Jump to content

Recommended Posts

Assuming a singled HDT that is used for both a heavy (27-29K) RV hauler AND a daily driver, what is the "ideal" singled WB?  Also assume no Smart or other vehicle carry. Trade-offs? 

Share this post


Link to post
Share on other sites

It depends on the sleeper size. Mine (179 actually) gives me 1'-6" clearance if I ever needed to do a 90 with my trailer. There is no ideal WB for every truck, It is what ever works with your truck. As I said to you previously it can also change with long or short nose and do you have fairings or not. Definitely not a one size fits all deal.

Edited by 13speed

Share this post


Link to post
Share on other sites

Chris is right....it "just depends". But given a 630 class truck you can only go so short.....And personally I'd want fairings, so that has to be there as well. If you did a new truck (VNR) with short hood then you can squeeze a little more out of it, but you are in the 180" range.  A couple of inches either way does not really matter at that point.

Share this post


Link to post
Share on other sites

With no Smart or other "obstacle" on a bed, I think the options open up and the priorities change significantly:

1) You could put the hitch just ahead of the drive axle (putting 90-95% of the pin weight on the drivers and 5-10% on the steers) or just aft (putting 105-110% of the pin weight on the drivers and -5-10% on the steers).

2) Swing clearance on the trailer dictates how far forward of the rear bumper (or equivalent) you can put the pin - full aft means you need barely more than 4'3", and it all comes down to the Pythagorean theorem: A*A (where A = 4'3" or half of the width of an 8'6" vehicle) + B*B (where B = the distance between pin and rear bumper) = C*C (where C = the swing clearance of your trailer).

3) Bed design just has to fit the outcome of #1 and #2 (OK, it has a small influence on weight & balance).

Share this post


Link to post
Share on other sites

Petty,

I know that I am getting old but how do you put 105% to 110% of the pin weight on the rear. You can put 100% on the rear and by being behind the axle, you can unload the front axle but you can never be more than 100%. Then again, You might be using some sort of new math I am not familiar with.

 

Share this post


Link to post
Share on other sites
27 minutes ago, GeorgiaHybrid said:

Petty,

I know that I am getting old but how do you put 105% to 110% of the pin weight on the rear. You can put 100% on the rear and by being behind the axle, you can unload the front axle but you can never be more than 100%. Then again, You might be using some sort of new math I am not familiar with.

 

No new math.  Did you ever use a pry bar on anything?  The longer the bar (distance of the hitch behind the axle), the more down pressure on the fulcrum (increased weigh on the rear axle) and the more lift on what you are prying (decreased weight on the front axle).  That weight that comes off the front axle has to go somewhere, it does not just disappear.  Pretty simple math to figure it out given wheelbase, distance from axle to pin, and pin weight.

Share this post


Link to post
Share on other sites

The pin weight whatever it is 5K-6K will be the same no matter where you put it (5K-6K). What will change is the axle loadings. 

Put the pin over the rear axle it will go up by 5K-6K. Put it behind the rear axle it will go up by 5K-6K, plus whatever the off-load was on the front axle. Put it in front of the rear axle, most of that 5K-6K will add to the rear axle and some will add to the front axle.

Share this post


Link to post
Share on other sites
7 minutes ago, phoenix2013 said:

The pin weight whatever it is 5K-6K will be the same no matter where you put it (5K-6K). What will change is the axle loadings. 

Put the pin over the rear axle it will go up by 5K-6K. Put it behind the rear axle it will go up by 5K-6K, plus whatever the off-load was on the front axle. Put it in front of the rear axle, most of that 5K-6K will add to the rear axle and some will add to the front axle.

OMG Henry be careful........you just might trigger one of my spreadsheet attacks.........NO known cure.......

This high 3rd grade math gets folks everytime.......

Drive on.........(Who shifted my.......mass??)

Edited by Dollytrolley

Share this post


Link to post
Share on other sites
On 7/21/2017 at 1:30 PM, TheLongWayHome said:

Assuming a singled HDT that is used for both a heavy (27-29K) RV hauler AND a daily driver, what is the "ideal" singled WB?  Also assume no Smart or other vehicle carry. Trade-offs? 

Dodge will tell you that they have your daily-driver in $tock in a wide assortment of colors and they are already singled......+30K weight ratings..........just hold your breath on the long downhill twisty grades.......

Drive on........(do you believe all the.......ratings??)

