What would be the downside of this setup ?

.....4 extra tires and wheels -2X extra tracton at a flip of a switch -more weight carrying capacity-resale should be more-less cost for a HDTV-could be converted to single axel instead whereas an upgrade is next to impossible at a reasonable price-better stopping 8 tires on road instead of 4......never tried a jacknife situation to test recovery....hope I never do. could use deck behind cab to carry a toad or bikes or Atv's with out extension....I'm too lazy and cheap to pay for a cut down anyway.....geofkaye

A rougher ride, even w/air susp. due to 40K# capacity when more than 20K is RARELY needed for any RV. But it's your choice, and your truck.

....I don't notice the ruffer/stiffer ride at all...'course I have a tag and not a 5th wheel....compaired to the rest of my vehicles my Volvo 610 rides better than a Eclass Mercedes Benz and certainally better than a BMW that my friends own.....I drove a Corvett to Florida and had to have help getting out of the dam thing.....Volvo rides better than my couch......Larry Zeigler was rite when he said "they ride better than a Caddy"....gotta give him credit for that!.....geofkaye

You guys need to look into super singles........this is the wave of the future.

.....until one goes flat. Then what? Yer stuck, 'cuz there's no dual to carry you outta there!

Michelin guarantees a tire to you in one hour or service call is free...............If you loose a tire on a conversion you are screwed anyhow, and not in a good way. Besides, when is the last time you had a flat on a drive tire? I remember twenty-five years ago, "I don't want one of those peanut spares, they'll never work. I want a full size spare" Full size spares..........another idea that got outdated.

As a wannabe and not yet an owner, that is frequently a question I ask myself.
Is it worth the Onezman's convention to drop the tandem and then build the coach or just stretch the frame and leave the twin screw?
Many on this site will argue (from experience) that even with a single pair of drive wheels it is nearly impossible to exceed GVWC.
With my young family in our motorhome, we can bring a lot wherever we go. I might take that challenge to overload a single axle conversion with a tow.

....unless yourkids are bigtime rock collectors you are not too likely to overload the rear-front maybe but not the rear. You have to consider the front load also-as removing the cenr axel will affect theeight distrubution.....GET AN EXPERT to hepl with that decision...no guesssing or opinions here....overloadedfront axel will make for an interesting ride and steering as well as braking......geofkaye

See they rate it now for 75mph .... cool

so that leaves me with just two more problems :

Did not find a Peterbilt Rim
and there are no 24.5 regular height super singles https://www.truckhome.com/infopop/emo...on_biggrin.gif

twinscrew,

we singled out because that makes it easier to register as a motorhome in AZ.
In CA you can drive a 40 feet singled out Rv with your regular car license, a twinscrew over 40' needs non commercial class A

both I was told by the local DMV/MVD ... I will soon find out how true the AZ part is https://www.truckhome.com/infopop/emoticons/icon_mad.gif

Blueskies,
I noted the comment on your "motorhome".. now that can open a whole can of worms... if you are talking about a truckconversion like the showhauler or Kingsleycoach or Butlercoach etc and not just a "toter" motorhome that is a different situation. Most of the people that I have talked to that built on a single rear axle frame were wishing they had gone to tandem. The 20,000lb rear axle IS overloadable with a big motorhome. It will probably be near the 32,000 lb limit.. or at least this is what I have seen... I will have a dual tandem setup when I finally get mine. The ones I have driven did not ride rough at all even though I didn't have them loaded.The two I drove that were single rear axle did ride marginally softer but did scale at near 30,000 lb without any water,little fuel, and no personal items. depending on the front axle rating that leaves approximately 2,000 lb assuming the weight is perfectly positioned. If it is a truck (oops,motorhome) /5er combination that is a totally diferent situation.. The totally unloaded dual tandem would have to ride a bit rough I would think.
JMHO
John

I have driven motorhomes with both single axle and tandem axle, loaded and empty. The ride is not rougher with the twin screw. I have weighed quite a few motorhomes and I have from 2,000 to 4,000 lbs. of payload remaining before being overloaded on a 30' or 32' conversion.

Bob

Although a Class 8 chassis can carry a lot, they seem to have limits especially with a couple of slides, etc. Sometimes the math can get a little "fuzzy" especially in mass production motorhomes, so much so that the RV Industry has tried to standardize weight capacities and recommends a CCC:

CARGO CARRYING CAPACITY (CCC) is the GVWR minus each of the following: Unladen Vehicle Weight (UVW), full fresh (potable) water weight (including water heater), full LP-gas weight, and SLEEPING CAPACITY WEIGHT RATING (SCWR). UVW is the weight of a vehicle with full fuel, engine(generator) oil and coolants. SCWR is the number of sleeping positions multiplied by 154 pounds.

Determining the GVWR on Truck Conversions is an additional challenge as this the axle ratings can be altered by how the chassis is stretched. As Geof notes, this will make a big difference on handling and safety and is not something to be guessed.

In trying to learn more about ideal axle spacing and load distribution, I came across this Back to Basics Article which reviews matching a body to a chassis along with Center of Gravity calculations and other facts like the Bridge Formula.

For me, the article was enlightening although probably old hat to many. Curious as to how many of you have had your trucks on the scales with a front/back, left/right breakdown as well as know your actual post conversion axle weight ratings? The end question is what is the actual CCC using the above formula? It might be smaller than you think.

I left mine as a twin screw and Lonnie weighed it as he does with all of the ones they build. My steering axle is at 12,480 and that left the rear at 21,000. I assume that once i have it loaded with water, fuel, and all the other stuff we will be a couple thousand pounds heavier. I'll weigh it then.
Wick