Weird Sensation

[johninedmonton]

Ok, this is kinda weird. When pulling my 8k 37' TT, I'm not experiencing "truck suck". You know, when an 18wheeler passes you and sucks you into his airstream.

Nope, no truck suck. I'm steady and solid as though he and my trailer don't even exist. But instead, I'm experiencing "small car suck".

A 40,000 lb 18 wheeler won't affect me at all. But a Toyota Prius will make my trailer dance like a tomatoe on a hot frying pan.

Has anyone ever experienced the same? Any thoughts?!?!?

[johninedmonton]

That totally makes sense. Thanks guys.

[facory]

Just kidding, of course. I really do know what a wake it.

[atreis]

Wake: Those waves that come out from behind boats. (Water and air are both fluids, and behave similarly - air is just a lot less dense.)

It really is the same as boats on water - a large slow moving boat leaves a very small wake. A small fast moving boat (like a jet ski) can make a decent wake despite being small. It's the same with cars. A semi passing slowly won't suck/push nearly as much as a Prius passing at high speed.

The large rental box trucks seem to have the worst wake - probably from those large cab-overs, and the people driving them tend to go fast.

[facory]

mosseater wrote:
I call it the "suck 'n push", because that's what happens. Think about the physics involved.

When a vehicle makes a wake through the air (yes it's air, but shooters know it's just really thin water) it first contacts the section of trailer behind the axles which pushes away and levers the front toward the passing truck, which has the effect of pushing the tow vehicle over to the center line as well.

As the bow wake nears the trailer axles, it evens out because the force is at the fulcrum (pivot point). Then, as the wake impacts the front of the trailer ahead of the axles, (which is usually a larger surface area) it pushes the front of the trailer away from the passing truck, taking the tow vehicle with it towards the berm. First it sucks, then it pushes.

It doesn't concern me much anymore. I have to only correct the wheel about 1/2" to compensate. Just that the wake is much stronger and sharper with small box trucks and the like.

HUH? You lost me at wake. Too techy for me. There is a lot going on though. :S

[JJBIRISH]

Even stranger is a truck coming from the opposite direction on a two lane road as almost no such effect at all…

[mosseater]

I call it the "suck 'n push", because that's what happens. Think about the physics involved.

When a vehicle makes a wake through the air (yes it's air, but shooters know it's just really thin water) it first contacts the section of trailer behind the axles which pushes away and levers the front toward the passing truck, which has the effect of pushing the tow vehicle over to the center line as well.

As the bow wake nears the trailer axles, it evens out because the force is at the fulcrum (pivot point). Then, as the wake impacts the front of the trailer ahead of the axles, (which is usually a larger surface area) it pushes the front of the trailer away from the passing truck, taking the tow vehicle with it towards the berm. First it sucks, then it pushes.

It doesn't concern me much anymore. I have to only correct the wheel about 1/2" to compensate. Just that the wake is much stronger and sharper with small box trucks and the like.

[facory]

Strange, but true. Some smaller vehicles affect a rig much more than a big tractor-trailer. Must be something to do with shape and speed.

[JJBIRISH]

mosseater wrote:
I've noticed the shape of certain vehicles rather than their size does effect me more. Not that any of them effects me much at all, but some of these newer trucks are very smoothe through the air and their size acts like a buffer when they pass.

I notice smaller, boxier trucks have a the worst overall effect. They push a big wake in front and their short overall length seems to bounce more air at my pivot point (hitch) as they pass.

2X, although I never heard it called truck suck, I completely agree shape not size is a major factor for some of the bow wave effect one vehicle has on another…

[352]

Tongue weight and truck sucking has surely got some attention. Please let me know how this works for you.

[johninedmonton]

ah64id wrote:
How much tongue weight do you have?

I'm at about 900lbs. , +/- 50 lbs depending on how we are loaded (water, bikes, etc.). My WD hitch is rated at 1,400 lbs.

[campigloo]

I love the "truck suck" description. It's going in my vocab. I have two of the above sway bars, they are the only type I have ever used, and have only loosened them to prevent extra wear on the friction surfaces. I back up, go forward, uphill downhill and all around. Haven't had one break in the last 20 or so years.

[Ron3rd]

wmoses wrote:

Ron3rd wrote:
You can back up with any hitch you choose. I don't know where that myth got started saying you have to remove things to back up.

Sure you can but it is not a myth when one has one of those anti-sway bars that you have to tighten to clamp the friction pads onto the slider bar - you know the type:



When backing and you turn too much the anti-sway bar can run out of travel and then you have problems.

Ran one of those for 9 years and never removed it backing up. YMMV.

[wmoses]

Ron3rd wrote:
You can back up with any hitch you choose. I don't know where that myth got started saying you have to remove things to back up.

Sure you can but it is not a myth when one has one of those anti-sway bars that you have to tighten to clamp the friction pads onto the slider bar - you know the type:



When backing and you turn too much the anti-sway bar can run out of travel and then you have problems.

[Doug33]

Question - do 18-wheelers get "truck suck" from other 18-wheelers? I've seen more than my share of 18-wheelers swerving on the highway, especially in higher winds.

I know cars can be more annoying than other trucks, because they tend to give you little respect on the highway, and will do anything not to be stuck behind you.