Edited by Dollytrolley

Share this post


Link to post
Share on other sites

As a general rule the minimum wheelbase should be 60-66" from the back of the cab/sleeper to the axle centerline.    On a truck with a 180" body (front bumper to rear of cab) with a 50" set back axle that is 190-196" WB.     The shorter the distance from the cab to rear axle the harsher the ride becomes, 55" would be the absolute min IMHO.      A short nose/small sleeper truck could have a175-180" WB.      I have often thought a 22' long HDT  would be an ideal Dually replacement.    That would roughly be a truck with a 160" body and a 102" bed, add 2" for body clearance to the bed.  

 

Steve

Share this post


Link to post
Share on other sites

Thanks, oh mighty HDT wizards. :wub:

I was wondering about that trade-off of short vs longer WB.  With a short WB when does the ride become harsh and less stable. Thanks Steve. And if you go too long then turning radius, daily driver city parking, etc. becomes more of an issue! Or more like driving a bus.

:unsure:

 

2 hours ago, Dollytrolley said:

Dodge will tell you that they have your daily-driver in $tock in a wide assortment of colors and they are already singled......+30K weight ratings..........just hold your breath on the long downhill twisty grades.......

Drive on........(do you believe all the.......ratings??)

Dollytrolly, tell us your "personal issues" with singled HDTs!!!!!!!  I'm from Colorado and we have the Ike, Floyd and Genesee hill tests around here. Can you say, "Where is the runaway trump ramp"? Oops, just past it.

Share this post


Link to post
Share on other sites
15 hours ago, peety3 said:

With no Smart or other "obstacle" on a bed, I think the options open up and the priorities change significantly:

1) You could put the hitch just ahead of the drive axle (putting 90-95% of the pin weight on the drivers and 5-10% on the steers) or just aft (putting 105-110% of the pin weight on the drivers and -5-10% on the steers).

 

More uninitiated HDT newbie questions,

Why do not more of the singled HDT put the hitch in front of the drive axle? Of all the HDT on http://www.hhrvresource.com/truckbeds that I have looked at (some drooling involved), they all look to be to the rear of the drive axle. Obviously 13speed is going the in front of the axle route.

Not sure what this guy (below) from Ottawa did (cd084), but that trailer looks very close to the cab. No hitch picture that I could find. This was a 53' trailer (had to be 30+K). Is there some sort of sidewinder or slider hitch for that heavy a trailer used on HDTs?

cd084_truck.jpg?itok=YIjzAhE_

 

Edited by TheLongWayHome

Share this post


Link to post
Share on other sites
6 hours ago, TheLongWayHome said:

Thanks, oh mighty HDT wizards. :wub:

I was wondering about that trade-off of short vs longer WB.  With a short WB when does the ride become harsh and less stable. Thanks Steve. And if you go too long then turning radius, daily driver city parking, etc. becomes more of an issue! Or more like driving a bus.

:unsure:

 

Dollytrolly, tell us your "personal issues" with singled HDTs!!!!!!!  I'm from Colorado and we have the Ike, Floyd and Genesee hill tests around here. Can you say, "Where is the runaway trump ramp"? Oops, just past it.

Well welcome to the wheel-ba$e-campfire wongway.....here we ALL have personal-issues and some have Impersonal-issues issues as well......and IF you reflect for a moment ......I bunch of geezers or soon2beegeezers  playing with class 8 trucks is a fairly crazy hobby......

Now not to poo-poo your home state but plenty of places have steep long grades and the super-duper-pickup makers used to make commercials of the latest wonder-wagon-pickup passing the compitations wonder-wagon-pickup with a D8 cat on a gooseneck with a Tom Cruise look alike with his arm around a Dolly Parton look alike smiling from ear to ear.......

Funny thing.....at the top of the Davis grade the wonder-pickup-movie-$tars would un-hitch and a pair of old Frightshakers would Jake brake the loads back down the Davis grade so that the lie could be filmed again and again....

Now my ......"issue"......well, wongway is this.....at the bottom of the Davis Grade is the Colorado River AND a STOP LIGHT ......and Wongway this STOP LIGHT was different than other stop lights in that when the cross traffic light turned green you remained STOPED while you let a herd of snowbirds blast thru the red light while their super-duper-wonder-pickup is being pushed brakes smoking thru the intersection.....and look hard because one day we sat stopped thru the entire green light while THREE snow birds flew by.... They often travel in flocks you know......

