle to the front axle THROUGH THE CHASSIS (assuming it can handle that extra load and you don't exceed the front axle loading), but does nothing to limit the actual weight on the hitch body itself. It does this by forcing the vehicle to be level when setup properly. It does nothing to change the strength of the hitch to the chassis which doesn't have a frame, which, on the X5 (at least on the model I have) says the max tongue weight is 551#. Throw in that a nice weight distribution hitch can weight 80-100#, that comes out of your GVW and tongue weight.

FWIW, if you're at the max front and rear axle loads in my 45e, you've exceeded the max GVW. If you're at the max tongue weight, you've got about enough load capacity for two people and some luggage, but not a huge amount. The PHEV batteries take up a lot of that capacity, keeping your load capacity down. The air suspension will keep both ends at the proper height as long as you do not exceed the max axle specs.

The manual says to use the max load table for tire pressure when towing, but does not actually include that in the manual! So, maybe they mean the higher speed numbers...

[bono]

A lot of different things thrown here and there... I understand we are on the same page that standard suggested tire pressure is no beueno for towing, correct?

What's the problem with transferring the load throughout the chasis? Unibody has A LOT much higher strength than body on frame. What is the problem? By the way are you going to provide this BMW statement that they do not allow using WDH?

Most, if not all, of the cars would be above GVW when adding axles limits. Easy explanation- manufacturers don't know how users will load their cars. Usually most of load goes to the back of the car. Therefore, payload spec does not matter that much when towing and using WDH. Load is distributed evenly between the axles, instead of throwing everything in the back of the car in the car.

[jad03060]

Under the section in the manual where it talks about tire pressure while towing, it says "For the vehicle, the tire inflation pressure for higher loads applies", but then, does not call that out in any of the tire/wheel/pressure tables...maybe it's on the label...I'd have to look. Later on, it says the tire's max load divided by the axle's max load should be at least 1.1, I assume, to give things a little margin for error (the tire max load must be at least 1.1* the max axle load).

[elp]

@bono can you share more info on your statement where unibody had more strength than body on frame? Everywhere I read/watched says the opposite. Maybe unibody design has evolved or our cars are better built than others, would love to learn more.

[bono]

What kind of sources do you use? The easiest would be to go to youtube and to look how trucks (body on frame) are bending on any uneven surface vs. unibody chassis, including X5.

The only challenge with unibody are the hitch mounting point. Therefore, for higher tongue weight and WDH, it is recommended to reinforce the hitch (in particular for E70 where hitch has long drop off plates).

Originally Posted by elp

@bono can you share more info on your statement where unibody had more strength than body on frame? Everywhere I read/watched says the opposite. Maybe unibody design has evolved or our cars are better built than others, would love to learn more.

[Bimmelim]

Originally Posted by elp

@bono can you share more info on your statement where unibody had more strength than body on frame? Everywhere I read/watched says the opposite. Maybe unibody design has evolved or our cars are better built than others, would love to learn more.

Just picked up my new boat. Easy peasy for the 45e.

[jad03060]

What have people found work well for mirror extensions when trying to tow a tall travel trailer? Interested in what may be available in the USA to fit an X5 45e.

[elp]

Originally Posted by jad03060

What have people found work well for mirror extensions when trying to tow a tall travel trailer? Interested in what may be available in the USA to fit an X5 45e.

I have been looking into some of the convex mirrors on Amazon and thought might worth a try depend on the Edith of the trailer. I prefer these so I don't have to deal with external attachments. Has anyone tried it on BMWs?

[LexxM3]

Originally Posted by jad03060

What have people found work well for mirror extensions when trying to tow a tall travel trailer? Interested in what may be available in the USA to fit an X5 45e.

