Wheelbase and axles

[ewacowboy]

I don't want to start a "war" here....but am curious as to what the "optimum" wheelbase and axle ratings for a singled HDT to haul a 25k 5ver with drom box and smart car.  I know there are other considerations, but am just beginning my research, so need a place to start....

[Brad & Jacolyn]

Don't know about optimum but mine has a 218" wheelbase singled short and we did not touch the frame length. One thing I have in my favor is a 14.6k front end. I also have a lousy ratio of 3.73. Gregg Shields will tell you that 2.67 is very good. But Gregg also said in a seminar the price to change the gears and he did an analysis. He told us that at 15,000 per year it took about 8 years to break even. Now I only travel about 8000 miles per year so it would take about 15 years for me. Now the price of fuel can be debated but I'm not going to do that and I'm not changing the gears. 

Now I'm of the opinion that is 1 - 1.5 MPG is going to be a deal breaker perhaps this is not the lifestyle for you. JMHO.

 

Brad

[GlennWest]

We will need more info. How long a bed, etc

[Dollytrolley]

35 minutes ago, ewacowboy said:

I don't want to start a "war" here....but am curious as to what the "optimum" wheelbase and axle ratings for a singled HDT to haul a 25k 5ver with drom box and smart car.  I know there are other considerations, but am just beginning my research, so need a place to start....

Hey e-cow

Let the "war" begin......

This subject is almost as $afe as what model Water Pick should I buy my bride for our anniversary.....( Last anniversary...)

Drive on.... (Tha devil is in the..

. details)

[ewacowboy]

1 hour ago, GlennWest said:

We will need more money info. How long a bed, etc

I don't know yet.  I was hoping to get some starting numbers and see what sort of costs would be involved.  As far as bed length....long enough to side load a smart with a behind the cab drom box.

[I'mdonewiththis forum]

2 minutes ago, ewacowboy said:

I don't know yet.  I was hoping to get some starting numbers and see what sort of costs would be involved.  As far as bed length....long enough to side load a smart with a behind the cab drom box.

Last year at the National HDT Rally I went around and measured beds. The consensus was you want 11 feet between the back of your cab, drom, whatever to the center of the pin. This year at the Rally the bed builders here said their beds are about $20k for a Smart loader type.

[Dollytrolley]

2 hours ago, ewacowboy said:

I don't want to start a "war" here....but am curious as to what the "optimum" wheelbase and axle ratings for a singled HDT to haul a 25k 5ver with drom box and smart car.  I know there are other considerations, but am just beginning my research, so need a place to start....

E-cow,

I have a live data spreadsheet that calculates the truck and trailer weight and balance with each number you type into the sheet......you can move axles, hitches, cars, gold bars, whatever .....it recalcs with each number you enter..

Now this may answer a few questions or....lead to more questions...

If you want to test drive the spreadsheet shoot me a email at.   Mmcdan3189@aol.com  or my cell (520) 891-3695.

Drive on.....(lots .....numbers)

[HERO Maker]

Are you sure that is a 25K DRV?  With only tandem axles, even with 9K axles, that is going to be a lot of weight on the pin.  The weight on the pin is good, but we all know that DRV is really building their rigs for the pickup market with axles a little farther forward that most of us would like, giving us light pin weights.

How big of a drom box are you going to have behind the cab?  More importantly, what are you going to carry in it?

Some have singled, with a drom, and carried a smart car, with a heavy pin, only to find that they are maxing their singled truck!

So, what is your pin weight?

You also have to consider what your truck bed will look like and how much weight will you have in your storage boxes there.

I personally stayed tandem on the truck.  I don't have any worries about weights on the axles.

 

[ewacowboy]

Sorry gang....didn't realize I was going to create so many questions.  Maybe I'm putting the cart in front of the horse, but was really looking for generic/optimum numbers.  As far as pin weight, I'm looking into the future at 25k.  Our DRV is only 21k and wanted some wiggle room for possible future plans.  I'm also assuming a max of 25% pin wt??  

[I'mdonewiththis forum]

What you should do is get Dolly to send you the spread sheet. You can make all sorts of guesses, but the spread sheet will tell you what your numbers will be IF you have all the correct numbers. I have that spread sheet and have played with all sorts of combinations and there is no "ideal" wheel base due to the face every one of us has different needs and wants.

Oh, BTW, don't worry about all your questions. There are HUNDREDS of years worth of experience here to help you decide how you should spend your money!!

[Brad & Jacolyn]

And we are ALWAYS willing to help spend it.

[Dollytrolley]

7 hours ago, ewacowboy said:

I don't want to start a "war" here....but am curious as to what the "optimum" wheelbase and axle ratings for a singled HDT to haul a 25k 5ver with drom box and smart car.  I know there are other considerations, but am just beginning my research, so need a place to start....

E-Cow

IF you would like to hand calculate some sample weight and balance without messing with the spreadsheet try the old thread listed below......