Sure the Davis Grade is a bit of a pull but it turns out that is a hell of a push when the stop light turns RED.......

Drive on........(my "issue" today is to not get creamed by a  ......super-duper-pickup.....)

 

.

Share this post


Link to post
Share on other sites
10 hours ago, Dollytrolley said:

Dodge will tell you that they have your daily-driver in $tock in a wide assortment of colors and they are already singled......+30K weight ratings..........just hold your breath on the long downhill twisty grades.......

Drive on........(do you believe all the.......ratings??)

 

1 hour ago, Dollytrolley said:

Well welcome to the wheel-ba$e-campfire wongway.....here we ALL have personal-issues and some have Impersonal-issues issues as well......and IF you reflect for a moment ......I bunch of geezers or soon2beegeezers  playing with class 8 trucks is a fairly crazy hobby......

Now not to poo-poo your home state but plenty of places have steep long grades and the super-duper-pickup makers used to make commercials of the latest wonder-wagon-pickup passing the compitations wonder-wagon-pickup with a D8 cat on a gooseneck with a Tom Cruise look alike with his arm around a Dolly Parton look alike smiling from ear to ear.......

Funny thing.....at the top of the Davis grade the wonder-pickup-movie-$tars would un-hitch and a pair of old Frightshakers would Jake brake the loads back down the Davis grade so that the lie could be filmed again and again....

Now my ......"issue"......well, wongway is this.....at the bottom of the Davis Grade is the Colorado River AND a STOP LIGHT ......and Wongway this STOP LIGHT was different than other stop lights in that when the cross traffic light turned green you remained STOPED while you let a herd of snowbirds blast thru the red light while their super-duper-wonder-pickup is being pushed brakes smoking thru the intersection.....and look hard because one day we sat stopped thru the entire green light while THREE snow birds flew by.... They often travel in flocks you know......

Sure the Davis Grade is a bit of a pull but it turns out that is a hell of a push when the stop light turns RED.......

Drive on........(my "issue" today is to not get creamed by a  ......super-duper-pickup.....)

 

.

LOL. Quality posts Dolly.  My 5er isn't nearly as heavy as some here and I still wouldn't try to pull it up or down a mountain with my pickup.

Share this post


Link to post
Share on other sites
7 hours ago, TheLongWayHome said:

More uninitiated HDT newbie questions,

Why do not more of the singled HDT put the hitch in front of the drive axle? Of all the HDT on http://www.hhrvresource.com/truckbeds that I have looked at (some drooling involved), they all look to be to the rear of the drive axle. Obviously 13speed is going the in front of the axle route.

Not sure what this guy (below) from Ottawa did (cd084), but that trailer looks very close to the cab. No hitch picture that I could find. This was a 53' trailer (had to be 30+K). Is there some sort or sidewinder or slider hitch for that heavy a trailer used on HDTs?

cd084_truck.jpg?itok=YIjzAhE_

 

Putting the pin before the drive axle will more than likely overload the steer axle.  That converted dry van in the picture looks to be close to the cab, but the pin will be back underneath over the drive axles.

Share this post


Link to post
Share on other sites

Our truck-

1998 610

Overall truck length with bed is 24'6"

Wheelbase is 182"

Our hitch -Center of Jaws- is located 39" forward from the rear of the bed

                                      or 11" behind the rear axle.  

We use our truck as a daily driver and it does fine for us.  It can be cumbersome in small areas like the French Quarter New Orleans, but we managed....

Having driven and ridden in trucks with a little longer wheelbase 200-226", the longer wheelbase is smoother on rough roads.  

 

 

 

Edited by Alie&Jim's Carrilite

Share this post


Link to post
Share on other sites

LongWay,

When we bought our truck I was looking for data to help make the decision to single or not.  All I could find was opinion....it was helpful but in God I Trust, everyone else show me data.  I took our truck (Volvo 770) to a school parking lot on a Sunday.  The truck was still tandem of course.  I cut the steering wheel as far as it would go and made a 360* turn, measured the inside track left by the tires scrubbing the pavement.   Took the chance and had it singled short as they say (leaving the axle closest to the cab in place).  Actually we moved the rear axle to that position.  We then repeated the school parking lot test.   The inside track radius was reduced by 10' or 25% +/- or from 43' to 33'.. About what we estimated.  We have found the reduced radius very helpful, particularly in tight campgrounds and when backing just the truck .Seems that the geometry backing a tandem is far different than going forward.    It did cost us about $2k for the work but have gotten that money back in cost avoidance i.e 4 tires, brakes, shocks, airbags......fuel savings?? really difficult to measure that one.   To be honest with you....If I were to do over again,  I would look at something like Jack Mayer's Volvo 610 set up for hauler/daily driver.  Outstanding turning radius. low enough you don't need to be to concerned with overhead obstacles (daily driver)  pulls and stops strong, comfortable enough for overnights.   