Not extension, but I use non-NA-stock EU version aspherical mirrors on both sides and they are fantastic in every way including towing. Completely transforms driving comfort due to increased visibility and doubles safety. Not exaggerating. It is insane that those are not legal and not standard in North America, completely insane. You mentioned in another post your mobility issues — you absolutely need these mirrors. https://g05.bimmerpost.com/forums/sh....php?t=1719804

[jad03060]

Originally Posted by elp

@bono can you share more info on your statement where unibody had more strength than body on frame? Everywhere I read/watched says the opposite. Maybe unibody design has evolved or our cars are better built than others, would love to learn more.

A body on frame has a stronger frame...the body hard to say, but it's often rubber isolated from the frame so not suitable for carrying a towed load...it must be attached to the frame.

A unibody requires the body to function as both the frame and the body. The unibody is still often rubber isolated from the drivetrain, but typically much more directly attached. A unibody will tend to resist twist, but should you exceed its limits, you can fracture it, or crush it. While you might not notice a slightly bent frame as long as you don't exceed the elastic limits so it can bend back once the load is removed, bad things happen to a unibody if you exceed the load on the body- it can't be bent much at all. It can bend or crush, or fracture when the load design is exceeded. While you could bend or crush a body on frame, usually the frame is designed to be more resilient.

It's not uncommon when jacking up a body on frame for you to have to raise it a fair amount before you see the wheel on the other end moving much. On a unibody, since it is stiffer, you will notice the other end of the vehicle on that side moving much more and sooner.

To get a load distribution hitch to transfer weight to the front suspension, instead of twisting the frame like a spring, you have to apply the whole force at the hitch's attachment point and twist the whole vehicle, as the unibody doesn't want to bend. The strongest portions of a unibody are the suspension and engine attachment points, not the end where the hitch is installed. The hitch's attachment points aren't all that tall top to bottom, so you're applying that force across a fairly small surface putting an awful lot of load on the threaded anchors and bolts. To keep the weight down, each area of the body is designed to withstand only certain loads, and with the crash protection, the ends are also designed to crush in an accident, so the ends aren't as stiff as the rest. A regular hitch is designed for primarily just push or pull, not twist as is the body on the X5.

A load distribution hitch can do two things: transfer weight to the front axle so the vehicle can ride more level (the dual axle air suspension does it and will adjust for the fuel use as you're driving along, too), and, depending on the design, apply yet more tension on things to put a preload on the trailer to help control sway.

I do not know exactly what BMW does in their vehicle software, but if you have the OEM electrical towing interface, and have something plugged in, it activates stability logic. You will not get that from any aftermarket electrical interface you might use to make the lights work on the trailer.

BMW sells millions of vehicles, and in some countries, caravanning (towing for the US!) is fairly common...IMHO, BMW knows best how to make their vehicles safe. This assumes that you load your trailer properly...you don't want to put all of the heavy stuff in the rear, but more balanced over the trailer's axles. You don't want it too far forward, either, as that will increase the tongue weight, potentially beyond specs.

I'm somewhat skeptical of the rule of thumb and logic built up on a chassis that is quite different in design and execution over time than the body on frame that existed for scores of years. While I did some systems design, I'm not a mechanical engineer. BMW has lots of them and they know their vehicle. The tongue weight limit is the tongue weight, regardless of whether you can transfer some of the load to the front or not, and the push/pull through the attachment points and twist will be higher if you think you can exceed that value just because some of that ends up on the front...it has to pass through the unibody, not the frame.

Lots of towing accidents come from people improperly loading the trailer or overloading it. Driving too fast for the conditions is cutting any margin for error you might have is probably the other big thing.

As a percentage of miles driven in a vehicle, for most people, towing a trailer is a fairly small percentage, and it may not be a regular thing, so skills are lost in between summer vacations.

All it takes is the combination of a few things to ruin your day. You might go many years and never trip that disaster point. I prefer to stay within the weight guidelines BMW lists for their vehicle. I'm not comfortable trying to twist my unibody to move weight forward. If your loading is within specs, the vehicle can ride level with the air suspension.

[elp]

Originally Posted by jad03060

A body on frame has a stronger frame...the body hard to say, but it's often rubber isolated from the frame so not suitable for carrying a towed load...it must be attached to the frame.