Drive on..........(Lotsa numbers......)

 

 

[rickeieio]

Many of us started by leaving the truck tandem and building a simple bed to start with, planning to later alter the truck as we saw fit.  Some of us have found that tandem ain't so bad, and a simple bed works fine.  Of course, I'm not full timing, and never will, and have no drom.

So, that's a long winded way of saying, there is no magic number.  Whatever works for you is correct.

[porky69]

Wheelbase will be affected by what make and model HDT you are working with.   The distance from the steering axle to back of cab (sleeper) varies by truck.  The numbers you need to figure are going to be cab-to-axle and cab-to-end of frame. 

Like others have said it is not a simple answer.

You would need to decide how long of a deck you want, where you want your rear axle to be in relation to the deck (do you want it right at the back under the hitch(makes for a longer wheelbase, therefore bigger turning radius) or do you want it forward 4,5,6....feet to help with turning radius, lift some weight off the steering axle,etc. So you kind of need to work backwards....envision the final product, calculate back to get rear axle position and then figure that onto you chassis to figure out wheelbase.

[Dollytrolley]

Hi E-Cow,

For the most part the big three pickup makers somewhat drive the RV trailer market and they for the most part offer only two wheelbases......longbox and shortbox......

Now a few folks offer RV weighing services and as I recall the last overloaded RV number spec I herd was that about 57% of RV's weighed were overweight on one or more wheel tire patches....gulp.

I would hazard to guess that if I waterboarded all of the current HD truck owners on the forum that 99.9% were gross RV overloaded in previous lives ( the remaining 00.1% is a fibber).

Now I used to operate aircraft and cranes barges where overloading had life-$pan shortening tendencies so when our RV pickup became too grossly overloaded I cobbled up a HDT to haul our ever growing RV ....."wants".

Now the RV gig is pretty hot right now and the big players are pushing bigger and bigger rigs and some are silly overweight and out-of-balance and for the most part the vast majority folks get by and get lucky.....once in a while folks runs out.....ouch...

Now this might sound weird coming from a geezer that tends to consider weight and balance of RV'$ fairly serious for a few reasons, but......but.....I do not recall any grossly overweight out of balance HDT RV units here on the forum except a few DRV "tail-waggers" that tend to have fairly small precentage of pin to gross weight ratios as well as other factors that like feed the rig instability........

My personal reasons for using a HDT tow unit is that we tend to be pretty cheep and Cary too much junk around and our cheep trailers have horrible suspensions and grossly undersized tires for the factory gross weight of the trailer so I calculate ways to keep the trailer at less than 80% of factory gross weight and so I dump as much weight onto the Tandem HDT to offload the cheep trailer.....

Now the majority of folks tend to go the other way by trying to "upgrade" their trailers to operate at gross or somewhat over gross weights....(tire upgrades, bigger axles, etc).

For the most part overloading your HDT by a few hundred pounds is likely no big deal and some get by over by a few thousand pounds....

Two factors give me pause......actual tire capacity and rig handling.

Tire capacity to me is factored by SPEED, HEAT and load in that order.

The second factor is rig balance and it's effect on handling ($tability or lack of...).

By nature HDT tractors are out of balance when bobtailing but that is just the normal of the trucking gigs so you just have to learn to deal with bobtailing but once you load the trailer and "other"  RV items the HDT tends to be a much nicer rig to operate.

Few folks have issues even just cobbling HDT'$ together even without calculating the loads......

Drive on......(HDT'$ tend to be forgiving of .....loads)

[ewacowboy]

Thanks for all the info guys....here is my ultimate wonder - is it worth it for me to go shop new trucks vs trying to find a good used truck.  I'm seeing very few used trucks on the market that would meet our needs and what we are interested in can be very expensive by the time we single and build a bed.  My thought was to get some basic info to allow us to talk to dealers and see what the difference in price would be new vs used.  Sometimes it's better for us to purchase new and get the latest bells and whistles for a little more cost.  I was hoping to get some numbers to start my journey and speak intelligently with the dealers so I could compare apples to apples....

Just my thoughts - let the bantering begin 

[Jack Mayer]

Well, now that Pandora's box is open..... 

In GENERAL terms.....

If you want a drom box that is at the fairing line on a Volvo (or likely any other brand, more or less), and want to be able to accommodate a 453 smart or anything else that size.  And want up to 7K pin weight. Then there are a few factors. 