BTW....   I am convinced we would have been in a bad way had we not had our HDT.  Seems our trailer brakes failed (air over hydraulic) and we did not know it.  Our trailer weighs in the neighborhood of 24K.  We went up and down a mountain pass (Mt Eagle TN) and a couple hills down to a stop light.  Still here to tell you about it.   A pickup can pull the bigger trailers as can a forklift at the dealer but simple physics proves they can't stop it.

Brad

 

 

Share this post


Link to post
Share on other sites
8 hours ago, TheLongWayHome said:

More uninitiated HDT newbie questions,

Why do not more of the singled HDT put the hitch in front of the drive axle? Of all the HDT on http://www.hhrvresource.com/truckbeds that I have looked at (some drooling involved), they all look to be to the rear of the drive axle. Obviously 13speed is going the in front of the axle route.

Not sure what this guy (below) from Ottawa did (cd084), but that trailer looks very close to the cab. No hitch picture that I could find. This was a 53' trailer (had to be 30+K). Is there some sort or sidewinder or slider hitch for that heavy a trailer used on HDTs?

cd084_truck.jpg?itok=YIjzAhE_

 

It's just a standard commercial 5th wheel, most likely a sliding hitch.  Trailer has a standard kingpin.  I believe it was a new race car type trailer converted to an RV.  

Share this post


Link to post
Share on other sites

On the question of comfort on short wheelbase tractors.....

As background I personally went from the Volvo 610 autoshift 182" wb previously shown, to a Volvo 780 IShift 232" wb. There is no doubt that the 780 was "different" than the 610. And certainly mitigated roughness on the roughest roads. The fact that it was so much newer and had front airbag suspension helped that. As far as the wheelbase - it certainly had to make some difference, but honestly the 610 was not that bad. I did not notice THAT big a difference. Less than I would have thought. And there is simply no comparison in maneuverability. It is not even in the same universe.

The bottom line to me - having been there - is that I would build the truck that met my needs, and not worry about comfort all that much. Either will be pretty comfortable. Not as comfortable as a modern car, as far as ride goes. But overall comfort will be far better than anything else towing that load (like any pickup or superpickup).

Edited by Jack Mayer

Share this post


Link to post
Share on other sites
12 hours ago, Hot Rod said:

No new math.  Did you ever use a pry bar on anything?  The longer the bar (distance of the hitch behind the axle), the more down pressure on the fulcrum (increased weigh on the rear axle) and the more lift on what you are prying (decreased weight on the front axle).  That weight that comes off the front axle has to go somewhere, it does not just disappear.  Pretty simple math to figure it out given wheelbase, distance from axle to pin, and pin weight.

 

11 hours ago, phoenix2013 said:

The pin weight whatever it is 5K-6K will be the same no matter where you put it (5K-6K). What will change is the axle loadings. 

Put the pin over the rear axle it will go up by 5K-6K. Put it behind the rear axle it will go up by 5K-6K, plus whatever the off-load was on the front axle. Put it in front of the rear axle, most of that 5K-6K will add to the rear axle and some will add to the front axle.

Hot Rod, this was what I was talking about, the pin weight doesn't change. The pin weight remains constant and you have a weight transfer from the front axle to the rear axle depending on the distances and weights involved. Peety might have meant that but it wasn't the way I read it.

As far as the OP question is concerned, he will need to let us know what brand of truck, sleeper size, fairing required or not, and in some cases, engine size to help with his question. My old truck had a 196 inch WB and out turned my dually any day of the week. The hitch on it was mounted on top of the rear axle.

Share this post


Link to post
Share on other sites
8 hours ago, TheLongWayHome said:

More uninitiated HDT newbie questions,

Why do not more of the singled HDT put the hitch in front of the drive axle? Of all the HDT on http://www.hhrvresource.com/truckbeds that I have looked at (some drooling involved), they all look to be to the rear of the drive axle. Obviously 13speed is going the in front of the axle route.