A unibody requires the body to function as both the frame and the body. The unibody is still often rubber isolated from the drivetrain, but typically much more directly attached. A unibody will tend to resist twist, but should you exceed its limits, you can fracture it, or crush it. While you might not notice a slightly bent frame as long as you don't exceed the elastic limits so it can bend back once the load is removed, bad things happen to a unibody if you exceed the load on the body- it can't be bent much at all. It can bend or crush, or fracture when the load design is exceeded. While you could bend or crush a body on frame, usually the frame is designed to be more resilient.

It's not uncommon when jacking up a body on frame for you to have to raise it a fair amount before you see the wheel on the other end moving much. On a unibody, since it is stiffer, you will notice the other end of the vehicle on that side moving much more and sooner.

To get a load distribution hitch to transfer weight to the front suspension, instead of twisting the frame like a spring, you have to apply the whole force at the hitch's attachment point and twist the whole vehicle, as the unibody doesn't want to bend. The strongest portions of a unibody are the suspension and engine attachment points, not the end where the hitch is installed. The hitch's attachment points aren't all that tall top to bottom, so you're applying that force across a fairly small surface putting an awful lot of load on the threaded anchors and bolts. To keep the weight down, each area of the body is designed to withstand only certain loads, and with the crash protection, the ends are also designed to crush in an accident, so the ends aren't as stiff as the rest. A regular hitch is designed for primarily just push or pull, not twist as is the body on the X5.

A load distribution hitch can do two things: transfer weight to the front axle so the vehicle can ride more level (the dual axle air suspension does it and will adjust for the fuel use as you're driving along, too), and, depending on the design, apply yet more tension on things to put a preload on the trailer to help control sway.

I do not know exactly what BMW does in their vehicle software, but if you have the OEM electrical towing interface, and have something plugged in, it activates stability logic. You will not get that from any aftermarket electrical interface you might use to make the lights work on the trailer.

BMW sells millions of vehicles, and in some countries, caravanning (towing for the US!) is fairly common...IMHO, BMW knows best how to make their vehicles safe. This assumes that you load your trailer properly...you don't want to put all of the heavy stuff in the rear, but more balanced over the trailer's axles. You don't want it too far forward, either, as that will increase the tongue weight, potentially beyond specs.

I'm somewhat skeptical of the rule of thumb and logic built up on a chassis that is quite different in design and execution over time than the body on frame that existed for scores of years. While I did some systems design, I'm not a mechanical engineer. BMW has lots of them and they know their vehicle. The tongue weight limit is the tongue weight, regardless of whether you can transfer some of the load to the front or not, and the push/pull through the attachment points and twist will be higher if you think you can exceed that value just because some of that ends up on the front...it has to pass through the unibody, not the frame.

Lots of towing accidents come from people improperly loading the trailer or overloading it. Driving too fast for the conditions is cutting any margin for error you might have is probably the other big thing.

As a percentage of miles driven in a vehicle, for most people, towing a trailer is a fairly small percentage, and it may not be a regular thing, so skills are lost in between summer vacations.

All it takes is the combination of a few things to ruin your day. You might go many years and never trip that disaster point. I prefer to stay within the weight guidelines BMW lists for their vehicle. I'm not comfortable trying to twist my unibody to move weight forward. If your loading is within specs, the vehicle can ride level with the air suspension.

Thanks for the thorough explanation, although I have to admit that I got lost a bit. Are you saying that WDH is not going to be ideal or effective on unibody because it is less stiff towards the end of the vehicle? But then you mentioned X5, is this meant to be special type of unibody implantation? I do trust BMW has a very sophisticated electronics to make towing easy and safer, my worry is that the company may have engineered the vehicle to be more focused on European towing style, which per my understanding are quite different/balanced when it comes to front and back weight distribution.

[teefive]

MB increases the hitch weight limit on their unibody SUVs when weight distributing hitches are used (about 200lbs IIRC).