• The back of cab to pin will be in the 150" area, more or less. 
• The hitch layout will determine the minimum bed length back from there. For example, the ET has the pin very far back (relative to the overall hitch) while the Comfort Ride has the pin more forward in the hitch profile. This affects the hitch mounting "tunnel" size.  And thus potentially the overall bed length. But we are talking inches, not multiple feet.
• The axle needs at least reasonable positioning under all this....typically on a singled Volvo 730/780 that is at a 232-236" wheelbase. That position can be refined with the spreadsheet tool of DT. Shorter trucks; shorter wheelbase. Deck proportions would stay the same - it is a shorter wb because the bumper-to-back of cab measure is shorter due to the smaller condo. 
• With a 7K pin weight (disregarding the trailer total weight), a smart, a drom, and typical load, you will be pushing the limits of a 20 K rear. In fact, you will likely be over. Your choices are: you can run over, you can put on the upgraded springs (on a Volvo) and  essentially rerate the rear to 23K, you can look for a 23K rear axle, or you can stay tandem.There is no technical issue with running over weight on that axle as long as it is reasonable...IMO. Staying tandem is the answer for any weights more than the 453 smart.
• Gearing of the axle is tricky. It depends on your intended cruise speed, the hp/torque of the truck,  overdrive or not, and the final drive ratio. For example, in my 2009 780 I cruised at 62, with a 515 hp/1850 torque D16, 3.xx ratio, overdrive. That was at around 1350-1400 rpm, if I recall correctly. The truck was set up for heavy haul.  On my 2015 D13 XE 455/1750 I cruise at 67mph, 2.67 rear, overdrive, 1150 rpm. The truck pulls my 28K+ trailer fine. It is set up for efficiency, and I get in the mid 9-low 10 mpg. Measured, not computer. Never got near that on the other truck. 

Since there was a comment on price, I'll comment as well. Price of a new (not used parts) smart  body that is not DIY is going to vary from 15K for something pretty minimal, to over 30K for something totally embellished, with a drom. And some accessories, etc. A body like on my new truck will be in the mid to upper 20's. Be prepared for price "creep" as you build, since there is always "something else" that you end up adding either as you think through the process or as you actually build. There is a fairly wide range of things you can do and costs associated with them.   Price of a "basic" body that looks like  the one on my truck, without some of the smart-specific items, and without some of the storage ideas in it, is $20K. It will vary based on the fabricator, but most are in the same relative ballpark.

[rickeieio]

Looking back to the original post.....  Why do you want an HDT?  Your avatar shows what appears to be a pretty nice MDT, so I'm guessing you are using it?  Are you moving to full time and want more storage?  Are you under powered, or plan to be if you get a bigger trailer?

No simple answers.........  And above all, YOU need to happy in the end, not a bunch of geezers ( like me) offering free advice.

[Jack Mayer]

4 minutes ago, ewacowboy said:

Thanks for all the info guys....here is my ultimate wonder - is it worth it for me to go shop new trucks vs trying to find a good used truck.  I'm seeing very few used trucks on the market that would meet our needs and what we are interested in can be very expensive by the time we single and build a bed. 

New vs used is a tough choice. for a newer model with some of the nicer features on it, the choice is even harder. 

There is no crisp clear answer. There are many factors to consider:

• What are your specific needs/desires. You may never find them in a used truck if you are very demanding.
• Used truck prices are at a very low level now....very advantageous to the buyer. You can get a nice truck for a decent price. In the comparison we are discussing I'd stick to below 250K mile trucks. With good warranties; either included or added. So you have to account for warranty cost on a used, and additional warranty cost on new (over top of the base warranty).
• The deltas between  new/used boil down to: warranty cost, feature availability, driveline "tweeking", color (which is really feature), and singling.  A new truck will be in the 120-160K areas, totally depending on what you buy and how you configure. That includes FET.  I can build a used truck within the criteria above, INCLUDING the smart deck, singling, some cab accessory upgrades etc, for around that or less. I typically say $40K less or better. But it varies and some will argue that number (David ). Considering I just went through the process on this 2015 truck we currently own, I feel confident in my numbers. But they reflect what *WE* want in a truck and it WILL vary. (The target used truck in this case is a 2015 780 XE with electric APU, full amenities, and 200,000 miles).

That should give you some things to think about. New is a good choice, but you can do well on used. I'd stick to trucks under the 250K mark if comparing to new. But there is NOTHING like a new truck if that is in your budget.

[ewacowboy]

17 minutes ago, rickeieio said:

Looking back to the original post.....  Why do you want an HDT?  Your avatar shows what appears to be a pretty nice MDT, so I'm guessing you are using it?  Are you moving to full time and want more storage?  Are you under powered, or plan to be if you get a bigger trailer?

Yes we have a pretty nice MDT, however, living out west we're finding that 330hp is shy of what we really want.  Love, love, love our MDT, but now that we're spending more time on the road it's difficult (not impossible) to use the MDT as a daily driver - so we're really looking at at a smart.  Our plan is to go full time in the next year (house sale), so that's why we'd like to consider an HDT over our MDT.

[NoDirectionHome]

If you "Love, love, love our MDT"  you could look at an M2-112 (DD13 engine) and carry a Smart the same as with an HDT.  The big balancing act in my opinion is as you questioned, the wheelbase, which drives the difference in front axle weight with the trailer attached vs without.  Overloading the front with just the Smart or under-loading with the trailer attached will both make you unhappy.