Not sure what this guy (below) from Ottawa did (cd084), but that trailer looks very close to the cab. No hitch picture that I could find. This was a 53' trailer (had to be 30+K). Is there some sort or sidewinder or slider hitch for that heavy a trailer used on HDTs?

HDTs put the hitch far aft for a few key reasons: to offset the weight of a Smart car or similar payload sitting in front of the rear axle, to ensure swing clearance behind said Smart car/similar, or because the pin location on their trailer doesn't offer enough swing clearance to allow it to be in a traditional position.

Commercial hitches are often slidable, but inevitably end up in one position for life. They're constrained by weight laws, with 34k on a tandem set, 20k on a single axle, and 600-800 pounds per inch of steer tire width (state-dependent). With a 12k or 13.2k steer axle, there's little to no margin if they want to get to their max legal 80k weight, and the right place for that is inevitably just a hair in front of drive tandem centerline. Check out most fuel haulers: you'll find a fixed (non-slide) fifth wheel, because they want every possible pound of payload and they know exactly how the weights will pan out.

Share this post


Link to post
Share on other sites
4 minutes ago, GeorgiaHybrid said:

 

Hot Rod, this was what I was talking about, the pin weight doesn't change. The pin weight remains constant and you have a weight transfer from the front axle to the rear axle depending on the distances and weights involved. Peety might have meant that but it wasn't the way I read it.

That's exactly what I meant and exactly why I wrote it the way I did. Make sure you notice the minus sign before the 5-10% of weight on the front axle: 105-110% of pin weight on the drivers and -5-10% of pin weight on the steers.

Share this post


Link to post
Share on other sites

On the topic of axle and hitch placement, Gregg and I did a video on it. LINK.

It certainly does not cover every point but it will provide basic information to those considering the topic. It does provide some examples of front unloading numbers. This is important - you cannot unload the front too much or you will have other issues to address. This topic was covered pretty well (exhaustively) during the initial discussion on this forum. A search here will find that. There are a bunch of smart people here, that shared a lot of knowledge on the topic.

There are many factors involved when you get to the "edge" conditions. And getting just ONE wrong will result in a truck that is "not right".....in one case Henry and I worked on, it was downright dangerous. You "can" mask handling issues with suspension and other "technology", but when the weights and measures are not right, you have an inherently unstable vehicle combination. 

Fortunately, with 99% of the trucks people build for recreational use, this is simply not a factor - the "edge" conditions are not "challenged". But cantilever a trailer pin beyond 5-6', and you better get your numbers right. An ET snugged behind the axle is not an issue.  Actually, I should let Henry say that, but I think he already has....

Share this post


Link to post
Share on other sites
8 hours ago, peety3 said:

Commercial hitches are often slidable, but inevitably end up in one position for life.

Usually true, unless the tractor pulls a variety of trailers, and gross weight is not a concern for some of them.  I've seen drivers trying to free a movable fifth wheel that had been in one place a long time, but mine gets moved many times per year.

And you're right about the pin being just forward of the drive axle center.  Just a little weight transferred to the steer makes for good handling.  Leave the pin a few inches back and it can be scary on wet roads.

Share this post


Link to post
Share on other sites

Our plan is to single short. And be short like Jack's 610 was. That way we have a truck to tow the camper. But also easy to get around in. Thus using it as our daily driver while on the road. Not looking at taking a lot of stuff with us. As were only  traveling for a few months at at time. Not full timers like a lot of people.

AS for the hitch positioning. If its forward of the axle, or even over it. The ride can be off, but move it back 6" and handling and ride changed for the better. When I was OTR, we did have to side the 5th wheel some. Not near as much as the rear tandems on the trailer. But even when I hauled tankers with oil. I did have to move it a few inches at time's. But it was for a better ride, not for movement of weights.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

RVers Online University

campgroundviews.com

Our program provides accurate individual wheel weights for your RV, toad, and tow vehicle, and will help you trim the pounds if you need to.

DFW RV Roof

RVAir The cleanest air in RVing!

Rv Share

Dish For My RV.

Find out more or sign up for Escapees RV'ers Bootcamp.

Advertise your product or service here.

The Rvers- Now Streaming

AGS Now Hiring

RV Pet Safety

RVTravel.com Logo



×
×
  • Create New...